Technical Papers

Safety issues in case of internal arc on HV cable terminations, bushings

Apr . 16 . 2015
Worldwide demand for new T&D networks will increase in the near future pushing the utilities to install a larger number of high voltage equipment like cable terminations, bushings and surge arresters. Meanwhile the attention to environmental and safety issues is generally increasing.   The aim of this paper is to analyze the potential risks associated with the use of such high voltage components in case of internal fault and to describe the relevant test modalities that are used to address such a behavior. Transmission System Operators (TSO) are looking for innovative solutions in developing the transmission grid and, as a result, it is likely that the application of extra high voltage AC and DC transmission systems on land will strongly increase in the coming years.   Recently a higher number of XLPE cable systems have also been introduced into HV networks, and more are planned for the future, therefore the number of cable accessories will increase. On the other hand, the increasing demand for a high quality supply will push the utilities to a larger use of the surge arresters both in the traditional area of the substations and in the more recent application on the overhead lines. In the first case the surge arrester, within the insulation coordination practice, helps to reduce the failure risk of equipment, in particular of power transformers, by reducing the lightning and switching overvoltage impact. In the second case it improves the lightning performance of the overhead lines by limiting the number of flashovers that occur along the insulators strings in case of lightning events that would lead to circuit breaker operations.   Besides, the more the network will be connected the more the number of power transformers will increase and consequently the number of bushings is lead to increase. A proper selection of the ratings and characteristics of the high voltage components together with their high quality level is important to reduce the probability of failures. These events cannot be disregarded. Thus, Internal-arc laboratory tests are considered a useful tool to select high voltage components having a safe performance in case of failure, reducing the risk of violent explosion and fire ignition.   The normative background differs when dealing with surge arrester with respect to cable terminations and bushings. For the surge arresters IEC and IEEE standards have, since years, established a defined short circuit test procedure. On the contrary an international consensus regarding internal arc tests on HVcables terminations and bushings has still to be agreed upon. For such components the experiences gained in recent years, based on laboratory test performed according to European technical specifications and standards, should be used as a base to develop an international standard. ​

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