Technical Specification

Project: KSRP Bhavan @ Madiwala, Bengaluru

Client : BMRCL

Document Description: TECHNICAL SPECIFICATIONS ON

MV DISTRIBUTION BOARDS

Scope: This Document Covers the design, manufacture, assembly, inspection,

Installation, connection, testing and commissioning of
415V MV DISTRIBUTION BOARDS

Specification No: TS-3A

Date of Issue :

Purpose of Issue: For Tender

Revision No : R0

Prepared By : PRS

Checked By : RR

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

3B. M.V.DISTRIBUTION BOARDS

SCOPE :

This section covers the design, manufacture, assembly, testing at manufacturer's works, inspection,
packing for transportation, delivery at site, installation, connection, testing and commissioning of 415V
switch boards with guarantee of performance for a period of twelve (12) months from the date of
commissioning. The contractor shall provide all materials, labor, equipment, scaffolding etc., as
required for the completion of the job.

STANDARDS APPLICABLE

The following standards and rules shall be applicable :

The Distribution Boards shall comply with the latest edition of relevant Indian Standards and Indian
Electricity rules and regulations. The following Indian Standards shall be complied with :

IS 4237-83 : General requirements for switch gear and control gear for voltages
not exceeding 1000V.

IS 5578-85 : Guide for marking of insulated conductors.

IS 11353-85: Guide for uniform system of marking and identification of conductors

and apparatus terminals.

IS 2147-62 Degree of protection provided by enclosures for low voltage switch

Gear and control gear.

IS 2675-83 Enclosed distribution fuse boards and cutouts for voltages not
exceeding 1000V.

IS 2551-82 Danger notice plates.

IS 2516 Circuit breakers Part 1. Requirements (Part I/Sec 1):and tests : Section 1.
Voltages not exceeding 1000V ac or 1200V dc.

IS 4064-78 Air break switches, air break disconnectors, air break switch disconnectors and fuse
combination units for voltages not exceeding 1000V ac or 1200V dc.

IS 1818-72 Alternating current isolators (disconnectors) and earthing switches.

IS 8623-77 Factory built assemblies of switchgear and control gear for voltages upto and including
1000V AC & 1200V DC.

IS 8828-78 Miniature air break circuit breakers for voltages not exceeding 1000V.

IS 9926-81 Fuse wires used in rewire able type electric fuses upto 650 Volts.

IS 8544-79 Motor starters for voltages not exceeding 1000 Volt A.C. or 1200 Volt D.C.

IS 2959-85 Contactors for voltages not exceeding 1000 Volt A.C or 1200 Volts D.C

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

IS 9224-79 Low Voltage fuses.

IS 12640-89 Residual current operated circuit breakers.

IS 1248-83 Direct acting indicating analogue (all parts) electrical measuring

instruments and their accessories.

IS 2705-81 Current transformers. (all parts)

IS 4201-83 Application guide for voltage transformers.

IS 8197-76 Terminal markings for electrical measuring instruments and

their accessories.

Indian Electricity Act and Rules.

415V SWITCH BOARDS

The 415 volt switchboard shall be metal-clad, dead front totally enclosed, indoor type, forming
a self supporting continuous board. The front portion of the board shall have individual
compartments arranged in tier formation to accommodate draw-out type air-circuit-breakers. The back
portion of the board shall contain three-phase and neutral air-insulated busbars, cable terminations,
instrument transformers, etc. The busbars and all other outgoing live terminals shall be protected to
prevent accidental contact while carrying out maintenance work.

DISTRIBUTION ARRANGEMENT

For single transformer load-centers, the panel shall accommodate one transformer secondary
circuit-breaker and specified number of outgoing circuit-breakers all connected to the common busbar.

For two transformer load-center, the 415 volt bus shall be sectionalized and each transformer shall be
connected to the corresponding bus-section over its secondary circuit-breakers. Bus-tie circuit breaker
shall be provided between adjacent bus sections and the outgoing switchgear distribution on each
bus-section shall be as specified.

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

415 VOLT MAIN BUSBARS

Aluminium bus-bars shall be used.

The continuous current rating and the short circuit values which the main busbars are able
to withstand shall be as follows :-

TRANSFORMER RATING CONTINUOUS CURRENT SHORT CIRCUIT

RATING CURRENT RMS
SYMMERICAL
Kva A A
400 630 15000
630 1000 21600
1000 1600 36000
1600 2500 36000
2000 3200 50000

The neutral bus bars shall be designed to carry 50 percent continuous current rating of the main
busbars. 0.8A/ Sqmm bus section should be considered upto 2500A & necessary rating factor there
after.

415 VOLT CIRCUIT-BREAKERS

The circuit-breakers shall be triple-pole, air-break draw-out type. All current carrying contacts
of the breakers shall be silver plated. Arc-chute fitted on each pole shall be easily removable for
inspection of the main contacts. Inter-phase barriers of proper design shall also be incorporated.

