Showing papers on "VLF cable testing published in 1998"
TL;DR: In this paper, the authors deal with the calculation of electric fields in HVDC cables and present a method to calculate the field distribution in a real HVAC cable, together with the computed results.
Abstract: HVDC cables start playing a more and more important role in interconnecting national grids. This paper deals with the calculation of electric fields in HVDC cables. The calculation of fields in an HVDC cable is far more complex than the equivalent case in HV ac cables. This is due to the fact that the conductivity of the cable insulation is temperature and field dependent and due to the fact that the electric fields under dc voltage may be time-dependent. The field distribution in an HVDC cable may be of a capacitive, intermediate (and time-dependent) or resistive nature. The kind of field depends on the stage the cable finds itself in: for instance, whether the voltage has just been applied, whether a polarity reversal has occurred or whether the field distribution has become stable. For each stage, the method of calculating, together with the computed results on a real HVDC cable are discussed. Usually, the effect of heating of the insulation by the leakage current may be disregarded. However, in certain cases, i.e. the cable temperature and applied voltage are high enough, the field distribution is influenced by these insulation losses. They even may lead to an instability that causes breakdown of the cable. A cable in service may be subjected to impulses superimposed on the dc voltage. The most severe case is that of an impulse superimposed on a dc voltage of opposite polarity. The calculation of the field distribution in this situation also is carried out.
130 citations
7 Jun 1998
TL;DR: In this paper, the attenuation and transmission speed of PD-pulses on the cable have been determined with respect to the parameters having influence on the evaluation of results from PD-measurements on paper/oil and XLPE-cables.
Abstract: Medium voltage cable characteristics have been determined with respect to the parameters having influence on the evaluation of results from PD-measurements on paper/oil and XLPE-cables. In particular, parameters essential for discharge quantification and location are measured. In order to relate a measured signal at the cable terminations to a specific PD-amplitude and location on the cable, the attenuation and the transmission speed of PD-pulses on the cable have to be known. Consequently, the main parameter to be determined is the complex propagation constant which consists of the attenuation and phase constants. A method to estimate this propagation constant, based on high frequency measurements, is presented and is applied to different cable types under different conditions. The influence of temperature and test voltage is investigated. The relevance of the results for cable diagnostics is discussed.
16 citations
25 Oct 1998
TL;DR: In this article, a new approach to conduct on-line partial discharge (PD) testing in a noisy environment is presented, which is based on conducting PD measurements in both the time and frequency domains.
Abstract: Power cables used in the distribution system, power plants and production facilities often are operated at voltages from 4 kV to 15 kV. These cables are laid next to each other in open or closed trays. In the distribution system, they are terminated to transformers at both ends or to an overhead line at one end and transformer at the other end. In power plant and production facilities, they are terminated to stepdown transformers at one end and often are terminated to high voltage motors at the other end. Partial discharge (PD) pulses measured from one of these cables also could be the results of PD activities in the adjacent cables, motors and transformers, or could be the results of electromagnetic interference from nearby equipment. This makes conducting on-line PD testing almost impossible. In such environments, off-line PD testing is also difficult to perform because it requires shutting down almost the entire system to minimize the interference effect. In this paper, a new approach to conduct on-line PD testing in a noisy environment is presented. The new approach is based on conducting PD measurements in both the time and frequency domains. The PD data collected in both domains are used to identify the PD source.
10 citations
KEMA1
TL;DR: In this paper, the maintenance of the distribution cable network is guided on a significant scale on the basis of the VLF partial discharge diagnostic mapping method, which enables the network owner to focus its maintenance and the replacements on the weak points only.
Abstract: The Dutch distribution network consists of 100% underground cables. The very wet soil and the dense infrastructure were the main reasons for that. The reliability of this network is very high. The total circuit length is more than 90000 km. It consists mainly of paper insulated lead cable, 3-phase belted types. The most commonly used rated voltage is 10 kV. Up till now, the circuit length of XLPE cables is limited, compared to PILC. The early generation of XLPE-cables of the 1970s suffered from water trees. The latest types have tree retardant XLPE insulation and water blocking systems and show good performance. The maintenance of the distribution cable network is guided on a significant scale on the basis of the VLF partial discharge diagnostic mapping method. This method enables the network-owner to focus its maintenance and the replacements on the weak points only. The maintenance costs are reduced considerably, while increasing the reliability of the cable system. This paper starts with a short introduction of the special circumstances in the Netherlands. The network situation is given, with focus on the medium voltage network and the performance of these cable systems. The VLF PD diagnostic method and its results are given.
8 citations
21 Apr 1998
TL;DR: In this article, the relationship between the original VLF (very low frequency) power supply results of PD mapping in medium voltage cables, and the newer on-line monitoring methods is discussed.
Abstract: Some advances have been with detection of the PD activity of medium voltage cables, using an on-line method of detection. This paper illustrates the relationship between the original VLF (very low frequency) power supply results of PD mapping in medium voltage cables, and the newer on-line monitoring methods. The on-line methods offer the possibility of scanning circuits quickly and relatively cheaply to obtain meaningful PD data for older installed cables.
6 citations
TL;DR: The following industry groups' specifications and standards provide different guidelines for DC field tests for cross-linked polyethylene and ethylene propylene rubber insulated cables: IEEE, Insulated Cable Engineers Association (AEIC), and the Association of Edison Illuminating Companies (AIC).
Abstract: Industry standards for shielded medium-voltage cables (5-46 kV) have been revised, changing the DC test voltages for field tests and test durations and limiting tests to newly installed cables. The following industry groups' specifications and standards provide different guidelines for DC field tests for cross-linked polyethylene and ethylene propylene rubber insulated cables: IEEE, Insulated Cable Engineers Association (AEIC), and the Association of Edison Illuminating Companies (AEIC). These specifications and standards are discussed, showing the differences in the recommendations and why the differences exist. The conclusion provides a guide for DC field testing shielded medium-voltage cables based on these industry standards.
3 citations
27 Sep 1998
TL;DR: In this article, the significance of on-line insulation diagnostic techniques for underground 6 kV cable networks in coal mine, and reviews the common measuring methods for the cable insulation are discussed.
Abstract: The paper briefly introduces the significance of on-line insulation diagnostic techniques for underground 6 kV cable networks in coal mine, and reviews the common measuring methods for the cable insulation. Considering the underground environment, an on-line monitoring system for underground 6 kV cable networks based on additional DC measurement has been developed and discussion is focused on the basic scheme of the system. The choice of additional DC power supply, and the analysis of anti-interference techniques. Finally, the measuring results are presented by using the on-line monitoring system.
2 citations
TL;DR: In this article, the optimal distance between single-conductor power cables in a three-phase power system for a given arrangement (horizontal in the plane or triangular) and ambient (ground) temperature are determined.