A CONTINUOUS UHF MONITOR FOR GAS-INSULATED SUBSTATIONS

Assessing the condition of a GIS by measuring the UHF signals generated in it by partial discharges gives warning of developing faults, and has enabled breakdowns to be avoided both during commissioning tests and in service. The signals are taken from couplers built into the equipment, until now by using portable instruments. In the latest development the couplers are continuously monitored using special amplifying and detection units connected in a digital optical fiber network. The data collected can be displayed to show the type of discharging source, and stored on disc in a condensed form so that the development of the discharge can be followed over a long period. It can also be interpreted by an expert system and an analysis of the situation sent via a modem link to a PC in the engineer's office, so that he can continuously oversee a number of remote substations. He would also be able to interrogate the coupler units remotely, and check that they are operating properly. Laboratory trials of the continuous monitor have been carried out on a test rig of 400 kV GIS chambers, prior to it being fitted in an operational substation. The basic principles of the monitor and the results of its trials are given.