Patent GB-568461-A (GB)
Title: Improvements in and relating to electrical instruments and relays
IPC: H02H3/40
Filed: 1943-10-15
Abstract: 568,461. Indicating and locating faults ; phase-difference and frequency measurements ; power meters ; supply meters. NALDER BROS. & THOMPSON, Ltd., and LIPMAN, C. L. Oct. 15, 1943, No. 16962. [Class 37] [Also in Group XXXVII] An induction type instrument or relay is provided at the exterior of its drum type rotor with a number of electromagnets spaced angularly around or axially along the drum and provided inside the drum with a number of similarly spaced electromagnets each arranged to provide a flux interacting with and in suitable phase relation with the flux produced by the corresponding external electromagnet. Fig. 1 shows an instrument or relay for indicating an earth fault on a distributing system protected by a Peterson arc suppression coil. Two external U-shaped electromagnets having laminated iron cores E1, E2, voltage windings V1, V2, and closed flux lagging coils F1, F2 are arranged around the drum rotor D displaced by an angle of 90 degrees with each other. Inside the rotor and similarly angularly displaced are two internal electromagnets having iron cores I1, I2 and polar projections on which are wound current coils, A1, A2, which are connected in series across current transformers LA energised from a three-phase system L1, L2, L3. The voltage coils are connected in parallel across a secondary winding PC2 energized from a Peterson coil PC1, each coil V1, V2 being in series with a rheostat R which is calibrated to give direct reading of the phase difference between the fluxes produced by the voltage coils V1, V2 and the current coils A1, A2. With the arm of the rheostat R in its mid position, resistances R1, R2 in series with the coils F1, F2 are adjusted to bring the fluxes of the electromagnets E1, II and E2, 12 into quadrature. By employing a third pair of electromagnets E3, I3 having windings V3, V4, both energized from the Peterson coil, the instrument can be converted to an earth fault wattmeter relay, the rotor D having a portion d, Fig. 2, of its periphery removed so that the third element E3, 13 is inoperative until the rotor has moved through about 40 degrees, whereupon the torque of this element assists in the closure of the relay contacts. In a modification the rotor is divided into two insulated coaxial cylindrical portions, of which one is acted on by the electromagnets E1, I1 and E2, 12 and the other is acted on by the electromagnet E3, I3 and has a gap d. Alternatively the wattmeter elements E1, I1 and E2, 12 are arranged axially along the drum, one acting on the plain portion and the other, together with the element E3, 13, acting on the gapped portion of the rotor. Fig. 4 shows an arrangement for measuring phase angle errors of instrument transformers. Two watt measuring elements E1, I1 and E2, I2 are diametrically oppositely disposed with respect to the drum rotor D. The voltage coil V1 is in series with a calibrated rheostat Rp1 and the coil V<2> is in series with a pair of rheostats Rp2, Hp2<1> calibrated in degrees and minutes respectively. The voltage coils V1, V2 are energized from a common source L1, L2, which may be connected to the secondary winding of a phaseshifting transformer. The torques of the two elements act differentiallv so that under identical conditions the rotor is stationary and gives a null indication. The current coils A1, A2 are energized. from the secondary windings of a standard current transformer TIs and the current transformer TIt under test. By adjusting the rheostats Rp2, Rp2<1> until zero reading is obtained, the phase angle error can be read off these rheostats. Fig. 5 shows a meter in which four pairs of electromagnets E1, I1. E2, 12, E3, 13, E4, 14 are arranged to serve as a summation wattmeter or watt-hour meter, for four single phase circuits, which may be of different voltages or frequencies. In a modification the axes of symmetry of all elements are arranged to lie in one vertical plane by mounting the element E3, 13 axially below the element E1, I1 and the element E4, I4 axially below the element E2, I2. The four elements may be used in a sensitive single phase instrument by connecting all the current coils in series Magnetic shunts may be provided near the poles of the electromagnets for fine adjustment of their relative torques. One or more of the wattmeter elements may work in opposition to the others, or the elements may work in pairs, for example two wattmeter elements may be connected in an unbalanced three-phase circuit and two others in a second similar circuit in order to summate the total power in the two circuits. A wattmeter element may be changed to a voltage or current element by arranging both the coils on the external and internal electromagnet to be voltage or current coils. The inner electromagnet of a wattmeter element may carry an auxiliary voltage coil in addition to the current coil. A multi-purpose instrument may be provided by arranging one element as a watt element and others as voltage and current elements. Further applications include the provision of reactive KVA. relays, indicating and recording instruments, integrating meters, frequency meters, phase meters, and ratiometers. One or more of the electromagnets may have shaded poles. Two or more of the internal electromagnets may be magnetically' coupled, or magnetic shields may be inserted between the separate electromagnets. The drum rotor may consist of a number of separate coaxial cylinders supported. from the rotor spindle at a common point. The rotor may be built up of a frame or ring of insulating material which carries spaced metallic bands. In order to avoid interference between the fluxes of the various pairs of magnets the diameter of the drum rotor is preferably greater than its axial length. In the case of a drum rotor formed by a single integral cylinder, the diameter of the rotor is preferably greater than the width of each electromagnet. In the case of a rotor consisting of a number of separate coaxial metallic bands, the poles of each external electromagnet are preferably arranged to embrace the appropriate metallic cylinder while the centrally placed co-operating internal electromagnet may be of cruciform shape carrying coils on two diametrically opposite polar projections thereof at right angles to the direction of the main flux due to the external electromagnet.