Overshoot and Calculation Method of Standard Lightning Impulse Voltage

Cui Dong, Wang Jiansheng, Zhang Xiaoyong
 HIMALAYAL - SHANGHAI - CHINA 

Abstract: The lightning impulse overshoot requirement is always an important parameter for lightning impulse withstand voltage test. With the development of test and measuring technologies and improvement of voltage grade, the current standard cannot meet the requirement of lightning impulse overshoot. In addition, it has been found that previous definitions and requirements have mutation possibility and average curve. In order to solve great uncertainty, latest revised IEC standards and national standards redefine the overshoot and its calculation method. Concrete examples are presented in this paper.  

1. Introduction 
It has been more than 10 years since the current version GB/T16927.1 was issued and enforced in 1997. During that period, the electric power equipments have rapidly developed, especially in China. With years of development and application of 800kV and 1100kV equipment, test voltage has reached power frequency 1200kV, switching impulse 1950kV and lightning impulse 2700kV. Regulations in the original version are not been suitable for such high voltage, especially lightning impulse. IEC 60060-1 latest revised version redefines the overshoot of lightning impulse and its calculation method. Combing with actual examples, the difference between both is compared and analyzed in this paper.        

According to GB/T 16927.1-1997, relevant information about lightning impulse test of high voltage product and voltage waveform of standard lightning impulse is as follows:
— As for smooth lightning impulse wave, the test voltage is peak;
— As for some test circuit, oscillation overshoot may occur at the impulse peak. If the oscillation frequency is no less than 0.5MHz or overshoot time is no higher than 1μs, a average curve should be drawn to facilitate the measurement. Maximum amplitude of the curve, also known as the peak, is defined as test voltage value;

As for smooth lightning impulse wave, it is believed that the overshoot does not exist; while if the oscillation frequency is higher than 0.5MHz, the overshoot exists. The overshoot is defined as per oscillation peak exceeding test voltage peak extent.