GB792989A - Power factor testing gear for electric circuits - Google Patents

Abstract

792,989. Electric measuring instruments. BRITISH INSULATED CALLENDER'S CABLES, Ltd. Jan. 11, 1956 [Jan. 11, 1955], No. 876/55. Class 37. Apparatus for measuring the power factor of a three-phase A.C. circuit by simultaneously determining the active and reactive components using two single-phase integrating wattmeters comprises a base having two sets of four terminal contacts engaging, supporting, and connecting to the current and voltage coils of a respective wattmeter; each voltage coil contact being provided with a flexible lead connecting such coils respectively across phase and neutral and across the remaining phases, and one current coil contact of each meter being connected in the current circuit to be tested while the remaining current coil contacts are interconnected in series. Integrating wattmeters 2, 3 are supported on a base 1 (Fig. 4) comprising parallel insulating plates 4, 5, separated by an inset vertical wall 6, which have respective groups of four upstanding plugs mounted thereon (Fig. 3, not shown) to engage sockets of the meter terminal blocks 17, 18. Outer plugs of each set are connected to the meter current coils and interconnected in series with leads 25, 40 (Fig. 1) and a pair of binding posts 22, 23 (Fig. 4) for connection to the output of a current transformer 24 (Fig. 1) coupled to the phase circuit R whose power factor is required, in series with any provided auxiliary control gear 54. Inner plugs of each set are connected to the meter voltage coils and to dependent flexible leads 37, 38, 39, 40 terminating in shrouded spring clip terminals (Fig. 3, not shown) for attachment respectively between the test phase R and neutral G, and between the remaining phases B and Y. Ammeter contacts 26, 27 (Fig. 4) are connected in series with the current coils and are short-circuited by other contacts 30, 31 situated between plates 4, 5 until the ammeter 34 is plugged in, when pin 33 of the latter separates them. Voltmeter 52 may similarly be inserted in a pair of sockets connected across either meter voltage coil, and the input current connections 22, 23 may be short-circuited by bar 47, inserted into sockets 48, 49 (Fig. 4) to disable the apparatus. In operation the voltage coils of the respective meters are energized with quadrature voltages ER and EYB = #3E R , while the current transformer energizes the remaining coils with a current I lagging voltage ER by #. It is shown that after the meters are allowed to operate for a fixed time determined by automatic or manual removal of short-circuiting connection 47, the reading of the first meter is proportional to the effective power ERI cos # and that of the second meter is proportional to the reactive power #3E R I sin # (Fig. 2, not "shown) so that if W, Wx are the readings of the meters, tan # = Wx/#3W from which the power factor cos # is determinable. The measurement is repeatable for each phase in turn, and the meters are interchangeable for different voltage and current ranges.