[Legacy Report] Variable Speed Drive Motor Insulation Challenges

#Variable #speed #Motor #Insulation #pulse #width #stress #grading #coil #bar

Today’s variable speed drive motor supplies are very simple in design and stem from advances that have been made in power electronic switches. They typically consist of a pulse width voltage source inverter to control frequency thereby controlling synchronous motor speed. This technique is widely used with pulses having 150 to 200 ns rise times and pulse repetition frequency of 1 to 10 kHz. Although the use of variable speed drives for motors has far greater benefits than the earlier techniques of controlling speed, from the onset of using these drives, various types of premature insulation failures have been reported. Generally, repetitive fast pulses enhance electrical stress on the insulation system that manifests itself by early degradation, which is caused by partial discharge and corona. However, for form-wound coils and Roebel bars that are used in medium and high voltage motors, the main challenge has been in addressing the adverse effects on the motor coil insulation system, including strand, turn, and groundwall insulation as well as the conductive armor and stress grading coatings that are applied for relief of electric stress. Although these coatings work well as an “anti-corona” or “stress relief” under power frequency, they exhibit poor performance under repetitive steep front pulses. In addition, dielectric loss in the insulation, particularly in the conductive armor and in the stress grading coatings become a problem at the higher frequencies.

The presentation will address the above issues along with research results along with possible solutions.

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• Toronto, Ontario
• Canada

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• Co-sponsored by Ali Naderian