Technical Specification For Supply 25kva

SPEC/TN-2689/ 25 KVA Three Phase BIS level-2 (STAR-1) 1
TECHNICAL SPECIFICATION FOR SUPPLY OF 25 KVA 11/0.433 KV THREE PHASE Formatted: Font: (Default) Tahoma, Font color: Black,
Complex Script Font: Tahoma
ALUMINIUM WOUND ENERGY EFFICIENT LEVEL-2 (STAR-1) COMPLETELY SELF
Formatted: Underline, Font color: Black, Complex Script
PROTECTED (CSP) DISTRIBUTION TRANSFORMERS WITH PROVISIO OF LT Font: Bold
BUSHING BOX AGAINST TN-2535. Formatted: Font: (Default) Tahoma, Font color: Black,
Complex Script Font: Tahoma
1. SCOPE:
This specification covers the design, engineering, manufacture, assembly, inspection

and testing at manufacturer’s works before supply and delivery at site of Oil immersed, Oil
Natural Air Natural (ONAN) outdoor type 11KV/433 V, three phase, 50 Hz, outdoor Type,
Aluminum Wound Energy Efficient Level-2 (Star-1) CSP Distribution Transformers of 25 KVA
ratings, complete with fittings and accessories with provision of LT Bushing Box for use in
Distribution System.
1.1 The Equipment Offered shall be complete with all parts necessary for their effective
and trouble free operation. Such parts will be deemed to be within the scope of the supply
irrespective of whether they are specifically indicated in the commercial order or not.
1.1.1 It is not the intent to specify herein complete details of design and construction. The
equipment offered shall conform to the relevant standards and be of high quality, sturdy,
robust and of good design and workmanship complete in all respects and capable to perform
continuous and satisfactory operations in the actual service conditions at site and shall have
sufficiently long life in service as per statutory requirements. In actual practice, not
withstanding any anomalies, discrepancies, omissions, incompleteness, etc. in these
specifications and attached drawings, the design and constructional aspects, including
materials and dimensions, will be subject to good engineering practice in conformity with the
required quality of the product, and to such tolerances, allowances and requirements for
clearances etc. as are necessary by virtue of various stipulation in that respect in the relevant
Indian Standards, IEC standards, I.E. Rules, I.E Act and other statutory provisions.
1.2 The Tenderer/supplier shall bind himself to abide by these considerations to the entire
satisfaction of the Purchaser and will be required to adjust such details at no extra cost to
the purchaser over and above the tendered rates and prices.
1.3 Tolerances on all the dimensions shall be in accordance with provisions made in the
relevant Indian/IEC standards and in these specifications. Otherwise the same will be
governed by good engineering practice in conformity with required quality of the product.
2. APPLICABLE STANDARDS:
Unless otherwise modified in the specifications, the Distribution Transformers,

including various accessories, shall generally comply with the following Indian Standards/REC
Specifications. The standard(s) shall be with latest amendment, if any, from time to time.
Note: Wherever ISS are mentioned, equivalent or better International standards are also
acceptable:
Page-168 of 456./ TN-523

Sr. Specification Details about International &

No. internationally
recognized standards.
1 IS: 1180 (PART-I)/2014 Specifications for outdoor type oil immersed IS: 1180
distribution transformers upto and including (PART-I)/2014
2500 KVA, 33 KV Class.
2 IS:6600/1978 Guide for loading of oil immersed Transformers IEC 76
3 IS:335/2018 New insulation oils for Transformers BS 148, D-1473, D-1533

– 1934, IEC PUB 296
4 IS:3347 (Part-I/ Dimension of Porcelain parts & Metal parts for DIN 42531 to 33
Sec. 1 & 2) Transformer bushing (1.1 KV).
5 IS:3347 (PART-III / Sec- Dimensions of Porcelain (parts & Metal parts)

1 & 2) & IS:8603:2008 for Transformer bushing for use in heavily
polluted atmosphere 12/17.5 KV,24 KV and
36KV (amalgamating 8603 (Part1, 2 & 3):1977)
6 IS:7421 Porcelain Transformer Bushings for low voltage

– upto 1 KV.
7 IS:2099/1986 Porcelain Transformer bushing for AC volts

above 1000 volts.
8 IS:3639/1966 Fittings & accessories for Transformers
9 IS:1866/1978 Code of practice for maintenance & supervision

of insulating oil in service.
10 IS:5484 Specifications for Aluminium wire rods. ASTM B – 233
11 IS:9335 Specifications for insulating kraft paper. IEC 554
12 IS:1576 Specifications for solid insulating press Boards IEC 641
for electrical purposes.
13 IS:616 (Part I) Specification for paper covered Aluminium
round conductors
14 IS:6162(Part II) Specification for paper covered Aluminium
rectangular conductors
15 IS:104 Ready mixed paint, brushing zinc chromate,
painting
16 IS:649 Testing of steel sheets and strips for magnetic
circuits.
17 IS:2362 Determination of water content in oil for
porcelain bushing transformers.
18 IS: 4257 Dimensions for clamping arrangements for
bushings.
19 IS 6160 Rectangular conductor for electrical machines.
20 IS:10028 Selection, Installation and maintenance of
transformers
21 IS: 3401 Silica gel
22 - REC Specification No. 2
- REC Specification No.
39/1993
- CEA Specification
Chapter 4
23 IS 6103 Testing of specific resistance of electrical
insulating liquids
24 IS 6262 Method of test for power factor and
dielectric constant of electrical insulating
liquids
25 IS 6792 Determination of electrical strength of
insulating oil
Page-169 of 456./ TN-523

26 IS -2026 Specification for Power Transformers

27 IS/IEC 60947-2:2003 Low Voltage Switchgear and Control Gear –
Part 2: Circuit Breaker
28 IS:9385 Part-II:1980 High Voltage Fuses : Part 2: Expulsion and
similar fuses
29 IS:1554-1988 PVC insulated (heavy duty) electric cables
30 IS:8130-1984 Specification for Conductors for Insulated
Electric Cables and Flexible Cords
Note:- Besides above changes, the technical parameters of the specifications

wherever are deviating from the IS:1180 (Part-I/2014), the same shall be in accordance
with IS:1180 (Part-I/2014) and its latest amendments, if any and the changes where the
IS:1180 (Part-I/2014) is silent for technical parameters, same shall be applicable as per
Discom specification
Material conforming to other internationally accepted standards, which ensure equal or

higher quality than the standards mentioned above would also be acceptable. In case the
Bidders who wish to offer material conforming to the other standards, salient points of
difference between the standards adopted and the specific standards shall be clearly brought
out in relevant schedule. Four copies of such standards with authentic English Translations
shall be furnished along with the offer.
3. SERVICE CONDITIONS:
The distribution transformers to be supplied against this specification shall be suitable

for satisfactory continuous operation under the following climatic conditions as per IS 2026
(Part- I) latest revision.
i) Peak ambient temperature : 50°C

ii) Minimum Ambient Temperature in shade : -5°C
iii) Maximum average ambient temp. in a 24 hours period in shade : 45°C
iv) Maximum yearly weighted average ambient temperature : 35°C
v) Maximum temperature attainable by an object exposed to sun : 60°C
vi) Maximum relative humidity : 100 %
vii) Average number of thunder storm days per annum : 40
viii) Average number of rainy days per annum : 120
ix) Average annual rainfall : 15-100 cm
x) Number of months of tropical monsoon conditions : 4 Months
xi) Maximum wind pressure : 195 Kg/mt²
xii) Altitudes : Not exceeding
: 1000 mtrs.
The equipment shall be for use in moderately hot and humid tropical climate,
conducive to rust and fungus growth.
4. PRINCIPAL PARAMETERS:
The Transformers shall be suitable for outdoor installation with three phase 50 Hz 11
KV system in which the neutral is effectively earthed and should be suitable for outdoor
service as step down transformers under fluctuations in supply voltage upto plus 10% to
minus (-) 15 % permissible under Indian Electricity Act and rules there under.
The transformer shall confirm to the following specific parameters:

i) Continuous rated capacity : 25 kVA
Page-170 of 456./ TN-523

ii) System Voltage (Max.) : 12 kV

iii) Rated HT voltage : 11 kV
iv) Rated LT voltage : 433 V (P-P) / 250 V (P-N)
(v) Line current HV : 1.31 A
(Vi) Line current LV : 33.33 A
vii) Frequency : 50 Hz
viii) No. pf phases : THREE
ix) Primary connection (HT) : DELTA
x) Secondary connection (LT) : STAR
xi) Vector Group : Dyn-11
xii) Percentage impedance at 75°C : 4.5 %
xiii) Taps (off circuits) : TAPS ARE NOT REQUIRED.
xiv) Type of cooling : ON AN
xv) Fault level of the system : 750 MVA
Primary winding shall be DELTA connected and the secondary winding shall be STAR
connected (vector symbol Dyn-11), so as to produce a positive displacement of 30° from the
primary to the secondary vectors of the same phase. The neutral of the secondary winding
shall be brought out to a separate insulated terminal. The transformers shall be Aluminium
Wound.
The transformers shall be designed and constructed to withstand without damage the
thermal and dynamic stresses of an external short circuit. The manufacturer/supplier shall
furnish all relevant design data and calculations in support of having fulfilled this requirement
as stipulated in IS:2026 (Part-I)
5. NO LOAD VOLATGE RATIO:
The No load voltage ratio(s) shall be 11000/ 433 Volts.
6. THE LOSSES:
The max. allowable losses at rated voltage and frequency and at 75 Deg. C. shall be
as under:
Rating (KVA) Total losses (watts) at 75 Deg. Total losses (watts) at 75 Deg.
C at 50% loading (Max.) C at 100% loading (Max.)
25 190 635
The above specified loss values are maximum guaranteed, as per Energy Efficient
level-2, without any positive tolerance. In case the actual loss values exceed the above
guaranteed values, the transformers shall be rejected at the risk, cost and responsibility of
the supplier.
7. TEMPERATURE RISE:
The temperature rises over ambient shall not exceed the limits given below:
i) Top oil temperature rise measured by thermometer 35 Deg. C.

ii) Winding temperature rise measured by resistance method 40 Deg. C.
Page-171 of 456./ TN-523

Temperature rise test shall be conducted on Maximum measured total losses (No load at
rated excitation + Load loss at max. current tap at 75oC) at 100% loading shall be supplied
during temperature rise test.
The transformer shall be capable of giving continuous rated output without exceeding
the specified temperature rise. Bids not meeting the above limits of temperature rise
will be treated as non responsive.
The Hot spot temperature at annual weighted average ambient temperature of 35o C
shall not exceed 98o C, when calculated as per IS: 2026 (Part-II).
However, the transformer shall be designed for class ‘A’ insulation.
8. UNBALANCE CURRENT:
The maximum value of unbalance current in transformers shall not exceed 2% of full
load current.
9. IMPEDANCE:
The percentage impedance at rated current and at 75°C shall be 4.5 % with (+/-) 10
% tolerance.
10. TAPPINGS: No taps are to be provided in these transformers.
11. FREQUENCY:
Transformers shall be designed for normal frequency of 50 Hz, but shall be capable of
giving the rated output with the variation of (+/-) 3 % from the rated frequency.
12. ELECTRICAL CLEARANCES:
(A) EXTERNAL (IN AIR)
Minimum external electrical clearances after mounting the bimetallic terminal

connectors in position shall be maintained, as under, however positive tolerance shall be
acceptable without any ceiling.
Voltage Medium Clearance

Phase to phase Phase to earth
11000 Volt AIR 255 mm 140 mm
433 Volt AIR 75 mm 40 mm
B) INTERNAL (IN OIL):
The following minimum internal clearances shall be maintained as per details given
hereunder:
PARTICULARS 25 kVA
a) Between HT outside surface & tank inside (non bushing side) 25 mm
b) Between HT outside surface & tank inside (HV bushing side) 40 mm
c) Between HT outside surface & tank inside (LV bushing side) 40 mm
Page-172 of 456./ TN-523

d) Between HV windings & yokes (end insulation) 20 mm

e) Between LV windings to core (Bare conductor) 3.5 mm
f) From top of yoke to inside of top cover of tank (with gasket) 200 mm
g) Between LT/HT winding (Radial bare conductor Clearance) 11 mm
h) Phase to Phase Clearance between HV limbs 10 mm
The aforesaid external and internal clearances are minimum clearances and no
negative tolerance on these clearances shall be allowed.
13. TEST VOLTAGE:
Transformers shall be capable of withstanding the power frequency and impulse test
voltage prescribed below:
Nominal system Highest system Impulse withstand Power frequency test

Voltage (RMS) voltage (RMS) voltage voltage in (RMS)
11 kV 12 kV 75 kVp minimum 28 kV
0.433 kV ---- ---- 3 kV
The Transformer shall have fully insulated windings designed for the above impulse level
14. HEAT DISSIPATION (COOLING) / RADIATOR CALCULATIONS & E T R / PSR

