Impacts of variable quadrature reactance on power system stabilizer performance

In the absence of rotor speed as a measured variable with acceptable resolution and accuracy, exciter manufacturers drive speed from other measurements. A common method used in the dual input PSS2A and PSS2B stabilizers is to derive the speed deviation Δω input by using generator internal voltage behind quadrature reactance Xq. The Xq of a synchronous machine deviates from the synchronous value when rotor speed oscillates during a disturbance, which is not always considered or analyzed in adequate depth in the Power System Stabilizer (PSS) time domain simulations during PSS planning, tuning and validation with respect to local mode and inter-area mode oscillations. Inappropriate Xq setting without considering its variations may result in underperformance of the PSS. This paper discusses the impact of the variable Xq on the PSS performance at local mode and inter-area mode. An appropriate Xq setting with emphasis in damping inter-area mode oscillations and a set of ramp tracking filter settings with low gain at local mode were recommended in a case study to ensure satisfactory PSS performance in both local mode and inter-area mode.