Switchyards

Question 1

What are the three site switchyards and what are their general arrangements described?

Answer 1

345kV - ring bus, 138kV - line bus, 34.5kV - line bus

Question 2

How does the 345kV switchyard provide power to the U2 and U3 RATs?

Answer 2

U2 - Through TR86 to the RAT OR (Unqualified) through 138kv Bus 1
U3 - Directly off Red Bus.

Question 3

What kind of circuit breakers are present in the 345kV yard?

Answer 3

Most are SF6 GCBs. The 4-8 breaker is an OCB.

Question 4

Where are the 345kV SF6 GCB powered from?

Answer 4

120/208 AC Dist via TELEMAND (Bus 25 and 36 respectively) and 345 kV 125vdc.

Question 5

Which unit is tied to which ring bus?

Answer 5

U2 Blue; U3 Red

Question 6

Where is 345kV shown in MCR? and what happens upon loss of power to panel?

Answer 6

923-2 - loss of DC 2A-1 will cause horn with no alarm tiles on panel.

Question 7

What are the normal feeds to the Red and Blue 120vAC circuits?

Answer 7

Red - Bus 36 (TR 83) Backup Bus 25

Blue - Bus 25 (TR 81)

Question 8

What is the normal Switchyard 480vAC power supply?

Answer 8

Bus 25; Backup Bus 36

Question 9

How is the SY AC controlled?

Answer 9

Telemands auto swap on loss of normal power; manual return required.

Question 10

What shows in MCR upon Breaker Operation?

Answer 10

Two red lights indicate breaker is shut with trip coil continuity

Question 11

Which MODs may be controlled from MCR?
Which may be controlled locally?
What is power for MOD?

Answer 11

Line 1223, TR 81, TR 83
ALL may be controlled locally
DC Powered from Relay House Battery

Question 12

When will a MOD Trip Open?

Answer 12

When Associated GCB trips open on low pressure.

Question 13

What are the setpoints for GCB’s?

Answer 13

Low SF6 Pressure - 92.8 psig - CB Trips and lockout
Low Oil Pressure - 3960psig - minor prevents closing; major prevents opening
TRIP ON POLE DISAGREEMENT - cycles twice then trips open

Question 14

What are the setpoints for 4-8 OCB?

Answer 14

Low air pressure 250psig

Lockout at 230psig (held closed by trip free latch, but will not reclose if open)

Question 15

Which 138kV Breakers are normally open? Closed?

Answer 15

2-3 is normally open, all others normally closed.

Question 16

How does the TR-22 Transfer disconnect function?

Answer 16

TR-22 normally powered through TR-86, but may be powered via 138kv Bus.

Only one disconnect may be closed at any time. Has mechanical linkage to prevent closing both with ASCO swap protective relaying

Question 17

What is normal DC power to 138kV yard old relay house?

Answer 17

Was the U1 125vdc battery Bus 2; reserve from Bus 1 with Normal Seeking ABT

Question 18

What normally provides 138kV 480 feed?

Answer 18

Unit 1 PC 4B via D7L in 138kV relay house:
to 34kV relay house.
Heaters
TR 143 for (120/208 VAC)

Question 19

What provides the 138kV OCB power?

Answer 19

Panel 19L - 120/208V - Reserve via MANUAL transfer to LP 22L

Loss of power to Air Compresser causes MCR alarm

Question 20

Where are 34kV breakers normally controlled from?

Answer 20

NOT MCR. Locally in Relay house or via LD from SCADA.

Question 21

What provides 34kV 480 feed?

Answer 21

138kV relay house panel

Question 22

What provides 125vdc power for 34kv SY?

Answer 22

has its own battery in relay house.

Question 23

Where does the power for the 138kV new relay house come from?

Answer 23

34kv Local lines

Question 24

What is Local Breaker Backup?

Answer 24

Upon line fault, a line breaker will open. If it does not, then the next breaker in line will attempt to open to isolate the fault. THIS DOES NOT CASCADE DOWN THE LINE.

Question 25

For the Breakers, how many times will a breaker attempt to reclose?

Answer 25

twice - used to reclose after a fault. After 3rd opening, will lock out.