Study On 10kV Square Wave Generator

In Gas Insulated Substation (GIS), grounding fault, particularly the rapid changes of voltage caused by small capacitive current interrupting by a disconnector, will induce Very Fast Transient Overvoltage(VFTO) in a coaxial bus of GIS. The short rise time (up to a few ns) and high amplitude of VFTO are great threat to the internal insulation in GIS. As the development of ultra high voltage grid in china, the VFTO is becoming more dangerous to the smaller margin insulation. In addition, over-voltage which has a shorter front time than the standard lighting wave (1.2μs) appears sometimes in the power system. In such conditions, the fast response voltage divider for accurately measurement is needed. To insure a high SNR for calibrating voltage dividers, a high voltage Square Wave Generator (SWG) is ideal to be the source. So it is meaningful to develop a high voltage SWG with a rise time in a few nanoseconds.This paper firstly analyzed the principle of the single transmission line and Blumlein transmission line pulse generator, and then deduced the relationship between the output pulse waveform and transmission line's length and voltage. Then the properties of capacitor discharging pulse generator and the principle of steeping device were studied in detail. Summarizing the advantages of transmission line pulse generator, it proposed a circuit of capacitor discharging pulse generator with a steeping device.The capacitance and resistance of the main circuit were analysed and a steeping switch was designed with a rising time less than 5ns. A single stage discharge circuit was established to investigate the performance of the steeping switch, in which the steeping switch composed of oil gap or gas gap. The experimental results show that the gas gap has a shorter rise time(about 5ns)with more stable performance.Various parameters of the circuit on the influence of the output waveform were studied by ATP simulations. The results present the influence of stray parameters on the output waveform. By the improvement of the circuit, a square wave was eventually obtained with rise time<5ns and pulse width>1μs.