Why High-Voltage Motors Experience Corona Discharge And Its Root Causes
Mar 12, 2026
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Corona discharge refers to a partial discharge phenomenon on the surface of a charged body in a gas or liquid medium. It often occurs around high-voltage conductors and near sharp points of charged bodies. During discharge, substances such as ozone and nitrogen oxides are produced, accompanied by blue light. Low-voltage motors do not suffer from corona discharge, but high-voltage motors, especially those rated at 10kV and above, frequently experience this phenomenon.
High-voltage motors generate corona discharge because non-smooth conductors form an uneven electric field. Around the uneven electric field and near the electrodes with small curvature radius, when the voltage rises to a certain value, discharge takes place due to air ionization, thus forming corona.
The main conditions for corona discharge include non-smooth conductors, an uneven electric field, and sufficiently high voltage. The end of the stator winding of high-voltage motors basically meets all the conditions for corona generation. At the ventilation slots and slot exits of their stator coils, the electric field distribution on the insulation surface is extremely uneven.
To prevent corona discharge from damaging the windings, necessary measures are taken in the manufacturing process of high-voltage motors to mitigate the spread of corona. These include wrapping their coils with sufficiently thick insulating materials, adding resistance tapes outside the coils, and coating key parts of components with anti-corona paint via stator wind shields.
For high-voltage motors of the same voltage rating but different operating conditions, environmental factors can trigger corona discharge. Higher altitude, more humid air, and higher temperatures all lower the corona inception voltage of their windings, making the motors more prone to corona. Therefore, for high-voltage motors operating under special conditions, anti-corona measures for their windings should be appropriately strengthened.
A large number of measurement data show that 6kV is the critical value of corona inception voltage for motors. 6kV high-voltage motors used in normal environments do not experience corona discharge. However, when the operating environment changes-such as in plateau areas-corona discharge may occur. Corona can degrade the winding insulation of high-voltage motors and ultimately shorten their service life. To ensure the performance and reliability of high-voltage motors, manufacturers usually design and manufacture their windings according to relatively harsh environmental conditions, which largely avoids damage to winding quality caused by corona discharge.