(ELLIPTICAL TUBE RADIATORS/ PRESS STEEL RADIATOR) PLACEMENT:
The transformers shall be capable of giving a continuous output without exceeding the
specified temperature rise. Radiator shall preferably be provided on non LV-bushing side of
the transformers tank. Both fin type (PSR) and elliptical tube radiators are accepted. It
should be fixed at right angle to the side and not diagonally. The radiator fins should be
made of 1.25mm thick M.S. sheet. The header pipe connecting radiator bank to the tank
shall be rectangular in shape with approximate size of 100x20 mm. alternatively round pipe
of dia 32 mm can also be used ` for connecting the radiator bank to the tank. The
placement of top header pipe to the tank body shall be above the top of yoke, to facilitate
cooling for hot oil sump over top yoke.
Cooling area of the tank/radiators should be sufficient to dissipate the guaranteed

losses satisfactorily. Necessary calculations in this regard shall be furnished by the Bidder
with their tender. For the purpose of heat dissipation calculations, the following criteria shall
be adopted:
Plain surface of tank – 500 W/m2
(Note: The area of top/bottom tank surface, headers, HV/LV bushing pocket and
conservator shall not be considered for purpose of above calculations).
15. WINDING AND INSULATION:
i) MATERIALS:
Super Enamelled/Double paper covered aluminium conductors shall be used for 11 Formatted: Indent: First line: 0.5"
kV class transformers of 25 kVA rating. The covering shall conform to IS:6162 (part I & II).
ii) CONSTRUCTION:
Page-173 of 456./ TN-523

The High-tension windings shall be concentric with the Low-tension windings. The
Arrangement of the windings shall be robust in electrical and mechanical construction and
shall permit free circulation of oil and avoid hot spots. The LT conductor shall be rectangular
in shape. Two layer of electrical grade insulation Epoxy Dotted craft paper of 2 mil
thickness or one layer of min. 4 mil thickness shall be used for interlayer insulation both for
HV and LV Coils. Insulation cylinder made from electric grade pre-compressed board(s)
having minimum total thickness of 1.5 mm shall be used between HV and LV windings.
Alternatively 20 mil pressphan paper making thickness of the cylinder 1.5 mm having similar
electrical properties may also be used.
For phase barrier, 2 Nos. of 1 mm thick press board shall be used for covering the tie
rods. Besides, tie rods shall be covered by SRBP tubes of suitable size.
2 mm press board shall be used for base support insulation and core clamping
channel insulation. For bottom and top yoke insulation, only PC Board of min. 2 mm
thickness will be used. Also, vertical spacers between HV and LV coils and radial spacers
(tickleys)/blocks etc. shall be of PC Board only.
A tolerance of upto plus minus 1% shall be permissible on ID and OD and axial length
of HV and LV coils. However, the above tolerances are subject to maintaining the min.
required clearances. The material and thickness of various insulation provided for phase
barrier, foot plate insulation, yoke insulation and core clamp insulation shall be clearly
indicated in the drawing and in any case shall not be inferior to those used in type tested
transformers.
Minimum Nos. of coils on HV side shall be 2 (Two) per phase for 25 kVA rating
transformers. Dovetailed shaped radial spacers shall be placed between HV coil sections,
suitably – locked with vertical spacers around the circumference of the coils. The number of
such spacers shall be 2 (Two).
In case of wound core one HV coil is accepted.
Current Density
The current density for HV and LV conductor shall not exceed the value given hereunder:
Rating Current density in Amp./Sq.2

HV winding LV winding
25 KVA
1.35 1.60
iii) INSULATION MATERIAL:
Electrical grade insulating Kraft paper of only Triveni / Ballarpur / Padamjee shall be
used. Press Board used shall be of senapathy whitely / Raman make. Perma wood or haldu
wood blocks shall be used for Top and Bottom yoke insulation.
iv) CONNECTIONS AND TERMINATIONS:
A) HV Winding: The following method shall be adopted for taking out HV connections-
Page-174 of 456./ TN-523

a) The coil series connections shall be made by soldering / brazing only, after completely
removing the insulation from the ends.
b) Starting and finishing leads of HT coils shall be covered with empire sleeve(s) of
proper size. These leads should be clamped with the body of the winding with the
help of cotton twine during manufacture of the coils.
c) All delta leads from the HT coils as well as HT line leads shall be taken out through
multiple paper covered (MPC) copper wires of sufficient cross section area to
impart the desired mechanical strength. The current density in HV lead wire shall
not exceed 0.8 A/mm². These lead wires shall be provided with multi layer paper
insulation of minimum 1.0 mm thickness i.e. minimum increase in diameter due to
paper insulation shall not be less than 2 mm. The layer of glass sleeves/ glass tape
shall also be provided on the delta MPC wire and it should be further covered with
minimum 12 mm dia SRBP tube. The SRBP tube shall be extended in such a way that
it is entered upto 50% of bushing height.
d) All the above leads shall then be clamped tightly with cotton twine directly on to the
special frame/bracket making “Pie” shape connection. This structure could be made
up of Bakelite/ Permalli wood/laminated PC board flats, having minimum size of
25x4.5 mm for 25 KVA Transformers. Line leads leading to the HV bushing
terminals shall be directly clamped to the horizontal support bar of the “Pie”
structure so that any tension which may develop in the HT leads due to jerks or at the
time of making the connection, is not passed to the HT coils.
e) Delta joint shall be made by brazing only. One end of HT Fuse is to be connected to
Delta joint by brazing only and the other end of HT Fuse is to be connected to
Bushing Rod through Nut-Bolt method/brazing.
B) LV Winding:
a) The LV connection shall be taken out by cut on the top yoke channel duly reinforced
to compensate for the mechanical strength.
b) The layers in LT Coil may be either even or odd in numbers but minimum layers shall
be two.
c) LV star point shall be formed of aluminium flat of sufficient strength. Leads
from winding shall be connected to the flat by brazing.
d) Firm connection of LT winding to bushing shall be made of adequate size of “L shape
flat”. Connection of LT coils to L shape flat shall be by brazing only.
e) “L” shape Flat shall be clamped to LV Bushing metal part(s) by using nut, lock nut and
washer.
f) Neutral of the Secondary winding (LV) shall be brought out to a separate insulated
bushing.
g) For Aluminium windings, L&T, ALKAPEE Aluminium brazing rods with suitable
flux will be used.
Formatted: Body Text Indent 3, Tab stops: 0.25", Left
16. CORE CONSTRUCTION & CORE COIL ASSEMBLY DETAILS:
A. CRGO CORE:
Page-175 of 456./ TN-523

(i) The core shall be stack/wound type of generally high grade cold rolled grain
oriented annealed steel laminations, having low loss and good grain properties, coated with
hot oil proof insulation, bolted together to the frames firmly to prevent vibration or noise. All
core clamping bolts shall be effectively insulated. The complete design of core must ensure
the permanency of the core losses with continuous working of the transformers. The value of
the flux density allowed in the designs and grade of laminations used shall be clearly stated
in the offer, along with the curves. The transformer core shall be constructed out of the
prime class of materials. CRGO/ amorphous Lamination used shall be of prime grade and not
second grade steel laminations.
(ii) It will be mandatory for all the transformer manufacturers to use only PRIME grade
CRGO Laminations with specific loss of 0.89 watt per kg. at 1.5 Tesla or any other
combination of better grades with any thickness subject to maximum specific loss of 0.89
watt per kg. at 1.5 Tesla will also be acceptable. The bidder shall furnish the core loss
(watt/Kg.) and power (VA/Kg) curves of the laminations used. The core shall be properly
stress relieved by annealing in inert atmosphere. The transformer shall be suitable for over
fluxing (due to combined effect of voltage and frequency) upto 12.5% without injurious
heating. The operating flux density shall be such that there is a clear safe margin over the
fluxing limit of 12.5%.
(iii) Full mitred core construction technique for stack core shall be adopted. Top yoke &
bottom yoke pieces shall all be in one single piece and no cut pieces shall be acceptable. The
cross sectional area of yoke & limb shall be approximately same.
(iv) The transformer core shall not get saturated for any value of V/f ratio to the extent of
115 % of the rated value of V/f ratio (i.e. 11000/50) due to combined effect of voltage and
frequency without injurious heating at full load conditions. The bidder shall furnish necessary
design data in support of this situation.
(v) The flux density at rated voltage and frequency of core and yoke shall not be more
than 1.55 Tesla. The Over fluxing shall be limited to 12.5% of rated value and flux density at
112.5% of rated voltage does not exceeds by 1.9 Tesla. (as per amended IS:1180 (Part-
I/2014) Actual core design along with calculations in support of it should be enclosed with
the offer.
The No Load Current (magnetising current) at rated voltage and at 112.5% of rated
voltage shall not exceed the values given below:
Maximum permissible magnetising current in percentage of rated full load current

Rating At 100% rated voltage At 112.5% rated voltage
25 KVA 3.0 6.0
The tolerance on magnetizing current shall be +30% on declared value of

magnetizing current as per IS: 2026.
vi) Core clamping:
i. MS Channel of 75 x 40 x 6 mm min. size shall be used on top and bottom (for Formatted: Font color: Black
stacked core transformers). Rolling tolerance will be as per IS:1852-1985 with

latest amendment.
ii. 2 x 12 mm high tensile bolts to be used in parallel at each end.
Page-176 of 456./ TN-523

iii. Channel on LV side to be reinforced at equidistance, if holes/cutting is done for

LT lead in order to avoid bending of channel.
iv. MS channel shall be painted with varnish or oil-resistant paint.
v. Tie-rods: 4 Nos. of M12 M.S steel rods shall be effectively insulated.
vi. All top and bottom yoke nuts & bolts and tie rods shall be painted with oil and
corrosion-resistant paint and phosphate coated paint for tie rods before use.
vii. Only prime quality CRGO sheets should be used in the transformers and no
Second/Defective/Scrap CRGO finds way into transformers.
B. AMORPHOUS METAL:
a) The core shall be high quality amorphous ribbons having very low loss formed into
wound cores of rectangular shape, bolted together to the frames firmly to prevent
vibration or noise. The complete design of core must ensure permanency of the core loss
with continuous working of the transformers. The value of the flux density allowed in the
design shall be clearly stated in the offer. Curve showing the properties of the metal shall
be attached with the offer.
b) Core Clamping – Amorphous Metal and CRGO wound core Transformers
1. Core clamping shall be with top and bottom U-shaped core clamps made of sheet steel
clamped with MS tie rods for efficient clamping.
2. MS core clamps shall be painted with varnish or hot oil resistant paint.
3. Suitable provision shall be made in the bottom core clamp/bottom plate of the
transformer to Arrest movement of the active part.
c) The transformer core shall be suitable for over fluxing due to combined effect of
voltage and frequency upto 12.5% without injurious heating at full load conditions and
shall not get saturated. The Bidder shall furnish necessary design data in support of this
situation.
d) Flux density should not be more than 1.38 Tesla for Amorphous core. No load current
shall not exceed 3% of full load current and will be measured by energizing the
transformer at 433 volts 50 c/s on the secondary. Increase of voltage of 433 volts by
12.5% shall not increase the no load current disproportionately high and shall not exceed
i.e., 6%. Test for magnetic balance by connecting the LV phase by phase to rated phase
voltage and measurement of an, bn, cn voltage will be carried out.
NOTE: Equal Weightage shall be given to the transformers with Amorphous

metal core and CRGO.
Formatted: Indent: Left: 0", Hanging: 0.75"
(C) CORE-COIL ASSEMBLY:
The core joints shall be interleaved and with full mitre design, as mentioned above.
Ample provision for free circulation of oil in the radial gap between the core & LV coils shall
be made. Eyes or lugs of sufficient size shall be provided for lifting core and winding
assembly out of the tank. The core shall be effectively earthed through copper earthing Foil
of 25 mm width & 1 mm thickness bolted on core frame channels after removing the channel
paint.
Page-177 of 456./ TN-523

For top yoke channels, if cut or holes are made for taking LV connections, suitable
reinforcement to channels shall be made by providing adequate size of MS Flat of the
thickness not less than 6 mm.
On the core-coil assembly, core clamping channels, tie rods, core studs, spacers,
assembly base supports, etc. shall be provided as per details given hereunder:
Sr. Item Particulars

No.
a) Tie rods Minimum 4 Nos. of 12 mm each properly insulated and covered with
SRBP tubes. Tie rods shall also be provided with lock nuts.
b) Core studs Minimum 4 Nos. of 12 mm each properly insulated and covered with
SRBP tubes. The core studs shall also be provided with lock nuts.
c) Spacers Minimum 4 Nos. dovetail type with min. peripheral coverage of 30%.
d) Support of core 2 Nos. MS channels OF 75x40 mm.

