Impulse voltage generator is one of the basic equipment in high voltage laboratory. It is a high voltage generator which generates pulse wave. Because the ability of insulation to withstand impulse voltage is related to the applied voltage waveform, and the actual impulse voltage waveform is dispersed, it is necessary to make uniform provisions for impulse voltage waveform parameters to ensure repeatability of multiple tests and comparability of results under different test conditions. China uses the international Electrotechnical Commission (IEC) standard standard impulse voltage waveform. That is to say, the impulse voltage waveform is double exponential type, the wave head time is 1.2us, the wave tail time is 50us, and the peak impulse voltage is generally tens of kilovolts to several megabytes of volts.
The selection of impulse capacitance value of impulse voltage generator
The maximum capacitance of the sample is 2000pF, and it is estimated that the stray capacitance of the impulse voltage generator to the ground and the capacitance of the high voltage leads and the ball gap are about 500pF, and the capacitance of the capacitance divider is about 600pF. Therefore, the total maximum load capacitance is:
C2 = 2000 + 500 + 600 = 3100 pf
To ensure voltage efficiency, the impact capacitance should be greater than or equal to 10 times of the load capacitance, so the impact capacitance is about: C1≥10C2≥31000pF.
Because the inductance in the circuit will affect the impulse voltage waveform of impulse voltage generator, the main capacitor should be selected with small intrinsic inductance. In this design, the main capacitor is pulse capacitor. The main types of impulse capacitors used in impulse voltage generators can be divided into: plastic paper tube type, porcelain case type and metal case type.
Rubber tube capacitor shape slender, mechanical strength is poor, it is not convenient to use the column generator structure, the need for another insulation bracket, and the capacity of the capacitor can not do very large, easy to be damp in use, so it is rarely used in large impulse voltage generator.
Porcelain capacitor has high mechanical strength and good insulation performance, suitable for column generator structure, but its energy can not be made very large, so this kind of capacitor is mostly used for medium impulse voltage generator below 2000kV.
Metal shell capacitor voltage and capacity can be made very large, and high mechanical strength, suitable for a variety of impulse voltage generator structure, so it is widely used.
Considering the influence of voltage grade, capacitor specification and capacitance, the iron-shell pulse capacitor with rated voltage of 100kV and nominal capacity of 0.2uF is selected from the pulse capacitor product list of a capacitor manufacturer.
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