SUPPRESSION METHODS OF VFTO'S IN GAS INSULATED SUBSTATION

ABSTRACT: Environmental constraints and the reliability of systems are the main reasonsfor the introduction of the gas-insulated substation (GIS).In our country a few Gas InsulatedSubstations (GIS) units have been in operation and large number of units is under variousstages of installation. These problems include, generation of over voltage during disconnectoroperation, line to enclosure faults. These over voltages are caused in two ways, viz., due toswitching operations of circuit breaker/disconnect switch and line to enclosure faults. Firsttransient waves in the gas-insulated substation (GIS) are analysed and methods forsuppression of very fast transients (VFTs) in GISs are introduced in this project. Forsuppressing VFTs, four methods are presented, including suppression by terminalcomponents, capacitance components, adopting a resistor- fitted disconnector, andferromagnetic rings. Finally, these approaches are compared with each other. These methodscan be divided into two groups. The first group contains the methods (such as terminalcomponents and reconfiguration) that can be used after installation of the GIS and during theoperation of the GIS. Then second group contains the methods (such as the resistor-fitteddisconnector and ferromagnetic rings) that must be used as an extra limitation beforeinstallation and during the design of the GIS. The above two groups are compared andanalysed. Finally, the best approach for the suppression of VFTs has been chosen based onthe criteria of the transient waves and feasibility.