Switchyard and Offsite Power Flashcards
What is power supply (control power) to 500 kV switchyard?
In house 4kV bus E B/u p.s. 4 kV bus D thru 230 kV control bldg
What protection relays does 500 kV switchyard posses?
Differential- current in = current out, if not Trip High speed reclose- see if fault is transient, burn off bird
What can be done if 230 kV voltage is low
Place shunt capacitors on service
What protection exists for a fault on a 12 kV SU bus?(ovrcrnt, diff, sudden Press)
What is b/u to that protection
That units circuit switcher will open and its SU feeder breaker will open (non faulted unit still has 230 kv power)
B/U= 212 will open and opposite units 12 kv SU bus feeder breaker
What is power supply (control power) to 230 kV switchyard?
In house 4kV bus D B/u p.s. 4 kV bus E thru 500 kV control bldg
Protection relays for 230 kV switchyard?
Distance relays- provide delay for other relays to clear fault before tripping breakers SU xfr isolated, circuit switcher and feeder breaker open(230) - Trip cut in -> (back feeding w/ MOD open) output breakers open
Backup Relay purpose
-Provides backup 500kv line protection by isolating the generator from a line fault
- Provides an additional line of time delayed protection for the generator if a fault occurs between the neutral and the bushings
-Operates if other primary relays fail to operate to clear the fault. Upon fault detection:
-relay waits 60 cycles (1sec) to allow primary relays to operate
- if fault persists after 60 cycles, it trips the 500kv PCBs
Generator under frequency relay
-provides turbine blade protection against resonant vibration.
-provides over current protection for plant motors, generator stator, and generator field winding
-Trips 500kv PCBs only
Three trip setpoint at
:57.55 hz for 7.7 sec
:57.95 hz for 31 sec
:58.35 hz for 92 sec
Generator negative sequence relay
Separates the generator from a system fault
- isolates fault and prevents generator from feeding high current to the fault
-detects unbalanced armature currents
-backup to primary and secondary line relays
-inverse times
-trips 500kv PCBs only
Generator out of step relay
Separates the generator from the system in the event the generator is out of synchronization with the system which may occur during major system disturbances. The device trips the 500kV PCBs only.
Special protection scheme relay
SPS protection is an anticipatory protection to maintain transmission system dynamic stability for specific 500kv transmission line and generator conditions. The SPS is designed to act before the generator out of step protection. This scheme is in the 500kv switchyard and trips only the 500kv generator output breakers. Switch in the CR selects which unit is the preferred unit to trip.
Purpose of the shunt capacitors
Two banks of shunt capacitors are installed in the 230kv switchyard to raise voltage if required during heavy loading of the system.
Purpose of 230kv circuit switchers
Allow removal of startup transformer from service without tripping the upstream 230kv breaker to allow preventive and corrective maintenance.
211-1 and 211-2
If there is a loss of offsite power, what do we do?
-Do STP I-1C in 1 hr
-check 500kv breakers with sync key( should see 120v on CC3)
-Call switchyards to see when we are getting it back
What is the 230kv system designed for? What will it cause?
To handle a DBA LOCA on one unit with a Unit trip on the other.
It will cause 100MW of load to transfer all at once. This should happen without the voltage dropping far enough to cause a DG Auto Start on UV(SLUR), which would cause a second start(double sequencing) of the eccs pumps.
