CIV ratings for electric motors need closer monitoring

November 2024 Motion Control & Drives

As most technical industries increasingly rely on advanced motor control technologies, understanding and selecting motors with appropriate Corona Inception Voltage (CIV) ratings is vital to prevent costly failures and downtime over time.

Corona is a luminous discharge phenomenon, which is induced by the partial ionisation of air around the conductor when the surface electric field strength exceeds a critical value. This needs to be monitored more closely to ensure the reliability and longevity of electric motors used with variable speed drive (VSD) control devices.

Electric motors connected to VSDs are susceptible to voltage transients that can exceed their insulation limits, particularly where long cable runs are involved between the VSD and motor. The high switching frequencies of modern VSDs, particularly those using Insulated Gate Bipolar Transistors (IGBT), can generate voltage spikes that exceed the insulation limits of standard motors.

These voltage transients, characterised by rapid rise times, can lead to elevated voltage gradients within the motor windings, increasing the likelihood of insulation breakdown. Understanding how VSDs create these voltage spikes is crucial for selecting a motor that can withstand such stresses.

For more information contact Referro Systems, +27 12 349 1297, [email protected], www.referro.co.za

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