An Effective Index for Islanding Detection Based on Fast Discrete S-Transform

Abstract

Passive methods of islanding detection have the advantage of not perturbing the system, but they suffer from large Non-Detection Zone (NDZ) and unpredictable detection time. In this paper, a new passive scheme for islanding detection, based on estimating a new index derived from summation of impedance values in all frequencies along the time at the Point of Common Coupling (PCC), is introduced using Fast Discrete S-Transform (FDST) method. The proposed method maintains both time and frequency information and as a result, helps to decrease the detection time. A frequency dependent model is proposed for characterizing the interconnection changes when islanding happens. The Cumulative Impedance Index (CII) is proposed to discriminate between islanding condition and normal operation. This technique is combined with under/over voltage protection method to decrease NDZ. Simulations for different conditions of normal and islanding operations verify the proposed algorithm. In all cases, islanding is detected within 0.01 s, and NDZ is decreased to 1% of power mismatch between local load and Distributed Generator (DG) output. The results demonstrate the capability of the method to islanding detection with minimum delay and least NDZ.