Disconnector Operation Research Articles

Influence of switching conditions on the VFTO magnitudes in a GIS

Estimation of very fast transient overvoltage (VFTO) has been carried out using EMTP for various switching conditions in a 420 kV gas insulated substation. The variation of VFTO peak along the GIS bus nodes for disconnector and circuit breaker switching operations as well as the variation of VFTO peak with different magnitudes of trapped charges have been studied. The results indicate a distinct pattern of variation of VFTO peak along the nodes of the GIS bus in the case of disconnector switch operation as compared to that of circuit breaker operation. It has also been noticed that the variation of VFTO peak levels are not in direct proportion to the trapped charge present on the HV bus.

Suppression of the high-frequency disturbances in low-voltage circuits caused by disconnector operation in high-voltage open-air substations

The switching off and on of small capacitive currents charging busbar capacitances, connection conductors and open circuit-breakers with disconnectors causes high-frequency transients in high-voltage networks. In low voltage circuits, these transient processes induce dangerous overvoltages for the electronic equipment in the substation. A modified construction of the disconnector with a damping resistor was investigated. Digital simulation of the transient process in a high-voltage network during the arcing period between the disconnector contacts with and without damping resistor were performed. A significant decrease of the arcing duration and the decrease of the electromagnetic field magnitude in the vicinity of the operating disconnector were noticed. In the low-voltage circuit protected with the surge arrester, the overvoltage magnitude was not affected by the damping resistor due to the arrester protection effect.

Preventing Earth Faulting during Switching of Disconnectors in G.I.S. including Voltage Transformer

Switching of disconnectors in G.I.S. in the presence of an inductive voltage transformer can give rise to extreme conditions which can seriously affect their dielectric withstand capacity. The case is studied in detail. A description of the various overvoltages generated by disconnector operation shows that they can reach 2.3 - 2.5 PU in real G.I.S. configuration. A synthetic test circuit in full phase opposition can reproduce the main voltage parameters and following an appropriate test procedure, check the capacity of the disconnector switching in these conditions. The present article gives general information on the behavior of the insulation between arc and enclosure.