A New Approach to the Measurement of Power, Reactive Volt-Amperes, and Volt-Amperes by Electronic Analog Multiplication

Present-day methods for the measurement and telemetering of active power and reactive volt-amperes (var) are, in general, based upon the zero-frequency term produced by the multiplication of two signals corresponding to the line voltage and the line current. Although these methods are usually satisfactory for local metering, various problems are presented when telemetering over long lines is considered. This paper suggests the use of the double-line-frequency term which is also produced by this multiplication. With suitable phase sensitive rectification this term can be made to indicate power, var and volt-amperes (VA) continuously and simultaneously on three meters, the indicating signals being suitable for accurate analog-to-digital conversion for telemetering over long distances. First experimental results show an accuracy of one per cent for a wide range of resistive and reactive loads, and for a voltage variation of 40 per cent. A discussion of factors affecting the accuracy of the method is given in the Appendix.