重复方波电压上升时间对交联聚乙烯电树特性影响研究

Impact of rise time of repetitive square wave voltage on electrical tree characteristics in XLPE

相对于传统燃油推进,全电推进具有低能耗、低噪音、稳定可靠等优势,已成为各国海军未来发展方向。变频驱动系统为全电推进提供核心动力,其安全至关重要。连接电缆位于逆变器和电机之间,是变频驱动系统的重要组成部分,长期承受高频过电压冲击,其绝缘有早期失效的潜在隐患。在电应力下电树产生是电缆绝缘失效的重要原因,研究电力电子应力下电缆绝缘的电树特性具有重要意义。本文在上升时间320~960 ns、峰峰值12 kV、频率5 kHz的重复方波电压下,研究了上升时间对交联聚乙烯电树特性的影响规律。研究表明:重复方波上升时间对交联聚乙烯电树引发特性影响显著,随着上升时间减小,相同时间内电树引发概率和引发长度明显增加,电树形态由丛状和单一的枝状逐渐转变为密集树枝状。其主要原因可能为:在重复方波电压的上升沿和下降沿,方波电压极性反转和介质中空间电荷迁移、恢复具有时间差,会引起背景电场与空间电荷的附加电场正向叠加。研究结果有望为逆变器供电条件下电缆绝缘设计提供实验和理论依据。

Compared with conventional fuel propulsion,the integrated electric propulsion technology has several advantages,such as low energy consumption,low noise,and high stability and reliability.Integrated electric propulsion technology has become the future direction of naval development in various countries.The inverter-fed system provides the power for integrated electric propulsion systems,and its safety should be carefully considered.As an essential part of the inverter-fed system,the connecting cable will be subjected to high-frequency overvoltages,leading to early failure risks.The electrical tree generated under electrical stress is a major cause of failure in cable insulation.Therefore,the electrical tree characteristics of the cable insulation under power electronic stress should be investigated.As one of the key parameters of power electronics,the rise time would have important influences on the generation of electrical trees under power electronic stress.In this paper,the influences of rise time on the XLPE electrical tree characteristics are investigated under the repetitive square wave voltage with 320 ns to 960 ns rise time keeping the peak to peak magnitude and frequency at 12 kV and 5 kHz,respectively.Experimental results show that the rise time of the repetitive square wave has a significant effect on the initiation features of XLPE electrical tree.Square wave voltage with shorter rise time will leads to higher XLPE treeing initiation probability and longer initiation length.Moreover,the electrical tree change from bush shape or single branch to dense branches when reducing the rise time.The main reason may be:at the rising and falling flanks of the repetitive square wave voltage,the faster polarity reversal of the square wave than the migration and recovery of the space charge can lead to a positive superposition of the background electric field.It is expected that the research results can provide experimental and theoretical basis for the design of cable insulation under inverter-fed conditions.