A Novel Algorithm Incorporating System Status to Prevent Undesirable Protection Operation during Voltage Instability

A novel algorithm is proposed to prevent undesirable protection operation during voltage instability taking the system status into account. The protection operation, aiming to protect the corresponding unit, may be harmful to the system. Moreover, some protective relays may operate undesirably not because of faults as designed but because of overloads. So the rate of change of voltage is used as the basic criterion to differentiate between faults and overloads. However, it may fail when the system is close to the collapse point. Hence, an indicator detecting the system status is proposed to complement this approach. Meanwhile, control can be applied to stabilize the system. As a result, the undesirable protection operation is avoided and the system is stable. The algorithm is demonstrated through a sample system.