Theory And Application Of PSS To Suppressing Low Frequency Oscillation

The safe and stable operation of power grid is a matter of national economy and people's livelihood.With the development of the nationwide network and large capacity transmission over a long distance,power system stability has become increasingly complex.The transient stability and static stability presented the new features,dynamic stability and voltage stability problems are increasingly prominent.Especially,low frequency oscillation problem which is representive of small signal stability of power grid stability has more and more prominent impact on power grid stability.In the process of the national network,low frequency oscillation have occurred many times and become a serious threat to the power grid security and the generators.Research and engineering practice both at home and abroad shows that,setting the related parameters reasonablely in the power system stabilizer can suppress low frequency oscillation effectively,improve the safe and stable operation performance of power grid and generators.In this paper,the mechanism and application effect of PSS suppressing low frequency oscillation is studied.Among them,the mechanism of PSS suppressing low frequency oscillation,PSS mathematical model,parameter setting method and field test of PSS is the key to PSS commissioning.This paper starts from the power system small signal stability analysis,which leads to the low frequency oscillation of power system,then summarizes variety of physical mechanism for low frequency oscillation and the related suppressing measures of the primary and secondary side.On the basis of negative damping mechanism,the Phillips-Heffron model is introduced.This paper expounds the principle of PSS suppressing low frequency oscillation,and introduces several types of mathematical model of PSS in current industry,thus establish the theoretical basis for PSS parameters setting.In field test,taking PSS2B of excitation regulator NES5100 as example,the PSS setting test standard process and risk control measures is summarized;Taking PSS2A of excitation regulator EXC9100 as example,an improved PSS parameter setting calculation method is proposed and verified by field test.The results of this research has been widely applied in all large and medium-sized generators in hunan province,especially when low frequency oscillation occurs to the 250MW generators of expansion project in zhexi hydroelectric power station.Through the field setting,putting into operation,and optimization of PSS parameters,suppress low frequency oscillation successfully,and solve the problem of less output power during the wet season.In case the local oscillation point is beyond 2 Hz in zhuxikou hydroelectric power station,the PSS parameters setting calculation software suitable for the 0.1 Hz?3 Hz frequency compensation scope is developed.It has been verified by field test and shows good damping braking effect.