直流叠加高频谐波下交联聚乙烯的电树枝引发特性研究

Study on Initiation Characteristics of Electrical Tree in XLPE Under DC Superimposed High Frequency Harmonic

复合电压中交流谐波分量的引入给直流电缆的安全带来了严重隐患,在实际直流系统中谐波频率可达千赫兹。为研究复合电压中高频谐波对电树枝引发特性的影响,在0.5~3 kHz交流谐波频率范围内正、负极性偏置电压下对XLPE材料进行了电树枝引发实验。结果表明:负极性直流偏置电压下电树枝比正极性直流偏置电压下更易引发,并且负极性直流偏置电压下电树枝的扩展系数更大。正极性下电树枝形态为枝状,分支较少,存在一条明显主干树枝,通道颜色较浅,电树枝长度增长较快;而负极性下电树枝形态为松枝状,有较多分支,通道颜色较深,电树枝长度增长缓慢。交流谐波电压频率或幅值的增加均会促进电树枝的产生和生长,因此直流系统中的高频谐波分量会对直流电缆绝缘系统构成潜在威胁,直流电缆在运行过程中应避免高频谐波的存在。

The AC harmonic component of composite voltage brings serious hidden trouble to the safety of DC cable, and the harmonic frequency can reach several k Hz in the actual DC system. In order to research the effect of high frequency harmonics in composite voltage on the initiation characteristics of electrical tree, the electrical tree initiation experiment of cross-linked polyethylene(XLPE) material was carried out under positive and negative polarity bias voltage at the range of 0.5 kHz-3kHz of AC harmonic frequency. The results show that under negative polarity DC bias voltage, electrical tree is induced more easily, and the propagation coefficient of electrical tree under negative polarity is larger. Under positive polarity, the electrical trees grow rapidly, its shape is dendritic with less branch, but there is an obvious trunk branch, and the electrical tree channel color is light. Under negative polarity, the electrical trees grow slowly, its shape is pine-branch type with more branches, and the electrical tree channel color is dark. The increase of frequency or amplitude of AC harmonic voltage can promote the generation and growth of electrical tree. Therefore, the high frequency harmonic component in DC system will be a potential threat to the insulation system of DC cable, and the high frequency harmonic should be avoided during the operation of DC cable.