assembly base
e) Channels for 4 MS Channels of 75 x 40 mm size (applicable for CRGO
clamping core transformers)
coil assembly
Guides on all the four sides shall be provided to prevent shifting of the active parts
and thereby accidental touching the tank. Alternatively boss nut arrangement at the top of
core coil assembly to lock the same with the transformer tank be provided.
The assembly fixing boss nut(s) are to be welded, 20-30 mm off the centre line (and
diagonally) of the tanks, so that assembly shifting during transport etc. is prevented. M S
Channel, tie Rods etc should be painted with hot oil and corrosion resistant paint after
phospating.
All core-coil assembly shall be punched on core channel / a identity plate welded on
core channel with following details:
1. Name of Supplier:
2. Order / TN No:
3. Rating:
In case if above marking is not found on the core assembly of physically opened
transformer selected for physical verification during final inspection then no further
inspection shall be carried out and re-inspection charges shall be payable by the supplier.
Note: 1. If the core is rusted or holes are found during testing at CTL, then the lot
may be rejected.
2. If the same observation is repeated, then apart from rejecting the lot,
firm’s balance order would be cancelled and such firms shall not be
awarded any order for one year or in next tender of tendered rating to be
opened/finalized whichever is later.
17. TRANSFORMER TANK:
Transformer tank shall be rectangular in shape, robust in construction and with

adequate strength to withstand the pressures developed at the time of severe fault
conditions. The tank body shall be suitably stiffened with two stiffeners of size
50x50x6 mm angle. The edge of the angle shall be continuously welded full
Page-178 of 456./ TN-523

length with the tank cover body as per drawing enclosed at Annexure-A. The tank
sheet shall be electrically continuous welded both from inside and outside to impart proper
mechanical strength and to plug leakage of oil. All joints of tank and fittings shall be oil tight
and no bulging shall occur during service. The tank design shall be such that the core and
windings can be lifted freely. The tank plates shall be of such strength that the complete
transformer when filled with oil may be lifted bodily by means of lifting lugs provided. All the
welding shall be continuous. The top cover plate shall be sloping down by more than 10
mm, opposite LV bushings side. The top cover edge should be extended by Min. 30 mm in such
a manner to cover gasket each side and it should be bent at Min. 15° angle. Accordingly length of
the lifting hooks shall be extended. The top cover shall have no cut at point of lifting lug. No
negative tolerance in the tank dimensions is acceptable in actual supply. There
should be no welding on corners (two ‘C’ shape sections be welded in such a way
that the joint of the cover should be at the centre of the tank on non-bushing
side). The bottom plate shall be extended at least by 5 mm outside on all sides to
facilitate proper welding with the vertical tank walls as per drawing enclosed at
Annexure-A. No grinding at welding portion is permissible. No joints in its bottom
and top cover will be allowed. LV Bushing pocket shall be continuously welded on all side
from both inside and outside on the tank wall.
Formatted: No bullets or numbering
C.(i)B.(i) Minimum size of MS Sections to be used in construction of transformer tanks shall be

as under:
Sr.
ITEMS 25 KVA
No.
1 Tank Cover plate thickness (mm) 5.0
2 Tank Sides wall thickness (mm) 3.15
3 Tank bottom plate thickness (mm) 5.0
4 Conservator body (mm) 2.0
5 Detachable Conservator side Cover N.A.
6 No. of stiffeners (To be welded on four 2
side of the tank in the angle forms
inverted “L”)
7 Size of M. S. stiffener (mm) 50x50x6 angle
8 Tank Top flange size (mm) 50 x 6 Flat
9 Cover Bolt Size ( Stainless Steel only) M10/ 3/8 x 1.5”

(Fixed Size)
10 Cover Bolt spacings (Maximum) 75 mm
11 Lifting lugs 2 Nos.
8t mm flat
12 Tank Base Channel of size 75x40 mm (weight 2 (75 x 40 x 6
= 7.14 Kg./mtr.) ISMC Type mm)
NOTE:
a) Each cover bolt shall be complete with two flat washers, one nut and one
spring washer.
b) Tank base channel shall be continuous welded with tank.
Page-179 of 456./ TN-523

The 12 Nos. nuts & bolts (4 Nos. each on length sides and 2 Nos. each on width sides
of tank body) to be tag welded on top cover/tank body of transformer.
The 04 Nos. Anti Theft Fasteners shall be provided - one each on all four sides in
centre of body of transformer.
Two holes shall be provided – one on top cover and other on collar of transformer to
facilitate providing of 2 Nos. poly-carbonate seals on longitudinal side.
The above mentioned M S sections shall be subject to tolerance as per ISS.
B.(ii) MEASUREMENT OF SHEET THICKNESS OF TRANSFORMER TANK:
The following measurements shall be carried out at Central Testing Lab

(CTL), JVVNL, Jaipur on the supplies of distribution transformers:
Measurement of Transformer Tank Thickness shall be done as follows:-
1. Top Cover At 2 places to be measured & average is to be

taken.
2. Bottom Cover -do-
3. Side Wall(s) On all four sides (average is to be taken)
 The nominal value of sheet thickness will be considered as mentioned in the

Specification.
 Rolling tolerance will be as per ISS:1852-1985 with latest amendment and
no penalty will be charged on such measured thickness till tolerance limit of
ISS.
 Sheet thickness of transformer tank for Distribution Transformers as per
relevant tender specification is as under for ready reference:
Sr. Rating Top Cover Bottom Side of

No. (mm) Cover Tank
(mm) (mm)
1 25 KVA Three Phase 5.0 5.0 3.15
The sheet thickness measurements will be carried out on all those sample
transformers which are tested in CTL and test results will be applicable to the
respective sub-lot or part thereof from which the sample is drawn.
(c) Lifting Lugs: Two Nos. welded heavy duty lifting lugs of MS plate of 8 mm thickness,
suitably reinforced by extended vertical supporting edge of same thickness in one piece
having size 125 mm width and 125 mm length, these shall be so extended that cutting of
bent plate is not required.
(d) Top cover gasket Nut & Bolt:
i) The gasket of provided in between top cover plate and tank shall be of min. 6 mm
thick neoprene rubberized oil resistant cork sheets conforming to type B or C as
per IS 4253 part II.
Page-180 of 456./ TN-523

ii) Stainless Steel Nut bolts (as per IS:1180 (Part-1/2014)) shall be of size M 10 x 40
mm / 3/8x1.5” long with two flat washers, suitably spaced (as specified) to press
the cover.
iii) Height of the tank shall be such that minimum clear height of 125 mm for 25 KVA
rating is achieved between top of yoke and under side of the tank cover (with
gasket in place).
iv) All screws, nuts, bolts and fasteners used in transformers should be of stainless
steel.
v) All sealing washers / gaskets shall be made of oil and heat resistant neoprene or
nitrile rubber. Gaskets made of natural rubber sheet are not permissible. The
minimum thickness of gaskets shall not be less than 6 mm for tank cover and
4 mm for HT/LT gasket washers.
vi) New cork/ Talbros make neoprene/nitrile based rubberized cork sheet – grade RC-
70-C shall only be used as gasket material.
vii) The 12 Nos. nuts & bolts (4 Nos each on length sides & 2 nos each on widths sides
of tank body) to be tag welded on top cover / tank body of the transformer.
viii) The 04 Nos. Anti Theft Fasteners shall be provided - one each on all four sides in
centre of body of transformer. Two holes shall be provided – one on top cover and
other on collar of transformer to facilitate providing of 2 Nos. poly-carbonate seals
on longitudinal side.
e) Tank shall be reinforced by continuously welded angle on all the four sides of the walls,
on the edge of tank, as specified above. The permanent deflection shall not be more than 5
mm upto 750 mm length and 6.5 mm upto 1250 mm length when transformer tank without
oil is subjected to the vacuum of 250 mm of Mercury.
f). PAINTING & FINISHING:
Steel surface shall be prepared by sand/shot blast or chemical cleaning including

phosphating, as per IS:3618. Inside of tank shall be painted with varnish or oil resistance
paint. For external surface, one coat of thermo-setting powder paint or one coat of epoxy
primer followed by 2 coat of polyurethane base paint of olive green colour confirming to
Shade No. 220 of IS:5-1961 to be applied in order to distinguish of star label transformer.
The paint thickness for normal to medium corrosive atmosphere is as per IS:1180 (Part-
1/2014).
The requirement for the dry type film thickness (DFT) of paint and the
materials to be used shall be as given below.
Sl. Paint Type Area to be No. of Total Dry film
No. Painted coats thickness (min.)
1. Thermosetting Paint Inside 01 30 microns
Outside 01 60 microns
2. Liquid Paint
a) Epoxy( Primer) Outside
01 30 microns
b) Polyurethene base (Finish 02 25 microns each

Outside
coat)
c) Heat resistance paint (Hot 01 35/10 microns

Inside
oil proof Paint)
Page-181 of 456./ TN-523

18. FITTINGS & ACCESSORIES:
The following standard fittings shall be provided on each transformer:
a) Earthing terminals of M10x40mm/3/8x1.5” with tinned lugs and symbol – (2 Nos.)

b) Lifting lugs – (2 Nos. for main tank).
c) Rating and terminal marking plate shall be non-detachable and affixed with Min. 10
rivets (One in centre of top and bottom and 4 Nos. each on both vertical sides at equal
distance), details to be included in one plate only. The plate shall be of stainless
steel/Aluminium only, with details clearly marked. The base plate of the Rating and
terminal marking plate shall be continuously welded with the tank. - (1 No.)
d) Bi-metallic terminal connectors on HT bushings and it may be ensured that connectors
shall be fitted before dispatch.
e) Oil level gauge of minimum 150 mm length of prismatic glass, indicating three positions
of oil, marked as follows, shall be provided at centre of the conservator tank:
1) -5 °C - Min.
2) 30 °C - Nor.
3) 90 °C – Max.
f) Free Air Type Breather – (1 No.)

g) Thermometer pocket, 12.5 mm dia with cap shall be provided –– (1 No.)
h) HV BUSHING: These shall be of 17.5 KV/ 250 Amp. Class porcelain/ polycrate with non-
adjustable, single gap type arcing horns – (3 Nos.).
i) LV BUSHING: 1.1 KV/ 250 Amp. Class porcelain/ polycrate (M12 stem) – 4 Nos.
j) Under carriage: For transformers of 25 KVA rating shall conform to REC specifications.
k) Brass rod 12 mm diameter for HT – (3 Nos.)
l) Brass rod 12 mm diameter for LT – (4 Nos.)
m) Pressure Relief Valve of Aluminium body with 1” BSP Thread capable to operate at a
pressure more than 0.4 Kg/cm2 (40 KPa) positive or negative and close at 30 KPa on
the top cover of the transformer tank with Anti-Theft Clamp be welded to safeguard the
valve. There shall be minimum gap of 10 mm between PRV Top Surface and Anti-Theft
Clamp.
n) Explosion vent: Explosion Vent shall be opening towards ground from LV bushing side
with M. S. mesh having Pipe Diameter of minimum 50 mm with 0.025mm copper shim
sheet/ Bakelite thick sheet of 0.4mm thick as diaphragm shall be provided on the top of
the cover of the tank such that the pressure released should be directed to the ground
& it should be inserted in the top cover of tank, welded outside & inside of top cover
and its pipe shall be connected with the conservator. Length of the explosion vent
should be minimum 700 mm. Nut bolts of flange of Explosion vent should be tag
welded. The vent shall be provided on opposite side of the circuit breaker operating
rod. The other end of the vent pipe shall be guarded with wire mesh for preventing the
entry of worms and nesting. The diaphragm shall burst at a pressure of 0.76 to 0.95 kg/ Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
sq.cm. There shall be minimum 140 mm clearance between live part of HV bushing to Complex Script Font: Tahoma, 14 pt, English (Australia)
Explosion vent. Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
Complex Script Font: Tahoma, 14 pt, English (Australia)
Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
o) QR code laminated P touch labels shall be fixed on transformer tank body below the Complex Script Font: Tahoma, 14 pt, English (Australia)
name plate and on the core coil assembly (on core channel) depicting various technical Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
details such as Name of manufacturer, rating, Serial no, TN No. etc. QR Code with Complex Script Font: Tahoma, 14 pt, English (Australia)
desired information to be printed on non-tearable matt finish label and to be covered Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
Complex Script Font: Tahoma, 14 pt, English (Australia)
Page-182 of 456./ TN-523

with transparent label to retain label life for minimum 20 years. Provision of Sr. No. on
QR Code to be affixed on Core Coil Assembly (on core channel) is optional.
Note: LV/ HV Connectors shall not be the integral part of the bushing stems.
19. CONSERVATOR:
When a conservator is fitted, the oil gauge and the breathing device shall be fixed to
the conservator. The conservator shall be of cylindrical shape and it should be provided
above the HV bushing with a minimum clearance of 50 mm and suitably inclined to maintain
the clearance.
The conservator tank should be connected with transformer tank with the help of two
hollow connecting pipes and should be located at the center of tank cover. The Flat shall not
be acceptable.
The total inner volume of conservator shall be minimum 10 ltr. for 25KVA
transformer. The inside diameter of the pipe connecting the conservator to a main tank
shall be min. of 30 mm and it should be projected into conservator in such a way that its end
is approximately 25 mm above the bottom of conservator so as to create a sump for
collection of impurities. The min. oil level (corresponding to – 5 deg. C.) should be above the
sump level. The connecting pipe from conservator tank to main tank shall have a sloping flap
so that oil falling from pipe shall not fall directly on the active job.
The oil filling hole cap of conservator should be welded with tank body with
the help of suitable inverted ‘U’ shape clamp.
21.20. FREE AIR TYPE BREATHER:
The breather shall be only from reputed and approved manufacturer and as per the
approved drawing. Inverted ‘U’ shape pipe shall be used for breather. Mounting arrangement
of the breather shall be flanged/threaded type as per details given in the illustrative drawing
attached.
22.21. HV BUSHING TERMINAL DETAILS :
3 Nos. 17.5 KV / 250 A class bushings, conforming to IS:3347 & IS:2099, shall be
fitted on a pocket made on top cover. These pockets shall be such that the HV bushing is
tilted more towards the HV side. The bushing of R & B phases may also be tilted sidewise to
maintain the required electrical clearances.
The clamping ring of HV bushing shall be of galvanised MS Sheet having minimum

thickness of 1.6 mm. The total weight of all the 12 aluminium caste member of HV bushing
shall not be less than 210 grams.
The inner porcelain portion of bushings shall be projecting approx. 50% of the length
inside the conical pocket. HT bushing (s) mounting bolts should be tag welded.
The arcing horn(s) shall be single gap and fixed type. HV bushings shall be of reputed
make such as BEPCO, JAYSHREE, WSI, SESHASAYEE, JAIPUR GLASS, BPPL Bikaner, Agarwal
salt Co. Bikaner, Bais Sanitary Works, Bikaner, Krishna Ceramics, Nasirabad, ADPRO,
Page-183 of 456./ TN-523

