Calibrated Single-Contact Voltage Sensor for High-Voltage Monitoring Applications

A single-contact voltage sensor designed for accurate measurements of ac voltages across a pair of conductors is described. The sensor design is motivated by remote monitoring applications where accurate voltage measurement of high-voltage transmission lines is required. The body of the sensor is electrically and mechanically attached to a single conductor: either the neutral or high-voltage conductor. A capacitive sensing plate attached to the sensor creates a capacitive voltage divider by using the stray capacitance to the noncontacted line. A very high-impedance buffer is used to measure the voltage across the divider output and estimate the line voltage. An important part of this paper includes a method of calibrating the sensor such that blind voltage measurements can be made without knowing the exact geometry of the conductors. Other important aspects of the design include a two-stage voltage divider for retaining accuracy and increasing the voltage range of the sensor. The work is supported by extensive numerical simulation models which were used to determine the optimum design for the sensing plate and to evaluate the sensitivity to different configurations including conductor spacing and the height above ground. For calibration values which are accurate to 1%, the line voltage can be measured with an accuracy of 10%. The paper describes the theory, design, and experimental verification of the sensor up to a line voltage of 7.5 kVrms.