Research direction of resistive high-voltage pulse divider

作者： GOZ Electric 时间：2014-04-30 11:24:11 阅读：20

At present, there are different research directions in resistive high-voltage pulse voltage dividers in China, including low-resistance nanosecond level and high-resistance with load.

This article describes the relevant matters that need to be considered in the production of high-resistance voltage dividers. The main work includes:

1. Material selection. Currently, the materials used to make resistor dividers are mainly Kama wire and nickel-chromium wire. Their structure has high toughness and good toughness, which meets the conditions for non-inductive winding resistors. Some also use high-voltage precision resistance welding. The process is extremely complex and uses core or DNA welding to reduce the impact of parasitic inductance on the pulse waveform. For voltage dividers with large mechanical dimensions (about 1.5 meters), the resistance value requirements are not high and can be made by welding process.

     Welding resistors to make high-voltage pulse voltage dividers: Theoretical analysis requires a large number of high-voltage precision resistors, and the end-connected series resistors are used. During the design process, the resistor series withstand voltage issue should be considered, but a certain margin should be retained. Determine the size of the single resistor and the welding method. When making the actual object, the handling of the resistance welding position and the ground compensation issue at the bottom of the high-voltage arm should be taken into consideration. A metal bracket can be added to the bottom of the high-voltage arm. Examine the related problems of the voltage divider through actual measurements.

     Winding value resistors are used to make high-voltage pulse voltage dividers: Kama wire and nickel-chromium wires can be used for winding value resistors. Kama wire has higher toughness and a higher resistance than nickel-chromium wire of the same diameter. The nickel-chromium wire has a high nickel-chromium content, so the nickel-chromium wire is not easy to deform, and the coil is not easy to knot during the winding process. This is of great help to the winding personnel during the operation and reduces the frequency of disconnections and jumpers.

The following takes a 200kV/100kΩ resistor divider as an example to describe:

The resistance value is a 100kΩ voltage divider, and the mechanical size is below 1000mm. Its production is difficult and the welding resistor production cannot be completed. It is specially wound with nickel-chromium wire.

2. Determine the parameters: the mechanical size of the voltage divider is 1000mm, the low-voltage arm is designed to be 200mm, and the high-voltage arm is designed to be 800mm. The winding resistance of the high-voltage arm should be about 750mm, leaving a certain flow rate to ensure that both ends are fixed.

3. Physical production, place the value-wound resistor into the high-voltage arm barrel. Since the instantaneous voltage at the top of the high-voltage arm is higher, place the high-resistance resistor at the top of the high-voltage arm and the low-resistance resistor at the bottom. The effect of inductance should be considered at the overlap. The voltage resistance of the voltage divider is the focus of the production part. Since the nickel-chromium wire knee bag has insufficient pressure resistance (1000-1500v), the pressure resistance issue needs to be considered between the gates and the top of the high-voltage arm needs to be considered. Resistors with better winding values are of great help in improving the measured waveform of the voltage divider. In addition, considering that stray capacitance affects the waveform response, its capacitance compensation should be increased, a voltage equalizing ring should be added to the top of the high-voltage arm, and a metal plate should be placed at the bottom of the high-voltage arm to artificially increase the capacitance to ground to prevent waveform oscillation.

     Overall insulation: The length of the high-voltage arm resistor of the impact voltage divider is considered based on the allowable potential gradient in oil E≤15kV/cm. The height of the outer insulating cylinder is calculated based on the allowable potential gradient E≤5kV/cm in air. In a voltage divider with an impulse withstand voltage of 220kV, the high voltage of the insulating cylinder must be ≥50cm. The insulating cylinder of the high-voltage arm of the voltage divider meets the relevant conditions and is soaked in insulating oil to improve the insulation level. During the welding voltage divider production process, insufficient voltage resistance occurred and the voltage divider broke down. We tried to improve the method by increasing the number of welds to increase the overall voltage resistance level and filling it with insulating materials. However, the overall improvement of the voltage divider was not satisfactory, so the non-inductive winding method was adopted. The winding work is complicated and there are many uncontrollable factors. It is impossible to control the influence of its own inductance and capacitance on the waveform and response time of the voltage divider.

4. Matching problem between coaxial cable and voltage divider, refraction and reflection of waves in the line

In power systems, it is often encountered that two lines with different wave impedances are connected together. Two matching methods can be used, end matching and low-voltage arm internal matching, both of which can suppress the occurrence of refraction.

5. Summary

     Resistive voltage dividers inevitably have stray capacitance and inductance, which will affect high-frequency performance and require compensation for measuring steep pulses. Looking through the high-voltage technical literature, it is proposed that the capacitance compensation method can reduce the influence of longitudinally distributed capacitance. However, several tests have shown that the error caused by the resistor divider when measuring the impulse voltage is related to the product of the resistance and the stray capacitance to ground. To reduce the error, the resistance of the voltage divider and the stray capacitance to ground must be reduced. Change the operating environment. Improperly made resistors will affect the generator to generate shock waves, and it will also be difficult to damp the oscillation between the residual inductance and stray capacitance. At the same time, the resulting step response will produce a high overshoot. Therefore, in order to reduce the error of the voltage divider, the main thing is to reduce the size of the stray capacitance to ground. Usually, a voltage equalizing ball is added at the high voltage end to compensate for the stray capacitance current flowing from the voltage divider body to the ground; at the same time, the voltage divider is reduced size to reduce stray capacitance to ground. The former will greatly increase the lateral size of the voltage divider and move the high potential downward, and the latter will be limited by the operating voltage.