The plug connections of main and auxiliary circuit shall be fitted with self-aligning contacts. The fixed
position of the plug connections shall be easily accessible for maintenance. Automatically operated
shutters shall be provided to screen the fixed portion of the plug when the breaker is fully withdrawn
from the cubicle.

The continuous current ratings of the various Circuit-Breaker units at specified ambient
temperature shall be as specified. The RMS Symmetrical breaking capacity of the
different air circuit-breakers shall be as follows, unless otherwise specified :-

CURRENT RATING OF THE ACBs BREAKING CAPACITY RMS

SYMMETRICAL AT PF OF 0.2 TO 0.3
A A

200 15000
400 21000
630 36000
1000 36000
1600 36000
2500 36000
3200 50000

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

OPERATING MECHANISM

The Circuit-breakers shall be either manually or electrically operated as specified. For

emergency closing and testing, the electrically operated breaker shall be capable of
manual closing. For manually operated breakers, manual, independent-type closing
mechanism shall be provided. If manual dependent mechanism is provided then the
breakers shall compulsorily have electrical closing and tripping devices. All types of
operating mechanisms shall be trip-free throughout the breaker travel and designed to reduce
mechanical shock to a minimum during operation.

Each breakers shall be equipped with visible 'ON' and 'OFF' position indicator on the front
door of the compartment, mechanically connected to the circuit- breaker mechanism.
Separate ON and OFF indicating lamps also shall be provided.

For electrically operated circuit-breakers, satisfactory operation shall be guaranteed for

closing the circuit-breakers with the operating voltage of the drive, in the range of 85 to
110 percent of the rated voltage. The electrical closing shall be either by solenoid or motor
operated spring charged mechanism suitable for 240 V AC.

The circuit-breaker shunt trip coil provided shall operate satisfactorily with the operating
voltage within the range of 70 t0 120 per cent of the rated voltage. The shunt trip coil shall be suitable
for 240 V AC. No separate control source will be available as such capacitor trip Circuit shall be
provided where shunt tripping is proposed with protective relay so that ability to trip is not impaired by
momentary drop in voltage at the time of a fault.

Each circuit-breaker shall be provided with four (4) normally open and four (4) normally
closed spare auxiliary contacts in addition to the ones already used for various control purposes. All
auxiliary contacts shall be wired internally up to the terminal block.

INTERLOCKS

The switchgear shall be provided with all necessary interlocks designed to prevent incorrect operation
and to ensure safety of operating personnel and also the equipment.

The moving portion of the circuit-breakers shall be so interlocked that with the breaker closed it shall
not be possible to isolate it from the connected position or to plug it in from the isolated position.

Interlocking shall be provided to prevent operation of the circuit-breaker unless it is fully plugged in or
fully isolated and is locked correctly in either position.

The circuit-breaker compartment doors shall be so interlocked as to prevent access to a breaker

which is in an energized and plugged in position. Special means shall however be provided for
undoing this interlock in an emergency.

Inadvertent withdrawal of a circuit-breaker movable unit too far beyond its supports shall be prevented
by a suitable mechanical stop.

The unit shall be provided with "test" position in which the circuit-breaker main contacts are in the fully
disconnected position with only the secondary circuits remaining connected. All secondary
connections including control, signaling and metering circuits between the fixed and removable
sections shall be by means of flexible able and plug and socket arrangement.

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

PROTECTIVE DEVICES

The circuit-breakers shall be provided on each pole with any combination of the following
protective devices with ratings as called for in the specification:

i) Direct acting over current tripping device with long time element having inverse
time current characteristic for protection against overloads and instantaneous
element for short-circuit tripping with alarm contact.

ii) Non-directional IDMT earth fault relay.

iii) The under voltage tripping device when specified shall be designed for the following operating
conditions:

a) The circuit-breakers shall trip for voltage value set between 70 and 35 per cent of rated
system voltage.

b)The under voltage relay shall not prevent manual closing of the circuit-breaker above 85
percent of rated system voltage.

iv) The CTs provided for protective devices shall have adequate VA capacity and accuracy class
of 10P10.

INSTRUMENTS AND METERS

Instruments, meters and relays shall be of flush-mounted design, housed in dust-proof casing located
in an accessible position on the breaker panel. All incoming circuit-breaker units shall be provided with
a voltmeter and changeover switch on the live side for indicating the three-phase voltages and
ammeter with a changeover switch complete with C.Ts for measuring the currents in all three phases.
Ammeters with C.Ts and selector switches shall also be provided for all outgoing feeders. For motor
feeders the ammeter shall be provided with a normal scale up to full-load value and a suppressed
scale beyond full-load for indication of motor starting current. C.Ts provided for ammeter shall have
accuracy Class of 1.0 MD meters, 15-minute maximum demand indicators shall be provided, where
specified.

