Compared to low-voltage motors, high-voltage motor coils are much more complex to manufacture. The stator windings of high-voltage motors use different electromagnetic wires depending on the rated voltage. During coil manufacturing, anti-corona material, also known as high and low resistance bands, is wrapped around the straight edges of the coil and the protrusions from the slots to prevent corona discharge during motor operation.
The generation and hazards of corona
Corona discharge is caused by an uneven electric field generated by an uneven conductor. Near electrodes with small radii of curvature, when the voltage rises to a certain value, discharge occurs due to air ionization, forming a corona discharge.
Because the electric field around the corona is very weak, collisions and ionization do not occur. The charged particles around the corona are mainly ions, and these ions form the corona discharge current. Simply put, a corona is generated when a conductor electrode with a small radius of curvature discharges into the air.
In high-voltage motors, the electric field is concentrated at the ventilation slots, straight outlets, and winding ends of the stator winding. When the field strength at a certain local location reaches a certain value, the gas undergoes local ionization, and blue fluorescence appears at the ionization point. This is the corona phenomenon.
The corona discharge produces a thermal effect and ozone and nitrogen oxides, which raise the local temperature inside the coil, causing the adhesive to deteriorate and carbonize, the insulation of the strands and mica to turn white, and in turn, the strands to loosen, short-circuit, and the insulation to age.
In high-voltage motors, the electric field distribution on the insulation surface of the stator coils at the ventilation slots and outlets is extremely uneven. When the local field strength reaches a certain value, the gas undergoes local ionization, resulting in a blue halo at the ionization point, which is known as corona discharge. The occurrence of corona discharge is accompanied by the generation of heat, ozone, and nitrogen oxides, all of which are extremely harmful to motor insulation.
Furthermore, poor or unstable contact between the thermosetting insulation surface and the slot wall can cause spark discharge in the slot gap under the influence of electromagnetic vibration. The localized temperature rise caused by this spark discharge will severely corrode the insulation surface, all of which will cause great damage to the motor insulation.
To effectively eliminate this corona phenomenon, it is crucial to correctly determine the anti-corona structural parameters and select good anti-corona materials. Generally, corona-resistant materials are selected for the motor's insulation, and corona-resistant paint is also used for impregnation. Furthermore, the motor design should consider the harshness of the operating conditions and reduce the electromagnetic load.
Disclaimer: This article is a reprint. If there are any copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
