Alterex Excitation System - .5

Question 1

Exciter Field Breaker Trips

Answer 1

• Breaker Failure Protection BS 6-5 or BS 2-6
• AVR Internal Fault
• Exciter Field Overvoltage
• Removal of the GFBI Key
• Generator or Unit Lockout Relay Trip
• Excessive Volts/Hertz (Paralleled to Grid)
  1.10 V/Hz (45 Sec) or 1.18 (2 Sec)
  No time delay if off grid and in Auto

Question 2

Can the field breaker be manually tripped when paralleled to the grid?

Answer 2

NO!

Question 3

What is the function of the Under Excitation Limiter (UEL)?

Answer 3

Prevents operating the generator in an under excited condition.

Question 4

What is the function of the Exciter Field Current Limiter (OEL)?

Answer 4

Limits exciter field current to ensure field current is maintained within 105% rated current. (Will not allow adjustments above 105% in auto OR manual.)

Question 5

What is the function of the Volts/Hertz Limiter?

Answer 5

Limits generator voltage based on frequency to prevent overheating. If at rated voltage, the V/Hz regulator limits voltage to 107%. (Protects transformers from core saturation & resultant heat damage)

Question 6

What does De-excitation mode do?

Answer 6

Enabled on exciter field breaker trip
1. Regulator reduces exciter output to minimum

Question 7

What cools the air cooler?

Answer 7

TACS

Question 8

What do AVR faults cause?

Answer 8

All AVR faults (due to internal or external trips) provide a trip input to the Generator Lockout Relay. Similarly, a Generator Lockout relay trip will cause an external fault/trip to the AVR.

Question 9

Describe the operation of the excitation system channels.

Answer 9

Features two fully independent (and equivalent) control channels. The backup (or inactive) channel is continuously and automatically updated to match the active channel. Each channel features an automatic voltage regulation (AUTO) mode and a field current regulation (MANUAL) mode.
- In AUTO mode, the generator voltage is regulated in a way that the voltage produced at the generator terminals is as constant as possible.
- In MANUAL mode, the field current is kept constant.

Question 10

Describe the exciter field breaker and ground switch interlock.

Answer 10

The exciter field breaker must be tripped to enable closure of the 25kV ground switch on 10G107 (potential XFMR cubicle on 102 elevation).
After the field breaker is open, H53516-1 the ground switch can be closed.
Closing the ground switch (H53516-1), sends an external trip signal to the AVR and also disables the manual exciter field breaker CLOSE PB on 10C651E. The key (removable in the CLOSED position) from the ground switch is then used to operate switchyard equipment.

Question 11

What indications do you have for MT paralleling?

Answer 11

MT will automatically pick up 2% load when paralleled
synchroscope will be stationary at the 12 position
bypass valves will close
stator current will increase