An improved three-phase, three-wire, reactive volt-ampere-hour meter

Reactive volt-ampere-hour meters of the type which necessitate only standard potential transformers, and where the neutral point is not available, have been known for some years, but have been subject to comparatively large variations in accuracy with change of frequency. They present some advantages over the type which necessitates a special and additional potential transformer to obtain the requisite voltage phase relation, in that a comparatively costly piece of apparatus, viz. the special potential transformer, is eliminated, and, further, the loading of the potential transformer is straightforward, thus simplifying the measurement of ratio and phase angle. In the type of meter described in the paper a method of considerably reducing the accuracy variation with change of frequency is presented. Difficulties in accurate calibration of reactive volt-ampere-hour meters have been experienced in the past. A simple method of accomplishing this result is described in some detail.