High Voltage Equipment

Question 1

Purpose of High Voltage Equipment

Answer 1

Protect, Isolate & Monitor High Voltage Lines in Switchyards

Question 2

Current Transformer

Answer 2

Measures the current flowing through buses for indication and protective relaying

Question 3

Potential Transformer

Answer 3

Used to measure voltage in switchyard buses and provides input to indication, relaying, and synchroscope

Question 4

Potential Device

Answer 4

Same as Potential Transformer, but uses capacitors to reduce voltage level.
Used to measure voltage in switchyard buses and provides input to indication, relaying, and synchroscope

Question 5

Wave Trap

Answer 5

Only found in 138kV. Prevents carrier signal from leaving designated line or entering/exiting switchyard on another line.
Prevents other lines from receiving trip signal during line testing

Question 6

WHat are Disconnects?

Answer 6

• Used to ensure positive isolation to keep electrical circuit completely de-energized.
• Must be oven 90 degrees to provide adequate air gap for isolation

Question 7

What is the Motor Operated Disconnects (MOD) power source?

Answer 7

• Uses 125vDC from switchyard to operate

Question 8

Oil Cooled Breakers

Answer 8

• Only present at 345kV 4-8 Blue to Red Breaker & in 138kV
• 3 Tanks (1 per phase)
• Mechanically linked to operate toegether
• Arc Suppression by Spray Oil
• Low Air Pressure prevents closing

Question 9

What is a Siemens SF6 GCB?
What are the temperature limits?
Wen does it Lock out: SF6? Oil? N2?

Answer 9

• SF6 Gas Used to quench Arc
• Operates via Hydraulic Oil - between -40C and 40C
  Lockout: SF6 Trip/Low Pressure -<3669psig
  Oil Trip/Low Hydraulic Pressure <3669psig
  Alarm: Loss of Nitrogen - Accum Pressure >= 5004psig

Question 10

Circuit Switcher

Answer 10

• Lift Station Only
• Combined funciton of circuit breaker and disconnect switch.
  Breaks the circuit within its interrupting section and isolates the cicuit with blades. Normally remote, but can be done manually
• May disconnect Under load

Question 11

How does a Motor Operated Disconnect function?

Answer 11

• Operates similar to manual disconnect, but with a motor operator.

Question 12

When is it okay for operator to blow down an OCB air receiver?

Answer 12

When air temp >40F

Question 13

What are alarm set points for OCB?

Answer 13

Low Pressure - Alarm 250psig; lockout 230psig

Question 14

What kind of coordination is required for SF6 GCB?

Answer 14

All 3 phases operate independently.

Question 15

What are alarms associated with SF6 breakers?

Answer 15

GCB Trip
Red or Blue Bus Pole Disagreement
Red or Blue Bus Minor Trouble
Red or Blue Bus Major Trouble

Question 16

What happens with a Bus Pole Disagreement?

Answer 16

CB trips open and MOD opens

Question 17

What are the cutout switches for trouble alarm for GCB?

Answer 17

LP in HP Gas - GCB trips open and MODs open

Question 18

Where can the circuit switchers be operated from?

Answer 18

Locally.

Remotely from Lift Station or MCR.