The insulation of three-phase asynchronous motors includes ground insulation, phase insulation, and turn insulation. Among them, ground insulation refers to the insulation between the stator core, the casing, and the end cover of the three-phase winding; Interphase insulation refers to the insulation between three-phase windings; Interturn insulation refers to the insulation between each turn of a winding coil.

The main cause of damage to three-phase asynchronous motors is insulation failure to ground, followed by insulation failure between phases, and then insulation failure between turns. The insulation performance of a motor is determined by the properties of the insulation material itself and the production and manufacturing process. Insulation material is the foundation of the reliability of motor insulation. The insulation materials of motors include not only the insulation materials of conductive materials such as electromagnetic wires and lead wires, but also reinforced insulation materials such as insulation paper, insulation tubes, insulation paint, mica tape, etc. used in the production and processing process. The heat resistance level of insulation materials is a crucial performance indicator that should match the temperature rise control level of the motor. This article mainly studies insulation faults in the manufacturing and assembly processes.

The main locations, causes, and treatment measures of ground insulation faults

The ground insulation faults of motor products can be divided into winding and iron core, winding and machine base, winding and end cover, as well as grounding insulation faults of lead wires and related components according to their occurrence locations.

1) The insulation fault between the winding and the iron core to ground mostly occurs at the slot position, as shown in Figure 1.

Most of them are related to the expansion and shaping of the iron core and the end of the winding. For products with high winding slot filling rate, insulation grounding faults are more serious. Another location for winding insulation grounding is inside the slot, which may be mainly caused by unevenness or foreign objects in the iron core slot, resulting in damage to the insulation at the bottom of the slot. It may also be due to insulation size mismatch or twisting in the slot. The possibility of repair varies for different insulation treatment processes; Most motor manufacturers use vacuum pressure coating, and the insulation paint becomes an irretrievable solid after curing, making it difficult to repair, especially for insulation faults in the iron core slot, which are basically irreparable. For ground faults in windings and iron core slots, due to the special shape of the slot, when a ground fault occurs, it is very likely that the paint film of the electromagnetic wire has been damaged. Even if the ground insulation fault is repaired, the possibility of inter turn insulation is still high