The measurement basis of electricity supply metering

The paper has a threefold object. First, to establish the precise significance of 3-phase power, reactive volt-amperes and total voltamperes, secondly to examine the suitability of these quantities as a basis for a tariff system and thirdly to analyse the possible metering circuits to determine what they actually measure and what are their errors. The accepted definitions of power, reactive volt-amperes and total volt-amperes are established for a single-phase circuit, and the relation between these and the physical conditions of energy flow is examined. The extension of these concepts to 3-phase systems reveals the somewhat arbitrary nature of the quantities which form the basis of many metering systems. Consideration is then given to what a metering system should attempt to measure and whether the integrated values of watt-hours, reactive volt-ampere-hours and total volt-ampere-hours, together with some indication of maximum demand, give adequate information for the assessment of tariff charges. The analysis of 3-phase metering circuits is made in terms of symmetrical component theory. The possible circuits are tabulated and the total measured quantity is specified as a function of the power and reactive volt-amperes of the positive-, negative- and zero-sequence components. By comparing these data with the symmetrical components actually present under any particular conditions, the suitability of the methods of measurement and their errors are readily derived.