SHINE or any other make - approved by the purchaser. The HV bushings shall generally
conform to IS: 3347 and IS: 2099. Embossing showing the manufacturer’s name and month
& year of manufacture shall be clearly visible on HV bushings, even after fixing on
transformer(s).
As mentioned earlier, suitable bi-metallic connectors shall be provided in lieu of ‘Note’

at page 14; Cl.18 (i), having capacity of about 1.5 times the rated current of the transformer.
22. LV BUSHING TERMINAL DETAILS:
LV Bushing side shall be opposite to the HV Bushing side. 4 Nos. LV Bushings (1.1 KV/
250 A) shall be mounted on a special pocket on the tank wall. Projection of the LV pocket
shall be such that inner portion of the LV stem shall not project more than 20 mm inside the
tank, to facilitate unhindered lifting of the core coil assembly. Bushing stem of M12 size shall
be of brass. Rest of the components shall conform to the requirement of IS:3347 (Part
I/section 2). The LV bushings shall be of reputed make such as JSI, JAIPUR GLASS, BPPL
Bikaner, Baid Sanitary Works, Bikaner, Agarwal salt Co. Bikaner, CJI, Genesis, ADPRO or
any other make approved by the purchaser. The LV bushings shall generally conform to IS:
3347 and IS: 7421.
Provision of LV bushing with tamper proof LT bushing Protection Box:- Formatted: Font: Century Gothic, Font color: Black, Complex
Script Font: 10 pt
Formatted: Right: 0", Space After: 0 pt, Line spacing:
(i) The LV bushings are provided on sheet metal pocket on the side wall of the tank single, No bullets or numbering
with tamper proof LT bushing protection box as detailed below:- Formatted: Font: Century Gothic, Bold, Font color: Black,
Complex Script Font: 10 pt
(ii) The outdoor type L.T. Bushings Protection Box to be provided along with one
L.T. Porcelain Bushing with metal part for separate ground earthing connection.
The box is to be provided to cover the L.T. bushings as shown in the drawing
attached with the TS.
The Enclosure shall be fabricated by using CRCA (Cold Rolled Close Annealed) Sheet
of thickness not less than 2mm.
4 number Heavy Duty Copper Lugs suitable for 16 Sq.mm Aluminium Cable should be
provided in place of L.T. bimetallic connectors as shown in the drawing enclosed with
the TS.
The Heavy Duty Copper Lugs must be of standard make i.e. Jainson, Dowell‘s etc.
conforming to the relevant IS & as per drawing enclosed.
The cover box must have some slope towards outside to drain out the rainy water.
The cover box must be painted with olive green colour confirming to Shade No. 220 of
IS:5-1961 as per the procedure for painting of main tank of the DTRs.
Other descriptions of the box are as follows:-
Page-184 of 456./ TN-523

(A) Back Plate of the cover box:-

Size – (500 x 250 x 2mm thick M.S. Sheet)
Back cover plate should be properly welded with L.T. bushing pocket of the
transformer with the help of angle of the 25x25mm size. There should be a
rectangular cut to accommodate the L.T. bushings pocket.
(B) LT bushing cover box:-

(i) Internal size of Box:- L = 500 mm, W = 250 mm, H = 200 mm.
(ii) Back side of the Box:- Back side of the box should be properly bolted with
the welded back plate (A) to the transformer tank by providing 25x5mm thick
gasket of Neoprene Rubberizes Cork sheet.
(iii) Front side of the box:- Front side of the box should be suitable to
accommodate the sliding type front cover plate (C) with provision of 3 nos.
nuts & bolts of 8mm Diameter on bottom side to tighten the cover plate.
(iv) One Hole to be provided at bottom with double compressed cable gland
suitable for 10 mm2, 4 cores Aluminium armoured cable.
(v) Provision of bushing for ground earth:- On top of the cover one LT
bushing with brass metal part towards Neutral bushing side of the DTR,
should be provided with earth sticker or colour embossing with earth symbol.
This bushing should be internally connected in proper way with the neutral
bushing of the DTR. This bushing will be used to connect the 2 nos. direct
earth wire from the earth pit without touching the body of the DTRs.
(C) Sliding front cover plate:-Size 500 mm x 275 mm x 2mm thick MS Sheet.
The front cover must be of single sliding door type and with the min. 15 mm wide,
collar plate. The bottom of the door must have 3 nos. holes to match the hole of
bottom collar plate of the box.
The LT Bushing Box be provided as per Annexure-A. A 4m 4 Core Armoured PVC

Cable confirming to IS:1554-1988 and amendments thereof of 10 sq.mm. be provided
for connections of LT terminal using lugs and coming out of the LT Box through hole
provided at bottom.
23. TRANSFORMER OIL:
The transformer shall be supplied complete with first filling of EHV Grade transformer
oil, up to the normal oil level. The oil shall conform to IS: 335-2018 (latest amended) and
should be ISI Marked and having the specified aging characteristics. The Break Down
Voltage Value of the fresh oil after filtration and before filling in the transformer should be
above 70 KV and after filling in the transformer it should be above 40 KV.
The make of Transformer Oil shall be either APAR/SAVITA/ RAJ LUBRICANTS/

ANAMIKA/SHARAVATI/ MADRAS PETRO/ RAJ PETROL/ LUBRICHEM, MUMBAI/ OPANAMA
PETROCHEM, ANKELSHWAR/ TASHKENT OIL, VADODARA/ COLUMBIA. The transformer oil
sample taken from the transformer shall be subject to testing as per provisions ofIS:1866.
Page-185 of 456./ TN-523

The oil manufacturer’s test certificate shall be made available at the time of inspection
to the inspecting officer.
24. IDENTIFICATION DETAILS:
A. Rating & terminal marking plate: Each Transformer shall be provided with non
detachable name, rating and terminal marking plate fitted in a visible position. All
details shall be given on one plate. Material of the plate shall be stainless
steel/aluminium only. Thickness shall be 0.9 mm (with a tolerance of ±0.1 mm).
The plate shall be made absolutely undetectable either through welding or riveting or
through any other approved method.
Each HV & LV terminal shall be duly indelibly marked with its terminal numbers. (e.g.
HV terminal with capital letter 1U, 1V, 1W and LV terminal by corresponding small letters 2u,
2v, 2w and the neutral terminal by 2n) by stamping with Min. letter size of 40x40 mm. In the
diagram to be given on the name plate, the relative position of various terminals- when
viewed from top – shall be clearly shown. Inspection shall not be undertaken unless all
these details are verified by the Inspecting Officer.
Besides other particulars, following details shall also be given on the name plate:
i) P.O. No. - Month& year.

ii) Sr. No. of transformer.
iii) Date of despatch - month & year
iii) Date of expiry of guarantee period – month & year
iv) Maximum Guaranteed Losses at 50% loading & at 100% loading.
v) Name & Full address of the manufacturer.
vi) Capacity of the transformer.
vii) Rating of the transformer.
viii) Type – Oil filled naturally cooled.
ix) IS 1180 part-1/2014.
x) BIS Level-2 with BIS Licence No.
ALL DETAILS ON THE NAME RATING AND DIAGRAM PLATE SHALL BE INDELIBLY
MARKED i.e. BY ENGRAVING, STAMPING or PUNCHING.
B. Technical cum Identification Plate - M.S. plate of size 125 x 75 x 2.5 mm having
following details punched with letters of size 8mm X 6mm shall be continuously
welded to the main tank body below the middle HV bushing in clearly visible
position:-
A) Name of the Firm

B) TN No.
C) Make
D) Sr.NO.
E) JAIPUR DISCOM
F) Rating
G) Date of Dispatch
H) Date of Expiry of G. P.
I) Core :-
1. Core Dia
2. Core Area
Page-186 of 456./ TN-523

J) LV Coil :-
1. ID/OD Dimensions
2. Conductor Size
K) HV Coil :-
1. ID/OD Dimensions
2. Conductor Size
L) Limb Centre
M) Window Height
Further following details is to be embossed on the width side of the tank preferably in
centre opposite to Name & Rating Plate. The dimensions of letters should be 10x10x1 mm.
The punching shall be distinct and visible.
MAKE __________
S. No. __________
TN __________
The details of Make, TN No. & Sr. No. of transformer shall also be punched on the top cover.
The punching shall be distinct and visible with letter size 10x10x1 mm.
25. GUARANTEED AND OTHER TECHNICAL PARTICULARS FOR

TRANSFORMERS:
Guaranteed Technical particulars of the transformers offered shall be furnished in A-4

size paper by the Tenderer in the proforma appended herewith. Complete details shall be
furnished. Tolerances on weight quantity and dimension figures shall be ± 5% (except for
internal configuration) at the tender stage, subject to maintaining the minimum electrical
clearances as per the specification. However, no negative tolerance shall be allowed on the
short circuit type tested design. Electrical performance data shall be subject to tolerances as
per ISS, unless otherwise specified in this specification. However, the Total losses (at 50%
and 100% Loading) shall be maximum guaranteed without any positive tolerance.
26. TYPE TEST CERTIFICATES:
The bidder shall furnish type test certificates of offered design / similar design,
wherever available, with the bid not older than five years from the date of opening of
technical bid.
27. DRAWINGS AND OTHER DOCUMENTS:
The tenders shall be accompanied with the following drawings/Calculation sheets, as

per the offered designs. The drawings shall be only on A-3 (420 x 297 mm) size paper and
calculation sheet shall be on A-4 size paper only.
a) Name rating / diagram plate drawing.
b) Outline and general arrangement drawing.
c) Core-coil assembly drawing.
d) Core section (for limb and yoke) along with flux density calculation sheet /
drawing.
e) Cooling area calculation sheet.
f) Thermal Ability short circuit calculation sheet.
g) Core loss and magnetization curves of the laminations.
Page-187 of 456./ TN-523

h) Heat dissipation calculations (heat dissipation by tank walls excluding top and
bottom should be 500 W/m2.
28. QUALITY ASSURANCE PLAN:
The purchaser intends to purchase Transformers only from quality conscious

manufacturers.
The tenderer shall furnish the details in respect of following, in the schedules
prescribed herein this specification, failing which the offer is liable for rejection.
a) List of testing equipment and instruments (with class of accuracy) available with
tenderer for inspection, testing and checking the Transformers offered, as per
tender specification in the schedule of testing facilities. The calibration details
should also be included.
b) List of machines/equipment/T&P available with the tenderer for manufacturing the
Transformers, in the schedule of plant and machinery.
c) Details of type tests conducted on the Transformers offered to supply in the
schedule of type test.
d) List of raw material components and sub-assembly to be used for manufacturing
the equipment offered, in the schedule of raw materials and components.
e) Statement giving list of important raw materials, names of sub-suppliers for the
raw materials, list of standards according to which the raw material are tested.
List of tests normally carried out on raw materials in the presence of Bidder’s
representative, copies of test certificates.
f) Information and copies of test certificates in respect of bought out accessories. Formatted: Font: (Default) Tahoma, 12 pt, Complex Script
Font: Tahoma, 12 pt
d)g) Level of automation achieved and list of areas where manual processing exists.
Formatted: Font: (Default) Tahoma, 12 pt, Font color: Black,
Complex Script Font: Tahoma, 12 pt
The tenderer should possess adequate facilities for inspection and testing of the
Transformers, as per requirement of the relevant ISS and this specification. In case any
supplier is found not having all the instruments/equipment required for testing, the offer
shall be ignored. No borrowing of instruments / equipment shall be allowed. Testing of the
Transformers shall also not be allowed at the works of any other manufacturer. However,
testing may be allowed at any Government Testing Laboratory.
29. INSPECTION AND TESTING:
(i) The inspection and testing shall be conducted as per relevant clause of the
General Conditions of Contract (Section-II) at the place of manufacture. The transformers
shall be completely assembled and tested at the factory. The inspection may be carried out
by the purchaser at any stage of manufacturing. The supplier shall grant free access to the
purchaser’s representative at all reasonable times when the manufacturing work is in
progress. Inspection and testing of any material under this specification by the purchaser
shall not relieve the supplier of his obligation of supplying the material in accordance with
the specification and shall not prevent subsequent rejection if the material is found to be
defective.
(ii) The supplier shall afford the inspector representing the purchaser all
reasonable facilities, without charge, to satisfy him that the material is being manufactured
in accordance with the specification. The bidders must have adequate set of instruments for
conducting testing as per ISS/ Specification. The instruments for measurement of losses shall
be of accuracy class of 0.5 or better. The instruments shall be duly calibrated and Calibration
Page-188 of 456./ TN-523

