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.
