Why High-Altitude Conditions Increase the Risk of Corona Discharge in Electric Motors

High-Altitude Operation Increases the Risk of Corona Discharge in Electric Motors

When operating in high-altitude environments, electric motors face two significant challenges: reduced cooling efficiency and an increased risk of corona discharge. At higher elevations, the thinner air leads to decreased heat dissipation, resulting in higher motor temperature rise. More critically, the likelihood of corona discharge—an electrical phenomenon involving localized ionization—becomes significantly greater.

Corona discharge occurs when the electric field around a charged conductor exceeds a certain threshold, leading to partial discharges in the surrounding gas or liquid medium. This often happens near sharp edges or high-voltage conductors, generating ozone and nitrogen oxides. High-voltage motor windings, especially at 10kV, meet the basic conditions for corona discharge, making preventive design measures essential. While 6kV motors generally do not exhibit corona under standard conditions, the probability increases at 10kV, and even more so at high altitudes.

At elevated altitudes, the breakdown voltage of air is reduced due to lower atmospheric pressure and decreased air density, weakening the dielectric strength of the insulation around the motor windings. This creates a higher susceptibility to corona discharge, posing a serious threat to the long-term reliability of the motor.

While high altitude does have some effect on motor temperature rise due to changes in air pressure and ambient temperature, the impact on corona discharge is far more significant. To ensure motor reliability in such environments, responsible manufacturers implement corona-resistant designs for both 6kV and 10kV motors—assuming the harshest possible operating conditions during design and production.

Common anti-corona measures include wrapping stator coils with high and low resistance tapes, applying anti-corona varnish, installing stator air baffles, and tightly controlling insulation taping processes. These steps are critical to preventing corona damage to motor windings and ensuring safe, long-term motor performance across diverse applications.