Patent GB-537885-A (GB)
Title: Improvements in or relating to electrical measuring instruments
IPC: G01R11/48
Filed: 1940-02-29
Abstract: 537,885. Supply meters ; power-factor measurements. SANGAMO WESTON, Ltd. Feb.. 29, 1940, No. 3825. Convention date, Oct. 30, 1939. [Class 37] Apparatus for measuring power factor in a circuit comprises a rotatable disc and means for periodically applying torque thereto in opposite directions in accordance with the volt - amperes in the circuit, a rotatable member and means for rotating the same through one revolution during the time of one cycle of torque application to the disc, and means for measuring the time required for rotation of the rotatable member from a predetermined position to that which coincides with the instant at. which the application of torque to the disc is reversed and thereby indicating the power factor of the circuit. A meter for registering volt-amperehours on a polyphase circuit is shown in Fig. 1 and comprises a pair of driving 'units 15, 16 which co-operate to apply driving torque to a disc 17. The winding of the current magnets 21, 22 are connected to the lines 11, 13 through current transformers 23, 24. The :windings of the voltage magnets 19, 20 are connected to the lines 11, 12 13 through a phase shifter comprising a stator 26 and a rotor 27. The rotor 27 is mounted on a shaft 30 which is driven at a constant speed by a synchronous motor 33. The meter disc 17 is mounted on a shaft 35 and drives counting gear 38 through worm gearing 36, 37. The disc 17 tends to rotate in one direction during one half of a revolution of the rotor 27 and in the other direction during the other half revolution. A ratchet-wheel 41 and pawl 43 are provided to permit rotation only in the direction of the arrow 44. During each revolution of the rotor 27 the currents in the voltage windings of the meter pass through all possible phase relationships to those in the current windings, and the meter registers volt-ampere-hours. The power factor is measured by measuring the angular movement of the rotor 27 from the assumed zero position at unity power factor to its position when the meter disc tends to reverse. This is effected by the mechanism shown in Fig. 4. The pawl 43, Fig. 1, is replaced by an arm 55 having a nose for co-operating with the teeth of the ratchet-wheel 41. This arm is pivoted at 56 and its movement in a clockwise direction is limited by a stop 57 against which it is brazed by a spring 58. When the disc 17 tends to reverse, the arm 55 closes contacts 59. Mounted on the shaft 30 is a cam 61 having a lobe 62 which is in the position shown when the meter disc 17 is rotating at its maximum speed when the power-factor is unity. The angular movement of the rotor of the phase shifter from this position to the position when the contacts 59 are closed is a measure of the powerfactor and is indicated by a pointer 67 moving over a scale 68 and mounted on a shaft 69. On this shaft is a ratchet-wheel or friction disc 70 with which a pawl 71 co-operates to permit rotation in one direction only. The pawl 71 is of magnetic material and is moved out of engagement of the ratchet-wheel 70 on energization of the winding 74 of an electromagnet 73 thereby allowing the pointer 67 to be rotated in a counter-clockwise direction by a weight 75 on a sector arm 76 which carries a toothed sector 78 engaging a pinion 79 on the shaft 69. Movement of the pointer 67 in a forward or clockwise direction is effected by means of a gear-wheel 82 carrying a pusher arm 83. The zero position of the wheel 82 is determined by a stop 84 against which the pusher arm 83 comes to rest in the zero position. The gear-wheel 82 is mounted on a shaft 85 which is co-axial with the shaft 69 and carries a pinion 86 which meshes with the teeth of a sector 87 forming'a part of a sector arm 88. This carries a weight 90 for returning the gearwheel 82 to the zero position. The gear-wheel 82 is driven in the forward 'direction by a pinion 91 on a shaft 92 driven by a synchronous motor 93. The shaft 92 is journalled in the end of an arm 95 pivoted at 96 and normally held against a stop 98 by a spring 97. Movement in the opposite direction is limited by a stop 99. The arm 95 carries a plate 100 of magnetic material which is attracted downwardly on energization of a winding 101, thereby disengaging the pinion 91 from the wheel 82. The winding 101 is.connected to an A.C. source 95<1> either through. the contacts 59 or through contacts 102 closed by an insulating finger 103 carried by the arm 95. The circuit from the contact members 59, 102, which are in parallel, to the source 95<1> is completed through contacts 104, 105, which are closed except when the contact 105 is lifted by the lobe 62 of the cam 61 so as to engage a contact 107 for energizing the winding 74 and thereby zeroizing the pointer 67. The contacts 104, 105 being open the winding 101 is de-energized and the pinion 91 engages the wheel 82. The pusher arm 83 then moves the pointer 67 forwards until the meter disc 17 has applied thereto a reverse torque which causes it to close the contacts 59. The winding 101 is then energized and the pinion 91 disengaged from the wheel 82, which is then zeroized by the weight 90. The pointer 67 remains in its position until the lobe 62 again lifts the contact arm 105 and completes the circuit of the winding 74. The gear sector 78 and its associated parts may be omitted, in which case the maximum power factor is indicated.