Certificate should not be older than one year on the date of presentation to the Inspecting
Officer. The calibration shall be arranged from NABL accredited testing house. A
comprehensive list of testing equipment/ instruments indicating make, Sr. No., type, class of
accuracy, calibrating agency, calibration date etc. should be furnished alongwith the bid. The
calibrated instruments shall be duly sealed by calibrating agency to avoid any tampering with
calibration and the details thereof shall be clearly mentioned in the Calibration Certificate(s).
(iii) The supplier shall keep the purchaser informed in advance, about the
manufacturing programme so that arrangements can be made for inspection. The supplier
shall give minimum fifteen days advance intimation to enable the purchaser to depute
his authorised representative for inspection/ witnessing of various tests on the
equipment/ material as detailed below:
NOTE:- Penal provision shall be made for any short technical parameters found /
noticed in the transformers at any time even beyond guarantee period.
30. ROUTINE/ACCEPTANCE TESTS:
A) 100% testing of the Distribution Transformers shall be carried out at firm’s

works for measurement of total load losses at 50% & 100 % loading.
Remaining testing shall also continue to be carried out as per practice.
B) All the assembled/finished transformers prior to despatch shall be subjected to routine

tests as per IS:2026. Minimum 25% of the offered lot size samples subject to
minimum 5 Nos will be taken for routine and acceptance tests. The supplier shall
invariably furnish manufacturer’s routine test certificate along with inspection call of
the offered transformers for pre-despatch inspection. The inspection offers
without furnishing of routine test certificates as per ISS of all the
transformers offered for final inspection shall not be entertained, and any
delay on this account shall be to firm’s account.
The selected samples shall be subjected to the following routine/acceptance tests at

the manufacturer’s works in accordance with the relevant ISS:
1. Insulation resistance
2. Separate source voltage withstand test
3. Induced over voltage withstand test
4. Measurement of windings resistance cold (at or near the test bed temperature)
5. Measurement of Voltage ratio and check of voltage vector relationship
6. Measurement of Impedance voltage.
7. Measurement of total losses at rated voltage and normal frequency (at 50% & 100%
loading).
8. Measurement of No load current at 100 % and 112.5% of rated voltage and normal
frequency.
9. Checking of rating and terminal marking plate.
10. Pressure Test & oil leakage test (As per IS 1180 Part-1:2014)
11. Checking of weights, dimensions, fittings and accessories, tank sheet thickness, oil
quantity, material, finish, paint thickness and workmanship as per purchase order
and contract drawings.
12. Physical verification of core – coil dimension, internal clearances, provisions of
required oil ducts in the HV and LV winding, conductor sizes, individual weights of
HV and LV winding core laminations etc., with reference to contract drawings and
Page-189 of 456./ TN-523

type test report(s) by dismantling selected unit(s). The physical verification shall be
conducted on units equivalent to one unit per 50 Nos or part thereof of offered
quantity randomly selected from the offered lot. The dismantled unit(s) after re-
assembly shall be accepted by the purchaser after routine testing in presence of his
representative.
13. Oil dielectric strength (break down voltage) test shall be carried out on the
transformers opened for physical verification and average value shall be calculated.
14. Checking of manufacturer’s test certificates and invoices for major raw materials
shall be done and copies thereof duly signed by firm’s representatives and
inspecting officers shall be enclosed with the inspection report.
Invoices of CRGO/ AMORPHOUS material shall be provided by the supplier to the

inspecting officer at the time of inspection and same shall be verified by the inspecting
officer.
Following tests shall also be carried out at manufacturer’s works on one complete unit
of 25 KVA Transformers unit:
i) Over Flux Density Test (in the first lot and may be repeated in subsequent lots
if desired by purchaser).
ii) Measurement of unbalance current.
iii) Magnetic Balance Test (See note below)
iv) Oil Leakage Test (See note below)
Note: It will be mandatory for the manufacturer firms to maintain record

of BDV value of the transformer oil and shall furnish to the
inspecting officer who in turn shall furnish the same to the
Nigam’s CTL for verification purpose. The Inspecting Officer during
inspection shall verify record of Meggar value of the offered DT’s
and furnish the same with inspection report to the Nigam’s CTL.
Simultaneously, record of Air Pressure Test shall also be checked
by the inspecting officer and same be furnished with report to the
CTL. CTL will conduct testing of DT’s only after receipt of record of
BDV value, Meggar value and air pressure test results.
Fifteen days clear notice shall be arranged for pre-despatch inspection by purchaser’s
representative as per General Conditions of Contract.
After successful inspection, the inspecting officer shall seal each and every
transformer by sealing the transformer with 2 Nos. poly-carbonate seals on
longitudinal side as per the manner mentioned in Clause No. 17 above. Before
sealing, the inspecting officer will ensure that all the offered transformers are completed and
duly fitted with name, rating and diagram plate, identification plate (on tank body & Top
cover) as specified in this specification.
i) INSULATION RESISTANCE MEASUREMENT:
Insulation resistance of selected samples shall be measured with a 2500 V Megger, of

standard make such as M/s AVO, M/s Sakova, M/s Wako, M/s Evershed, Vignole or
Metrawatt. The minimum insulation resistance, in Mega Ohms, shall be as indicated in the
table below:
Page-190 of 456./ TN-523

200 C 300 C 400 C 500 C 600 C

11000 Volts
800 400 200 100 50
(HV)
433 Volts 25
400 200 100 50
(LV)
PRESSURE TEST: (As per IS: 1180 (Part 1):2014) -This test shall be conducted as type
test at a Govt. approved/ a Govt. recognized/ NABL accredited laboratory. The pressure
gauge and vacuum gauge shall be duly calibrated and sealed by an independent recognized
test lab(s).
The test procedure shall be as detailed below:
The tank subjected to pressure of 80 KPa for 30 minutes and vacuum of 250 mm of
mercury for 30 minutes. There should be no air leakage at any point. The Permanent
deflection of flat plate, after pressure has been released, shall not exceed the values given
below:
Length of plate up to Deflection
750 mm 5.0 mm
751 to 1250 mm 6.5 mm
1251 to 1750 mm 8.0 mm
iii) MAGNETIC BALANCE TEST:

This test shall be conducted as an additional test on one sample transformer from
each lot offered for inspection.
The application of low voltage to the middle limb will induce approximately equal
voltages on the two end limbs. The application of voltage to the end limbs will induce greater
voltage in the middle limb and less voltage in the other end limb. Uniformity of induced
voltages shall confirm the healthiness of the transformer windings.
The procedure for the test shall be as under:
a) Apply 250 Volts between LV terminals-2u-2n and measure voltages between 2v-2n &
2w –2n.
b) Apply 250 Volts between 2v-2n and measure voltages between 2u-2n & 2w-2n.
c) Apply 250 Volts between 2w-2n and measure voltages between 2u-2n & 2v-2n.
The measured voltages shall satisfy the conditions detailed as above.
iv) OIL LEAKAGE TEST (As per IS 1180 Part-1/2014):
The oil leakage test shall be conducted on one unit selected from the offered lot.
The assembled transformer for non-sealed and sealed Type with all fittings
including bushing in position shall be tested at a pressure equivalent to twice the
normal head measured at the base of tank for 8 hrs. There should be no leakage
at any point.
Page-191 of 456./ TN-523

Note: ISI marking and overall diameter of the cable used in the transformer are also
to be checked during inspection at firm’s works.
31. TYPE TESTS:
The firm shall furnish complete type test reports as per IS:1180 Part-I 2014 of this
rating transformer (submitted for BEE labeling) for verification and checking along with
drawings to be got approved later on.
Type tests required – The following Tests shall be conducted on one unit as per
IS:1180 Part-I 2014 at NABL/Govt. approved Lab as under:-
i) Short circuit test for dynamic and thermal ability: The short circuit test for dynamic and
thermal ability shall be arranged at a Govt. approved/ a Govt. recognized/ NABL
accredited laboratory/ILAC i.e. International Laboratory Accredited Laboratory/ ILAC i.e.
International Laboratory Accreditation Cooperation (in case of foreign laboratory) on one
unit. The transformer(s) for the test shall be selected/ sealed by our inspecting officer
from the first lot which shall be of minimum 20 Nos. (if ordered quantity is 500 Nos.) OR
50 Nos. (if ordered quantity is more than 500 Nos.).. The short - circuit test shall be
conducted only after successful routine tests including measurement of total losses at
50% and 100% loading. The supply shall be accepted only after arranging successful
type test on the selected transformer(s).
ii) Impulse voltage withstand test: The impulse voltage withstand test shall be arranged
at any testing house accredited to NABL or a Govt. approved/ a Govt. recognized/ NABL
accredited laboratory/ILAC i.e. International Laboratory Accredited Laboratory/ ILAC i.e.
International Laboratory Accreditation Cooperation (in case of foreign laboratory) for
purpose of impulse test. The test shall be conducted on one unit of each rating to be
selected by our inspecting officer from the first lot which shall be of minimum 20 Nos. (if
ordered quantity is 500 Nos.) OR 50 Nos. (if ordered quantity is more than 500 Nos.).
The test procedure shall conform to the requirement of Clause 13 of IS: 2026 (Part-III).
Impulse voltage withstand test shall be minimum 75 KVp. The supply shall be accepted
only after arranging successful impulse test on the selected transformer(s).
iii) TEMPERATURE RISE TEST : [ As per IS 2026 (Part 2) ]
Temperature rise test shall be conducted on Maximum measured total loss

(No load at rated excitation+Load loss at max. current tap at 75 oC) at 100%
loading shall be supplied during temperature rise test at a Govt. approved/ a Govt.
recognized/ NABL accredited laboratory/ILAC i.e. International Laboratory Accredited
Laboratory/ ILAC i.e. International Laboratory Accreditation Cooperation (in case of foreign
laboratory).
The transformer shall be capable of giving continuous rated output without exceeding
the specified temperature rise. Bids not meeting the above limits of temperature rise will be
treated as non responsive.
Page-192 of 456./ TN-523

(iv) AIR PRESSURE TEST: (As per IS 1180 (Part 1):2014)
PRESSURE TEST: (As per IS: 1180 (Part 1):2014) -This test shall be conducted as type
test at a Govt. approved/ a Govt. recognized/ NABL accredited laboratory. The pressure
gauge and vacuum gauge shall be duly calibrated and sealed by an independent recognized
test lab(s).
The test procedure shall be as detailed below:
The transformer tank shall be subjected to air pressure of 80 KPa for 30 minutes and
vacuum of 250 mm of mercury for 30 minutes. There should be no air leakage at any point.
The Permanent deflection of flat plate, after pressure has been released, shall not exceed the
values given below:
Length of plate up to Deflection

750 mm 5.0 mm
751 to 1250 mm 6.5 mm
1251 to 1750 mm 8.0 mm
No extra time shall be allowed for arranging these type tests. The cost of above Type
Tests shall be borne by the supplier.
The programmed indicating date and place of type test(s), be intimated enabling
purchaser to depute his representative to witness the test if desired. The testing house shall
be advised to arrange type test result directly alongwith drawings duly attested by the
testing authority for our scrutiny and approval. The type-tested transformer(s) shall also be
accepted as the part of the supplies.
The requirement of arranging above type tests shall however not to be insisted on the
suppliers who have arranged the above type tests within last 5 years from the date of
opening of this tender on similar design. Minor changes in the present specification will not
necessitate repetition of type test(s), if design of core-coil assembly is similar in essential
details.
32. RANDOM SELECTION AND TESTING (RST):
32.1 The purchaser may select transformer(s) from the supplied lot(s) at random from the
stores for conducting the following type tests, at any test house(s) as mentioned above. The
supplier shall arrange these tests including loading, unloading and to & fro transportation
from our stores to the test house(s). The charges for such tests shall be reimbursable to the
supplier on actual basis on production of documentary evidence in case the selected sample
successfully withstands type test(s). In case of otherwise, no charges will be reimbursed.
i) Short circuit withstand test for Dynamic & Thermal ability. Measurement
of total Losses at 50% and 100% loading shall form part of tests conducted
before and the after the short circuit test and recorded in the report.
ii) Impulse test as per Clause No.13 of IS:2026 (Part-III). Impulse voltage shall be
minimum 75 KVp.
iii) Temperature Rise Test as per IS-2026 Part-2.
Page-193 of 456./ TN-523

iv) Pressure Test as per IS 1180 Part-1:2014. Pressure of 80 kPa for 30 minutes
and a vacuum of 250 mm of mercury for 30 minutes ( As per IS:1180 (Part
1):2014)
Purchaser reserves the right to carry out any site tests he may decide upon at
his own expenses. In case equipment/ material are not found as per P.O., all
expenses incurred during the testing will be to supplier’s account and material
shall be replaced by the supplier at site free of cost.
Formatted: Indent: Left: 1"
FAILURE IN TYPE TEST (S):
In the event of failure/unsatisfactory results of the transformer(s) in Dynamic &

Thermal Ability to withstand Short Circuit Test/impulse type tests /Temperature rise Test/Air
Pressure Test, the supplier shall have to replace the supplies already made and no further
transformers shall be accepted. The purchaser however, at his option, may accept the
transformers already supplied with the following conditions:
i) Guarantee period of the supplied transformers issued to the field shall be

increased by double the normal Guarantee period.
ii) Bank Guarantee shall be extended to cover the additional Guarantee period.
iii) For failure in any of the type tests listed under RST i.e., short circuit test &
Impulse withstand test, Temperature rise test & Air Pressure Test, no further
supplies shall be accepted. The type test charges shall also not be reimbursable in
this case and shall be borne by the supplier.
iv) The transformers lying in the store(s) shall be replaced as per sub para (v) below.
v) The bidder shall, however, be allowed to check the reasons of failure and if need
be, to improve/modify the design. Further supplies, including replacements against
supplies already made, shall be accepted only after successful type test(s) are
arranged on fresh transformer(s) selected by the authorized representative of the
purchaser. All the type tests shall be arranged in case there is change in the
design, otherwise, type test shall be repeated only for the test in which failure has
occurred. Charges for such test(s) shall be borne by the supplier. However, in the
event of failure of transformer in the repeat type test, the purchaser may take
following actions:
a) Cancel pending orders of the rating in which failure(s) has occurred
b) Not place any order of Distribution Transformers on the firm for one/two
year(s).
32.2 Measurement of Total Losses (at 50% and 100% Loading)
i. After pre-dispatch inspection of material at firm’s works, the dispatch instructions will
be issued for the respective store(s) as per requirement of Nigam. Sample(s) will be
drawn from the lot(s) received in store(s) and will be subjected to the following
test(s):
a) One transformer will be selected out of every lot of 10 Nos. or part thereof for
measurement of Total Losses of transformer at 50% & 100% loading at rated
voltage; No Load current (at 100% and 112.5% of rated voltage); Impedance
voltage. The testing shall be arranged either at purchaser’s own testing lab and
/ or at independent test lab. The testing charges for such tests shall be borne
by the purchaser. The test results will be applicable to the respective lot of 10
Page-194 of 456./ TN-523

