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 overhead double circuit transmission line with line length of 20 kms. The traction substation of 132/2×25 kV was supplied by grid sub station(GSS). The 132kV from GSS was further supplied to other locations through overhead double circuit transmission line for 60 kms. 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 as per IEC
– Scott Transformer with center tap
– Scott Transformer without center tap



Temporary Over Voltage Study

From temporary over voltage study, the following points were concluded for various conditions.
– At nominal system voltage, the maximum over voltage was analysed.
– At maximum system voltage, the maximum over voltage was analysed.

Lightning Over Voltage Simulation

The lightning over voltage simulation was performed with network modelling of grid sub station/ traction sub station/ 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 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.

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