Electrical power distribution systems often include overhead electrical power distribution lines mounted upon poles by a wide variety of mounting structure. Other distribution systems include underground distribution lines in which protected cables run under the ground surface. It is often necessary to take phase-to-phase voltage measurements across transmission lines while testing for induced or live power line or equipment.
Known high voltage safety line detectors, meters and testers comprise high resistance probes connected in series with a calibrated panel meter to read the voltage across the phase-to-phase or phase-to-ground terminals. They are designed for use as safety tools by high voltage line maintenance workers to verify the status of the line or equipment as nominal, induced or de-energized. Known devices for providing such measurements include contact type and non-contact type. With contact type a reference probe or transmitter and a meter probe or receiver are connected in series with a cable as the loop is closed with load terminals. With the non-contact type each probe has a meter and the probes close the circuit through wireless means.
Accuracy of the meter readings is governed by the geometrical configuration of connecting the probes to transmission lines or other high voltage equipment, by environmental conditions such as distance from nearby electromagnetic fields, and by distance of the cable, meter probe and reference probe from the earth. Particularly, the measurements are largely affected by the electromagnetic interference, stray capacitance effect and coupling from the high voltage fields that are present around electrical transmission lines. Also, the sensing elements add to inaccuracy due to uncertainty and tolerance on design and fabrication. All of these factors act as common mode errors in the meter circuit. Thus, the readings become highly inaccurate and measurements are not suitable for usage.
Adequate insulation and safety must also be addressed in design of high voltage probes. Any failure, such as by short circuit, in the high voltage resistance in the probe results in arcing and breakdown of insulation.
With these problems, the electrical line worker could be misguided on the status of the transmission line while the lines are being maintained. Also, improper use may result in injury to electrical line workers and also damage to the high voltage transmission line system.
The present invention is directed to improvements in high voltage phasing voltmeters.