Insulation Co-ordination Study For Selection &

Placement Of Surge Arrestors

T . E . C . T Tackling Electrical Concerns of Today

Written By : Mr. Sonjib Banerjee

Edited By : Dr. Diksha Rohra

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A new 220/132 kV GSS air insulated substation (AIS) was having its incoming supplied by a 220kV grid through an overhead double circuit transmission line with a line length of 20 km. The traction substation of 132/2×25 kV was provided by the grid substation (GSS). The 132kV from GSS was supplied to other locations through an overhead double-circuit transmission line for 60 km. The aim was to perform the insulation coordination study to validate the selection and placement of surge arrestors for 220kV, 132kV and 2X25kV switchyard.


The study was performed for the following scenarios to provide adequate insulation coordination as per IEC
– Scott Transformer with centre tap
– Scott Transformer without centre tap


Temporary Over Voltage Study

The following points were concluded from a temporary over-voltage study for various conditions.
– At nominal system voltage, the maximum overvoltage was analysed.
– At maximum system voltage, the maximum overvoltage was analysed.

Lightning Over Voltage Simulation

The lightning over-voltage simulation was performed with network modelling of grid sub-station/ traction substation/ sub-sectioning and paralleling post (SSP)/ sectioning and- paralleling post (SP) equipment along with its conductor properties in detail. Various lightning conditions were performed in the network, along with a surge transfer study.

Switching Over Voltage Study

This study was performed under various conditions and with different switching scenarios. It was observed that the over-voltage due to switching was not exceeding its limit.