Abstract
This paper addresses the accelerated aging of medium-voltage (MV) cable terminations with resistive stress-grading due to supraharmonics. The paper introduces a simple and quick way to relate the risk of cable termination failure to the characteristics of supraharmonic distortion in the system. The motivation is to give practical recommendations and guidelines to evaluate the risk of failure of cable terminations under the presence of supraharmonics in MV networks. The underlying model relates the heating in the cable termination linearly with the frequency of the voltage applied and proportionally with the square of the magnitude of the voltage. The indicator can be used to decide whether given levels and frequencies of supraharmonics in the MV network represent a risk to cable terminations. The parameters of the cable termination design are not needed for that decision. However, the decision criterion is based on one sample data (Eagle Pass) and more field information is crucial to improve the approach.
Highlights
Supraharmonics or high-frequency distortion are voltage and current waveform distortion in the frequency range 2 to 150 kHz
For the failure of the cable termination due to supraharmonics to occur, the termination has to be of the resistive stress-grading type and certain conditions must hold. These conditions can be visualized as a chain of events and described as follows: 1) High levels of supraharmonic voltages must exist in the MV network
A simple and quick way to relate cable termination failure conditions to the characteristics of supraharmonic distortion present in the system is introduced in this paper
Summary
Supraharmonics or high-frequency distortion are voltage and current waveform distortion in the frequency range 2 to 150 kHz. Aging happens because resistive stress-grading materials, by design, have inherently high conductivity at supraharmonic frequencies [13] The latter results in the appearance of hotspots on the surface of the stress-grading layer and the subsequent failure of the insulation system at the cable termination [4], [12]. For the failure of the cable termination due to supraharmonics to occur, the termination has to be of the resistive stress-grading type and certain conditions must hold These conditions can be visualized as a chain of events and described as follows: 1) High levels of supraharmonic voltages must exist in the MV network. 2) The high levels of supraharmonic voltages must affect the cable termination stress-grading material significantly enough to cause power losses, which must be high enough to create hotspots in the stress-grading layer.
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