Patent GB-420389-A (GB)
Title: Improvements in or relating to apparatus for measuring or indicating the power factor of an alternating current supply system
IPC: G01R25/00
Filed: 1933-07-14
Abstract: 420,389. Power-factor measurements. ELLIOTT BROS. (LONDON), Ltd., Lewisham, London, and SHOTTER, G. F., 14, The Ridgeway, Friern Barnet, Middlesex. July 14, 1933, No. 19958. [Class 37] Apparatus for measuring or indicating powerfactor comprises two elements, each consisting of two parts, namely an electromagnet and a conductor arranged in its field, the parts of each element being energized by connection to the supply, one as a voltage component and the other as a current component, the parts of each element being relatively movable and the movable parts being connected together so that their torques oppose one another. One electromagnet has a rectangular magnetic core 1 with a transverse core 2 extending between opposite sides and poles 3 extending inwards from the top and bottom towards the member 2, which is of larger section opposite the poles. The winding consists of two parts 4, 5, connected in series and wound on the poles 3, a moving coil 6 embraces part of the transverse core 2 and is narrow compared with the width of the poles 3 so that it remains always in the field of the electromagnet 1. A second coil 9 embraces the transverse core 11 of a second electromagnet 12 which is similar in shape to the electromagnet 1 except that the poles 13 are narrower than the poles 3. The coil 9 is in two parts wound in opposite directions and is of greater width than the poles 13 so that when it moves from its central position it passes more out of the field of the electromagnet 12. The windings 4, 5 of the electromagnet 1 are connected across the supply mains so as to produce a flux in quadrature with the voltage. The windings 16, 17 of the electromagnet 12 are connected in series with the supply so as to produce a flux in phase with the supply current. The moving coil 6 is connected in series with the supply through a transformer, the moving coil 9 being connected across the supply mains in series with a resistance. The electromagnet 1 exerts a driving force on the moving coil 6 proportional to the sine of the angle of lag or lead of the supply current in relation to the voltage. The electromagnet 12 acts differentially on the halves of the moving coil 9 producing a controlling force proportional to the cosine of the angle of lag or lead of the current, this force tending to restore the coil to its central position. The coils 6, 9 are fixed to the spindle 8 by means of arms 7, 10 so that their torques oppose one another, the moving system taking up a position of balance in accordance with the power-factor, which is indicated by a pointer on the spindle 8. Fixed coils 19', 19<2>, placed within the coil 9 as shown, or on the poles 13, are connected in series or parallel with the coil 9 to produce a flux which tends to neutralize the self-inductance of the coil 9. Coils 20, short-circuited through variable resistances 21, are arranged on the transverse core 2 of the electromagnet 1 to correct the quadrature between the flux of the magnet and the supply voltage. Instead of, or in addition to these windings, the poles 3 may be provided with tips 22 for the same purpose. For use on a three-phase three-wire system two pairs of elements are employed, the movable systems being mechanically connected, as by mounting on the same spindle. The movable coils of the sine elements may be arranged in one plane on the spindle, the movable coils of the cosine parts being arranged in a common plane at another part of the spindle. The movable coil of one sine element is connected in series with the magnet windings of the corresponding cosine element in series with one phase of the supply, through a transformer, the other similar elements being similarly connected to a second phase. The movable coils of the cosine elements and the magnet windings of the sine elements are connected across the appropriate phases of the supply. In modifications, the coils may be fixed and the electromagnets, which have air cores, movable. Any of the windings or coils may be connected to the supply through a transformer. Both electromagnets may be energized from the supply as current components, the coil of one of the elements being energized as a direct voltage element and the coil of the other element being energized as a voltage element with a capacitative or inductive reactance in its circuit. Specification 398,838 is referred to.