PRACTICAL USE OF MUTUAL INDUCTION WHEN MARKING STATOR WINDING OF THREE-PHASE ELECTRIC MOTORS

Abstract

The conventional methods of "selection" and "transformation" for marking stator windings of three-phase electric motors are characterized by considerable time consumption and significant number of switching operations. The authors offer a new method for marking stator windings, which is based on an analysis of the interaction of magnetic fluxes inside the electric motor and the phenomenon of electromagnetic mutual induction between phases of a three-phase electric motor. First, using a control lamp, an ohmmeter, a voltmeter, etc., one can determine the relationship between the two terminals and each of the three phases of an electric motor. Then three windings (phases) are connected in series (to form an open triangle). The electric circuit assembled in this way is connected to an alternating current network with a voltage of 220 V, and three identical voltmeters are connected in parallel to each phase. If the motor phases are turned on according to a “start-end-start-end-start-end” pattern, the voltmeters will show the same voltage values. If one of the phases in an open triangle turns out to be set in an opposite manner to the other two phases, a voltmeter connected to it will show a greater voltage than the voltmeter readings in the other two phases. Basing on the readings of voltmeters, one can immediately mark the beginnings and ends of the electric motor phases. Given the fact that the phases of three-phase motors are connected in series during the marking process, an open triangle can be connected to a mains voltage of 220 V with an assembled electric motor and a remote rotor. Large differences in phase voltages are observed in case of a remote rotor. The proposed method for marking the phases of three-phase electric motors is more convenient for use in practice due to its decreased time consumption and fewer switching-over acts.