Generator Controls Flashcards
Classify the main generator?
- 4 pole, 1800 RPM, 22 KV, 902 MW @ 0.9 PF (1002 MVA), brushless
Explain operation of exciter and generator.
PMG induces voltage into stationary armature and sends through exciter field breaker to SCRs where field current is regulated. Signal is converted to DC to supply stator of AC exciter. This generates a magnetic flux proportional to SCR current. AC is then converted to DC through diodes and then AC voltage is induced into stator armature to produce 3 phase voltage (~22 KV)
What is the purpose of the digital generator control (AVR)?
Has 2 redundant systems that monitors conditions of the generator and controls generator output using firing circuits and power amplifier panel. If setpoint is low, raises the SCR firing rate to increase magnetic field and raise voltage.
What is the OptoPAR?
Manual operation of excitation from the base adjuster HS. DGC tracks manual to provide bumpless transfer.
How many generator output lockouts are there?
3 Gen LOs. 286-G1-1/2/3
1 and 2 trip EDG output bkr to A-3 if closed, energizes turbine trip solenoid, trip UA feeder bkrs and closes appropriate SU Xfmr feeds
3 will trip output bkrs, exciter field breaker, and blocks cooling fan and pump for main transformers.
What are the different modes of operation?
OFF mode (manual) - Use base adjuster to control output voltage. DGC protection functions are operable. Automatically selected when field breaker open.
TEST mode - Use base adjust to control output voltage. Voltage adjuster set point tracks the generator terminal voltage. Regulator output is held at 0 VDC. Used to test regulator output meter
ON mode - Uses voltage adjuster to control gen output voltage. Generator terminal voltage is actively controlled by DGC using feedback. Limiters and protection functions are operable. Base adjuster follows automatic.
FORCED mode - Failure of both DGC computer channels.
What are the 3 excitation limiter functions?
Maximum Excitation Limiter - Protects the generator rotor from damage due to overheating caused by excessive current flow in the field windings
Volts/Hz Limiter - Protects the generator armature cores and the main transformer cores from damage due to overheating
Minimum Excitation Limiter - Protects end iron region from overheating and prevents electro-mechanical damage that can result from a loss of synch due to insufficient magnetic field (pole-slippage).
What are the 2 protective functions built into the DGC?
Over Excitation Protection - disables base adjuster follow mode. When times out, forces DGC to manual. If manual does not clear condition after time delay, generator lockout relay trip initiated.
Minimum Excitation Protection - If reactive power approaches the MEP curve limit, warning alarm occurs on DGC. If reaches the MEP setpoint, generator lockout relays are tripped.
Describe the generator capability curve.
What is the purpose of the radio frequency monitor?
Looks for arcing (faults in Gen, xfmrs, & unit aux xfmr).
More than 30% for 60 min gets a main generator winding trouble.
What is band for generator output voltage?
21.3 - 23.1 KV
Why is H2 used in main generator?
1) high thermal conductivity and high heat transfer coefficient
2) Maintenance expenses are reduced because freedom from dirt and moisture
3) Stator winding insulation breakdown due to corona discharge is reduced due to absence of O2 and moisture
4) Generator windage and ventilation losses are reduced because of its low density.
What’s the purpose of the Generator Condition Monitor?
Detects stator core insulation degradation which provides early warning sign of generator overheating.
