Development and application of a 10 MHz digital system for current-zero measurements

After a short historical review, the development of an accurate digital system is described that is intended for measurement of arc currents and voltages in the current-zero period of circuit breakers during high-power tests. Two channels with 12-bit resolution and 10 M samples per second can each store 4 K of data using 400 μs. The transmitting unit is battery operated near to the test object, free from ground. The receiving unit is at ground potential, coupled by an optic fibre synchronous link. As a current device, an M coil is applied to measure the derivative of the current. For the voltage device, a special capacitive divider has been developed. Results of current-zero tests in vacuum and SF₆ circuit breakers are presented and discussed