Station Power Flashcards

Question

What happens if Rear Bus receives a fault?

Answer 1

* Primary (487B-P/R) - R Bus Differential isolates R bus (trips R bus breakers) and initiates a transfer trip to trip all S/U xfmr low side breakers * Zone of Protection - From each R bus breaker to high side of each S/U xfmr * Operates aux relay (486S-X) which initiates a trip to trip all S/U xfmr low side breakers). * Backup (487B-B/R) - same function as primary.

Answer 2

* Primary scheme (486B-P/F) - initiated by bus differential voltage and S/G transformer differential current and ground relays * Backup scheme (486B-B/F) - initiated S/G transformer overcurrent and sudden pressure relays, Load Tap Changer Pressure relief Device and LTC hand crank removal. * Relays initiate: * a) Trip of F bus breakers * b) Trip of Safeguards Bus Feeder breaker 152‑401 * c) Fast transfer of 2400V busses to S/U 1-2

Answer 3

1) Differential relays (187-1) 2) Trips 152‑401 or 152‑402 breaker 3) Initiates fast transfer of 2400V Busses when 152‑401 is closed. 4) If 152-402 ( from SP 1-2) is closed and fails to trip open when this differential relay operates, a breaker failure relay on this breaker will detect this and will initiate a unit trip.

Answer 4

Differential protection (487U) (C04 panel) * Zone of Protection - Main Xfmr, Main Gen., and high voltage of S/P 1-1 and 1-2 * Operates the 386B lockout relay which trips Main Gen. Sudden Pressure (463M) * Detects a sudden rise in gas pressure caused by a fault internal to the xfmrs. * Aux relay 463MX actuates 386P (plant trip) * Aux relay 463XX causes an alarm and actuates deluge system. Ground Protection (451MN * Actuates 386B (trips the Main Gen)

Answer 5

Differential protection * Primary (487LU1, 450PU1) (Switchyard to Plant) actuates 386P and B (Main Gen trip) * Secondary Protection (450BU1&421U1, 467U1) (Switchyard to Plant). Actuates 386P & B (Plant trip) Ground Protection (451MN) * Actuates 386B (trips the Main Gen

Answer 6

1) Differential * S/P Xfmr 1-1 - (287) * S/P Xfmr 1-2 - (187) * S/P Xfmr 1-3 - (487-SP3) * Zone of Protection - From the high side of the transformer to the bus side of station power breakers. * Actuates 386B (plant trip) 2) Sudden Pressure * S/P 1-2 (163), S/P 1-1 (263), S/P 1-3 (463) will operate a 163X, 263X, 463FPX aux. relay, which initiates: * Deluge system * Alarms * Actuates the 386P relay. 3) S/P Xfmr 1-2 With the 152‑402 closed a fault will trip the plant. 2400 V buses will transfer to S/U power.

Answer 7

* Zone of Protection - from transformer to low side of S/U breakers * Primary Protection - differential relays (487-S1, 487-S2 and 487-S3); S/U 1-1, S/U 1-2, S/U 1-3, respectively * Opens all R bus breakers, and S/U low side breakers (isolates R bus) * Backup Protection (Phase Protection 450-451/S1): Actuates the same respective lockout relay (486-11, 486-12 or 486-13) as the (487-S1, 487-S2, 487-S3) primary differential relay

Answer 8

(SP463-S1, SP463-S2, SP463‑13) 1) Trips R Bus, trips all S/U Xfmr low side breakers, and actuate deluge valve. 2) Is actually a backup to other protective relaying. Sudden pressure condition would occur only as a result of some huge fault within the transformer that would cause oil vaporization (winding to ground, or winding to winding if the distance were far enough to draw a large arc) - but on a fault of this nature, other relaying should isolate the fault before sudden pressure actuates.

Answer 9

1) Each xfmr is equipped with one overcurrent relay connected to the 345 KV side of each xfmr (451‑SN1, 451-SN2, 451-SN3). 2) Trips R Bus and trips all S/U Xfmr low side breakers. Important Point: Any fault on any S/U Xfmr will actuate protective relaying which de-energizes ALL three S/U Xfmrs

Answer 10

* Each 4160V incoming breaker has phase time overcurrent relays and one ground time overcurrent relay to protect against switchgear bus faults and to provide backup protection for feeder circuit faults. * When supplied from S/U transformer Buses 1A, 1B, 1F, & 1G overcurrent relay trip their associated incoming breaker. * When supplied from S/P transformer Buses 1A, 1B, 1F & 1G overcurrent relay trip their associated incoming breaker, block fast transfer and block manual closure.

Answer 11

Each bus has inverse time undervoltage relay that trips PCPs, Cooling Tower Pumps and condensate pumps to prevent damage to the motors. Relays on breakers 252-101 and 252-201, 252-301, 252-401 actuate a lockout relay to trip and lockout the incoming breaker, and prevent a fast transfer to the start-up transformer. The purpose for this is to prevent connecting a source of supply to a faulted bus.

Answer 12

* Phase overcurrent relays protect against switchgear bus faults and to provide backup protection for feeder circuit faults. * In the event of a 2400V bus fault, relays on Breakers 152‑105, 152-203 and 152-302 (incoming breakers from the Safeguard Bus) actuate a lockout relay to trip and lockout the incoming breaker, D/G output breaker will not close. The basis for this is to prevent connecting a source of supply to a faulted bus. * 2400V AC breakers supplying motors have overcurrent relays (protect against overload, locked rotor and faults). Actuation of the relay isolates the faulted motor from the 2400V bus.

Answer 13

Ground relays are not used for system protection in the 2400V AC distribution system since this is an ungrounded system. However, ground relays are used to alarm and indicate the existence of a ground fault on the 2400V AC system. Ground Detection Lights are mounted adjacent to the relay. * Normally dimly lit. * In the case of a ground on the bus, the intensity of the lights would vary. * Alarms only If busses are fed from the same source the ground could be on any of the connected busses. Relays on all connected busses would likely target. Isolate to identify.

Answer 14

First Level (127-1, 2) * Set at 77% of rated voltage with an inverse time relay. The greater the voltage drop, the quicker the relay response. Protects against a sudden loss of voltage as sensed on the bus. Second Level * Set at 93% of rated voltage. Protects against sustained undervoltage conditions on the bus. * When under voltage condition exists for 0.65 second, they initiate a Diesel Generator start. If under voltage continues for an additional six seconds a load shed occurs and the Diesel breaker closes. The NSD or DBA sequencer then sequences on loads. Both will: * Trip respective incoming bus breakers * Initiates load shedding (D/G breaker must be open) * Starts respective diesel