Analysis of very fast transient overvoltages (VFTO) from onsite measurements on 800 kV GIS

In IEC 60071-1 and 62271-102, there is neither standard voltage shape nor standard peak value for very fast transient overvoltages (VFTO). Previous work by other researchers had classified VFTO into two types. A new type was identified in this paper based on an onsite test on a commercially-operated 800 kV GIS. Disconnectors were opened/closed under real operation conditions. Characteristics of the new VFTO type were analyzed, including times of the arc restrikes between the contacts of the disconnectors, trapped charge, damping time constant, magnitude, rise rate, and oscillating frequency. The results of this paper are expected to be of help for the completion of standards on VFTO.

1. Introduction

When a disconnector in gas insulated switchgear (GIS) is being closed or opened, its contacts move considerably slow. Arc strikes (including prestrikes and restrikes) take place between the contacts, and hence very fast transient overvoltages (VFTO) are generated. Broad studies have been carried out to understand and control VFTO [1]–[9], resulting in a large amount of literature.