Theory of Action of the Induction Watthour Meter and Analysis of its Temperature Errors

The question of changes in the registration of watthour meters due to variations in temperature is receiving considerable attention at the present time from manufacturers and public utilities alike. This paper discusses the development of a temperature compensated watthour meter. The effect of certain changes in the fundamental constants of the meter circuits and the materials of certain vital parts are shown to point out the necessity of two independent compensating devices. The compensating devices found most effective consist, first, of a permanent magnet flux diverter mounted on bimetal strips in such a way that it shunts more or less of the permanent magnet flux around the disk, on a decrease or an increase in temperature, respectively, and second, a moving lag plate controlled by bimetal strips arranged in such a way as to cause the plate to move up or down with an increase or a decrease of temperature, respectively. In Appendix I is given the construction of a theoretical vector diagram of an induction type watthour meter showing the relative phase positions of the various fluxes, Voltages, and currents that are present. In Appendix II is given a discussion of the sources of temperature errors in watthour-meters as derived from an analytical study of this diagram. An attempt is also made in this paper to summarize these sources, the reason for their existence, and their effect upon the registration of the meter, in convenient tabular form.