New Techniques for VFT Mitigation in GIS

Abstract

Switching operations in a Gas Insulated
Substations (GIS) generate very fast transient
over voltages (VFTO) which are dangerous
for the transformer and the system insulation
because of their short rise time. Under special
circumstances the overvoltages can arise close
to the transformer Basic Insulation Level
(BIL). The reduction of VFTO amplitudes is
considered main challenges. Therefore, VFTO
in the 220 kV Wadi-Hoff GIS is analyzed and
the worst case for disconnector switching is
predicted using EMTP/ATP in this paper.
VFTO mitigation techniques are studied in this
work. Furthermore, in this paper, proposed
techniques are presented for mitigating the
VFTO. The proposed techniques can be used
by the maintenance engineers, transformer
designers, and GIS insulation manufactures.
The results show that the proposed techniques
highly reduce the VFTO in a simple manner.