Traditionally we inject power from synchronous machine to limit the frequency of the power system. However, while we know that damper winding within the synchronous machine does provide damping, such damping is seldom considered alone in practice. What might be the reason?
Rapid Frequency Response From Smart Loads in
Great Britain Power System
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7448474
Frequency of the power system will be within tolerance when real power generation is equal to load real power and real power losses. This comes under frequency stability. When the load is more than generation the system loses synchronism, if continued in that mode.
Similarly voltage stability requires reactive power balance.
Thanks for the answers, but I am looking for load damping provision from traditional machines. E.g. amortizer windings of synchronous machine.
Amortizer windings and Governors damp out the load fluctuations but with some steady state error. These come under primary controllers of LFC system. Hence the power system frequecy will not be rated 50/60 HZ with these primary controllers alone. So we go for AGC with secondary controllers like ADRC, PID controllers which damp these oscillations very quickly with zero steady state error resulting in rated frequency and contracted tie-line powers.
@Krishnarayalu Movva, thank you so much for your response. You have correctly indicated that PFR alone will not be able to reduce the SSE to zero. And also, amortizer windings and speed governors together damp out the frequency oscillation because of load fluctuation. However, my question is, why governor response has to be considered along with traditional damping provided by the synchronous generators to calculate overall frequency deviation? Is the damping provided by these windings is not able to stabilize the power system? Or in other words, is D
Governor controls the mechanical (prime mover) energy based on the load of synchronous generator so that the system works at rated frequency. It is a speed controller. Better recollect load test on alternator where speed changes as load changes.
Your D is frequency sensitive load coefficient, not related to damping (Hadi Saadat; Wood and Wollenberg). D can be zero if there is no motor load which is sensitive to frequency.
Thank you so much for your comments. It is well understandable that if the feedback signal is provided in proportion to the changing speed (or frequency), there will always be drop in speed (or frequency). However, if the generator is isochronous, then speed change will never occur.
I also know that D is frequency sensitive load coefficient. Note that, if the reduction in load demand with changing frequency is higher in contrast to drop in frequency because of power imbalance (because, frequency imbalance results from power imbalance), the frequency sensitive load coefficient will be able to stabilize the system. Because, system power requirement declines in proportion to D, D can be thought of inducing damping into the system.
Actually I was wondering, can I ignore D throughout, saying that the damping induced by D is far far small compared to response from regulation provided by speed governors.
BTW, thank you for mentioning those two references. I have read them to make my understanding better.
Please note that D term decreases the load power by a small value
(D *delta w) only if the system frequency is below rated value. In case of system frequency is above rated value, D term increases the load power (D *delta w). Also D is expressed in per unit. Better not to ignore unless specified.
Various load types/classes have different sensitivities to voltage and frequency deviations. The aggregate effect on the system stability and performance is highly dependent on the load composition.These sensitivities can contribute to the power balance of the system under abnormal and emergency conditions due to the changes in the voltage and frequency. You may refer to:
Article Impact of load models on the static and dynamic performances...
Book Dynamic Security of Interconnected Electric Power Systems - ...
Kundur P, Balu NJ, Lauby MG. Power system stability and control. New York: McGraw-hill; 1994
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