A (3 + 3)-phase voltage and current source of high stability

Absolute ac calibration of wattmeters demands sources of exceptional stability. It is felt that for this purpose amplifiers are more superior to rotating generators. Stability and spectral purity of waveforms generated by an amplifier power system lead to the reconsideration of calibration methods, one of which is the use of a differential calorimeter. The result obtained by our method and by power definition through measuring U, I, and angle φ agreed to within 5 × 10⁻⁵.