Virtual power sources

For the calibration of power meters, it is preferred to use virtual sources. Due to the direct calibration procedure, these sources are required to be stable and accurate as well. As a transformer is included in the voltage- and current amplification circuits, the inherent nonlinearity of transformers and the handling of problems due to the effect of diffuse parameters (stability, accuracy and distortion) become of great importance. The high accuracy requirements reawakened the mathematical-and physical models that describe the operation of transformers as a function of frequency, with various diffuse parameters also taken into account. In the implementation the dependence of various diffuse quantities (inductance, capacitance) and the iron losses on the signal level raises difficulties; in fact, these result in the alteration of the corner points in the transfer function as well as undesirable accentuation.