Acoustic emission analysis of high voltage insulation

A portable acoustic emission monitoring system has been developed and used to test both laboratory samples and practical equipment. A fibre optic cabl e provides electrical isolation and protection for the operator and the mon itor. This has been tested on high voltage equipment up to 400kV. In labora tory samples it has been possible to distinguish between discharges arising from different sources by converting the acoustic emission sinal from the time domain to the frequency domain by fast Fourier transformation and reco gnition of the frequency spectra ('signatures') thus produced. By a similar procedure it has been possible to discriminate between signals generated b y discharge activity in oil in a ring main unit, in the oil alone and in oi l containing dry and wet fibres. The optically isolated acoustic emission d etector has been successfully used to locate and identify a number of pract ical sources of discharge activity, for example in transformer tanks and ca ble terminations, A portable system, including the detection and signal pro cessing capability, has been developed and installed for the on-line monito ring of substation equipment.