How to carry out an emergency coil repair with the removal of damaged coils from the circuit

If the shutdown of the electric motor due to damage to its winding caused the shutdown of important equipment, then the easiest and fastest way is to replace the damaged electric motor with a spare one.

In the absence of a spare electric motor, the duration of emergency removal will depend on how quickly it is possible to restore the damaged electric motor. Even a partial rewind of the electric motor with the replacement of several damaged coils, if they are located next to each other, will take at least 4 - 6 days. If the damaged windings are located at different places along the circumference of the stator, it will be necessary to completely rewind the stator of the electric motor, which takes even more time.

Under these conditions, it is advisable, if the number of damaged coils is small, to carry out an emergency (temporary) repair of the stator winding by removing damaged windings from its circuit.

How many windings of the motor winding can be disconnected from the circuit?

If the voltage supplied to the electric motor is equal to or lower than normal, then in each phase it is possible to turn off up to 10% of the number of coils per phase. For example, if there are 24 windings per phase, then no more than 24 x 0.1 = 2.4 windings can be disconnected from each phase.

Since the damaged coil must be completely disconnected, then the number of coils to be disconnected must be an integer, in this case no more than two. In all three phases in this case six windings can be switched off.

When no more than 10% of the total number of windings per phase is removed from the circuit, on each of the coils that remain in operation, the voltage relative to the rated voltage will increase by no more than 10%, which is perfectly acceptable.

If the voltage supplied to the electric motor exceeds the nominal, in each phase it is possible to turn off only such a number of windings that the overvoltage of each of the coils remaining in operation would not exceed 110% of the nominal. For example, if the voltage supplied to the electric motor is 105% of the nominal, then no more than 5% of the number of windings in a phase can be removed from the circuit.

If the voltage applied to the motor is 110%, removing the damaged coils from the circuit will overheat the stator steel. However, in exceptional cases, in order to eliminate the emergency situation and at such a voltage, it is advisable to temporarily turn off the damaged coils.

Engine with front cover removed

In the event of a short circuit during the operation of the electric motor, an unacceptably large current will flow, which will cause burning not only of these turns, but will lead to overheating and damage to the insulation of the turns in the adjacent channels. Therefore, in the damaged coils removed from the circuit, cut all the turns with pliers and bend their ends in such a way as to exclude the accidental formation of a short circuit during the operation of the electric motor. For this, it is important not to let the ends of the wires of one groove touch the ends of the wires of the other groove. It is also impossible for the ends of the wires to touch the active steel and the stator housing, as this may create a short circuit. The connection between the ends of the wires on the same groove is not dangerous.

If the winding insulation is damaged in the two channels belonging to these turns, then the turns must be cut on both sides of the stator. The cut ends of the winding are screwed, if they are reliably bent and do not touch steel or the motor housing during operation, they do not need to be insulated.

The ends of the circuit wires disconnected from the damaged windings must be firmly bridged to restore the integrity of the phase circuit.

Experience shows that electric motors with de-circuited windings can operate successfully for years. However, at the next overhaul of the electric motor, it is recommended to replace the damaged coils with new ones.