Main Generator

Question 1

Electrical flow path from PMG to isophase buses

Answer 1

PMG(spins, induce voltage)
PMG stator(3 phase ac)
FCB
voltage regulator (ac->dc)
AC exciter stator(stationary mag field)
AC exciter rotor (3 phase ac)
Fuse wheel (diodes ac->dc)
Gen rotor (rotating mag field)
Gen stator (induced 3 phase ac)
Isophase buses

Question 2

What does a high RF monitor reading mean?

What does a high Gen Condition monitor reading mean?

1-High RF, high GCM

2-High RF, low GCM

Answer 2

RF- arching is occurring

GCM- no degraded insulation in gen

1-arching outside gen
2-arching inside gen

Question 3

How can you verify a valid low GCM reading?

Answer 3

Place filter in service, if reading rises=> valid reading (filtering out insulation degradation)

Question 4

What does the supplementary excitation (power system stabilizer) do?

Answer 4

Minimize the effects of grid transients on Generator by making AVR goes with transient not fight it.

Question 5

How does exciter ground detector work?

Answer 5

Once /24 hrs for one minute brushes contact slip rings on exciter, detect for grounds on exciter and Generator rotor

-100vdc placed on exciter, if no ground alarm circuit is not completed=> no alarm

Question 6

How is main Generator cooled?

Answer 6

H2 gas and stator core cooling water

Stator water flows through 1/3 of stator coils

H2 gas cools rotor and Generator core

Both H2 gas and stator water is condensate cooled

Question 7

Difference between U-1 and U-2 generators?

Answer 7

U-1. Axially cooled

U-2. Zone cooled

Question 8

What interlocks take effect when Field Circuit Breaker is closed?

Answer 8

• MOD is prevented from operation
• 24 hr ground detector timer starts
• AVR and MVR able to adjust from no load position
• exciter cooling starts
• MBT cooling oil fans start
• ISO-phase bus duct cooling starts

Question 9

What interlocks must be met to close field circuit breaker?

Answer 9

• MOD must be fully closed or fully open

- isophase ground switch must be open(not grounded)

Question 10

What must be met to open exciter field breaker?

Answer 10

Both Generator output breakers must be open

Question 11

What will place AVR to manual on main Generator ?

Answer 11

Excessive V/Hz

Loss of sensing inputs

Over-excitation

Question 12

What actions happen on Unit Trip (per lockout relays 86G1 and 86G11

Answer 12

Turbine Trip
Aux xfr feeders Trip
Auto xfr to S/u
500 kv Generator bkrs Trip
Exciter field bkr Trip
Trip #2 htr drn pump
If aligned to degraded 230 kv 
   - Trip cond bstr running in auto
   - prevent any auto start of cond bstr pump

Question 13

What will happen if MW transducer fails?

Answer 13

MW feedback out
Programmed ramps disabled
LDA disabled

Question 14

What are the Generator output breaker Trip relays?

Answer 14

Backup
Out of step
Negative sequence 
Under frequency 
Special protection