工频电压下有机硅凝胶的电树枝发展规律及其局部放电特性

Propagation of Electrical Tree and Characteristic of Partial Discharge in Silicone Gel Used for the Encapsulation in Power Module

有机硅凝胶作为高压大功率IGBT器件灌封的绝缘材料,其自身的绝缘性能直接决定着IGBT器件的耐压可靠性。为此,针对高压大功率IGBT器件封装用有机硅凝胶内局部放电产生的电树枝发展规律及局部放电特性开展实验研究。实验中采用针-板电极结构,实时记录了交流电压下有机硅凝胶内电树枝的发展规律以及局部放电特征参量。实验结果表明在室温及工频电压作用下,有机硅凝胶内的电树枝主要由气道与气泡构成,电树枝的生长速度与树枝长度无关,依据有机硅凝胶材料的高分子主链结构分析了电树枝通道的不导电性或弱导电性,此外,实验观测到有机硅凝胶材料的电树枝具有独特的自愈特性,并分别从物理自愈和化学自愈解释了电树枝的自愈机制;有机硅凝胶内局部放电脉冲序列主要分布于一、三象限,符合典型的材料内部沿面放电特征谱,随着电树枝的生长,局部放电脉冲的放电量增大,但脉冲频率几乎不变,脉冲相位受到空间电荷调制效应的影响。研究结果对于指导有机硅凝胶在IGBT器件灌封时的应用具有一定的指导意义。

This paper focused on the partial discharge properties of silicone gel used as an encapsulant in high voltage and high power IGBT power modules. A needle-to-plate electrode was applied to imitate the concentration of the electric field. Under 50 Hz AC voltage, the growth patterns of the electric tree were observed, and the phase-resolved partial discharges(PRPD) were measured. The growth and dissipation patterns of the electric tree were observed. The electric tree consists of tree-like cavities and spherical-like bubbles. It is found that the propagation direction of the electric tree is affected by electric field distribution and trap inside silicone gel. Furthermore, the electric tree is non-conductive due to the Si-O structure of the main chain. Thus, the propagation speed is independent of the length of the tree. Simultaneously, the unique self-healing properties of electric tree were observed in silicone gel after partial discharge. The self-healing mechanism was analyzed from the physical and chemical principles. The experimental results show that the PRPD in silicone gel is mainly distributed in the first and third quadrants, which conforms to the characteristic pattern of the typical internal creeping discharge in materials. With the propagation of the electric tree, the pulse frequency of partial discharge is almost constant, while the pulse phase gradually widens due to the effect of the space charge field. The research results in this paper will be helpful to guiding the application of silicone gel in the power modules.