Nos. from which sample was drawn. The tolerance in losses on account of 4m
16 sq. mm PVC Armoured Cable confirming to IS:1554-1988, lugs and working
tolerance towards crimping, connections, etc. shall be 10.0 watt at 50% loading
and 39.0 Watt at 100% loading at 750C.
Note: 1. During Physical verification, one transformer will be tested on LT

Bushing (after removing cable) to ascertain the losses as per
technical specification.
2. ISI marking and overall diameter of the cable are to be checked
during inspection at firm’s works as well as in CTL.
b) If dispatch instructions are less than 10 Nos. than one sample shall be
selected from each store(s) and the test results so obtained shall be for the
quantity consigned/ received by store(s).
The above information shall be mentioned in the CTL Report.
The percentage impedance voltage at rated current shall not exceed the permissible
limit of 4.5% with plus minus 10% tolerance failing which the sub lot of transformers
represented by the sample shall be rejected.
The I.R. values of the sample(s) shall be measured at CTL, Jaipur and it must be more
than 50 MEGA-OHM.
One sample (randomly selected by CTL) out of 100 Nos. transformers or part thereof shall
be selected for physical verification/ checking of window height & limb centre (with tolerance of
+2 mm) and checking of insulation of HV and LV windings at CTL.
Metal Parts of Bushing assembly shall be checked in CTL as per specification/IS on

the transformer which is physically opened in CTL (from the lot of 100 Nos. or part
thereof). The tolerance may be allowed in accordance with coarse class of IS 2102-1969.
If sample does not confirm the requirement of specification/IS, then lot of 100 nos. or
part thereof shall be rejected.
The No Load Voltage Ratio (Transformer Turn Ratio) shall be checked in CTL with
the tolerance as per specification/ IS 2026 on the transformer from the lot of 10 Nos. or
part thereof and the concerned sub lot shall be rejected if not meet out the requirement
of IS.
Further, Internal clearances shall be checked without opening of core coil

assembly in each of the transformers which have been selected for physical verification
at CTL (i.e. one sample from a lot of 100 nos. or part thereof) in presence of firm’s
representative. No negative tolerance shall be admissible. If clearances are not found as
per specification then the lot of 100 Nos. or part thereof shall be rejected.
The sample of Oil be taken at CTL from the Transformer opened for physical
verification in presence of firm’s representative and same shall be tested at Nigam’s
CTL/NABL accredited Lab. If sample does not confirm the requirement of specification/IS,
then lot of 100 nos. or part thereof shall be rejected.
Besides above points following shall also be checked in CTL on the transformer
opened for physical verification and if the sample(s) does not meet the above requirements
then the entire lot shall be rejected:
Page-195 of 456./ TN-523

1. Marking on HV terminals on transformer tank by stamping (i.e. 1u, 1v, 1w).
2. Marking on LV terminals on transformer tank by stamping (i.e. 2u, 2v, 2w & 2n).
3. The earthing of the core through tinned copper earthing Foil of 25 mm width & 1 mm
thickness bolted on core frame channels, after removing the channel paint.
NOTE:
If the total losses are found more than 10% of specified losses at 100% loading, then
apart from rejecting the lot, firm’s balance order would be cancelled and such firms shall not
be awarded any order for one year or in next tender of tendered rating to be opened/finalized
whichever is later.
If the window height and limb centre are found more than 7.5 mm, then apart from
rejecting the lot, firm’s balance order would be cancelled and such firms shall not be awarded
any order for one year or in next tender of tendered rating to be opened/finalized whichever
is later. However, a tolerance of ± 2mm shall be allowed in window height.
32.3 CHALLENGE TESTING CLAUSE:
The other manufacturers who have participated in the instant tender enquiry
can request challenge testing for tests covered in this clause based on specification &
losses. The challenger would request for testing with testing fee. The cost of to & fro
transportations of all transformer tested under the provision of this clause along with
loading & unloading and transit insurance at actual shall be borne by Challenger firm.
The challenge testing fees shall be at least three times the cost of testing. The
challenger would have the opportunity to select the sample from the store. The party
challenged, challenger & the utility could witness the challenge testing. The
challenge testing would cover the
i. Measurement of Magnetizing current

ii. No Load Losses test
iii. Load Losses test
iv. Temperature Rise Test.
The challenge test could be conducted at any Govt./NABL accredited Lab. like
ERDA/CPRI. If the values are within limits as per specification including tolerance
allowed in CTL, the products gets confirm else not confirmed. If the product is not
confirmed, the manufacturer will pay the challenge fee and challenger would get the
fee refunded. However, as a redressal system, the manufacturer (challenged firm)
would be allowed to ask for fresh testing of two more samples from the store and the
same be tested in a NABL/Govt. laboratory in presence of party challenged,
challenger & the utility. If any one or both sample does not confirm the tests then the
product is said to have failed the test. In such cases, the manufacturer (challenged
firm) will be declared as unsuccessful manufacturer for the said product and balance
supply shall not be availed and the balance order shall be cancelled with levy of
maximum penalty. Firm shall also be debarred for one year or participating against
next tender for that rating, whichever is later. The transformers already supplied
(including tested in challenge testing) shall be accepted with the following
conditions:
Page-196 of 456./ TN-523

i) Guarantee period of the supplied Transformers shall be increased by double

the normal guarantee period.
ii) Bank guarantee shall be extended to cover the additional guarantee period.
33. GUARANTEE PERIOD:
I. Performance guarantee of the transformer(s) with LT protection unit shall be for the
period of 36 (Thirty Six) months from the date of dispatch of material. The date of
expiry of guarantee period shall be marked on the rating plate. Transformer(s)
alongwith LT protection unit failed within such guarantee period shall have to be
replaced free of cost expeditiously. The Manufacturer may use Core,
Transformer Tank and LT Bushing Box of the GP failed Distribution
Transformer. All other materials shall be replaced by new materials such as
Transformer Oil, HV & LV Windings, Metal Parts and Fittings & Accessories,
etc. The Testing Procedure of such replaced Distribution Transformer
including Physical Verification shall be same as per Testing of New
Distribution Transformer at Firm’s Works as well as at CTL without any
tolerance in the losses at 50% and 100% loading.
i) The firm will replace all type of GP failed Distribution Transformers without asking
any segregation on account of manufacturing defect. However, the Discom will
compensate the cost of missing parts as per practice in vogue.
ii) The guarantee period failed transformers will directly be lifted by the suppliers from
the respective circle store within a period of 60 days from the date of
intimation by the respective consignee and will replace Distribution
Transformers against G.P. failed within 30 days from the date of lifting in
the ACOS, JCC (Achrol) store/central store along with the joint inspection sheet of
missing parts issued by the respective consignee. After receiving the material at
ACOS, JCC store, the same shall be tested at CTL as per provisions of the relevant
contracts and will be issued to the circle store as per requirement on Nigam’s account.
The invoices of missing parts shall be verified by the ACOS, JCC store as per the joint
inspection sheet issued by the circle store as per practice in vogue and accordingly,
the Sr. A.O. (CPC) will make the payment of missing parts, if any.
iii) The loading of G.P. failed Distribution Transformers at circle store and un-loading of
replaced Transformer at ACOS, JCC (Achrol store) will be on suppliers’ account.
iv) The firm will replace G.P. failed transformers irrespective of breakage of body seals
as well as physical damage of transformer tank body due to bursting. The period
during which transformer remained defective/failed will not be accounted in the
performance Guarantee period. The period of defective will be reckoned from the date
of first intimation (i.e. field officer/consignee whichever is earlier) to date of delivery
replaced transformer.
a) Firms shall lift the G.P. failed Transformer(s) within a period of 60 days from the
date of issue of notice/email by the concerned circle ACOS/ ACOS (JCC) from
where the supplier has been authorized to lift the transformer.
b) However, the period during which Transformer remained defective/ failed will not
be accounted in the Performance Guarantee Period. The period of defective/ failed
Page-197 of 456./ TN-523

will be reckoned from the date of first intimation (i.e. field officer/ consignee,
whichever is earlier) to the date of delivery after successful replaced transformer.
The record of Performance Guarantee Period of Distribution Transformer will be
worked out in the above manner and record of the same shall be maintained by
the SE(I&S)/ ACOS (JCC)/ concerned ACOS at their level to ensure that
Distribution Transformer shall work for the complete Guarantee Period.
c) The supplier will deliver back after successful replacement of G.P. failed
Distribution Transformers within 90 days from the date of issue of Notice/ email
as mentioned above positively as mentioned at point No. (a).
d) In case firm fails to deliver replaced Transformer(s) within 90 days from date as
mentioned at point No.(a)above, the cost of under Guarantee Period failed
transformer(s) not repaired by the firm shall be worked out on the basis of
ordered price of latest TN and the same shall be withhold tentatively from the
firm’s financial hold and a penalty at the rate similar to that of delay in delivery (as
for new supplies) subject to maximum 5%, shall be levied for the late delivery of
replaced Transformer(s). The delay in delivery of G.P. replaced Distribution
Transformer shall be worked out from the date of issue of notice/email by the
concerned circle ACOS/ ACOS (JCC) from where the supplier has been authorized
to lift the transformer.
e) In case firm fails to lift the G.P. failed Distribution Transformer(s) beyond 3
months (90 days period) as mentioned in point no. (a), Ground rent shall be
recovered @1% per month or part thereof (for actual delay in lifting the material
beyond 3 months (90 days) from the date as mentioned above, subject to a
maximum of 5%. This amount of 5% will be in addition to recovery mentioned in
point no. (d). After this clause following clause will also come into effect.
f) In case firm fails to lift the G.P. failed Transformer(s) within 6 months from date
mentioned in point no. (a), then Nigam may proceed for auction of these GP failed
Distribution Transformer at the risk and cost of the supplier after giving 30 days
final notice to the firm. The amount recovered through auction may be adjusted in
any type of recoveries (if any). The recoveries of this point will be in addition to
recoveries mentioned in point no. (d) and (e).
II. All the replaced transformers by the manufacturer under guarantee clause shall carry
a further guarantee of 12 months after replacement or unexpired guarantee of 36
months from the date of supply, whichever is later, after replacement. The bank
guarantee equivalent to cost of replaced transformers shall be furnished after expiry
of performance guarantee period to cover such guarantee. The purchaser also
reserves the right to withhold the payment of supplier firm, under any other contract,
if the performance of the supplier in replaced transformers is not satisfactory. Each
supplier shall invariably furnish the detailed information about the total number of
transformers failed and replaced by them, every month after commencement of
supplies.
III. In order to ascertain that transformers have successfully completed guarantee period
the following details shall be provided on the transformer body:
Page-198 of 456./ TN-523

A. A replacement identification steel plate on replaced transformer against G.P.

failed transformer of size 75 x 75 x 2.5 mm duly engraved with following
details shall be welded on the transformer body.
Particulars Original Supply 1st Replacement 2nd Replacement 3nd

Replacement
Firm’s
Name/Logo
TN
Rating (KVA)
Sr. No.
Date of Dispatch
Date of failure
Guarantee period
Upto
B. Such metallic plate fixed on first replacement should not be removed at the time of
second replacement or any subsequent replacement. However, necessary details of
failure and replacement shall be graved on the identification plate, each time it is
replaced in guarantee.
Note:- All other plates such as rating and terminal marking plate and Technical
cum Identification Plate have to be affixed on the replaced transformers. In
case it is felt that these are loose, then it should be repaired suitably by
welding or riveting.
C. The replaced transformer shall be provided with 40 mm wide red color band all around
transformers including radiator each time it is replaced in G.P. Thus if a transformer is
replaced three time in G.P. then there should be three colored bands each of size 40
mm.
IV. Test checking of G.P. failed transformers will be allowed to the supplier at Nigam’s
store before lifting of G.P. failed distribution transformers to repair at supplier’s works
so that minor mistakes be rectified at Nigam’s stores. The Consignee will accordingly
intimate to the Supplier to lift the GP failed Distribution Transformer.
IV. Formatted: Numbered + Level: 1 + Numbering Style: I, II,
III, … + Start at: 1 + Alignment: Right + Aligned at: 0.25" +
V. The Testing Procedure of such replaced Distribution Transformer including Physical Indent at: 0.5"
Verification shall be same as per Testing of New Distribution Transformer at Firm’s
Works as well as at CTL without any tolerance in the losses at 50% and 100%
loading.
NOTE:- Firm shall keep the records for at least 8 years of transformers supplied
by them.
34. SAFE CUSTODY BANK GUARANTEE:
Safe custody Bank Guarantee (SCBG) not to be taken from those supplier firms
whose available financial hold in the form of composite Bank Guarantee(s) is more than the
amount of SCBG as per following slab:
In case if order is upto 1000 Nos. DT’s the firm have to give safe custody Bank
Guarantee for Rs.5.00 Lacs and if order is more than 1000 Nos. but upto 3000 Nos. then
the safe custody BG for Rs.10.00 lacs and for orders more than 3000 Nos. DT’s the
Page-199 of 456./ TN-523

value of safe custody BG shall be Rs.20.00 Lacs. The safe custody bank Guarantee
(SCBG) shall be of 1% of the value of the contract or as per above mentioned slab,
whichever is lower.
The Safe custody Bank Guarantee (SCBG) be taken as per above mentioned slab from
those supplier firms whose financial hold is not available in the form of Composite Bank
Guarantee(CBG).If the available financial hold in the form of CBG is less than the SCBG
amount as per above slab, then SCBG for the additional amount will be taken.
The Composite Bank Guarantee(s) equivalent to amount as per above slab

shall only be released after fulfilling the contractual obligations by the firm
regarding under guarantee period failed distribution transformers.
NOTE: Payments shall be made only after receipt of successful test report from our Central
Testing Laboratory (CTL) on the samples selected from the material received at the stores,
however, the payment priority shall be maintained from the date of submission of bills
alongwith receipted challans to the Sr. Accounts Officer (CPC), JVVNL, Jaipur.
35. CSP Features:

