The Vulnerability Analysis of Transmission System Based on the Performance of Mho Relay and SVC

Abstract

The security of the transmission system is dependent on the relays’ performance after various disturbances. Undesirable relay operation will trip the lines and lead to cascading events. In this paper the operation margin of mho relays is equivalently redefined as function of bus voltages instead of line impedance. The sensitivities of the operation margin to bus voltage and bus power is applied to quantify the vulnerability of transmission system. The contribution of the shunt compensation by SVC is analyzed based on the sensitivities (control factors) of the operation margin to the shunt susceptance. It is found that the control effect of SVC is approximately linear when the mho relay has relative smaller operation margin. In this range the linear model based on the control factors is accurate enough to simulate the control effect. It is also found that the shunt compensations at different locations may yield opposite effect to the operation margin of the mho relays, which can be easily judged by the value of the control factors.