Protection of Reactors and FACTS Devices

Abstract

Reactors and static var compensator (SVCs) protection strategies are presented in Chapter 9. Reactors are used in AC networks to limit either overvoltage for series connections or short-circuit current if connections are parallel. SVC systems come in a large number of arrangements, and they are custom-designed for specific applications such as reactive power compensation, voltage regulations, and protection. For SVC applications, the control and protection systems play an essential role in the overall performance of the power system network stability and reliability. From the protection standpoint, an extensive protection system is generally required for reactors and SVCs to optimise the equipment operational limits for maximum utilisation. Therefore, different protection principles applicable to reactors, SVCs and other related reactive power compensating devices are presented in the chapter. It also includes an overview of protection methods, and the overview covers protection strategy, configuration approaches at substation busbars, transmission lines, impedance calculation and protective relay sizing. For example, for the medium voltage (MV) busbar and the active branches, thyristor switched capacitors (TSCs), thyristor controlled reactors (TCRs), and harmonic filters are of specific interest when considering the protection system for most of the FACTS devices like the SVCs and STATCOMs. These branches are exposed to severe fault current and voltage transients during system disturbances. SVCs are normally ungrounded on the MV bus, with the residual voltage protection used to detect the ground faults. On the other hand, when selective earth fault protection is required for SVCs, it can be accomplished by using either a grounding transformer or automatic recloser scheme. Special protection functions are integrated in the SVC control system to detect abnormal operating conditions and to react rapidly to avoid damage and unnecessary tripping of the plant protection system. Those kinds of protection functions, and their interaction with the power system as an important criterion for selection and application, are covered in detail in this chapter.