Wind power plants and facts devices' influence on the performance of distance relays

Abstract

The continuous growth in power demand in the electric power system allowed the development of various power electronics-based schemes for compensation and optimization of transmission systems. The converter-based systems like wind power plants (doubly fed induction generator or DFIG scheme), flexible AC transmission systems (FACTS) devices such as static synchronous compensator (STATCOM), unified power flow controller (UPFC), and series compensator are power electronics-based equipment, so the inclusion of the converter-based systems in the power transmission system generates frequency components that affects the performance of the distance relays, the relays have constant pickup values which will be exposed to these new power system conditions causing fault detection problems. The modern power converters generate a wide spectral band of frequency components which compromise the quality of the energy delivered, which affects the operation of the electric power grid, power consumers, and relay protection systems. Relay operation should be established using only the fundamental signal components at the nominal frequency because these are proportionately affected by the fault location. The main purpose of the conventional digital filters in distance relays is to estimate the fundamental frequency phasor of the electric input signals required by the relay, but when frequency components as interharmonics or sub-harmonics exist in the voltage and current signals, the conventional digital filters as Cosine or Fourier will cause an error in the fundamental frequency phasors estimate, and by consequence an error in the estimate of apparent impedance, this will compromise the performance of the distance relay causing underreach or overreach (fault detection problems). This book chapter is intended to present the effect and compensation of nonfiltered frequency components, such as interharmonics and subharmonics in the performance of conventional distance relays. Prony method is implemented as a filtering technique as a solution of the apparent impedance measurement error due to nonfiltered frequency components; simulated cases and real fault events are evaluated to validate the proposed distance relay algorithm. © Springer Science+Business Media Singapore 2014.