System Integrity Protection Scheme for Enhancing Backup Protection of Transmission Lines

Abstract

Contingencies such as faults, loss of generation or load may produce undesirable relay operations which can lead to cascade tripping causing system catastrophic failure. Thus, security of power system protection is a major concern for utilities. In this article, an approach based on system integrity protection scheme is proposed for enhancing the security of protection functions. Synchronous data measurements from strategic portions in the system are utilized for separating fault from stressed conditions. Determining the vulnerable relays (VR) which may maloperate during a stressed condition and incorporation of remedial strategy are proposed. It includes two algorithms; the first of which computes the relay margin to form a look-up table containing VR at different fault scenario and operating condition, in offline studies. Then, in accordance with the real-time system conditions, the relay characteristics are set for VRs based on the local information to avoid maloperation. The second is activated during critical heavy loading condition that may lead to voltage collapse and determines the load to be shed based upon sensitivity calculations of relay operation margin. The proposed method is tested for an IEEE-39 bus New England system as well as validated on real-time digital simulator (RTDS) platform for various operating scenarios and found to be robust. Thus, improvement in security of protection operation is achieved without compromising the dependability factor.