Medium Voltage Switch Gears In Electrical Construction



The contractor shall supply, install, test and commission the medium voltage switch gears (13.8 KV) as shown and described on the drawings, specification and bill of quantities.



The medium voltage switch gears for the project

1. The MV switch gears shall consist of one indoor air vacuum circuit breaker cubicles for incoming line and number of indoor load break fuse switch, to feed power to the package substation separately (Radial distribution).

2. The load break fuse-switch shall be rated for 13.8 KV, 3 phase, 60 Hz and shall be suitable for normal operation at a load breaking of 630 A, with 80 KA run maximum short circuit breaking capacity for main incomer fuse switch and 400 A with 40 KA, RMS maximum short circuit breaking capacity.

3. The load break fuse switches arrangement shall be by providing separate cubicle unit for main and sub-main load break fuse switches.

4. Single bus bars in the cubicle shall be housed in a separate compartment and they shall be of the modular type that can be extended as required. Each bus bar shall be of copper and enclosed in a layer of insulation. The bus bar chamber shall be naturally ventilated.

5. The cable compartment shall be arranged so that access is impossible unless the short circuit and earthing switch has been closed. The load break fuse switch shall be arranged to close independently against a direct short circuit if the cable ends remain alive accidentally.

6. The operating mechanism of the load break fuse switch shall be through stored energy mechanism of the spring charged type by means of an electric motor. After the motor has fully charged the spring, another push button is depressed to close the switch. A three position indicator on the front of the panel shall be provided open charged close.

7. A separate trip free release shall be provided on the mechanism for hand tripping and a trip coil operating from the protection relays shall be provided.

8. Interlocks shall be provided for ensuring that:

1. The main switch cannot be closed unless the earthing switch is open and the access cover in position.

2. The earthing switch cannot be closed unless the main switch is open.

3. The access cover cannot be removed until the earthing switch is closed.

4. With the access cover removed the main switch is locked in the open position and the earthing switch is free to operate.

9. High voltage switch boards shall comprise of individual units connected together to form one unit. Each unit shall be bolted to the floor and bolted together through their frame work. The bus bars in each unit shall be bolted together to form a continuous unit. Each high voltage unit forming the switch board will be delivered to site by the manufacturer separately, and the Contractor shall connect the units together in accordance with the manufacturers instructions. All units forming a switch board shall be lined and shined before final connections are tightened.

10. The following tests shall be carried out by the manufacturer in the factory after the switch board has completed.

1. High voltage insulation test 50 KV, RMS peak.

2. Polarity test on main connections.

3. Megger tests between phase to phase.

4. Megger tests between phase to neutral.

5. Close operation tests.

11. Each switch board shall have an adequately sized bar running the complete length of the switch board. All non current carrying metal work shall be bonded to the earth bar. All armor of high voltage cables shall be bonded to the switch board earth bar.

12. Switch gear shall be complete with cable boxes, galvanize, armor clamps, cable connectors, earthing bar, earthing connectors, floor fixing bolts, and all necessary accessories.

13. The switch gear shall be suitable normal indoor operation under the following environmental conditions:

1. Atmosphere. Dusty with occasional sand storms.

2. Ambient temperature. 55 degree C.

3. Relative humidity. Frequently 100%.

14. A separate metering cubicle housing indicators, ammeters and voltage transformers, as indicated on the drawings. All instruments and meters shall be of the semi flush pattern mounted on the front of the switch board.