A variable frequency drive allows a customer to change the motor’s operating speed by changing the frequency (Hz) of the power supplied to the motor. While this is convenient for the customer, it causes several problems for the motor and special consideration must be given to the motor’s ability to operate on various frequencies.
Power supplied by (PWM) variable frequency drives contain harmonic content in the electrical waveforms they generate at various frequencies. The harmonic content and non-sinusoidal waveforms generated by the drive can cause the following problems:
The motor insulation system for VFD approved TECO-Westinghouse motors is based on and exceeds NEMA
Standards. As defined in NEMA MG-1 Part 126.96.36.199 the insulation system must be capable of withstanding voltage spikes of 3.1 x rated line to-line voltage for motors rated ≤600V and 2.04 x rated line-to-line voltage for motors rated >600V with a rise time of ≥ 0.1μs. TECO Westinghouse motors rated ≤600V have been designed to withstand voltage spikes up to 2000V with a rise time of ≥ 0.1μs. Voltage spikes and rise time should be measured at the motor terminals and should not exceed the above given values.
Cable length and type connecting the motor and drive have a significant influence on the peak voltages occurring at the motor terminals.
The following conditions should be met when installing TECO-Westinghouse motors on an inverter: