Common Causes of Turn-to-Turn Insulation Failure in Motor Windings

Analysis of Characteristics and Causes of Turn-to-Turn Faults in Electrical Failures of Motor Windings

Turn-to-turn insulation failure is one of the most common electrical faults in motor windings. It can occur in both single-phase and three-phase motors, except in cases with single-turn windings. In motors where the cross-sectional area of a single conductor is relatively large, the number of turns in the coil is usually fewer. Conversely, in cases where the conductor has a smaller cross-sectional area, the number of turns is often higher, which increases the probability of turn-to-turn insulation failure.

For windings where multiple wires are wound in parallel, there is no turn-to-turn insulation issue between wires within the same coil. However, insulation issues can arise between different coils. Generally, preformed coils have fewer turns, while flexible wound coils tend to have more. Therefore, for low-voltage, high-power motors, high-voltage motors, and motors operating in special conditions, it is recommended to use preformed windings.

1. Why Does Turn-to-Turn Insulation Failure Occur During Manufacturing?

Theoretically, the turn-to-turn insulation of wires with their own insulation layer, such as enameled wires or mica wires, can withstand the impact of turn-to-turn voltage. However, during the actual manufacturing of motor windings, some steps can damage the insulation layer of the wires. In some cases, these damages cannot be fully repaired by the impregnation and baking process, or the repair may not be sufficient, leading to turn-to-turn faults during motor testing or operation.

During the production of motors, various stages like winding, coil insertion, wiring, transportation, and assembly can cause damage to the insulation layer of the wires. This has been discussed in detail in previous articles. Besides production-related damage, the quality of the wire itself is critical. Factors like the adhesion of the insulation layer, the uniformity of the insulation, and the smoothness of the conductor directly impact the reliability of the motor windings. For preformed windings, the mechanical strength of the insulation layer is crucial during the coil-forming process. Poor-quality wire can easily lead to insulation damage, resulting in serious turn-to-turn insulation faults.

To address this issue, it is essential to carefully select the electromagnetic wire and ensure that the winding process meets all technical requirements, avoiding any damage to the insulation during production.

During the impregnation and baking process, efforts should be made to enhance the filling effect of the insulating varnish. The choice of equipment, performance parameters of the insulating varnish, and process control are key factors in ensuring good insulation during production.

2. Analysis of Turn-to-Turn Insulation Faults During Motor Operation

Damaged sections of the wire during production are potential sources of quality issues during motor operation. In addition, the first coil in the winding, which is directly connected to the power supply, is subject to the highest stress during motor startup. This coil also tends to undergo significant deformation during the winding process. Case studies of actual faults show that, in motors without reinforcement, turn-to-turn faults often occur in the first coil. Many motor manufacturers and repair units apply special insulation measures to the first coil, which can effectively reduce turn-to-turn insulation failures.

In high-voltage motor windings, inspections of turn-to-turn faults often reveal that the affected windings have poor impregnation, with loose turns. This could be due to issues during the impregnation process, or it may relate to processes such as coil wrapping and curing.

Electrical failures in motors are influenced not only by material performance but also by the quality of the manufacturing process. Different motors and manufacturers employ different production techniques, and targeted reinforcement measures can effectively prevent problems. Learning from motor faults is a more effective way to improve motor quality than shifting blame.

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