The significance of the peaking capacitor integrated capacitor voltage divider

Author： GOZ Electric Time：2024-11-01 09:54:26 Read：12

Peaking capacitors are usually measured indirectly due to their compact structure, while direct measurement of the peaking capacitor voltage has always been a difficult problem. In order to solve this problem, a new type of resistance-compensated self-integrating peaking capacitor integrated capacitor voltage divider was developed based on the peaking capacitor. Secondly, the theoretical voltage divider ratio of the peaking capacitor integrated capacitor voltage divider was analyzed according to the new structure of the voltage divider, and the theoretical voltage divider ratio calculation formula was given. The factors affecting the low-frequency response were analyzed and circuit simulation verification was performed. At the same time, a square wave calibration experiment was carried out to obtain the voltage divider ratio and response time of the two probes, and the probe response time was less than 6.2n. In addition, in order to obtain a more accurate voltage divider ratio and verify the stability of the voltage divider ratio of the integrated capacitor voltage divider under normal working conditions, a high-voltage online calibration experiment was carried out, and the voltage divider ratio of the 1# probe was 11071. The voltage divider ratio of the 2# probe was 15148. At present, at higher voltage levels, the measurement relative error of the capacitor divider probe is small, and the voltage divider ratio stability is good.

Keywords: peaking capacitor; resistance compensation; capacitor voltage divider; voltage divider ratio; high voltage pulse

In the electromagnetic pulse source device, it is very important to accurately measure the pulse breakdown voltage of the output switch. Since the output switch and peaking capacitor of the electromagnetic pulse source are both encapsulated in high-pressure insulating gas, and the pulse voltage amplitude is high and the insulating cavity structure is complex, it is difficult to measure the electromagnetic pulse source in operation. Under the premise of not changing the basic structure of the electromagnetic pulse source as much as possible, it is a feasible method to determine the breakdown voltage of the output switch by measuring the voltage of the peaking capacitor and the load voltage according to the difference between the two. The problem that needs to be solved by this method is the voltage measurement of the MV-level coaxial film capacitor. Due to the compact structure of the peaking capacitor, the direct measurement of the peaking capacitor voltage is currently a major problem, and related literature reports are also relatively rare. Therefore, this paper is dedicated to studying the method of realizing the direct measurement of the peaking capacitor voltage.

Capacitor voltage dividers are widely used in the measurement of high-voltage narrow pulses due to their advantages such as fast response speed, large voltage divider ratio, wide bandwidth and small load effect. In the field of pulse power technology, the measurement of nanosecond narrow pulses generally adopts the measurement method of capacitor voltage dividers and oscilloscopes, especially in pulse power devices, such as the measurement of MV-level pulse voltages such as coaxial water and oil transmission lines. According to the relationship between the output signal and the input signal, capacitor voltage dividers can be divided into self-integrating type and D-dot type. Since the output voltage measured by the D-dot capacitor voltage divider is the differential of the input voltage, in order to measure the actual waveform of the input voltage, the output signal needs to be integrated, that is, an integrator or numerical integration is connected at the output end to achieve the purpose of integration. Compared with the water-oil transmission line with a pulse front of hundreds of nanoseconds to microseconds, a single structure and uniform dielectric in the Tesa transformer, the peaking capacitor pulse front is faster, and the high-voltage arm capacitance value is not easy to estimate, which affects the design of the back-end integrator. However, the numerical integration method has problems such as poor anti-interference and differential signal exceeding the oscilloscope screen when measuring square wave signals. Therefore, this paper intends to use a self-integrating capacitor voltage divider.

Since the measured pulse width is mainly determined by the product of the input impedance and the low-voltage arm capacitance, if the measured pulse width of the voltage divider is to be increased, the low-voltage arm capacitance must be increased or the input impedance must be increased. However, using capacitor compensation to increase the low-voltage arm capacitance will introduce parasitic inductance. The presence of parasitic inductance of the compensation capacitor will cause the measured waveform to oscillate, and the larger the parasitic inductance, the more serious the oscillation! The peaking capacitor has a compact structure, while the low-inductance compensation capacitor is large in size, so it is difficult to realize the design and installation of the capacitor compensation structure. Therefore, this paper finally uses the resistor compensation method to achieve the self-integration condition.

In summary, in order to realize the measurement of nanosecond pulse voltage of MV-level coaxial film capacitors, this paper develops a peaking capacitor based on a large voltage divider ratio, simple structure and compact structure. A compact resistor-compensated capacitor voltage divider is proposed. Firstly, the structure of the peaking capacitor integrated capacitor voltage divider is designed, and a polyimide copper-clad film is cleverly embedded in the ground terminal of the outermost concentric capacitor of the peaking capacitor, forming a peaking capacitor integrated capacitor voltage divider with a new circuit structure. Secondly, the circuit theory analysis and simulation analysis of the voltage divider ratio and frequency response characteristics of the proposed capacitor voltage divider measurement equivalent circuit are carried out. Finally, the developed peaking capacitor integrated capacitor voltage divider is calibrated by step square wave and high-voltage online, and the phenomenon of the probe voltage divider ratio change when the peaking capacitor is affected by plasma under high voltage is analyzed. In addition, the stability of the probe voltage divider ratio of the peaking capacitor at higher voltage levels is verified by further experiments.