ELECTRONIC THREE-PHASE FOUR-WIRE SYSTEM WATT-HOUR METER

摘要

1491290 Energy measuring OSAKI ELECTRIC CO Ltd 7 Oct 1975 40953/75 Heading G1U [Also in Division G4] In a poly-phase watt-hour meter, voltage and current measurements for the individual phases are made cyclically, each pair of voltage and current measurements are multiplied, and the resulting products are summed to provide a measure of the instantaneous power, which is then integrated, with respect to time, over the period for which measurement of the total energy is required. Cyclical sampling of the individual phases can either be at a frequency asynchronous with, and considerably higher than, the supply frequency - as in a first embodiment Fig. 2 which employs amplitude and duration modulation of pulses to effect multiplication - or the sampling can be synchronized with, and at, the supply frequency - as in a second embodiment Fig. 6 which employs sums of quarter-squares to effect multiplication. In the first embodiment each negative-going edge of a sampling pulse Q, Fig. 2, causes a sequencer B cyclically to mark one of three leads bl, b2, b3 to open a corresponding pair of voltage and current switches S1, S1'; S2, S2'; S3, S3'; for the three phases of a supply 123N. Each lead b1, b2, b3, when marked, for example lead bl, which closes switches S1, S1' as shown, remains marked for a duration linearly proportional to the phase voltage e at that instant, this being achieved by comparing D the phase voltage e with a linearly rising voltage produced by charging a capacitor Co at a constant rate from a constant current source Tr2. When the voltage across the capacitor Co has risen to the phase voltage e (plus a small bias Ea), the PUT comparator D fires to raise the input to the sequencer B which then terminates the marking on lead b1 and the switches S1 and S1' open. Thus, the current sensing switch S1' will have been open for a duration linearly dependent upon the corresponding phase voltage, so that the pulse that passes to a summing capacitor C4 represents, by its area, the instantaneous power in the phase being sensed. Successive power representing pulses are summed, and the result is converted to a corresponding frequency, the cycles of which are counted F. A modified duration modulation circuit Fig. 5 (not shown), is described. In the second embodiment Fig. 6 the sequencer B is advanced by pulses Q derived from one of the supply phases. When one of the leads b1, b2, b3 is marked, for example bl, in the first half-cycle a voltage e + iR, where e is the phase-voltage, i is the phase-current, and R is the resistance of each of the resistors rl, r2, is applied to the base of a squaring circuit Tr7, and during the second halfcycle the voltage e - iR is applied to the squaring circuit. The result is that currents proportional to + (e + iR)SP2/SP and to - (e - iR)SP2/SP are applied successively to a summing capacitor C5, to produce frequency significant pulses as before.