GENERATOR SET SWITCHBOARD
The generator set switchboard shall be of the self-contained cubicle type, free standing floor mounted, metalclad, flush fronted suitable for front and rear access housing switchgear and controlgear, protective relays, meters, indicating lamps, cable terminating boxes, and all other necessary items of equipment whether specified hereinafter or on the Drawings or not, suitable for operation on a 240 V/415 V, 3 phase, 4 wire, 50 Hz system with solidly earthed.
Whether or not shown in the Drawings, the generator set switchboard for all operation modes described in Section 17.0 – Operation Modes shall be of stand-alone type, not forming part of the main switchboard but having the same dimensions in height, depth and section width as that of the main switchboard.Unless otherwise specified elsewhere, the generator set switchboard shall be in general compliance with MS IEC 60439-1, and capable of withstanding without damage fault condition of not less than 50 kA at 415 volts for 1 second.
Unless specified otherwise, the generator switchboard shall be of Form 2b. The frame work of the switchboard shall be fabricated from rolled steel sections of thickness not less than 2.5 mm and shall be self-supporting when assembled, uniform in height and depth from front to back. The rigid construction shall be designed to withstand without any sag, deformation or warping, the loads likely to be experienced during normal operating, maintenance or maximum fault conditions.
The front shall be provided with covers/doors of box formation. The rear shall be provided with hinged removable doors of box formation. The rear doors shall be of double-leaf type with rebated edges and each leaf should preferably not be wider than 450 mm. Each leaf of door shall have 2 pairs of approved hinges. The door shall be fitted with approved type of surface-mounted espagnolette or cremone bolts complete with approved locking device operated by a satin chrome lever handle at the centre fixing. The top and sides shall be of removable panels. All panels, covers and doors shall be fabricated from sheet steel of thickness not less than 2.0 mm and so constructed as to provide a clear, flush and pleasing appearance. The panels, covers and front doors shall be secured to the enclosure by means of chrome type of screws with cylindrical knurled head complete with retaining clips. Welded cross struts shall not be used. The generator set switchboard shall be dust and vermin proof. All covers and doors shall be provided with grummets and seals to exclude dust and dirt. Louvres or ventilation vent with filter shall be provided at the sides and back for adequate ventilation. The whole cubicle shall undergo de-rusting treatment, followed by anti-rust treatment and the exterior finished with epoxy dry-powder and oven baked semi-gloss enamel grey and interior finished matt white.
Busbars shall be tinned hard drawn high conductivity copper of adequate
rectangular cross section to carry continuously the rated normal current at a rated
frequency of 50 Hz with a temperature rise in accordance with the requirements of BS 159.
Busbar sizes must not be less than specified in the Drawings. However if not specified,
then the busbar rating shall be based on the current density of not more than 1.5 A/sq.mm.
Busbars shall be arranged and rigidly mounted on non-hygroscopic insulators so as to
withstand any mechanical forces to which they may be subjected under the maximum fault
conditions. Where multiple parallel bars are used, they shall be separated by tinned copper
spacers at spacing equal to the bar thickness.
The main busbars shall be run for the full length of the generator set switchboard without reduction in size and shall be arranged in the horizontal plane and in the order Red phase, Yellow phase, Blue phase and Neutral from back to front. In each panel, connections shall be Red phase, Yellow phase, Blue phase and Neutral from left to right, viewed from the front of the panel. The neutral busbar shall be of full size and full length as that of the phases. Tinned copper earthing bar of 6 mm x 25 mm cross section shall run to the full length at the base of the generator set switchboard. Busbars shall be identified with standard colour code Red, Yellow, Blue, Black and Green at appropriate points to distinguish the phases, neutral and earth respectively. Connections from busbars to the switchgears shall be effected by means of copper bars or copper insulated conductors and shall be identified by means of coloured plastic sleeves or painting in accordance with the standard colour code. All connections shall be made up with bronze or other copper alloy bolts and nuts utilizing tension washers on both outer faces.
Precautions shall be taken to prevent overheating through hysteresis and Eddy current losses.
All secondary wiring shall be minimum 1.5 sq.mm. section insulated with PVC and shall be fixed securely without strain by cleats of the compression type. All secondary wiring shall be properly labelled with number sleeves. Flexible protective conductor of not less than 2.5 sq. mm section insulated with PVC shall be fixed securely between the lids, doors, cover plates etc. with electrical equipment attached to them and the main cubicle to ensure continuity of the protective circuits. All switchgears, controlgears, indicating and measuring instruments, measuring transformers, electrical protection relays etc. provided shall comply with the relevant sections in this Specification and/or specifications stated elsewhere.
Whether or not specified elsewhere, the circuit breakers for the generator sets for parallel operation shall be of motorised type and where four pole circuit breakers are specified the neutral pole shall be of full size as those of the phases. One number anti-condensation heater shall be installed for every two (2) sections at the generator set switchboards. Each heater shall be complete with automatic thermostat, control switch and indicating lamp.
A tools compartment of sufficient size shall be provided at the base of the generator set switchboard for storage of tool kit used for the generator set. The door for tools compartment shall be hinged type complete with lockable handle with keys. Engraved labels with white lettering on a black background made of laminated materials shall be provided and fastened on the front panels for each and every switchgear and items of equipment. Wording shall be clear and coincide and shall be approved by the S.O.’s Representative. Engraved name plate showing the relevant earth fault setting, over current setting, current transformer ratio, fuse rating, name of the circuit to which it is connected, etc. shall be fixed to the switchgear panel to which it refers.Not with standing specified above, the generator set switchboard shall complywith the requirements of relevant sections of the specification – Specification for LowVoltage Internal Electrical Installation.