Comparison of Two Methods for Phase Angle Measurement

Two methods of measuring the phase angle were used during the evaluation of the metrological characteristics of the measure of the power quality parameters. A precision voltmeter and a precision phase meter were applied to determine the indication errors of the three-phase calibrator as a measure. The measurement uncertainty (UM) during the application of each of these methods was evaluated; herewith, the characteristics had different kinds of dependence on the measurand. In particular, it was observed that there was no direct correlation between the uncertainty and the measurand in the phase meter method. On the contrary, the voltmeter method caused the question about the reason for the strong correlation between measurand and uncertainty. During the study, it was found that the sensitivity coefficients of the shifted voltages depended heavily on the magnitude of the difference between them. The sensitivity coefficient of the opposite vector to the measured angle does not have such dependence if there is a small difference in the amplitudes of shifted voltages. Instead of this, the standard UM of this input quantity has a significant effect on its contribution to the combined standard UM. Unfortunately, the voltmeter method is not suitable for using, when the shifted voltages vary greatly in amplitude. However, its main advantage is in much less uncertainty during the measurement of small phase angles.