Determination of the beginning and end of the windings of the electric motor by Petrov's method

Sometimes, after repair, an asynchronous electric motor can come without marking the output ends of the windings, then their marking can be determined by sequential execution of test firings or by the Petrov method.

The marking of the output ends of the windings of an asynchronous electric motor by Petrov's method is that one of the windings is taken as the beginning of one of their phases, and its end is connected to the output of the other phase. These two series-connected phases are switched on at reduced voltage (15 — 20% of nominal) to avoid overheating of the windings; in the case of a phase rotor, its winding must be open. The third phase is connected to a voltmeter.

If the EMF of this phase is zero, then the first two windings of the electric motor are connected through the wires of the same name. The experiment is then repeated in such a way that its phase, previously connected to the voltmeter, is changed by one of the two phases connected to the network. The found beginnings of the phases are marked as C1, C2, C3, and the ends are C4, C5, C6.Further connection of the windings is carried out, depending on the voltage of the network, in a triangle or a star.

Table. Marking the output ends of the squirrel-cage induction motor windings.

Phases Marking for asynchronous winding electric motor Start winding End winding L1 C1 C4 L2 C2 C5 L3 C3 C6

Determination of the beginning and end of the coils by Petrov's method