Application of Precision Voltmeter for Assuring Traceable Measurement of Power Quality

Both special three-phase AC calibrators and instrument transformer test units (ITTU) are used to assure the reliability of determining the accuracy of devices that are directly used in the circuit of obtaining information concerning the power quality parameters. To establish the relationship of measured power quality parameters with the units of the SI system (traceability of measurements), a precision AC voltmeter, the readings of which were compared with the values reproduced by the national standard of AC voltage unit, was used. Particularly, the paper proposes two metrological procedures for characterizing both a three-phase calibrator and ITTU concerning the phase shift angle using a high-precision voltmeter. A mathematical model for determining the angle between the phase voltages of the calibrator, using three voltages measured by a voltmeter, taking into consideration the corrections, is presented as well as the formulas for determining the sensitivity coefficients are derived. The mathematical model for determining the readout deviation of the ITTU, based on the equality of the small angle with its tangent, taking into account the corrections of the measurand values, is also given.