The transformers shall have the following CSP features.
a) INRERNAL HV FUSES ON THE HT SIDE OF TRANSFORMER as per IS9385 Formatted: Font: 11 pt, Font color: Black
Part-II:1980 Formatted: Line spacing: single, Numbered + Level: 1 +
Numbering Style: a, b, c, … + Start at: 1 + Alignment: Left +
Specification for the H.T FUSES: Expulsion/any other suitable fuse placed in Aligned at: 0.52" + Tab after: 0.77" + Indent at: 0.77"
series with primary winding. This fuse is mounted normally inside of the primary Formatted: Indent: Left: 0.77", First line: 0"
bushing and is connected to the high voltage winding through a terminal block.
This has to protect that part of the electrical distribution system which is ahead
of the Distribution transformers from faults which occur inside the Distribution
transformers i.e., either the windings or some other part of the transformer.
It shall be ensured that this fuse does not blow for faults on the secondary side (LT side) Formatted: Indent: First line: 0.12"
of the transformer i.e., the blowing characteristic of the fuse and LT breaker shall be so
coordinated that the fuse shall not blow for any faults on the secondary side of the
transformer beyond LT breaker and these faults shall be cleared by the LT breaker only.
The fuse shall be make of ABB/ERMCO/Global/samrakshna/Transguard or any other
duly type tested make approved by JVVNL.
ii) INTERNALLY MOUNTED OIL IMMERSED LT BREAKER ON THE LV SIDE Formatted: Font: 12 pt
OF THE TRANSFORMER as per IS/IEC 60947-2:2003: Formatted: Font: 11 pt
LT Circuit Breaker:All LT faults after the breaker shall be cleared by this breaker. As Formatted: Font: Bold, Font color: Black
such, it shall be designed for the perfect coordination with the HT fuse link. The
supplier shall furnish the time/current characteristics of LT circuit breaker and 11 kV
fuses for various current multiples. The two characteristics shall be drawn on the same
sheet to indicate coordination between the circuit breaker and fuse. This shall be
based on the type test carried out on one of the transformers. In addition, the
supplier shall carry out coordination test as indicated above, and this forms one of the tests
for acceptance.
The breaker is to be mounted on the secondary side of the transformer under oil to
minimize premature operations from primary surges as would be with undersized line
fuses. Three single pole elements are preferred. THE BREAKER SHALL BE COORDINATED
THERMALLY WITH THE TRANSFORMER RATING TO FOLLOW CLOSELY THE
VARIATIONS OF COIL TEMPERATURE DUE TO FLUCTUATIONS IN LOADS AND
Page-200 of 456./ TN-523

AMBIENT TEMPERATURES.
This is to be accomplished by connecting the breaker in series between the secondary
winding and the load current. The breaker shall be located in the same oil as the core and
coil assembly so that the bimetal are sensitive to the temperature of oil as well as the load
current.
(c)The circuit breaker may be an electromechanical device with three main elements viz..
(i) Temperature sensing (ii) latching and tripping and (iii) current interrupting. The
temperature sensing function might be accomplished through the use of bimetallic
strips, which would be built into the breaker, such that load current of the
transformer flows through them. In addition to this, a magnetic tripping device is to be
provided for increasing the opening speed of the breaker under high fault conditions. The
circuit breaker shall be mounted inside of the transformer so that these bimetallic strips
are within the top oil layer of the transformer. The latching and tripping functions of the
circuit breaker may be carried out within assembly similar to those used in industrial
type air circuit breaker. The circuit breaker shall also be closed and opened manually
standing on ground and with a magnetic trip device also. The current interruption element
shall consist of copper current carrying parts plus a set of copper tungsten current
interrupting contacts. The cross section of the current carrying parts of the breaker shall Formatted: Font: Bookman Old Style, 11 pt, Complex Script
withstand the full load current at a current density not more than2.0 A/Sq.mm (for Font: 11 pt, Bold
additional mechanical strength the area should be more). The magnetic element shall
increase the opening speed of the circuit breaker under high fault current conditions. The
response of circuit breaker to the activity shall remain unchanged by the addition of the
magnetic trip element. The specification to which the breakers conform shall be indicated.
The LT circuit breaker shall be make of samrakshna/Transguard/ Vijai Mercantile/
Global/ P&A/ ARDRY/ERMCO or any other duly type tested make approved by JVVNL.
iii) LOAD MANAGEMENT SIGNAL LIGHT:A signal light, controlled by a bimetal in

the breaker shall switch on when the transformer load reaches a predetermined level
indicating that the transformer has been overloaded. The loadmanagement signal light
shall perform two functions. It shall show visually when the particular
Transformer has been operating in an overload condition and shall provide knowledge for
good system management, the economic change out point for the transformer is fast
approaching. The signal light need not indicate temporary overloads and shall turnon only
when the overload condition has existed at a given level for a certain length of time.
The LT circuit breaker shall have a set of auxiliary contacts builtin for signal light Formatted: Indent: First line: 0.5"
operation. These, normally open contact, shall form part of the signal light circuit. The
signal light circuit shall consist of an auxiliary transformer winding (one or two turns)
which generates about 4V, for the signal light contact set within the circuit breaker,
and the signal light is to be mounted on the transformer tank. The signal light
contact set is mechanically connected to the main circuit breaker latching and bimetal
system. The signal light mechanism is adjusted so that the signal light contacts will close at
a preset thermal condition which occurs before the main latching system opens the main
contact. The net result is a visual external indication that a preset load condition has
reached by the transformer. The signal light mechanism does not reset itself when the load
drops off, the signal light remains lighted once the signal light contacts closes and can only
be turned off by manually operating the external circuit breaker handle.
The breaker should withstand dielectric test of 11kv and the same shall be verified
during acceptance test.
Page-201 of 456./ TN-523

The type tests shall be carried out on Circuit Breaker of rated current or higher
current rating as per IS/IEC 60947 for Sequence-I, II, and III amended upto date from any
independent laboratory recognized by NABL.
Note: Mechanical operation test on LV circuit breaker shall be carried out in oil medium as
per IS 13947.
Additional Routine and Acceptance Tests

Demonstration of Trip and Reset operation by applying atleast 500% of the rated current.
38. QUANTITY:
Sr. No. Item/Rating Quantity in Nos.

1. 11/0.433 KV, 25 KVA Aluminium Wound ENERGY EFFICIENT
LEVEL-2 (STAR-1) Completely Self Protected (CSP) Distribution
Transformers with provision of LT Bushing Box. The prices shall
be variable as per IEEMA Price Variation Formula without any
ceiling .
Note: 1.Price bids shall be opened only of the firms who are having “BIS
Certificate” as on opening of technical bid.
2. Besides above changes, the technical parameters of the specifications

wherever are deviating from the IS:1180 (Part-I/2014), the same shall be in
accordance with IS:1180 (Part-I/2014) and its latest amendments, if any and the
changes where the IS:1180 (Part-I/2014) is silent for technical parameters, same
shall be applicable as per Discom specification.
3. The Star Rated will be as per notification letter dated 16.12.2016, Ministry
of Power, Govt. of India, New Delhi.
4. The lot wise destinations are tentative and JVVNL reserves the right to change
the destination at the time of issue of Dispatch Instructions without any
financial implications.
39. Make of Brought Out Items:
The Make of brought out items like Bushings, Transformer Oil, etc. other than Make specified
in the specification/work order may be accepted if confirms to relevant IS with due approval
of JVVNL.
Page-202 of 456./ TN-523

MANUFACTURER’S GUARANTEED TECHNICAL PARTICULARS

25 KVA (AL Wound) 11/0.433 KV ENERGY EFFICIENT LEVEL-2 (STAR-1)
COMPLETELY SELF PROTECTED (CSP) WITH PROVISION OF LT BUSHING BOX
AGAINST TN-2689
S. No. PARTICULARS 25 KVA

1. Manufacturer’s Name and Address
2. Service (Outdoor, continuously rated)
3. Type (CRGO/Conventional)
4. Continuous max. Rating under peak ambient temp. of 50° C
5. Rated voltage :
(a) HV
(b) LV
6. Rated current
(a) HV
(b) LV
7. Rated Frequency
8. No. of phases
9. Method of connection :
(a) HV
(b) LV
10. Vector group reference
11. Method of cooling
12. Max. temperature rise obtained by the transformer when run at the
maximum ambient temp. of 50°C
(a) Of top oil by thermometer
(b) Of winding by resistance
13. Hottest spot temperature, at rated current and voltage, calculated
corresponding to the yearly weighted average ambient temp. of 35°C
14. Total Load losses (Watts) at 75 Deg. C. at 50% loading (Max).
15. Total Load losses (Watts) at 75 Deg. C. at 100% loading (Max.).
16. Percentage impedance at full load and at 75°C
17. Percentage resistance at full load and at 75°C
18 Percentage reactance at full load
19. Efficiency at 75°C :-
a) At unity power factor :-
i) At 125% of full load
ii) At 100% of full load
iii) At 75% of full load
iv) At 50% of full load
v) At 25% of full load
b)At 0.8 power factor :-
i) At 125% of full load
ii) At 100% of full load
iii) At 75% of full load
iv) At 50% of full load
v) At 25% of full load
20. Maximum efficiency
21. Load at which maximum efficiency occurs
22. % regulation at full load & at 75°C:
a)At unity power factor
Page-203 of 456./ TN-523


b)At 0.8 power factor
23. Max. flux density at rated voltage and rated frequency
24. Percentage no load current at rated frequency (without any positive
tolerance)
a) At rated voltage
b) At 112.5% rated voltage
25. Insulation level of transformer :-
a) Impulse strength of HV
b)Power frequency withstand voltage
HV
LV
26. H V Bushing details:-
(a) Rating of the bushing
(b) Impulse strength
(c) Power frequency withstand voltage, dry and wet
(d) IS reference
27. LV Bushing details :-
(a) Rating of the bushing
(b) Power frequency withstand Voltage, dry and wet
(c) IS reference
28 Core Details
a) type of core
b) Grade
c) Thickness
d) Core Dia
e) Effective Core Area, taking stacking factor as 0.97
f) Centre distance between limbs
g) Window height
29. H V coil constructional details:-
(a) type of winding
(b)No. of coils per phase
(c)Conductor cross Section(min.)
(d)Bare conductor dia
(e)Covered conductor dia
(f) Phase current (H V)
(g)Current density
(h)Coil I. D
(i)Coil O.D
(j)Coil axial length
(k) Total no. of turns per phase
(l) Resistance per ph. at 75°C
(m) Weight of covered conductor per transformer
(n) Inter layer insulation
(0) No. of vertical spacers per circle (in the annular gap between LV
& HV)
30. LV coil constructional details:-
(a) type of winding
(b)No. of coils per phase
(c) Conductor cross section(min.)
(d)Bare conductor size
Page-204 of 456./ TN-523


(e)No. of conductors in parallel
(f)Covered conductor size
(g)Phase current ( L V )
(h)Current density
(i)Coil I. D.
(j)Coil O.D.
(k)Coil axial length
(l)Total no. of turns per phase
(m) Resistance per phase at 75°C
(n) Weight of covered conductor per transformer
(o) Inter layer insulation
(p) No. of vertical spacers per circle
31. Minimum external clearances in air (with B M C s mounted)
(a) HV phase to phase
(b) HV phase to earth
(c) LV phase to phase
(d) LV phase to earth
32. Minimum internal clearances (in oil)
(a) Between HT outside surface and tank inside (non bushing side)
(b) Between HT outside surface & tank inside ( HV & LV bushing
side)
(c) Between HV windings and yokes (end insulation)
(d) LV windings & yokes
(e) From top of yoke to inside of top cover of tank (with gasket)
(f) LT/HT coil annular gap. (bare Conductor)
(g) Radial clearance between core &
LV coil (Bare conductor)
(h) Phase to phase Clearance between Limbs (HV Conductors), with
a minimum of 2 Nos. x 1mm Press board covering the tie rods
(i) Minimum thickness of locking Spacers between HV coil sections
(including 1 mm ring of press board)
(j) Maximum clearance of core channels from tank walls at each end
33. Tank details :-
(a) Clear inside tank dimensions:
(i) Length
(ii) Breadth
(iii) Height
(b) Tank sheet thickness
(i) Sides
(ii) Top
(iii) Bottom
(c) Tank stiffener details
(i) No. of stiffeners around the tank
(ii) Size
34. Cooling radiator details :
(a) Cooling tube size
(b) Total length of tubes used
(c) Whether cooling calculations attached?
(d) No. of tubes on each side
35. Tie rod details
Page-205 of 456./ TN-523


