MGE

Question 1

State how the static exciter generates a field

Answer 1

The PPT taps off the line going to the GSUs/UATs and lowers the voltage for use in SCRs. The SCRs convert the AC to DC for use in the field. C controls M1 and M2
which regulate the SCR DC output voltage

Question 2

State what will cause voltage control to shift to manual from automatic

Answer 2

A loss of PT feedback voltage is detected then the voltage regulator will swap to Manual

Question 3

State what will cause a 94EX-1 signal

Answer 3

2/3 logic for any trip signal

• Loss of excitation
• Excessive V/Hz
• Generator Field Current Over Excitation
• Exciter not running with MGB closed
• Generator Over Voltage

Question 4

State how the static exciter PTT is protected

Answer 4

a SR745 relay monitors current and voltage

a trip signal will generate a 86GB

Question 5

State actions that are caused by 86GP/GB

Answer 5

MGB trip
Exciter trip
Turbine trip
Trip signal to MGB cooling
Trip signal to Isophase bus duct cooling

Question 6

Discuss operation of the MGB cooling system

Answer 6

With MGB shut one bank is running with the other is in standby. Duty Bank swaps every 12 hrs.
Standby bank starts at 167F

Question 7

State Turbine setback for loss of MGB cooling

Answer 7

55% at 5%/min if:
loss of all fans for >3 seconds OR
HIGH temp of 185F 1/2

Question 8

State the MGB air system interlocks with pressures

Answer 8

<470# Closing circuit is disabled

<435# Trip open circuit is disabled

Question 9

State how GSU transformers are cooled

Answer 9

2 banks are in service (group 1)
2 are in standby (group 2)
1 is swing
standby auto starts at 75C or 80C

Question 10

State turbine setback on loss of GSU cooling

Answer 10

If no coolers are in service then:

alarm comes in and after 30 minutes setback to 40% at 2%/min

Question 11

State the meaning of the lights on MCB for the MGB

Answer 11

Green: Breaker open
Amber: Breaker disagreement
2 Red: Control power available
all poles closed
Selector in remote
Continuity through all three trip coils
Low pressure MGB tripping interlock is satisfied (435#)

Question 12

Meaning of lights on MCB for Static exciter

Answer 12

Red: Exciter is running
Green: exciter is shutdown

Question 13

Meaning of lights on MCB for Generator Voltage regulator

Answer 13

Left-to-right
Potentiometer is below normal: 22.5kV
Normal: 25kV
Potentiometer is above normal: 27.5kV

Question 14

Discuss the shaft voltage monitor

Answer 14

Senses and grounds any induced voltage on the TG shaft to prevent damage to the bearings

Question 15

State when the MGB standby air cool fans start

Answer 15

standby fans start at 167F and stops at 157F

Question 16

Discuss MGB compressed air flasks setpoints and capacity

Answer 16

Lead compressor maintains 3400#-3700#
Lag Compressor maintains 3300-3600#
flasks hold compressed air and is enough for 5 cycles of MGB
-each pole cabinet has a flask of 490# air, enough for 1 cycle

Question 17

State what the Voltage regulator senses and maintains in Auto

Answer 17

Terminal voltage is sensed and output is Field Voltage

Question 18

State what the Voltage Regulator senses and maintains in Manual

Answer 18

In manual field voltage is directly maintained

Question 19

State what will put the Voltage Regulator in Manual

Answer 19

Loss of PT feedback voltage will swap the voltage regulator to Manual

Question 20

State limitation on VARS with one line OOS

Answer 20

With one line OOS VARS should be Lagging only

Question 21

State purpose of De-excitation relay

Answer 21

A thyristor fires to dissipate the energy of the generator field during shutdown