Patent GB-812904-A (GB)
Title: Improvements in or relating to multielement induction instruments or devices
IPC: G01R11/40
Filed: 1956-06-15
Abstract: 812,904. Supply meters. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 15, 1956 [June 23, 1955], No. 18566/56. Class 37. In a polyphase watt-hour meter or device of the type described in Specification 812,903, one stator element is provided with light load adjustment and the other stator element with adjustment for torque balance between the two elements, both adjustments being made by rotary means at the front of the device. Adjustment for the phase angle between the flux of the voltage and current poles is also described. Errors due to the interaction between current induced in the rotor by the voltage pole of one stator with the voltage pole field of the other are minimized by mounting the stators symmetrically about the rotor axis with the voltage poles on a diameter. Errors due to interaction between current induced in the rotor by the current pole of one stator with the current pole field of the other are minimized by mounting each stator with the current poles symmetrically disposed about a diameter. Errors due to the current induced in the rotor by the voltage pole of one stator interacting with the current pole field of the other are minimized by compensating windings (Fig. 13). The compensating winding 233 having from 0.005 to 0.05 of the turns of the normal voltage winding 75 is wound on the voltage pole 61 and connected in series with winding 75 to induce current in the rotor in the region of the current poles 65, 67 to oppose that induced by voltage pole 45. A similar winding 235 on voltage pole 45 minimizes interference due to the current induced in the disc by voltage pole 61. Another method makes use of a rotor disc having an insulated centre 237, Fig. 14. The induced currents in the region of the current pole 67 due to the voltage pole 45 are caused to flow substantially circumferentially, hence the interference torque due to reaction with the field of the current pole 67 will be radial and not result in rotation. Compensating windings having 0.009 of the turns of a voltage coil give very effective compensation when used with a rotor of this type. Adjustment for light load conditions.-Fig. 9 shows a plan view of one of the stator elements. A conducting loop 177 is positioned about the voltage pole by a spring 185 secured by lugs to a bracket 181. A screwed spindle 179 having a milled head 180 is screwed into a hole in the loop 177 to provide means of adjusting the light load torque by varying the position of the loop 177 relative to the voltage pole. Torque balancing.-The torque provided by the two stators for given energization may be equalized by means of an adjustable magnetic shunt on one or both stators. Fig. 7 shows the plan view of the second stator to which a magnetic bracket 195 is secured. The position of a magnetic block 191 relative to the projection 193 is adjustable by means of the milled head 197 of the non-magnetic screw 194. Adjustment of phase angle between the fields of the voltage and current poles. The current poles on each stator are surrounded by a conducting loop such as 198 (Fig. 7) having one or more perforations 205. The portion of the loop 209 surrounding one or more perforations may be severed so that the fields of the voltage and current poles are in quadrature when the instrument is connected to a load of unity power factor.