EHV Equipment in Indian Nuclear Power Plants - Failures and Corrective Actions

Switchyard plays a major role in safe and reliable operation of Nuclear Power Plant. It is required for evacuation of generated energy to the grid and also supplies continuous electrical power to station auxiliaries with maximum reliability. In Indian NPP, 220 kV indoor, outdoor and gas insulated as well as 400 kV air insulated and gas insulated switchyards are in operation. Normally a common switchyard for twin units of NPP and in few cases, a common switchyard for four units is provided. Even though all switchyard equipment and components are confirming to applicable standards, failure of EHV equipment including Lightning Arresters, Instrument Transformers, Circuit Breakers, String insulators etc are reported from station due to pre-mature, random to ageing related degradation of dielectric. Failure of these EHV equipment leads to forced outage of unit or multiple units which poses a challenge to safety system apart from significant economic loss. Various measures like FMEA during design stage detailed quality control during manufacturing, installation and commissioning, condition monitoring and timely replacement of degraded equipment along with review of protection setting coordination have been initiated to avoid unit outage due to EHV equipment failure.