Non-contact Voltage Measurement Technique for On-Line Monitoring of Transient Overvoltages

Resumé

The electric power system is continuously growing in its size, complexity and required reliability. There is an increased risk due to transient overvoltages which can deteriorate the insulation for different power system components. There is a need for monitoring of transient voltages to better monitor the effects due to them on the insulation of the components. It can be achieved using a non-contact voltage measurement technique. The study elucidates the theory and practical application of the non-contact voltage measurements. The measurement of voltage is achieved by utilizing the stray parasitic capacitance between the high voltage conductor and the ground. A metal plate is used as a sensor to detect the voltage, which indirectly acts as a capacitance divider for voltage measurement. The current study uses operational amplifier based differential-integrator circuit topology in order to accurately measure the voltage over a wide bandwidth of 20 Hz - 1 MHz. The measurement technique is used for measurement of three phase voltages and a methodology is proposed for it. The sensor system is also tested in an online test scenario in a substation for monitoring the shunt reactor switching transients.