Search

The purpose of HV after-laying tests on cable systems on-site is to check the quality of installation. The test on extruded MV cable systems is usually a voltage test. However, in order to enhance the quality of after installation many researchers have proposed performance of diagnosis tests such as detection, location and identification of partial discharges (PD) and tan [delta] measurements. Damped ac voltage (DAC) also called oscillating voltage waves (OVW) is used for PD measurement in after-laying tests of new cables and in diagnostic test of old cables. Continuous ac voltage of very low frequency (VLF) is used for withstand voltage tests as well as for diagnostic tests with PD and tan [delta] measurements. Review on the DAC and VLF tests to detect defects during on-site after-laying tests of extruded MV cable systems is presented. Selectivity of DAC and VLF voltages in after-laying testing depends on different test parameters. PD process depends on type and frequency of the test voltage and hence, the breakdown voltage is different. The withstand voltage of XLPE cable insulation decreases linearly with increasing frequency in log scale. Experimental studies with artificial XLPE cable model indicate that detection of defects with DAC or VLF voltage can be done at a lower voltage than with dc. DAC voltage is sensitive in detecting defects that cause a breakdown due to void discharge, while VLF is sensitive in detecting defects that cause breakdown directly led by inception of electrical trees. Index Terms--Damped ac voltage, very low frequency voltage, voids, defects, breakdown voltage.

Water treeing is one of the factors leading to failure of medium voltage XLPE cables in long-term service. Increased moisture content inside oil-paper insulated cable is not desirable. To identify water tree degraded XLPE cables or oil-paper cables with high moisture content, diagnostic tests based on dielectric response (DR) measurement in time and frequency domain are used. Review of individual DR measurement techniques in the time and frequency domains indicates that measurement of one parameter in either domain may not be sufficient to reveal the status of the cable insulation. But a combination of several DR parameters can improve diagnostic results with respect to water trees present in XLPE cables or increased moisture content in oil-paper cables. DR measurement is a very useful tool that reveals average condition of cable systems. However, it is unlikely that DR measurement will detect few, but long water trees. In addition, DR cannot locate the defect or water tree site within the cable system. Combination of DR and partial discharge (PD) measurements can improve diagnostic results with respect to global and local defects. However, it is doubtful whether PD test can identify the presence of water trees inside a cable in a non-destructive manner. Further research is needed for more detailed conclusions regarding the status of a particular insulation and for predicting the remaining life of the insulation system. Index Terms--Dieletric response, insulation, partial discharge, moisture content, water tree, defects, cable.

A main purpose of doing a diagnostic in cable system including its accessories such as impregnated paper insulated oil filled cable termination is to predict failure before they occur. Those cable and accessories, which are about to fail, can be replaced, thereby reducing the incidence of electrical system failure, thus reducing the electricity outages. This paper presents the work carried out to find any possible method that can be used to detect a drying out of oil impregnated paper tape cable terminations. Furthermore, the diagnosis has to be used without destroying the terminations. Two diagnosis methods; infrared (IR) thermography and X-ray imaging are reviewed and the diagnosis result is presented. By comparison of two-diagnosis method in this work, the X-ray imaging method is the best approach to observe and detect a drying out of paper tape oil impregnated cable terminations. Key words: IR Thermography, X-ray imaging, insulation and cable diagnosis, INTRODUCTION The background of this work is a diagnosis of a medium voltage (MV) oil filled cable terminations. In general, terminations are required when MV cables are connected to the [...]