36 Core Details
(i) Size of core frame channels
(ii) Core diameter (mm)
(iii) Core stud details
(iv) Core coil assembly base supports (2 Nos)
(v) Window Height (mm)
(vi) Limb Centre (mm)
37. Transformer weight details:
(a) Core coil assembly
(b) Tank with fittings
(c) Oil weight
(d) Total weight of transformer
(e) Volume of oil (minimum quantity for first filling)
38.. Overall dimensions
(a) Length
(b) Breadth
(C )Height
39. Whether the bidder is an ISO: 9001/9002 certified company?
40 Whether the metal parts of HV/LV Bushing are as per relevant IS and not under YES/NO
size (YES/NO). If Metal parts are under size, then the lot may be rejected at firm’s
works.
41 Whether the BEE Label sticker has been affixed on transformer. If No, then the lot YES/NO
may be rejected at firm’s works.
42 Whether the HV terminals on transformer tank are duly indelibly marked by YES/NO
stamping (i.e. 1u, 1v, 1w) with Min. letter size of 40x40 mm. If No, then the lot
43 Whether the LV terminals on transformer tank are duly indelibly marked by YES/NO
stamping (i.e. 2u, 2v, 2w & 2n) with Min. letter size of 40x40 mm. If No, then the
lot may be rejected at firm’s works.
44 Whether the Two Nos. welded heavy duty lifting lugs of MS plate of 6 mm (10 KVA YES/NO
to 16 KVA), 8 mm (25 KVA to 100 KVA) & 10 mm (160 KVA to 500 KVA) thickness,
suitably reinforced by extended vertical supporting edge of same thickness in one
piece having size 125 mm width and 125 mm length has been provided, these shall
be so extended that cutting of bent plate is not required. If No, then the lot may be
rejected at firm’s works.
45 Whether the LV Bushing Pocket has been continuously welded from both inside and YES/NO
outside on tank wall. If No, then the lot may be rejected at firm’s works.
46 Whether, the Lugs for LV terminal of transformer have been crimped with crimping YES/NO
tool and duly insulated. If No, then the lot may be rejected at firm’s works.
47 Whether the Lugs for terminal end for meter of transformer have been crimped YES/NO
with crimping tool and duly insulated. If No, then the lot may be rejected at firm’s
works.
48 Whether the Lugs for outgoing bushing of transformer have been crimped with YES/NO
crimping tool and duly insulated. If No, then the lot may be rejected at firm’s
works.
49 Whether one end of HT Fuse is connected to Delta joint by brazing only and the YES/NO
other end of HT Fuse is connected to Bushing Rod through Nut-Bolt
method/brazing. If No, then the lot may be rejected at firm’s works.
50 Whether the Core has been earthed through copper earthing foil of 25 mm width & YES/NO
1 mm thickness bolted on core frame channels after removing channel paint. If No,
then the lot may be rejected at firm’s works.
51 Whether the Sloping flap are provided on conservative pipe to main tank inside top YES/NO
cover. If No, then the lot may be rejected at firm’s works.
Page-206 of 456./ TN-523


52 Whether the Rating & Terminal Marking Plate is non-detachable & has been affixed YES/NO
with Min. 10 rivets and the base of the Rating & Terminal Marking Plate is
continuously welded with the tank. If No, then the lot may be rejected at firm’s
works.
53 Whether the Internal electrical clearances in oil are found as per specification. If YES/NO
No, then the lot may be rejected at firm’s works.
54 Whether all the External Electrical clearances are found as per specification. YES/NO
If No, then the lot may be rejected at firm’s works.
55 Whether the Antitheft clamp on top cover of tank for pressure relief valve is YES/NO
painted & tightly packed and the gap between clamp & pressure relief valve is Min.
10 mm. If No, then the lot may be rejected at firm’s works.
56 Whether two flat washer, one nut and one spring washer have been provided with YES/NO
top cover nut bolts. If No, then the lot may be rejected at firm’s works.
57 Whether Conservator is provided above the HV bushing with min. clearance of 50 YES/NO
mm. If No, then the lot may be rejected at firm’s works.
58 Whether any core stamping found rusted & damaged (hole observed in stamping). YES/NO
If Yes, then the lot may be rejected at firm’s works.
59 Whether the top cover and tank top flange is deformed and sunked at center of YES/NO
non-bushing side or hammer marks are also observed, as such top cover is not
sloping down opposite LV bushing side as per requirement. If Yes, then the lot may
be rejected at firm’s works.
60 Explosion Vent shall be opening towards ground from LV bushing side with M. S. Required as
mesh having Pipe Diameter of minimum 50 mm with 0.025mm copper shim sheet/ per spec.
Bakelite thick sheet of 0.4mm thick as diaphragm shall be provided on the top of
the cover of the tank such that the pressure released should be directed to the
ground & it should be inserted in the top cover of tank, welded outside & inside of
top cover and its pipe shall be connected with the conservator. Length of the
explosion vent should be minimum 700 mm. Nut bolts of flange of Explosion vent
should be tag welded. The vent shall be provided on opposite side of the circuit
breaker operating rod. The other end of the vent pipe shall be guarded with wire
mesh for preventing the entry of worms and nesting. The diaphragm shall burst at
a pressure of 0.76 to 0.95 kg/ sq.cm. There shall be minimum 140 mm clearance
between live part of HV bushing to Explosion vent. If not found as mentioned
above, then the lot may be rejected at firm’s works.
61 Whether the Details of Make, Rating and TN/Order No. are punched or an identity YES/NO
plate with said details is welded on core coil assembly. If No, then the lot may be
62 Whether Bi-metallic connectors on Bushings are provided as per specification. If YES/NO
No, then the lot may be rejected at firm’s works.
63 Whether the 12 Nos. nuts & bolts (4 Nos each on length sides & 2 nos each on YES/NO
widths sides of tank body) have been tag welded on top cover. If No, then the lot
64 Whether the tank base channel and stiffeners are continuously welded. If No, then YES/NO
the lot may be rejected at firm’s works.
65 Whether the header pipe connecting radiator bank to the tank is rectangular in YES/NO
shape with approximate size of 100x20 mm. Alternatively round pipe (of dia 32 mm
in case of upto 100 KVA and 80 mm in case of 160 KVA to 500 KVA Three Phase
Distribution Transformers) can also be used for connecting the radiator bank to the
tank. Whether the placement of top header pipe to the tank body is above the top
of yoke, to facilitate cooling for hot oil sump over top yoke. If No, then the lot may
be rejected at firm’s works.
66 Whether 2 Nos. of 1 mm thick press board has been used for covering the tie rods YES/NO
for phase barrier. Besides, tie rods have to be covered by SRBP tubes of suitable
size. If No, then the lot may be rejected at firm’s works.
67 Whether 2 mm press board has been used for base support insulation and core YES/NO
clamping channel insulation. For bottom and top yoke insulation, only PC Board of
min. 2 mm thickness has to be used. Also, vertical spacers between HV and LV
coils and radial spacers (tickleys)/blocks etc. shall be of PC Board only. If No, then
68 Whether Press Board used has been of senapathy whitely / Raman make and YES/NO
Page-207 of 456./ TN-523


Perma wood or haldu wood blocks has been used for Top and Bottom yoke
insulation. If No, then the lot may be rejected at firm’s works.
69 Whether the size of core clamping MS Channel used on top and bottom (for YES/NO
stacked core transformers) is as per specification. If No, then the lot may be
70 Whether core clamping Channel on LV side has been reinforced at equidistance, if YES/NO
holes/cutting is done for LT lead in order to avoid bending of channel. If No, then
71 Whether core clamping MS channel has been painted with varnish or oil-resistant YES/NO
paint. If No, then the lot may be rejected at firm’s works.
72 Whether Tie-rods used in core clamping arrangement has been effectively insulated YES/NO
as per specification. If No, then the lot may be rejected at firm’s works.
73 Whether all top and bottom yoke nuts & bolts and tie rods has been painted with YES/NO
oil and corrosion-resistant paint and phosphate coated paint for tie rods before use.
74 Whether the sizes of following items are as per specification: YES/NO
i. Tank top flange
ii. Cover Bolt (Stainless Steel only)
iii. Cover Bolt Spacings
iv. Tank Base Channel (continuous welded)

75 Whether top cover edge has been extended by Min. 30 mm in such a manner to YES/NO
cover gasket each side and it has been bent at Min. 15° angle. If No, then the lot
76 Whether 04 Nos. Anti-Theft Fasteners has been provided - one each on all four YES/NO
sides in centre of body of transformer. If No, then the lot may be rejected at firm’s
works.
77 Whether two holes has been provided – one on top cover and other on collar of YES/NO
transformer to facilitate providing of 2 Nos. poly-carbonate seals on longitudinal
side. If No, then the lot may be rejected at firm’s works.
78 Whether dry type film thickness (DFT) of paint is as per specification. If No, then YES/NO
79 Whether Oil level gauge of minimum 100 mm length of prismatic glass has been YES/NO
located at center of conservator tank. If No, then the lot may be rejected at firm’s
works.
80 Whether make of HV/LV Bushings is as per specification/PO. If No, then the lot YES/NO
81 Whether HV Bushing pockets are such that the HV bushing is tilted more towards YES/NO
the HV side. The bushing of R & B phases may also be tilted sidewise to maintain
the required electrical clearances. If No, then the lot may be rejected at firm’s
works.
82 Whether Technical cum Identification Plate of size 125 x 75 x 2.5 mm having YES/NO
details as per specification punched with letters of size 8mm X 6mm has been
continuously welded to the main tank body (In case of 10 KVA rating, this plate
may be continuously welded on stiffener) below the middle HV bushing in clearly
visible position. If No, then the lot may be rejected at firm’s works.
(Signature)
Name & Designation with seal of the bidder
Page-208 of 456./ TN-523

Technical Specification For Supply 25kva

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Technical Specification For Supply 25kva

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SPEC/TN-2689/ 25 KVA Three Phase BIS level-2 (STAR-1) 1

This specification covers the design, engineering, manufacture, assembly, inspection

Unless otherwise modified in the specifications, the Distribution Transformers,

Page-168 of 456./ TN-523

Sr. Specification Details about International &

3 IS:335/2018 New insulation oils for Transformers BS 148, D-1473, D-1533

5 IS:3347 (PART-III / Sec- Dimensions of Porcelain (parts & Metal parts)

6 IS:7421 Porcelain Transformer Bushings for low voltage

7 IS:2099/1986 Porcelain Transformer bushing for AC volts

9 IS:1866/1978 Code of practice for maintenance & supervision

Page-169 of 456./ TN-523

26 IS -2026 Specification for Power Transformers

Note:- Besides above changes, the technical parameters of the specifications

Material conforming to other internationally accepted standards, which ensure equal or

The distribution transformers to be supplied against this specification shall be suitable

i) Peak ambient temperature : 50°C

The transformer shall confirm to the following specific parameters:

Page-170 of 456./ TN-523

ii) System Voltage (Max.) : 12 kV

5. NO LOAD VOLATGE RATIO:

The No load voltage ratio(s) shall be 11000/ 433 Volts.

i) Top oil temperature rise measured by thermometer 35 Deg. C.

Page-171 of 456./ TN-523

However, the transformer shall be designed for class ‘A’ insulation.

10. TAPPINGS: No taps are to be provided in these transformers.

12. ELECTRICAL CLEARANCES:

(A) EXTERNAL (IN AIR)

Minimum external electrical clearances after mounting the bimetallic terminal

Voltage Medium Clearance

B) INTERNAL (IN OIL):

Page-172 of 456./ TN-523

d) Between HV windings & yokes (end insulation) 20 mm

13. TEST VOLTAGE:

Nominal system Highest system Impulse withstand Power frequency test

14. HEAT DISSIPATION (COOLING) / RADIATOR CALCULATIONS & E T R / PSR

Cooling area of the tank/radiators should be sufficient to dissipate the guaranteed

Plain surface of tank – 500 W/m2

15. WINDING AND INSULATION:

Page-173 of 456./ TN-523

In case of wound core one HV coil is accepted.

Rating Current density in Amp./Sq.2

iii) INSULATION MATERIAL:

iv) CONNECTIONS AND TERMINATIONS:

Page-174 of 456./ TN-523

16. CORE CONSTRUCTION & CORE COIL ASSEMBLY DETAILS:

Page-175 of 456./ TN-523

Maximum permissible magnetising current in percentage of rated full load current

The tolerance on magnetizing current shall be +30% on declared value of

vi) Core clamping:

stacked core transformers). Rolling tolerance will be as per IS:1852-1985 with

Page-176 of 456./ TN-523

iii. Channel on LV side to be reinforced at equidistance, if holes/cutting is done for

b) Core Clamping – Amorphous Metal and CRGO wound core Transformers

NOTE: Equal Weightage shall be given to the transformers with Amorphous

Formatted: Indent: Left: 0", Hanging: 0.75"

(C) CORE-COIL ASSEMBLY:

Page-177 of 456./ TN-523

Sr. Item Particulars

d) Support of core 2 Nos. MS channels OF 75x40 mm.