Research on Suppression Methods of Overshoot and Power-frequency Voltage Drop During Lightning Impulse Test of UHV Switchgear

With the rapid development of China's UHV power grid, UHV switchgear has been widely used in UHV power system. Due to the large capacity of UHV switchgear, the overshoot and power-frequency voltage drop are also too large during lightning impulse test. This problem has become a hot issue that is widely concerned by engineers. Taking 1100kV GIS lightning impulse test as an example, this paper establishes two simulation models of lightning impulse withstand voltage test and lightning impulse combined voltage test circuits with the software MATLAB/Simulink. The causes of lightning impulse overshoot and power- frequency voltage drop are analyzed. Comparisons of simulation and test show the correctness and effectiveness of these models. Then an overshoot suppression circuit and a power-frequency voltage drop suppression circuit are proposed. A new overshoot suppression circuit composed of a capacitor Cc and a resistor Rc connected in parallel. Simulation and test results show that, in a certain range, waveform front time will reduce and oscillation extent will exacerbate if Cc increases; Oscillation extent will decrease and waveform front time will be stable if Rc increases, but lightning waveform will occur a double peak phenomenon if Rc is too large. Experiments show that, to join the overshoot suppression circuit, waveform can fully meet the requirement of relevant standards, lightning wave overshoot suppression device is designed to provide a theoretical basis. The power-frequency voltage drop suppression circuit is composed of a power-frequency voltage divider and an adjustable capacitor, which can effectively work to control voltage drop.