A computer controlled partial discharge measurement system for capacitor evaluation

Abstract

Continuous measurement of partial discharges gives information not available by conventional corona measurements. Partial discharge activity may be related to dynamic variables, such as time under voltage, overvoltages, and changes in temperature and/ or pressure. A computer controlled system which monitors such variables, in addition to partial discharge characteristics, is described. To improve the productivity of the system, several samples are energized simultaneously while the data acquisition is multiplexed. The temperature of the test samples may be controlled with ovens. A data logger measures test voltage and temperature of the units. Partial discharge activity is monitored both by a pulse height analyzer and the data logger. A mini-computer is used for control and data analysis. Results may be utilized immediately, as for adjustment of parameters, or subsequently used for correlation of partial discharge activity with other parameters in longer term tests. Results illustrating the use of the system are presented. Effects of temperature cycling on the partial discharge activity in several types of liquid impregnated capacitors, with differing dielectric pads (paper, film) and electrodes (foil, metallized), are shown. The applications and limitations of the system for capacitor evaluation are discussed.