Novel Relative Slip Based Under-Voltage Load Shedding Protection Scheme to Mitigate FIDVR

Induction motors play a vital role in the voltage stability of power systems. This role would become more significant after clearing short-circuit faults in which the system voltage slowly recovers with a time delay referred to as fault-induced delayed voltage recovery (FIDVR). The FIDVR phenomenon can be classified into the stable and unstable types. To preserve network stability and reliability, the under-voltage load shedding (UVLS) protection schemes should i) be secure for the stable case and ii) quickly remove the disturbed loads for the unstable case. To do this, a new decentralized UVLS protection scheme against FIDVR events is proposed in this paper. A novel concept named relative slip, which is equal to the ratio of the motor slip to the critical one is developed. Using the proposed concept, the behavior of motor loads during stable and unstable regions can be discriminated. Since the proposed index can be exploited just by using the electrical signals, it can be simply implemented in the UVLS schemes without requiring any additional information and infrastructure. To evaluate the efficiency of the proposed method, multiple test systems are considered. Based on various simulation studies, the proposed UVLS scheme can superiorly preserve system voltage stability.