Step response of optimally damped EHV capacitive dividers

The optimally damped capacitive voltage dividers have superior characteristics for fast-rise impulse voltage measurements in the megavolt range. The step response for these EHV dividers is required for determination of their dynamic properties as well as for calculation of the response to arbitrary waves. Presently methods are available only to determine the response time of the EHV dividers.The lumped constants of the high voltage arm can readily be measured whereas the measurement of low voltage arm parameters is very difficult. As divider response is very sensitive to latter parameters the determination of step response by theoretical calculations will have restricted validity. In this paper a new experimental method has been proposed to synthesize the step response of the terminating system. It consists in the determination of the responses of the measuring system to a step voltage and an exponentially decaying wave of proper magnitude and sign and super-position of the two to obtain the step response of the terminating system. This procedure has been applied to a model damped capacitive voltage divider with satisfactory results. Numerical calculations for a practical 5MV, EHV divider available at EdF France has shown that the technique is suitable even for EHV dividers.