Advanced digital instrumentation for partial-discharge measurement

A new computer based partial-discharge (PD) measuring system was successfully tested in the laboratory in long duration tests on dielectric materials and capacitors. The system measures each current pulse generated by partial discharge during a predetermined time. The pulses are digitized by a 200 megasample/s real-time waveform digitizer and stored in a fast memory unit. The data obtained are transferred to a personal computer for analysis. This system records a large number of pulses without dead time and produces statistical information related to amplitude, polarity, energy and charge content of the PD-generated current pulses. The operation, analysis and display of results are controlled by software. The software can easily be modified to obtain different evaluation methods. This gives flexibility to the new PD detection system and allows its use as a design tool. The operation of the system is automatic, and no human supervision is required. Long duration tests of ceramic capacitors were performed to validate the operation of the diagnostic system. One result indicates that the aging of the tested capacitors changes the charge distribution curve, which was obtained by the statistical analysis of current pulses. The distribution curve shifts towards higher levels of charge as the capacitors deteriorate. This result agrees with the experimental data reported in the literature. The system is particularly suitable for aging studies on dielectric materials under different test conditions.