Electrical Safety and Protection of Ehv Substation Including The Effects of Power System Transients

ELECTRICAL SAFETY AND PROTECTION
OF EHV SUBSTATION
INCLUDING THE EFFECTS OF POWER SYSTEM
TRANSIENTS
A PROJECT REPORT
Submitted By
PRATAP BHUNIA
(Roll No.)
In partial fulfillment for the award of the degree
of
BACHELOR OF TECHNOLOGY
in
ELECTRICAL ENGINEERING
TECHNO INDIA SALTLAKE
MAULANA ABUL KALAM AJAD UNIVERSITY OF TECHNOLOGY

Index
Sl. No. Topic Page No.

1 Substation Network and 1
Load Distribution
2 Substation Network 2
3 Civil Works Specification 4
4 Various Subsystems in 10
Substation and Their
Functions
5 Substation Equipments and 11
Their Functions
6 Design of Capacity of 12
Transmission Lines
7 Calculation of Line 14
Constants and SIL
8 Bus Bar Arrangement 15
9 Power Transformer 17
10 Substation Earthing 20
11 Circuit Breaker 28
12 Isolator 31
13 Current Transformer 34
14 Capacitor Voltage 36
Transformer
15 Lightning Surge 38
16 Switching Surge 41
17 Lightning Arrester 47
18 Surge Absorber 57
19 References 61
Electrical Safety and Protection of EHV Substation Including
the Effect of Power System Transients
Substation Network and Load Distribution:
The first step towards the design of 400/220 kV substation is to determine the
load that the substation has to cater and develop it accordingly. The substation is
responsible for catering bulk power to various load centers distributed all around
through six 220 kV feeders and one 400 KV feeder. The substation is fed 950 MVA
power from 2 generating stations through two 400 kV single circuit lines. The power
is received on 400 kV busbar. 350 MVA power is dispatched to a 400 kV load. The
remaining power is fed to 3 400/220 kV 315 MVA transformers and further fed to 220
kV busbar. From 220 kV busbar, 6 loads are supplied. The main 3 transformers are 3
winding transformer. A total loss of 76.47 kVA occurs in 3 315 MVA transformers.
Table 1: Load flow through the 400/220 kV substation
Incoming Power Amount in MVA Outgoing Power Amount in MVA
From 2 generating 950 To 400 kV load 350

stations
To 220 kV loads 599.83
Loss in 3 315 0.076

MVA transformers
Total 950 Total 950

Substation Network
Substation Design
Civil Works Specification
General:
All structures, buildings, foundations etc., layout & other details shall be
designed and developed keeping in view the functional requirement of the line and sub-
station facilities.
Licensed Premises (Substations Sites):
1. Formation Levels: Formation Level (FL) of substations shall be fixed

minimum 600 mm higher than the surroundings on the basis of the drainage conditions
and the Highest Flood Level in the area.
2. Site Preparation: Necessary earth cutting / filling (spreading), leveling,
compaction and dressing should be done to reach the desired formation level.
Backfilled earth shall be free from harmful salts; viz, Sulphates, Chlorides and / or any
Organic / Inorganic materials and compacted to minimum 95% of the Standard
Proctor's Density (SPD) at Optimum Moisture Content (OMC). The subgrade for the
roads and embankment filling shall be compacted to minimum 97% of the SPD at
OMC.
3. Site Surfacing in Switchyard Area: Site surfacing should be carried out to
provide
 A safe & hazard free high earth resistivity working area (switchyard)
 To prevent growth of weeds & grass within the working area.
The site surfacing will be restricted up to 2.0 m beyond the last structure / equipment
foundation. A 100 mm thick base layer of lean concrete of 1:4:8 using coarse aggregate
of 20 mm nominal size shall be provided in the areas with covering with M-20 concrete
layer with minimum thickness of 50mm in the switchyard excluding roads, drains,
cable trenches etc. 30-40 mm Stone / Gravel spreading shall be done in areas presently
in the scope of the scheme. No stone spreading shall for the time being done in the
areas (bays) kept for future expansion. To hold the stone (gravel) from spreading out
of the surfaced / gravel filled area, a 115 mm thick and 300 mm deep toe wall 25 mm
above top of gravel shall be provided. All visible portions of toe-wall shall be plastered
& cement painted.
4. Outside Switchyard Area: Areas lying outside the switch yard shall be
landscaped, developed and maintained in a clean and presentable fashion.
Water Supply, Sewerage & Drainage System:
1. Water Supply & Sewerage: Water supply & sewerage system shall be to
meet the total water requirement of the substations, facilities and emergency reserve
for complete performance of the works. The design and construction of septic tanks
and soak pits shall be suitable for a minimum 100 users with a minimum 10 year span.
2. Design of Drainage: The concessionaire shall obtain rainfall data and
design the storm water drainage system including culverts, drains etc. to accommodate
the most intense rainfall that is likely to occur over the catchments area in one hour
period on an average of once per ten years.
 Slope of Drainage System: Invert level of drainage system at outfall point
shall be decided in such a way that any water over flow from water harvesting recharge
shafts can easily be discharged outside the substation boundary wall. For easy drainage
of water, minimum slope of 1:1000 shall be provided from the ridge to the nearest
drain. The above slope shall be provided at the top of base layer of cement concrete.
Roads, Culverts &Pcc Pavement / Parking:
All internal roads, culverts and PCC pavements / parking within the sub-
station area and approach road from main PWD road to the sub-station main entry
gate(s) should be constructed as per transportation of heavy equipments.
Transformer Foundations:
1. General Scope:
 RCC foundations & plinths should be designed and constructed having
minimum Grade M-20 laid on base concrete (1:4:8) of minimum thickness 100 mm
along with a pylon support system for supporting the fire fighting system for placing
350 MVA Power Transformers compatible with the type of equipment &fire fighting
systems and manufacturers’ drawings and equipment parameters.
 The foundations of transformers and circuit breakers shall be of block
type. Minimum reinforcement shall be governed by IS: 2974 and IS: 456 suitable for
equipment load requirements of transformer including impact load equivalent to 15%
of total transformer load with oil etc. or total Jacking Load whichever is more.
 An RCC Rail cum Road system shall be provided duly integrated with
the transformer foundation to enable installation of a new unit and the replacement of
any failed unit. The rails shall be fresh, firstquality 52-kg / meter medium manganese
steel as per Indian railway specification T-12-64 and laid to maintain the required rail
gauge.
2. Emergency Oil Evacuation System: Design & construction of
Emergency Oil Evacuation System shall be suitable to the type of fire protection &
emergency oil drainage system selected.
Fire Protection Walls:
1. Fire protection walls in order to protect against the effects of radiant heat
and flying debris from an adjacent fire for 315 MVA Transformers and 100 MVA
Transformers shall be designed & provided in accordance with Tariff Advisory
Committee (TAC) stipulations.
2. A minimum of 2 meters clearance shall be provided between the
equipments and fire walls.
3. The building walls which act as fire walls shall extend at least 1 m above
the roof in order to protect it.
Foundations for RCC Construction Works:
1. General: All the foundations except walls of switch house cum

