Main Generation and Regulation System Flashcards
What is the purpose of the main generation system?
Convert mech power from the turbine into electrical power and step up the voltage for transmission by the EHV (extra high voltage transmission system)
What does the main generation system consist of?
Main generator
Isophase bus
Bank of generator transformers
Unit aux transformer
In order for a generator to produce a voltage, what three things do I need?
Magnetic field
conductor
Relative motion
When a generator is operating, why does it have to add an additional amount of mech energy above and beyond that needed to overcome friction to keep the rotor rotating?
The current on the stator armature windings creates a magnetic field that interacts with and opposes the rotors magnetic field
What system provides the excitation energy for the main generator?
(MB) Excitation and voltage regulation system
What system provides trip signals to the MA system generator trip logic?
(MB) Excitation and voltage regulation system
How do we keep the rotor of the main generator cool during normal operations?
Hydrogen
Besides providing lubrication to the main generator and exciter bearings, what other service does the generator lube oil provide (LO)?
a low pressure supply of seal oil upon a loss of the main seal oil pumps
What does the generator seal oil system (SO) do for the main generators?
Controls the atmospheric leakage of generator hydrogen gas at the annulus between the rotor shaft and the generator
Maintains hydrogen purity by preventing atmospheric contamination
Main turbine system (MT) provides the motive power for the main generator. what other function does it perform?
Provides valve position signals to the MA system for generator trip logic and event recording
The generator protection system receives control power from what system?
NK (125VDC)
What does CE stator cooling water provide?
Cooling for stator windings, generator lower frame housing, bushings and rectifier excitation system
What system provides cooling water for the isolated phase bus duct cooling coils and main gen hydrogen coolers?
TC
What classification is the main gen?
turbine 1800 rpm
What allows electricity to flow thru the generator even tho it is spinning at 1800 rpm?
Slip rings and brushes
Brief explanation of how the generator operates
DC supplied to induce a magnetic field on the rotor which then goes to the windings on the stator.
Turbine spins the rotor, magnetic field passes over the armature windings, producing a voltage on those windings
What part of the stator frame supports the weight of the rotor and contain gas at max pressure?
End shields
What is the purpose of the stator?
to generate the voltage and current supplied to the unit aux and main transformer which in turn supplies the power to the power system
The armature is composed of insulated copper conductor grouped together to form rectangular bars. How does stator cooling remove the heat from these bars?
Each copper conductor is hollow to allow stator cooling water to flow down its length
Why are the stator conductors water cooled?
To minimize the size of the unit
What are the highest stressed components in the generator? why?
Retaining rings that hold the end turns of the rotor windings against centrifugal force
What is the general construction of the isophase bus?
3 aluminum conductors, 1 per phase and supported by porcelain insulators. each contained in a dust and water tight enclosure
What is the purpose of the isophase bus?
Supplies power to the main and aux transformer
How long could an isophase bus operate without cooling before permanent damage may occur?
30 mins
Where is the purpose of the unit aux transformer?
converts 24kv from the main gen to 13.8kv for used by plant loads
How is aux transformer cooled?
Forced air and oil (480VAC)
How do we prevent oxygen from infiltrating the aux transformer oil?
Inert gas used to blanket transformer oil
What is the purpose of the main transformers?
Transform 24kv from the generator to 525kv for the power grid
How are the main transformers cooled?
Forced air and oil
When does the first cooling bank of the main transformers start operating?
When does the 2nd and 3rd bank start?
As soon as voltage is induced
2nd - 70C
3rd - 75C
Main transformer oil temp should be between?
105-114F
Where are 525kv breakers operated from?
control room
Where are the 525kv motor operated disconnects operated from?
Control room or locally
What is the purpose of the main generator excitation and regulation system?
Supplies excitation power for the generator and controls the main generator output voltage from the startup of rated power operations
What converts the AC signal from excitation dome to DC signal sent to the rotor?
Rectifier
Where is the shorting break locate and what does it do?
in the breaker section of the exciter cubicle
It shorts the rotor DC field to remove excitation from the main generator
What will be done if the shorting breaker fails to close during a test?
AO will be directed to depress the reset button at the excitation cubicle
General sequence of starting the main generation system
pressurize with hydrogen
Start isophase bus and gen stator cooling
Bring turbine to speed
apply field excitation
Main trans first stage banks start
Generator synced and loaded to 65 mw
Load is increased and NAN-S01 & S02 are transferred to the aux transformer
Why is the generator initially loaded with 65 MW?
To prevent reverse power
What will occur upon a loss of main generator system?
Loss of all or part of load on the main
generator the load rejection procedure will be used for plant stablization
Steam bypass control system, reactor power cutback system and CEDM will operate to control reactor power cutback. if system fails to function a reactor trip may occur
NAN-S01 and -S02 will “fast bus transfer” to offsite power if main gen trips
What effect on the main gen system will occur upon a loss of TC ?
Load reduction and possibly a reactor trip. TC is cooling the hydrogen coolers and isophase bus duct coolers, stator cooling water system and lube oil system.
What happens to main generation upon a loss of stator cooling water?
After a short delay an auto generator trip will occur
What will happen on a loss of seal oil?
Requires the generator to be unloaded and depressurized
What will happen upon a loss of generator lube oil system?
Cause a turbine trip
Explain the drop test in regards to testing hydrogen leakage from the generator
Isolate hydrogen to generator and measure how much is lost in 24 hours
1500SCFD or increase of 300SCFD from last valve, retake the test
exceeds 8500SCFD then immediately initiate steps to shut down the unit
If a loss of non class 125VDC occurs and a turbine and reactor trip occurs, will the generator output breaker trip as well?
No, manual action from the control room operator needed to open the breakers
