Patent GB-694887-A (GB)
Title: Improvements in or relating to apparatus for indicating phase relationship between electrical quantities
IPC: G01R29/18
Filed: 1951-01-24
Abstract: 694,887. Phase difference measurements. GENERAL ELECTRIC CO., Ltd., ANTRICH, D., and BRYDEN, J. E. Jan. 18, 1952 [Jan. 24, 1951], No. 1852/51. Class 37. Apparatus for indicating the phase difference between two quantities comprises a phase discriminator to which each of the quantities is applied, one of them through a phase shifter which is adjustable in accordance with the response of the discriminator to obtain a predetermined response, and an indicator showing the adjustment of the phase shifter. An arrangement is shown for indicating the phase difference between the voltage and current in a three-phase system with a balanced load. The primary winding of a current transformer 10 is connected in one line 11 of a three-phase supply 11, 12, 13. Across the secondary winding is connected a load resistor 14 and a potential divider comprising resistors 15, 16 and a non-linear resistor 17 to reduce potential variations due to variations in current in the line 11. The junction of the resistors 15, 16 is connected to the control grid of a cathode follower valve 20 through a filter 18 to eliminate harmonics. The cathode of the valve 20 is connected through the primary winding of a transformer 23 to the junction of the resistors 14, 17. The voltages between the lines 11, 12, 13 are applied to the delta-connected primary windings of a transformer 30 having six-phase star-connected secondary windings, the star point 31 of which is connected to the centre tapping 24 of the secondary winding of the transformer 23. The secondary windings of the transformer 30 are connected to six equallyspaced points on a circular resistor 32 having a slider 33 connected to the negative H.T. terminal 22 so that the voltage from the slider is applied between this terminal and the point 24. The secondary winding of the transformer 23 is connected through rectifiers 34, 35 and a filtering network comprising resistors 36, 37, 38, 39, 40, 41 and condensers 42, 43 to the control grids of two cathode follower valves 44, 45, the cathodes of which are connected through equal load resistors 46, 47 in parallel with a D.C. motor 48. This is mechanically connected to drive the slider 33. A device 50 may give a remote indication of the position of the slider 33. The voltage obtained from the slider 33 is added vectorially to the equal and opposite voltages across the halves of the secondary winding of the transformer 23. When the slider voltage is in quadrature with the voltages across the halves of the secondary winding of the transformer 23 the voltages applied to the control grids of the valves 44, 45 and hence the voltages across the resistors 46, 47 are equal and no voltage is applied to the motor 48. If the slider voltage is not in quadrature with the secondary voltages a voltage is applied to the motor 48 which causes it to rotate the slider arm 33 so as to restore the quadrature relation. In a modification the network between the transformer 23 and the motor 48 comprises magnetic amplifiers and full-wave rectifiers. Specifications 632,007 and 642,855, [both in Group XXXV], are referred to.