Estimation of load capacitance and stray inductance in lightning impulse voltage test circuits

• This paper deals with lightning impulse voltage testing of a capacitive load.
• New GA based method for estimation of load capacitance and circuit inductance is presented.
• The method is successfully verified on several examples in high voltage laboratory.
• It enables fast and accurate estimation of unknown test circuit parameters.

In order to obtain the lightning impulse voltage waveshape regarding front time, time to half and relative overshoot magnitude within the limits prescribed by IEC 60060-1, it is useful to accurately estimate the test circuit parameters, e.g. load capacitance and circuit inductance. A stray inductance consists of the inductance of impulse generator and the inductance of connecting leads. Load capacitance consists of voltage divider capacitance, test object and parasitic capacitances. In practice, the test object capacitance is often unknown. Capacitance measurement takes time and makes testing procedure more complex. Also, it is very difficult to estimate parasitic capacitances although their influence can sometimes be significant.This paper presents a new genetic algorithm (GA) based method for fast and accurate estimation of load capacitance and circuit inductance during lightning impulse voltage testing of a capacitive load. Computational and experimental verification of the method is successfully performed for standard and non-standard lightning impulse waveforms with various relative overshoot magnitudes.