Prequalification of capacitors for high-precision voltage dividers

To ensure long-term stability, it is very important to prequalify capacitors used in high-precision voltage dividers. This paper analyzes how film and foil capacitors change due to charge and discharge cycles under different test conditions. The presented experiments aimed at simulating the electric stress associated with high voltage tests in a laboratory. The test procedure considers parameters like magnitude of test voltage, number of impulses, series resistor, test circuit geometry, cooling, selfheating, and temperature. The results indicate that with a variation of up to 500 ppm the change of capacitance caused by repetitive impulse stress can be significant. However, this effect will be smaller when there is natural cooling between test cycles. In this case, the best-suited capacitors showed a variation of less than 200 ppm. In addition, the comparison of different tests shows that the temperature coefficient plays a significant role in the change of capacitance. During the whole test, some of the capacitors show non-recoverable damage. The prequalification testing identified a suitable type of capacitor, which will be used for the realization of a high-precision RCR divider in the European research project "HV-com²".