NG TGN(E) 157 PDF

INTRODUCTION

National Grid has a number of gas-insulated substations (GIS). While their reliability is high, any failure of the insulation system is likely to be a costly event. In most cases, such failure is caused by defects which generate partial discharge activity for some time before complete failure occurs. The UHF method of Hampton and Meats [a] is an effective means of detecting partial discharge in GIS so that action may be taken to prevent failures. In the UHF method, couplers installed at intervals round the GIS are monitored to detect UHF energy radiated by discharging defects. Monitoring has been performed in periodic site surveys by engineers using portable instruments. More recently, systems have been developed that provide continuous monitoring of a GIS and which are connected to a headquarters location by telecommunications link. The continuous monitor is able to detect and store information on defects which might be missed by periodic monitoring, such as those that discharge intermittently or develop between surveys and is therefore the more effective means of monitoring. In comparison with periodic site surveys, the continuous monitor makes minimal demands on the engineers' time. The system operates unattended and an engineer need only intervene when the system signals that a discharge has been detected. The master station for the system is located at the headquarters location and receives data from a number of out stations located at substations with GIS.