In this paper, the effect of harmonic voltage on partial discharge properties of LN ₂ /PPLP (Liquid nitrogen/ Polypropylene-Laminated-Paper) insulation system for high-temperature superconducting (HTS) DC cable is studied. The harmonic components with a frequency from 50 to 350 Hz are superimposed on the DC voltage to analyze the mechanism of the harmonic amplitude and order on partial discharge (PD). The experimental results show that when the V _rms of the composite voltage remains consistent, the increase in the proportion of the harmonic amplitude will cause the enhancement of partial discharge amplitude, discharge counts and pulse repetition rate, especially as the amplitude of harmonic component exceeds that of DC voltage. The increase of the harmonic order results in variation of the derivative of the applied voltage with time (dv/dt) along the phase, which further causes the pulse repetition rate to increase. It is concluded that the harmonic components superimposed on DC voltage promote the occurrence of PD, which poses a significant threat to the insulation of superconducting DC cable.

中文翻译：

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谐波电压对高温超导直流电缆LN2/PPLP绝缘局部放电特性的影响

本文研究了谐波电压对 高温超导（HTS）直流电缆LN ₂ /PPLP（液氮/聚丙烯层压纸）绝缘系统局部放电特性的影响 。将频率为 50~350Hz 的谐波分量叠加在直流电压上，分析局部放电（PD）谐波幅值和阶次的机理。实验结果表明，当复合电压的V _rms保持一致，谐波幅值比例的增加会引起局部放电幅值、放电次数和脉冲重复率的提高，特别是当谐波分量的幅值超过直流电压时。谐波次数的增加导致外加电压随时间的导数（dv/dt）沿相位发生变化，这进一步导致脉冲重复率增加。结论是叠加在直流电压上的谐波成分促进了局部放电的发生，对超导直流电缆的绝缘构成了重大威胁。