What is Marx generator

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What is Marx generator

Marx generator

The Marx Generator is a high-voltage device that generates high-voltage pulses from a low-voltage DC power supply, charges them in parallel through capacitors and then discharges them in series. This structure was proposed by Erwin Otto Marx in 1924. It can imitate lightning and operating overvoltage processes. Therefore, it is often used in high-energy physical tests such as insulation impact withstand voltage, dielectric impact breakdown, and discharge. For example, simulate the impact of lightning on power line gears and aviation equipment. The foreign name is Marx Generator. The high-voltage device for substantial discharge was proposed in 1924, the inventor Erwin Otto Marx

Introduction

The Marx Generator is a high-voltage device that uses capacitors to be charged in parallel and then discharged in series.

application

This structure was proposed by E.Marx in 1924, and it can imitate the process of lightning and operating overvoltage. Therefore, it is often used in tests such as insulation impact withstand voltage, dielectric impact breakdown, and discharge.

principle

Working principle: as shown in Figure 1. In the figure, C is the stage capacitor, which is connected in parallel by the charging resistor R, and is charged to V through the rectifier circuit T-D-r. At this time, because the protective resistance r is generally about 10 times larger than R, it not only protects the rectifier equipment, but also ensures that the capacitors at all levels are charged uniformly. In the first level, g0 is the ignition ball gap, which is started by the ignition pulse; in other levels, g is the intermediate ball gap, and they are adjusted to act one by one after g0 starts. These ball gaps play the role of control switches in the loop. When they are all activated, all the capacitors C are connected in series through the wave head resistance Rf of each level and charge the load capacitor C0. At this time, the total capacitance after series connection is C/n, and the total voltage is nV. n is the number of stages of the generator loop. Because C0 is small, it will be fully charged soon, and then it will be discharged together with the stage capacitor C through the tail resistance Rt of each stage. In this way, an impulse voltage with a very high voltage and short pulse waveform is formed on the load capacitor C0. In this short period of time, because the charging resistance R is much larger than Rf and Rt, they play the role of isolation resistance between all levels. The impulse voltage generator uses multi-stage capacitors to be charged in parallel and discharged in series to generate the required voltage. Its waveform can be adjusted by changing the resistance of Rf and Rt, the amplitude is adjusted by the charging voltage V, and the polarity can be reversed by the silicon stack D Two poles to change.

In the figure, C1 is the main capacitor, also known as the impulse capacitor. It is equivalent to the total capacitance after all levels are connected in series, namely; C2 is the load capacitance, that is, C2=C0, which includes the wave-modulating capacitor, the capacitor of the sample, and the measuring equipment (voltage division Parasitic capacitance such as capacitance and connection; G represents the ball gap that controls the discharge; Rf and Rt are the wave head resistance and wave tail resistance respectively, which are equivalent to the sum of rf and rt at all levels, namely Rf=nrf, Rt=nrt ; U1 is the charging voltage, which is equivalent to the total voltage after all levels are connected in series, that is, U1=nV; U2 is the output voltage, that is, the required impulse voltage. This equivalent circuit is equivalent to the circuit of a single-stage impulse voltage generator. According to the circuit analysis, the output voltage U2(t) is a double exponential function

Marx (Marx generator)

　Τ1>>τ

Half peak time T2≈0.69Rt(C1+C2)

Efficiency The ratio of the output voltage amplitude V2m of the impulse voltage generator to the charging voltage пV is called the efficiency η of the generator, namely

η=(V2m /nV)×100%

For lightning shock waves, η is generally about 80%; for operation shock waves, η is sometimes only 60%.

The impulse voltage waveform parameters T1 (Tcr), T2 and generator efficiency η are related to the loop structure and parameters, and all need to be adjusted and determined through actual debugging.

For power equipment with windings, such as power transformers, lightning impulse chopping tests are usually required. The impulse voltage generator is connected to a cut-off gap to generate shock cut waves. The standard lightning chopping wave is the waveform of the standard lightning shock wave truncated by 2～5μs.

The impulse voltage generator is one of the basic test equipment in the high voltage laboratory. The highest rated voltage of impulse voltage generators built in China is 6MV, and some countries are as high as 10MV.

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