1

Consumer’s Main Switchroom & Main L.V. Switchboard

• Learning outcome from this topic, the student is able to

– state the functions and requirements of a main switchroom– state the functions and requirements of a main switchboard– sketch a single-line LV supply diagram from a main switchboard to different parts of a building– describe different tests for a switchboard (the type tests and routine tests)

2

Consumer’s Main Switchroom

• General requirements for main switchroom– Sufficient space for work and to house the main switchboard and other distribution equipment (600mm for switchgear ≤ 100A, 900mm for those >100A)– Next to transformer room– Supply taking from a LV network, the room should be at the building entrance– Clear access – Good ventilation– Minimum illumination: Floor – 150 lx, wall: 120 lx– No water or drainage pipes inside

3

Consumer’s Main Switchroom

• Function of a main switchroom– power is taken from a transformer room

– power distribution to different parts of a building and for different usages

– separate the consumer side from the power company

4

Layout of cubicle-type main

switchboard • Components in a main switchboard

– Body built with 2 mm-thick steel and coated with suitable paint– A busbar compartment with hard drawn copper and high conductivity to BS1432 or BS1433– Compartment for the incoming and outgoing cables – Neat internal wiring and with sufficient clearance– A compartment housing ACB, MCCB, fuseswitch, motor starter, capacitor bank, auto-changeover switch– A meter compartment to show the energy consumption or maximum demand

5

Layout of cubicle-type main switchboard

• Components in a main switchboard– Measuring CTs and protection CTs– Meters showing current, voltage, power factor (and max. demand), etc. Now A digital multi-purpose is used for all– IDMT relays for overcurrent and earth-fault protection (Now a digital relay)– Charger and battery for closing/tripping of ACBs– Phase indication lamps– Anti-condensation heaters– Spare compartments

6

Layout of cubicle-type main switchboard

• The main switch in a switchboard– For three-phase 4-wire supply, a triple-pole & neutral (TP&N) main switch (or circuit breaker) is used– The TP&N switch should interrupt all the phase conductors (R/Y/B)– A link (fixed by bolts or screws) should be inserted in the neutral conductor– For single-phase installations, a double-pole (DP) main switch should be used

7

Layout of cubicle-type main switchboard

• If the supply is taken directly from a transformer room, the main incoming ACB

– should be of draw-out type– should have a breaking capacity at least 40 kA– should be equipped with overcurrent & earth-fault protective relays

• For an overall installation serving more than one building, the installation in each building should be treated as a separate installation. Each building should have a main switch.

8

Load Distribution in a Building• Refer to slide 10 for illustration• Tenant Supply Board

– Connection to a transformer – Main incoming circuit breaker (ACB/MCCB) for overload and fault protections to the whole installation– Busducts leading to different load centres in the building– Bus section switch interconnects adjacent busbar section

• Non-essential Public Supply Board– Bus section for the power supply to public facilities

• Plumbing and drainage pumps, passenger lifts, non-essential lighting, A/C plant and spares, etc

– Cable risers to different loads in the building– Protective devices for cable overload protection– Bus section switch interconnects adjacent busbar section

9

Load Distribution in a Building• Emergency Supply Board

– Connection with an emergency generator / UPS– ACB, MCCB, fuseswitch for overload and / or fault protections to essential loads– Automatic changeover switch

• Two mutually exclusive switches– Normal open (N/O)– Normal close (N/C)

• Switch ON/OFF– Sprinkler pumps, hydrant / hose reel pumps, firemen’s lifts, emergency lighting and spares, etc

• A single-line low voltage schematic for the power distribution to different loads in a building is shown on slide 11

10

A single-line LV schematics

11

L.V. Switchboard

12

Air Circuit Breaker (ACB)

13

14

15

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