CABLE TERMINALS

The cable terminal arrangement for incoming 415 volt circuit-breaker from 400 KVA transformer
secondary and for all outgoing feeders shall be suitable for single-core and multi-core aluminium
conductor PVC insulated cables of number, type and sizes as specified. The termination arrangement
of multiple cables shall permit connection and disconnection of each individual cable without
disturbing the other cables. For termination of cables suitable lugs of proper size shall be provided.
Where armored cables are to be terminated suitable armor clamps shall be provided.

LOW VOLTAGE BUS-DUCTS

Bus-ducts with 3 phase and neutral busbars shall be able to withstand the short-circuit
currents as specified in item 1.04 above. It shall be designed for a rated voltage of 1,000 volts.

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

The bus-duct shall be of metal-enclosed, dust and vermin proof type divided into factory made
sections suitable for easy assembly at site. It shall be complete with mounting arrangement and all
necessary accessories required to make the installation complete.

The bus-duct shall have suitable side covers where required for easy access to all the busbars. Space
shall be provided within the bus-duct for taking secondary wiring as required, The bus-bar supports
and their terminal connections shall be designed to permit expansion and contraction of the bar with a
variation in the site ambient temperatures. Throat connection with links shall be provided at the
transformer terminal for easy removal of transformer, when necessary.

ALARM AND INDICATION

Each load-centre substation shall be provided with static audible and visible alarm indication with
alarm accept and cancellation device. The system shall have arrangement for repeat alarm facilities
as well as testing the alarm circuits. The scheme shall be designed to give the following indications:

i) When any circuit-breaker trips on fault only

ii) Temperature rise of winding

iii) Earth fault indication

Provision shall be made for transmitting signals if required to remotely located signaling system to
indicate tripping of incoming circuit-breaker on fault and operation of earth fault relay provided in the
transformer neutral circuit. Provision shall also be made to transmit the alarm and tripping signals to
22 kV switchboard from which the transformer is fed or to a remote signaling panel.

REMOTE CONTROL SCHEME FOR BREAKERS

For electrically operated circuit-breakers in addition to ON-OFF control switch provided on the front
side of the panel, provision shall be made where required for remote closing and tripping of circuit-
breakers from an external control desk with arrangement to prevent closing of the breaker by the
control switch mounted on the front of the circuit-breaker cubicle by providing a local/remote switches.

OTHER CONSTRUCTIONAL FEATURES

All operating handles, control switches, push-buttons, indicating lamps, instruments, meters
etc shall be mounted on the front of the cubicles.

The auxiliary relays for temperature alarm and tripping shall be mounted on the incoming
breaker panels. Terminal boards shall be provided at the transformer sections for all
control circuit taken out from the transformers. All wiring from these terminal boards to the
switchgear sections shall be provided with the equipment.

All wiring within the cubicles shall be with PVC insulated cables and shall be effectively protected from
possible damage by electrical flashover. As far as possible each essential control circuit shall be
contained in the respective cubicle. All wiring shall be such that it is easily identifiable and accessible
for maintenance.

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates

 Technical Specification

For equipment earthing a suitable copper earthing bus shall be provided for the complete length of the
switch board and bonded to all the units including the transformer and high tension cubicles. Proper
terminals shall be provided for external earth connections to be fully in conformity with IER.

A suitable universal type truck shall be provided with each load-centre substation for
withdrawing the breakers from the board. The trucks shall have platforms of adequate
mechanical strength for bearing the weight of the circuit-breaker units and shall be provided
with necessary guide rails and stops. The height of the platform shall be adjustable to suit the
levels at which the different circuit-breakers are mounted on the switchboard.

Identification labels shall be provided for each circuit-breaker and control devices to be
located in readily visible positions.

All steelwork of each load-center substation shall undergo rust removal procedure before application
of primer and shall be given epoxy paint finish of Aircraft Grey colour as per ISS Shade 693 or any
other color of approved shade.

The busbars of each unit substation shall be painted as per following norms:

A Phase - Red
B Phase - Yellow
C Phase - Blue

Insulated neutral - White

Earthed neutral - Black

ABC are the three phases of AC circuit with anti-clockwise vector rotation.

Busbar insulation: Aluminum busbars shall be bare with colour coding at the ends/Copper shall be
bare with colour coding at the ends/For Humidified ares the copper busbars shall be tin coated and
aluminum busbars shall be silver painted

TEST

All equipment shall be tested in accordance with the relevant clauses of applicable standards.
All internal wiring shall be checked for correct operation before dispatch.

Consultants: Sampath Kumar Associates Architects: Venkataramanan Associates