Analysis and Damping of Subsynchronous Oscillations Using STATCOM

Abstract

Series compensation of long transmission lines is an economic solution to the problem of enhancing power transfer and improving system stability. However, series compensated transmission lines connected to the turbo generator can result in Subsynchronous Resonance (SSR) leading to undamped Subsynchronous Oscillations (SSO). The advent of Flexible AC Transmission System (FACTS) controllers using high power semiconductors has made it possible to apply these controllers in conjunction with fixed series compensation, not only to improve system performance, but also to overcome the problem of SSR. FACTS controllers based on Voltage Source Converter (VSC) are emerging controllers that have several advantages over the conventional ones using thyristors. STATCOM is a shunt FACTS controller suitable for voltage regulation and damping of oscillations. This chapter describes the analysis and simulation of a series compensated system with STATCOM connected at the electrical center of the transmission line. The SSR characteristic of the combined system is discussed. A new technique of SSR damping is presented in which a STATCOM injects subsynchronous current.