Monitoring of transient overvoltages from switching in high-voltage networks using non-invasive capacitive sensing

Recording of transient overvoltages at a location without pre-installed high-voltage dividers can be achieved by non-invasive capacitive sensing. As part of a differentiating-integrating topology, the transient waveforms were accurately measured with a bandwidth up to 15 MHz. This paper shows that such a technique has the maturity to be applied to real problems. Three use cases are described. Switching transients were recorded at a substation with a 380 kV switchgear and at two overhead line to underground power cable transitions to verify system modelling. For a 50 kV shunt reactor connected to the tertiary windings of a 380/220 kV transformer, overvoltages in access of 3 p.u. occurred during energizing with an SF6 circuit breaker. Repetitive restrikes were observed when de-energizing a 33 kV shunt reactor connected to the tertiary windings of a 330/220 kV transformer by means of a vacuum circuit breaker.