Fray's Flashcards
What two control systems control the operation of a generator
1 Governor control systems that control unit speed and active power.
2 excitation control systems that control voltage and reactive power
Discuss the terms “buck” and “boost” as it applies to a generator
•Decreasing the amount of DC field current applied to the rotor decreases the amount of induced AC Armature current in the stator, thus decreasing the output voltage.
▪︎This opposite is true when the DC field excitation current is increased.
•When both of the DC field excitation current in the rotor and the induced AC current in the stator are high, the unit has a “lagging” power factor and is supplying VARs, or boosting.
•When both are low the power factor is “leading” and the unit is absorbing VARs from the system or bucking
For what type of routine work would an operator need to contact RAS dispatcher prior to work
Scheduled maintenance on RAS equipment ( power rate relays, line loss logic equipment)
Powering down and RTU that transmits RAS data. Unexpected RAS alarms, RAS equipment trouble, RAS testing.
Updating on return to service of critical equipment affecting path limits (may be discussed through the system dispatcher)
What are SOL studies and why are they significant
SOL is system operating limits which are studied to know the condition of the system and how it will respond to certain situations.
Since August 10th 1996 WECC and NWPP have said “if you haven’t studied the specific system condition, you can’t operate the system that way
Explain the reactive device switching scheme and what it’s designed to prevent
Added as a result of the August 10th 1996 incident used to prevent voltage instability following unexpected outage conditions
When a key line is lost, a trip signal is sent from the RAS controllers at DCC to Grizzly, Ostrander, Pearl, Keeler, Raver, Hanford, Malin, and Marian substations, for 20 minutes. At those substations, the voltages are monitored for two critical voltages , 535 and 515 KV. If during the 20 minutes, the voltage at the substation dips below 535 KV, a single reactive device is Switched. Voltage is automatically checked every second. If voltage remain stable, another reactive device is switch until the voltage climbs above 535 (for there are no more reactive devices to switch) . If voltage is below 515 KV, all devices are switched (reactors removed comic apps inserted) with no time delay
Describe the RAS dispatchers responsibilities for the various RAS under his jurisdiction
▪︎Responsibility for monitoring paths (flowgates) and ensuring they are maintained within System Operating Limits(SOL).
▪︎Responding to loss of equipment on the power system and setting new path limits based on DSO`s or real-time studies.
▪︎Curtailing paths based on new limit.
▪︎Arming and disarming RAS based on loading and nomogram charts.
▪︎Working with field and other utilities to remove equipment from service for trouble or scheduled work that affects RAS
Describe the generation dispatcher’s responsibilities
▪︎Monitor pa ACE, AGC, frequency and generation.
▪︎Interchange (estimate or “dummy” quantities for metering work) , hourly numbers checking.
Hourly acceptance of basepoint
▪︎hourly call to Celilo for DC power order.
▪︎Curtailing or limiting wind generation.
▪︎Redispatching generation for real-time contingencies.
▪︎Real time cuts ( increasing or decreasing generation with other utilities to reduce flows on Flow Gates or paths) .
▪︎Request from other utilities for emergency power
What role does the PowerHouse have in preventing any one of the states of voltage instability
▪︎Powerhouse may be part of reactive Reserve calculations for that day.
•Excitation Control Supplies reactive needs to our system. We try to minimize power transfer in order to supply reactive power needs.
▪︎Power transfer equation and role of maintaining voltage is to permit transfer of power. ▪︎Strategically-placed reactive support on the system supports localized voltages to permit the transfer of power and reactivity
Explain the impact to the power system when an inadvertent operation occurs, tripping a generation line
▪︎Loss of reactive support the power system.
▪︎Consideration needs to be given to whether the generation is above or below a flow gate. If it is below a flow gate, reactive support may not make it through the flowgate.
▪︎May lose reactive Reserve.
▪︎If significant, will cause the system to be in an unstudied state. May initiate RAS action
Describe reactive reserve and reactive margin and why reactive is critical
▪︎Reactive Reserve is the unloaded Dynamic reactive capacity of generators close enough to the problem to actually support voltages in the area.
▪︎Reactive margin represents in, MVAR, how much additional stress can be put on the system before system break up occurs. This measurement of MVAR relies on available rotating capacity for appropriate system response. Reactive response relies on speed to prevent system voltage collapse.
▪︎Before August 10th 1996, transient stability was the limiting factor on intertie lines. Since then, voltage the stability has become an equal limiting factor. By running generators close to the california-oregon intertie in “bucking”, they can quickly change to “boosting” and provide reactive support. RAS such as FACRI and reactive device switching schemes also assist in reactive support
Define system stability include what quantities are monitored to maintain a stable power system
▪︎Stability is the ability of a system to maintain synchronism following a disturbance.
▪︎System stability is the ability of the power system to sustained various disturbances such as transmission line fault, equipment failures, or inadvertent operational errors and return to steady-state operations while maintaining an interconnected system.
▪︎Voltage, frequency, MW, MVAR, and interchange schedule are monitored and controlled to maintain systems stability
