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Motor life span - to understand the impact of inverter operation on motor life span it is instructive to refer to two standards: IEC 34-17 and DIN VDE 530.
These state that a general application motor used with an inverter shall withstand voltage peaks (Vpeak) up to 1,000V and dV/dt (change of voltage with time) up to 500V/ms without any significant decrease in motor life.
However, in practice, the values motors are exposed to are substantially higher, reaching 5000V/ms and 1,500V.
To illustrate this point: in a 400V supply drive-motor application the voltage on the motor terminals might be as high as Vpeak = 400V x 1.1 x Oe2 x 2 = 1245V Where: 1.1 = positive supply voltage tolerance, Oe2 = voltage peak and 2 = inverter overshoot factor.
The rate at which these voltage peaks - or spikes - occur depends on the inverter carrier frequency, but typical values are 2,000 to 20,000 times per second.
The repeated stress these cause at motor terminals gradually breaks down the dielectric strength of the winding, resulting in corona and partial discharges that eventually destroy the motor.
Thanks for your answer, but i have the new IEC standard IEC60034-17-2002 and there is not write that. The WEG article is old, of 1998. I really appreciate if you have that old standard and what they specifically say.
