On-site voltage measurement with capacitive sensors on high voltage systems

In Extra/High-Voltage (EHV/HV) power systems, over-voltages occur e.g. due to transients or resonances. At places where no conventional voltage measurement devices can be installed, on-site measurement of these occurrences requires preferably non intrusive sensors, which can be installed with little effort under all circumstances. This paper presents three methods, which involve different algorithms based on a capacitive measuring system using simple design and easy-to-install sensors which couple with air-capacitors to the lines. Each capacitive sensor couples in principle to all phases. The presented methods differ in the pre-assumptions needed to determine the coupling matrix to reconstruct the phase-voltages, either power frequency, transient or resonant over-voltage on each of the three phases. The feasibility and the performance of the methods are discussed