Innovative Contactless Measurement of High Voltage Impulses

Abstract

High voltage impulse testing is a standard test procedure for most high voltage equipment. The usual test setup consists of a Marx-Generator, the device-under-test (DUT) and a damped-capacitive divider for the voltage measurement. The divider is a rather big and expensive piece of equipment, as it has to withstand the maximum impulse voltage of the generator. It also adds to the load and thus reduces the efficiency. The electromagnetic field of the high voltage impulse can also be detected with a simple antenna and an oscilloscope. In this study the measurement of lightning impulses with a conventional divider and a contactless measurement with an oscilloscope and different field sensors and antennas are compared. The measurements are performed on a simple one-stage 140 kV Marx-generator and a commercial 3 MV 15-stage generator. The low cost Red Pitaya STEMlab development board is used as a remote controlled battery operated oscilloscope. With the battery powered oscilloscope, it is possible to position the measuring system on the ground or on top of the Marx-Generator. Both placements are tested and compared. The results show that even with a simple monopole antenna, it is possible to accurately record the impulse waveform and with a simple calibration the peak voltage can be measured. The contactless measurement can replace a divider for repetitive testing of DUT with known capacitance, for example in factory testing.