Characterization of Combined High Voltage and High Current Sensors with Very Low Output Voltages

Abstract

In order to respond to a new industrial need, LNE (National Laboratory of Metrology in France) has developed a new reference system for the precise calibration of combined high voltage and high current sensors at 50 Hz and 60 Hz. The output voltages of these sensors are very low; the lowest measurable voltage is 100 µV. The phase shift between the output and the input could take any value from 0° to ± 180°. Existing commercial methods are able to perform measurement of scale factors and phase-shifts but for higher output voltages. For example for voltage transformers calibrations, the output voltage is usually greater than several volts but the phase shift is usually next to zero. New Fully automated method has been proposed and developed. The calibration of the combined transformers is performed in controlled temperature chamber by comparison to a standard current transformers and a standard voltage transformer. The output voltages coming from the combined transformer and the standards are sampled using two sampling voltmeters. The samplers are processed by a DFT algorithm allowing the possibility to have access to the amplitude and the phase of the fundamental components. The uncertainties of measurement are 0,5% for the scale factor and 0,5 mrad for the phase shift when the output voltage is equal to 100 µV. They are better than 0,01% for the scale factor and 0,01 mrad for the phase shift when the output voltages are equal to 10 mV.