Patent GB-162471-A (GB)
Title: Improvements in or relating to alternating current electric instruments for indicating synchronism, power factor, phase difference or the like
IPC: G01R25/00
Filed: 1920-02-27
Abstract: 162,471. Nalder Bros. & Thompson, Ltd., and Lipman, C. L. Feb. 27, 1920. Phase-differences and power-factors, measuring. -In an alternating-current instrument for indicating synchronism, power-factor, phase-difference, &c., the production of a rotating field is avoided by arranging the field coils with their axes parallel in different planes, the magnetic system comprising a spindle and vanes mounted thereon in these parallel places. In the synchroscope shown in Fig. 1, quadrant-shaped sectors A, A<1> of thin soft iron are mounted in parallel planes normal to a spindle, of which the portion B between the vanes is of magnetic material, a tube being mentioned in the Provisional Specification. The axes of symmetry of the vanes A, A<1> are at right-angles to one another. A magnetizing-coil C surrounds the magnetic portion B of the spindle. Two field coils D, D<1> are arranged with their common axis in the plane of the sector A, two other field coils D<2>, D<3> being arranged with their axis parallel to the axis of the coils D, D<1> and in the plane of the sector A<1>. The pairs of coils D, D<1> and D<2>, D<3> are connected in parallel across bus-bars L, L', a non-inductive resistance K and an inductance J being employed to produce a phase difference of 90‹ between the currents in the pairs of coils D, D<1> and D<2>, D<3>. The magnetizing-coil C is connected as a pressure-coil to the incoming machine. The field coils D, D<1>, D<2>, D<3> are formed with narrow central slots in which the sectors A, A<1> move; they may be wound on formers and bobbins or may be windings supported on insulated pins. An eddy-current brake is provided. For use as a single-phase power-factor meter, the magnetizing.coil C is connected as a current coil in the same system across which the field coils are connected. For use as a two-phase power-factor meter for a balanced load, the coils D, D<1> are connected as current coils in one phase and the coils D<2>, D<3> in the other phase, the resistance K and inductance J being omitted. The magnetizing- coil C is connected as a pressure coil in series with a resistance across either phase. Fig. 5 shows the application to a two-phase power-factor meter for an unbalanced load. Two pairs of sectors A, A<1> and A<2>, A<3>, each connected by a magnetic portion of the spindle, are mounted on the same spindle and separated by a non-magnetic portion B<2>. The pairs of coils D, D<1> and D<4>, D<5> are connected in parallel in one phase, the other two pairs D<2>, D<3> and D<6>, D<7> being connected in parallel in the other phase. The magnetizing-coils C, C<1> are connected as pressure coils across the two phases. Modifications for three-phase balanced and unbalanced loads are described in which there are two sets of three sectors arranged with their axes at 120‹ to one another in parallel planes, each sector being a segment of 120‹. The field coils are star connected. For balanced loads one magnetizing-coil is employed, connected across one phase; for unbalanced loads two magnetizing-coils are employed, connected as pressure coils across two phases.