Numerical electromagnetic analysis of impulse voltage measuring systems

The unit step response (USR) of lightning impulse voltage measuring systems is numerically calculated with the help of the Numerical Electromagnetic Code (NEC-2), which calculates the three-dimensional electromagnetic field around conducting wires. The accuracy of this analysis is proved satisfactory through comparison of the results of measurement with calculation. The advantage of this method is that the influence of the geometry of the circuit can automatically be calculated without evaluating stray capacitance in the system. Therefore, this method of analysis can be applied to the development of an impulse voltage divider, or in analyzing the influence of elements of a USR measuring circuit. The influence of the shield ring attached to a resistance divider, and of the vertical metal sheet in the IEC-recommended USR measuring circuit on the USR waveform is analyzed as an example.