Complex dielectric constant of various insulating fluids

摘要

Maintenance and condition monitoring of high voltage transformers is of utmost importance, so that local defects can be eliminated before they grow to a failure. The most important part of a transformer with respect to reliability is its oil-paper insulation. Local defects formed here can be detected and located by the means of UHF partial discharge measurement. The applicability of the method relies heavily on the signals to propagate to the sensors through the oil. To determine the properties of the propagation, the high frequency behaviour of the oil must be understood. This article presents the results of a series of measurements on various types of insulating fluids. The applied method relies on the measurement of the impedance of the oil at high frequency. With this, the complex frequency dependent dielectric constant of the oil can be determined. This later enables the calculation to determine whether the PD signals can be detected at the sensors.