Reasons and solutions for the occurrence of open circuit faults in motor windings

Reasons and solutions for the occurrence of open circuit faults in motor windings

Due to poor welding or the use of corrosive flux, if the winding is disconnected and not cleaned thoroughly after welding, it may cause pot welding or loosening; When subjected to mechanical stress or collision, coil short circuit, short circuit and grounding fault can also cause wire burnout. When one or several wires are short circuited among the burnt wires, the temperature of the other wires rises due to the increase of current, causing the winding to heat up and break. It is generally divided into one phase winding end breakage, inter turn short circuit, parallel branch breakage, multiple wires burning in one wire, and rotor cage breakage.

Fault phenomenon

The motor cannot start, the three-phase current is unbalanced, there is abnormal noise or vibration, the temperature rise exceeds the allowable value, or smoke is emitted.

cause

(1) Breaks or manufacturing quality issues during maintenance and repair.

(2) Poor welding of various components, pole (phase) groups, and terminals between windings and lead wires, resulting in overheating and desoldering during long-term operation.

(3) The winding is damaged or pulled apart by mechanical and electromagnetic forces.

(4) Short circuits between turns or phases, as well as grounding, can cause severe burning or melting of the winding.

Inspection Method

(1) Observation method. Most of the breakpoints occur at the end of the winding, check for any dents or disconnections at the joints.

(2) Multi meter method. Using resistance mode, connect one meter rod to the center point of the "Y" shape for the "Y" connection method, and then connect the other rod to the first end of the three-phase winding in sequence, with the infinite phase as the breakpoint; After the short circuit connection of the "△" type connection, measure each set of windings separately, and the infinite one is the breaking point.

(3) Test lamp method. The method is the same as before, and the phase that does not light up is considered a circuit breaker.

(4) Megohmmeter method. The phase with a resistance value approaching infinity (i.e. not zero) is the breaking  point.

(5) Ampere meter method. When the motor is running, use an ammeter to measure the three-phase current. If the three-phase current is unbalanced and there is no short circuit, then the winding of the smaller phase has a partial short circuit fault.

(6) Electric bridge method. When the resistance of one phase of the motor is greater than that of the other two phases, it indicates that there is a partial open circuit fault in the winding of that phase

(7) Current balance method. For the "Y" type connection, the three-phase windings can be connected in parallel and then subjected to low voltage and high current alternating current. If the current difference in the three-phase windings is greater than 10%, the end with the smaller current will be considered a circuit breaker; For the "△" type connection method, first disconnect one contact of the stator winding, and then gradually introduce low voltage and high current into each phase, with the phase with lower current being the open circuit.

(8) Inspection method of broken cage reconnaissance device. During inspection, if the rotor cage breaks, the reading on the millivolt meter should decrease.

processing method

(1) When the circuit is broken at the end, it should be welded firmly after connection, wrapped with insulation material, covered with insulation tube, tied up, and then dried.

(2) If the winding is severely burnt due to inter turn, inter phase short circuit, grounding and other reasons, it should generally be replaced with a new winding.

(3) Emergency treatment shall be carried out for a small number of broken points in the slot. The grouping elimination method shall be used to identify the broken points, and they shall be connected and insulated properly in the winding break section before use.

(4) Welding, cold welding, or strip replacement can be used to repair the broken cage of the cage shaped rotor.