Electrical

Question 1

Explain the operation of the tap changers for the 6900 and 4160 Volt station power from the screens. Include startup and normal source.

Answer 1

Tap changers are devices that control output voltage from the transformer. Adjusting 6900V voltage will also adjust 480V voltage. Normal source voltage is adjusted by tap changers on the the normal source transformers. Startup voltage is adjusted by tap changers on the startup transformers.

Question 2

2. Explain the procedure to swap from start up station power to normal source station power.

Answer 2

On the station power screen, open the normal source breaker overlay and the corresponding startup breaker overlay. On the normal source overlay put the synch switch in service, check the incoming and running voltages (adjust if needed to ensure incoming is a little higher than running). Ensure Delta Hz and Delta V permissive is met. Close in the breaker ensure NAC. The startup breaker should open, clear trip and ensure NAT. The synch switch will automatically take itself out of service. Repeat procedure to swap the remaining transformers. After swapping transformers check all phases and voltages, and adjust if necessary

Question 3

3. How is the 230 KV voltage changed and what happens to the other units when you raise or lower the 230 KV voltage?

Answer 3

From the generator master page, make sure the voltage regulator is in the “auto” position and use the voltage adjuster to raise or lower voltage.
If you increase voltage, VARS on that unit will increase and the other units will take more VARS in.
If you decrease voltage, VARS on that unit will decrease and the other units will put more VARS out.
You should adjust voltage on all three units together so that you maintain about the same amount of VARS on all three units.

Question 4

5. Explain the procedure to put 1J4K in service.

Answer 4

1. On station power page
2. Click on 1J4K tie breaker
3. Select sync switch, ensure Delta Hz and Delta V permissive is met and incoming and running voltages are matched
4. Close breaker

Question 5

6. What action should be taken if you lose the main and /or back-up auxiliary power on the main power transformer?

Answer 5

Have plant operator check out transformer. If problem cannot be corrected begin dropping load to come off line. Monitor the main power transformer temperature.

Question 6

7. Explain the procedure you would follow for a dead bus on 4160 or 6900 bus.

Answer 6

1. Verify dead bus condition exists and select station power page
2. Select “motor” block on the dead bus to check equipment that was running before dead bus occurred. (red run indicator light will still show red if that equipment was running before dead bus)
3. Clear the bus of any motor or feeder supply breakers that show closed and were I/S before the bus went dead.
4. Once cleared the bus can be restored
5. Select source breaker to be restored
6. Open synch switch and check voltage (dead bus will only show running voltage) 7. Close source breaker
7. Power is now restored to the bus, equipment can now be returned to service