Nonintrusive AC Voltage Measurement Unit Utilizing the Capacitive Coupling to the Power System Ground

A fully nonintrusive type ac voltage measurement scheme is presented in this article. Most of the existing noncontact voltage probes require a direct connection to the power system ground. A few other schemes rely on the capacitive coupling between the body of the human operator, holding the probe, and the ground to connect to the power system ground. This is a less reliable method as the direct contact of the hand of the operator to a specified conductive part in the probe is mandatory. Besides, the existing methods do not take care of the effect of the nature of the impedance of the current path through the earth between the human body and the power system ground. In this article, a new measurement approach that provides reliable output from the nonintrusive probe, irrespective of the variations in the probe-to-wire capacitance and impedance between the measurement system and power system ground through the earth, is presented. This includes the capacitive coupling between the measurement system and the earth. A detailed simulation study of the proposed approach has been conducted, and various sources of error and the effects have been quantified. A prototype probe and measurement unit have been developed and tested in the laboratory for a range of distribution voltage (0-600 V), at 50 and 60 Hz. Tests were also conducted in the actual field (distribution voltage). The output was linear with a maximum error of 0.6%.