Systems Exam 1 - AC Distribution And Transformers Flashcards
Which transformers have inert gas oil preservation?
→1UT
→2UT
→XST1
→XST1A
→XST2
What is inert gas oil preservation?
→nitrogen blanket on oil with pressure between 0.25 and 6.5 psig
→regulator maintains tank pressure greater than 0.5 psig
→as oil temp changes, density changes and causes nitrogen to flow either into the transformer via a regulator or bleed off via a relief
→relief valves in nitrogen bottle cabinet (7# and 7.5#) and on top of xfmr (7.5#)
Which transformers have Modified COPS Oil Preservation?
→1MT1/2
→2MT1/2
→1ST
→2ST
→XST2A
What is COPS Oil Preservation?
→Each transformer has a Constant Oil Pressure Preservation System (COPS) Tank mounted above the transformer tank.
→A bladder inside the tank is surrounded by oil and vented to atmosphere.
→Bladder inflates and deflates to accommodate volume changes due to oil expanding and contracting.
→Designed to allow for volume changes associated with oil temp variations from -4° to 230° F.
→A pressure vacuum bleeder valve prevents excessive pressure or vacuum
Main Transformer Cooling and Rating?
Forced Air/Forced Oil
The MTs are only rated for Forced Air/Forced Oil. If all cooling is lost, the operator is directed by the ALM to rapidly reduce turbine load to less than 50% within 30 minutes and to monitor oil (100° C) and winding (130° C) temps.
UTs and 2ST Cooling?
Natural Circulation through radiator banks and attached fans
What is static electrification?
The buildup of a static charge in the transformer oil. Can occur when relatively cool oil is circulated through a transformer at high flow rates.
1ST, XST1, XST2 Cooling?
2 sets of coolers with each cooler having a pump and 3 fans
Which transformers DO NOT have deluge systems?
1ST, 2ST, XST2A
(All others have deluge.)
What are the automatic actions for an “XFMR 1ST LOR TRIP?”
LOR = Lockout Relay
→1A1-2, 1A2-2, 1A3-2, 1A4-2, and XA1-1 breakers will trip. (Could cause Rx trip if RCPs are powered from 1ST below 20% power)
→Incoming feeder breakers 7970 and 7980 will trip, then re-close when MOAS 8052 opens
→All 1ST transformer cooling will stop; MOAS 8052 opens and will not re-close.
→Note: XST2 will temporarily lose power on a 1ST LOR resulting in a slow transfer on the U1 1E busses and a BOS actuation
What are the automatic actions for “XFMR 2ST LOR TRIP?”
LOR = Lockout Relay
→2A1-2, 2A2-2, 2A3-3, 2A4-2 and XA1-2 breakers will trip (may result in Rx trip if RCPs are powered from 2ST at below 20% power)
→Incoming feeder breaker 8075 and 8080 will trip.
→All 2ST transformer cooling will stop.
What are the automatic actions for “XFMR XST1 LOR TRIP?”
LOR = Lockout Relay
→High speed ground switch 8083 will close
→MOAS 8085 will open
→1EA1-2, 1EA2-2, 2EA1-1, and 2EA2-1 will trip open. Slow transfer on preferred unit, BOS fires
→138 kV switchyard breakers 7030 and 7040 will open
→Transformer deluge valve will arm
What are the automatic actions for “XFMR XST2 LOR TRIP?”
LOR = Lockout Relay
→MOAS 8012 opens
→MOAS 8032 opens
→1EA1-1, 1EA2-1, 2EA1-2, 2EA2-2 will trip open. Slow transfer on preferred unit, BOS fires
→Feeder breakers 7970 and 7980 will open and then re-close after MOAS 8012 and 8032 open
What kind of lockouts do the Main Transformers have?
They only have a Sudden Pressure Relay that generates a Main Generator lockout if activated. This disconnects the transformer from its power source.
(A sudden pressure relay is actuated by a sudden pressure increase due to an electrical arc vaporizing oil into gas.)
Do transformer alarms have reflash?
No. If an additional alarm comes in while there is already a trouble alarm in, the trouble alarm will not reinitiate.
UTs during backfeed operations…
…should not be used to power the RCPs for extended periods due to increased amps in this alignment.
What powers Unit 1 Safeguards Buses?
Normal: XST2
Alternate: XST1
Emergency: Diesel
What powers Unit 2 Safeguards Buses?
Normal: XST1
Alternate: XST2
Emergency: Diesel
What powers the non-safeguards buses?
Normal: UTs through main generators
Alternate (or unit shutdown): STs
Main Transformers
Which 480 VAC supply breakers connect power to the transformer control panels?
Which 125 VDC supply breakers connect power to the alarm circuits?
→uB4-1 (preferred) and uB3-1 (alternate)
→uD2-1 (preferred) and uD2-2 (alternate)
UTs - Unit Auxiliary Transformers
Which 480 VAC supply breakers connect power to the transformer control panels?
What supplies power to the alarm circuits?
→uB4-1 (preferred) and uB3-1 (alternate)
→125 VDC uD2 input
Main Transformers Basic Facts
→voltage input and output
→cooling system
→oil preservation system
→What does it power and when does it operate?
→22 kV in, 354 kV out
→FAO
→COPS
→sends power to the grid when generator output breakers are closed (xfmr load ↑ as gen load ↑)
UTs - Unit Auxiliary Transformers Basic Facts
→voltage input and output
→cooling system
→oil preservation system
→What does it power and when does it operate?
→22 kV in (<3.5% of total power output through main generator), 6.9 kV out
→FA
→inert gas system
→non-safeguards buses when above 20% power
STs - Station Service Transformers Basic Facts
→voltage input and output
→cooling system
→oil preservation system
→What does it power and when does it operate?
→345 kV in, 6.9 kV out
→FOA
→COPS
→non-safeguards buses when below 20% power
XSTs - Startup Transformers Basic Facts
→voltage input and output
→cooling system
→oil preservation system
→What does it power and when does it operate?
→138 kV (XST1/1A) or 345 kV (XST2/2A) in, 6.9 kV out
→FOA (XST1, XST2, XST2A) or FA (XST1A)
→inert gas
→safeguards buses at all times
25 kV Loop - Plant Support Power System Basic Facts
→What is it powered from?
→What does it power normally?
→What does it power during outage?
→two transformers in the 138 kV Switchyard
→buildings like warehouses, MSC, AAP& PAP, met tower, CPE, NOSF, sewage treatment facility, LVW discharge path (WM-181s fail closed on loss of power), etc.
→refueling equipment like containment elevator, polar crane, refueling communications, etc.
(outage power transferred by manual switch in key-locked boxes)
What are some early indications of a transformer fault?
→presence of combustible gas
→increased oil/winding temps
→weird noises from transformer tank
→increased COPS tank level
→increased pressure
