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) 1
Consumer’s Main Switchroom • General requirements for main switchroom – Sufficient space for work and to house the main switchboard and other distribution equipment (600 mm for switchgear ≤ 100 A, 900 mm for those >100 A) – 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 2
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 3
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 BS 1432 or BS 1433 – 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 4
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 5
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 6
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 k. A – 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. 7
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 8
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 9
A single-line LV schematics 10
L. V. Switchboard 11
Air Circuit Breaker (ACB) 12
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