administrative and fire hydrant building shall be of Reinforced Cement Concrete.
2. Depth of Foundations:All foundations shall rest below virgin ground
level and the minimum depth excluding lean concrete of all foundations below virgin
ground level shall not be less than 500 mm.
3. Height of Foundations: The Switch Yard foundations shall be at least
100 mm above the finished ground level or as per the manufacturers’ design.
Excavation shall extend minimum 150 mm around foundation (from RCC portion
and not from lean concrete).
Buildings:
1. Design Criterion: The buildings shall be designed to withstand the earth

quake pressure as per the requirements of the National Building Code of India.
2. Design Loads:
 Building structures shall be designed for the most critical combinations
of dead loads, superimposed loads, equipment loads, crane loads, wind loads, seismic
loads, short circuit loads and temperature loads.
 Dead loads shall include the weight of structures complete with finishes,
fixtures and partitions and should be taken as per IS: 1991.
 Super-imposed loads in different areas shall include live loads, minor
equipment loads, cable trays, small pipe racks/hangers and erection, operation and
maintenance loads.
 Equipment loads shall constitute, if applicable, all load of equipments to
be supported on the building frame.
3. DG Building Cum Fire Fighting Pump House and RCC Water Storage
Tank: The DG and FF buildings designed to accommodate up to 2 DG sets, motors /
pumps as per fire fighting requirement and a permanent crane, hoist and service
trucks mounted on suitable steel structure (I-section / RS joist) below the ceiling for
servicing, lifting and maintenance of the heavy equipment shall be constructed
adjacent to each other for convenience of maintenance of equipment.
4. Brick Work: All brickwork shall strictly be done according to the
Haryana P.W.D. specifications.
5. Damp Proof Course: On outer walls horizontal DPC shall be provided at
level with plinth protection and on inner face vertical DPC 20 mm thick shall be
provided. On all inner walls horizontal DPC shall be provided at floor/plinth level.
Switch - Yard Fencing and Gates:
Fencing & Gates shall be provided for Switchyard area as per General
Electrical Layout Plan and any other specified area along the lines shown. Chain link
fence fabric shall have size 75 mm; coated wire shall be of 3.15 mm diameter having
zinc galvanizing after weaving. The barbed wire shall be of 12 SWG galvanized steel
with its weight 155-186 gm/m length of wire. Maximum distance between two barbs
shall be 75mm. The barbs shall carry four points and shall be formed by twisting two
point wires, each two turn tightly round one line wire making altogether 4 complete
turns. The barbs shall have a length of not less than 13 mm and not more than 18 mm.
The points shall be sharp and well pointed and single strand galvanized steel wire
conforming to requirements for fence fabric 4 mm diameter or single strand, high
tensile, galvanized steel wire 4 mm diameter shall be used. Cast aluminum alloy or
galvanized steel malleable iron D-Clamp drop forged with bolt, check nut, thimble
and other clamps & material required shall be supplied and installed for stretching the
Barbed wire complete in all respect.
Boundary and Retaining Walls:
A Boundary wall shall be constructed all around the entire substation land.
The front wall shall be 1.4 m high and in addition 0.600 m galvanized iron grill & the
boundary wall on the other three sides shall be 1.8 m with 0.600 m U/C barbed wire
fencing over the wall. All retaining walls and dual purpose boundary walls shall be
designed to withstand sliding and over turning loads.

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ELECTRICAL SAFETY AND PROTECTION

In partial fulfillment for the award of the degree

TECHNO INDIA SALTLAKE

MAULANA ABUL KALAM AJAD UNIVERSITY OF TECHNOLOGY

Sl. No. Topic Page No.

Table 1: Load flow through the 400/220 kV substation

Incoming Power Amount in MVA Outgoing Power Amount in MVA

From 2 generating 950 To 400 kV load 350

To 220 kV loads 599.83

Loss in 3 315 0.076

Total 950 Total 950

Licensed Premises (Substations Sites):

1. Formation Levels: Formation Level (FL) of substations shall be fixed

Water Supply, Sewerage & Drainage System:

Roads, Culverts &Pcc Pavement / Parking:

Fire Protection Walls:

Foundations for RCC Construction Works:

1. General: All the foundations except walls of switch house cum

1. Design Criterion: The buildings shall be designed to withstand the earth

Switch - Yard Fencing and Gates:

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