No abstract

No abstract

The Pulsed Electroacoustic (PEA) method is now widely accepted as one of the most simple and effective techniques for the measurement of the dynamic space charge distribution in solid dielectrics. Recently, the PEA method has been applied also to laminar test objects composed of two or more layers of different dielectrics (multidielectrics). However, when a multi-dielectric is tested by means of the PEA method, the different acoustic and electric properties of the materials affect the detected space charge signal. In this paper, the principle of the PEA technique is reviewed in case the test object is a multi-dielectric. The generation, transmission and reflection of electrically-induced acoustic waves are described. Based on the proposed approach, results of PEA measurements performed on various kinds of multi-dielectrics are presented and discussed.

No abstract

Abstract-The measurement of partial discharge (PD) activity has become an invaluable tool for monitoring the insulation condition of high-voltage components in service. In particular, it is important for factories and for the utilities to get an indication of the time to breakdown. In this paper, the authors describe a study on the use of a damped ac voltage (DAC) method and a very low frequency (VLF) method to stress insulation and to detect partial discharge activity. The main goal of this study was to find out whether the PD patterns obtained at 50 (60)-Hz voltage correspond to those obtained at either lower frequency voltage (VLF) or higher frequency voltage (DAC). For this purpose, a combined theoretical and experimental approach for dielectric bounded cavities was used. The effect of the frequency and the shape of the voltage (DAC) on the PD phase-resolved pattern were studied in the laboratory. Tests were performed on dielectric bounded cavities in polyester with the DAC method, the VLF method (0.1 Hz), and the 50 (60)-Hz method. Moreover, the PD phenomenon was theoretically analyzed at different stress frequencies, and a comparison was made between theory and measurement.

In addition to after-laying of new-installed high voltage (HV) power cables the use of on-site non-destructive on-site testing and diagnosis of service aged power cables is becoming an important issue to determine the actual condition of the cable systems and to determine the future performances. In this paper based on field experience an overview is presented on on-site testing and partial discharge diagnosis of HV power cables with regard to on-site testing methods: energizing, diagnostic aspects, possibilities and implications for new and service aged power cables.

No abstract

No abstract