Testing the performance of three-phase induction watthour meters in the presence of harmonic distortion

The authors deal with computer-based testing of a three-phase induction watthour meter in the presence of harmonic distortion. Two three-phase harmonic generators produce the distorted current and voltage waveforms. Each waveform has a prespecified harmonic magnitude and phase. Therefore, balanced or unbalanced conditions can be simulated in the testing. A fiber-optic sensor is designed to convert the rotation of the disk of the meter into digital signals to be stored in an IBM PC/AT. A data acquisition system transfers the samples of current and voltage waveforms so that the power and energy can be computed for comparison. Induction watthour meters are shown to be affected by harmonic distortion. The error increases at light loading conditions. For a three-element watthour meter, the maximum negative error was observed when the harmonic current was in phase with the harmonic voltage. This applies to all harmonic orders. The maximum positive error was observed when the harmonic current was shifted by 180°