Abstract: 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 /spl 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 /spl 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.

Abstract: The advantages on VLF (very low frequency) on site testing compared to conventional testing at power frequency are shown in practical and dielectrical aspects. Furthermore VLF test voltages enable the possibility of diagnosis on site. The two well established diagnosis methods, dissipation factor (DF) measurement and partial discharge (PD) measurement are explained. Where the DF diagnosis gives a tool for judgement of the ageing status especially of plastic cables, the PD diagnosis enables detection of single defects within a cable system. The economic advantages of diagnosis are shown in practical examples. An outlook for application on VLF high voltage on site test systems concludes the paper.

Abstract: It is important for power cable, especially high voltage single core cable, to have a healthy sheath. Once the cable sheath is faulty, it would accelerate the aging process of cable insulation, and result in failure of the conventional on-line condition monitoring system due to inaccurate insulation measurement. Traditional fault location methods for main insulation of power cable such as the radar method are no longer valid for sheath insulation fault. The bridge method and voltage comparison method are applicable for sheath fault location, but their accuracies are subject to influences of the contact resistance and resistance of test leads. A novel fault location method for power cable sheath fault is presented in this paper. The resistance of outer metal layer of the fault cable between the terminal and the fault position is measured, and then compared to the known unit resistance to calculate distance to fault. Therefore, it is free from the influence of contact resistance and intrinsic resistance of test leads. Case studies show that the proposed method is effective to determine the position of sheath faults of high voltage power cable on-site.

Abstract: Device for VLF testing of cables in which the switching process is undertaken over serially connected and inductively coupled or light triggered thyristors.

Abstract: There are many different methods of employing a high potential test on a stator winding. Three such methods that this paper will explore with reference to one another are the AC (50-60 Hz), DC, and very low frequency (VLF) (0.1 Hz). Some users choose the AC high potential test knowing that this test best simulates the voltage stress on the winding while in service. Other users prefer the DC high potential test largely due to ease in performing the test. However, the DC voltage does not stress the stator coils the same way as when they are in service and may result in overly pessimistic results due to the influence of surface contaminants in the end windings. Finally, the VLF test, due to recent advances in technology, is becoming more practical for use in field conditions. However, the present standard governing the test is almost 40 years old and there is significant interest in what VLF voltage level best correlates with the AC and DC high potential tests. This paper reports preliminary test results on three generator windings that were destructively tested using the AC, DC, and VLF methods as part of an ongoing effort to provide a database upon which to set the appropriate VLF hipot level for modern synthetic resin-based stator insulation systems.

Abstract: Cable diagnostic with very low frequency (VLF) measurements has gradually evolved from laboratory research to field testing. VLF dielectric test aims to replace DC dielectric test for extruded cables because of the potentially harmful effects and ineffectiveness of DC voltage in polymeric insulation. Furthermore, dielectric loss measurements are often used for insulation diagnostic. Its application at very low frequencies has led to the development of different cable diagnostic methods. However, despite recent technical guide for dielectric tests and existing criteria of dissipation factor measurements for cable diagnostic, field experience remains unconvinced and widely divided. This paper presents some field and laboratory results on VLF testing and measurements to gain a better understanding.

Abstract: A testing method for evaluating the quality of ADSS fiber optic cable is presented Aging effect due to arcing under different voltage and pollution levels (heavy and light) is described Measurement of area and depth of damaged cable is conducted to analyze the damage severity Experiments show that 2 mA and 7 kV are threshold current and voltage which might cause cable failure Cycle to failure of the cable decreases from 330 to 65 when voltage changes from 11 kV to 14 kV, and it is inversely proportional to the damage area of the cable