Measuring device for measuring electrical power and power factor or loss angle at low power factor

摘要

895,629. Measuring power, power factor or loss angle. ALLMANNA SVENSKA ELEKTRISKA A.B. Aug. 15, 1960 [Aug. 15, 1959; July 8, 1960], No. 28118/60. Class 37. A circuit for measuring power, power factor or loss angle comprises a Hall plate the output of which is reduced to zero by adjustment of an impedance in the circuit, the quantity to be measured being then determined from the circuit parameters. In Fig. 1 the power Pz consumed by a load Z is measured and three parallel circuits, comprising respectively a Hall plate H in the field of an iron core J, a variable-resistance R in series with winding N2, and load Z in series with winding N1 are connected across the supply V. It is shown that the galvanometer deflection alpha=c JH(n1 Jz cos #- n2 Jr), where c is a constant, JH, Jz, JR are the current as shown, # is the phase angle of the load current Jz and n1, n2 are the number of turns of windings N1, N2. R is varied until alpha becomes zero so that n1 Jz cos # - n2 JR = 0, and the power Pz = n2 V.Jz cos # = V.JR-. A circuit for the mean1 surement of power factor or loss angle in a capacitative load Z is shown in Fig. 3 and comprises a winding N on core J in series with Z connected in parallel with a series parallel circuit consisting of the Hall plate H, variable capacitor C and resistances R and RH. It is proved that when capacitor C is so adjusted that the deflection on meter G is zero, tan # (or cos #) where # is the loss angle in load Z is equal to Jc #- = wC.RH provided that R # RH. An in- JH ductive load may replace the capacitative load but the variable capacitor must then be replaced by a variable inductance. A further embodiment employing current and voltage transformers are described (Fig. 4, not shown) and two Hall plates are used in a two-wattmeter connection.