High-voltage motors, under the long-term influence of electromagnetic vibration, high temperature, and high voltage, suffer from mechanical wear due to electromagnetic vibration, corona corrosion, and insulation aging due to heat generation. This leads to adverse phenomena such as delamination, burning, wear, and reduced insulation strength in the overall insulation of the motor coils, ultimately resulting in insulation breakdown. Ms. Can will briefly discuss the impact of corona and vibration on coil insulation today.
1. Corona discharge damage to motor windings
During the operation of a high-voltage motor, the coil insulation is subjected to a high electric field intensity. If the anti-corona layer (high or low resistance band or anti-corona varnish) on the insulation surface has poor contact with the stator core, the vibration of the coil in the slot will wear down the anti-corona layer on the insulation surface. At this time, the insulation surface has a high potential relative to the core, generating corona discharge at the worn part, causing localized instantaneous high temperature, which burns and chars the main insulation of the coil and other auxiliary insulation materials.
Corona discharge can also produce a highly destructive chemical reaction, severely corroding insulation and coil wires. Therefore, areas with severe internal corrosion are often covered with a large amount of green powder. In addition, inadequate anti-corona treatment at the winding ends can cause excessive capacitive current, leading to overheating of the stator end windings and accelerating thermal aging and corrosion of the end winding insulation.
2. Damage to winding insulation caused by motor vibration
Motor vibration includes mechanical vibration and electromagnetic vibration. Various vibrations during motor operation will wear and corrode the coil insulation. Among them, the most significant is the impact of electromagnetic vibration on the motor end windings and slots.
● If the stator core pressing quality is poor, the winding end binding process is inadequate, or the impregnation effect is poor, the coil will vibrate in the slot due to poor fixation. The interlayer spacers and temperature sensing element spacers will then shift between the upper and lower coil layers, causing wear on the coil and damaging the coil insulation.
●If the current passing through the conductor during coil operation generates a second-harmonic electromagnetic vibration force, it will not only cause vibration between the coil and the iron core and the spacer at the end of the winding, causing wear on the surface of the main insulation, but also cause frictional vibration between the conductor and the main insulation, and between the turns and strands of the conductor, resulting in loosening, short circuits, and broken strands between the turns and strands of the conductor.
If an insulation short circuit occurs, additional losses and temperature rise will occur at the short circuit site, which will accelerate the aging of the local main insulation, reduce the insulation strength, and even cause insulation breakdown faults under normal operating voltage.
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