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
-relief valves in nitrogen bottle cabinet (7# and 7.5#) and on top of xfmr (7.5#)
Which transformers have 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?
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
-during backfeed, the UTs shouldn’t be used to power RCPs for an extended amount of time due to increased amps in this alignment
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
What are the automatic actions for an “XFMR 1ST LOR TRIP?”
-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?”
-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?”
-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?”
-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.)
