Flashcards in High Voltage AC Deck (14):
What is the difference between the control room bus voltage and the local bus voltage?
The control room's indication is phase to phase so you cant tell what phase the ground is on.
The local indication is from phase to ground so the phase that has the ground would be lower than the other two phases which would be higher.
What is the output voltage of the Unit 1 and the Unit 2 main transformers?
Unit 1 is 345Kv
Unit 2 is 765Kv
What are the off site Tech Spec. Power supplies?
Reserve power (RATS)
What are the normal and back up power supplies to the RATs?
AB RAT's are normally supplied from Transformer 5.
CD RAT's are normally supplied from Transformer 9.
Transformer 4 is the backup supply for both.
What is Back feed?
Back feed is how we power the plant during an outage when we want to do work on a RAT. We Divorce the generator from the UAT by removing the Bus links, then 345kv power comes from the grid backwards through the main transformer which steps it down to 26kv, then backwards through the Unit Aux Transformer which steps it down to 4kv to the RCP Bus.
What will trip the UAT supply breaker to the RCP bus?
Turbine trip the unit and overall differential relays open.
Overload / Overcurrent.
What is the interlocks for RCP supply breaker from UAT?
The UAT must be energized to close.
What are the auto trips of the RCP bus supply breaker from the RAT?
RAT transformer Fault.
What will auto close a RCP supply breaker from a RAT?
Unit and Overall differential relays open (turbine trip).
Why do we have breakers before and after the step down Transformers between the A and D T bus and the A and B 600v buss?
To protect the T buss if there is a fault the breaker after the transformer will trip open, after a set timer if the fault is still there the breaker before the step down transformer will open to protect the T Bus's.
What happens on 4kv under voltage protection (Degraded Voltage)?
The under voltage relays on the A and D busses sense low voltage. If the power supplied to the RCP busses from the UAT is 88% of normal voltage following a time delay of 99 seconds. Then it initiates a fast transfer to RAT for the associated train. If the degraded voltage continues for 21 seconds (after transfer to RAT) it trips the associated RCP bus tie breaker.
What happens on 4kv under voltage protection ( Load Shed)?
If 2 of 3 sense loss of voltage then
The bus supply breakers trip open
The large load breakers trip open
The EDGs start.
What are the normal and emergency power supplies to the T bus?
The T bus is normally supplied from the corresponding RCP buss. During emergencies the T bus can be powered from the EDG's or EP.