Abstract
Unit step response (USR) characteristics of a measuring system for the test of chopped-lightning impulse voltages, which were computed by the Numerical Electromagnetics Code (NEC-2), are compared with those of the USR measuring circuit recommended by IEC. When an impulse voltage generator of high impedance is used in the test of a chopped-lightning impulse voltage, its response is similar to that of the USR measuring circuit, while a low-impedance generator is used, its response differs.
Although the influence of sphere electrodes of the chopping gap is identified as a spike in the initial rising part of the USR, it little influences the USR parameters of a system including a shield ring and a high-impedance impulse voltage generator. In the case of a system having a 100Ω or 200Ω damping resistor and a low-impedance generator, however, the response times become longer owing to the presence of sphere electrodes.
