Aux Power / 4kV Ops Flashcards
When is it permissible to use BOTH the Div I and Div II 4kV crossties (procedurally)?
The Div I and Div II Dash Bus Cross ties cannot be used concurrently unless the source unit is in a split configuration (Div 1 from UAT and Div II from RAT)
What are the limits for loading on emergency 4kV buses when crosstied? What is the limiting component?
The combined load on both the 23-1 and 33-1 buses as fed from 23/33 (or 24-1 and 34-1 as fed from Bus 24/34) should not exceed 600amps due to bus tie cable current carrying capacity.
Procedurally:
1 cross-tie - max cross-tie load is 450amps
Both cross-ties - max cross-tie load is 350amps each
What limitations exist for performing an emergency Bus cross tie?
Bus voltage difference should be minimized when performing live bus transfer to limit circulating currents. Can be accomplished by adjusting VAR loading on running unit or requesing TSO adjust voltage on 345kV Bus or using Tap Changers
Limit voltage difference to 150volts to limit phase difference when closing
Synchroscope should be within 5 degrees of vertical when sychronizing - notify US if not
What is the sequence used to operate the emergency 4kV crosstie breaker?
When performing a dead bus transfer, the source breaker must be closed first to supply voltage to the dead bus’s undervoltage relay.
The TIE ACB control switch must be held in CLOSE for a minimum of 3 seconds to allow the undervoltage relays to reset or the TIE ACB will trip on undervoltage.
What are the loading limitations for the Unit 1 480V transformers?
4kV to 480 V transformers 14,15, 16, and 17 are limited to 750 KVA or 150 amps each
What are the consequences of having 4kV buses in parallel for excessive period of time when transferring from one feed to another?
Parallel operations can cause circulating currents that could exceed breaker load limits.
What indications should be present when placing 4kV buses in parallel and predict the consequences if these are not observed?
Verify the synchscope is on
Incoming and running voltage are approximately equal.
Synchscope is at 12 o’clock and not rotating
synch lights NOT illumiated
After breaker switch is taken to closed position:
meter is at 12o’clock
breaker indicates closed,
Main and Reserve ACB in Parallel alarm sounds
If breaker does not close or closes out of phase:
Meter not at 12 o’clock
breaker not indicating closed
synch lights glowing
incoming/running bus current/voltage variations
Could cause bus loss and EDG start
When transferring feed power back from 28-7 to 29-7, what actions must be performed?
Open breaker from 28 to 28-7 and simultaneously close breaker from 29 to 29-7. otherwise 28-7 will re-energize
