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 cable provides electrical isolation and protection for the operator and the monitor. This has been tested on high voltage equipment up to 400kV. In laboratory 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 recognition of the frequency spectra ('signatures') thus produced. By a similar procedure it has been possible to discriminate between signals generated by discharge activity in oil in a ring main unit, in the oil alone and in oil containing dry and wet fibres. The optically isolated acoustic emission detector has been successfully used to locate and identify a number of practical sources of discharge activity, for example in transformer tanks and cable terminations, A portable system, including the detection and signal processing capability, has been developed and installed for the on-line monitoring of substation equipment.