PWM脉冲电压下电缆终端多热点特征的形成机理

Mechanism of Multiple Hot Spots at PWM Pulse Voltage for Medium Voltage Cable Terminations

为了研究脉冲电压下电缆终端过早失效的机理,对脉冲电压下电缆终端的红外成像特征和内部电场强度分布进行了研究,阐明了热点特征和内部电场强度分布之间的联系。实验通过高频脉冲电压电源对应力控制型冷缩电缆终端施加电压,同时也施加了相同频率和幅值的正弦电压作为对照,使用红外热成像仪分析不同类型的电压对电缆终端表面温度分布的影响。此外,通过瞬态电场仿真分析发现,电缆终端在半导电层截断处和接地点2个位置的电场较强,且该处热功率密度最高,脉冲电压下的电缆终端阻性发热量也明显高于正弦电压。结果表明,脉冲电压下电缆终端的发热区域面积和热点温度明显大于正弦电压,其热点形成的实质是因为快速的脉冲上升沿包含较高的频率成分,导致电缆终端局部电场增强,阻性发热增加,引起温度升高而形成热点。

In order to investigate the premature failure of medium voltage cable terminations under PWM（ pulse width modulated） voltages,the relationships between surface hot spot characteristics and electric field distribution were investigated. A pulse voltage generator was applied to a cable termination（ stress grading termination）. Also,a high frequency sinusoidal voltage generator was applied to the termination with the same frequency and voltage amplitude. Through the results of infrared thermal images,the distribution of surface temperature was analyzed for the cable termination at pulse and sinusoidal voltages. In addition,according to the analysis of transient electric field based on finite element simulation,the maximum values of electric field at pulse voltages in stress grading termination located in the two positions where semiconducting layer cut off and where connected to the ground potential were obtained. The hot spots were related to the maximum value of electric field strength. Since pulse voltages include high frequency components during the rapid rising process,enhanced electric field on the local area resulted in higher resistive heating. As a result,the temperature at pulse voltage was more than at sinusoidal voltage and multiple hot spots form on the surface of the termination.