3 Key Factors That Cause Corona Discharge in High Voltage Motor Windings

Three Key Factors That Can Trigger Corona Discharge and Reduce the Corona Inception Voltage of Motor Windings

01 — Effect of Altitude on Corona Discharge
Altitude has a direct impact on the occurrence of corona discharge. In high-altitude environments, the air density is lower, which leads to a reduction in the corona inception voltage of motor windings.
Under normal environmental conditions, the corona inception voltage of high-voltage motors is generally around 6 kV. This means that motors with a rated voltage not exceeding 6 kV usually do not experience corona discharge issues. However, in plateau or high-altitude regions, the corona inception voltage will be lower than this value. As a result, high altitude becomes one of the inducing factors for corona discharge.

02 — Influence of Ambient Humidity and Temperature
When the ambient humidity of the motor operating environment increases, the corona inception voltage decreases accordingly. Therefore, in environments with high humidity—such as water supply facilities, coastal or near-sea areas, and production processes where water vapor or mist is present—the corona inception voltage of motors will be reduced.
In such cases, motors with a higher protection degree should be selected based on the actual operating conditions to effectively prevent the occurrence of corona discharge.

In addition, high temperature also affects corona discharge. Some insulation or anti-corona materials may suffer performance degradation as temperature rises, especially when the winding temperature rise is excessive. Once the material properties deteriorate, the risk of corona discharge will increase.

03 — Influence of the Gap Between Windings and Stator Slots
During the manufacturing process of high-voltage motor windings, appropriate slot fill factors and necessary insulation measures are adopted, such as mica taping, resistive stress-grading tape wrapping, filling insulation materials in void areas, and applying VPI (Vacuum Pressure Impregnation). These measures aim to minimize the gap between the conductor and the stator core slots.
Effectively eliminating these gaps is a necessary and efficient way to reduce corona discharge and is also a critical control point in high-voltage motor winding manufacturing.

Therefore, purchasers of high-voltage motors should provide motor manufacturers with as much detailed information as possible regarding the actual operating environment. By applying appropriate technical measures, the negative impact of corona discharge on motor performance and quality can be significantly reduced or even eliminated.