VARIABLE FREQUENCY DRIVES(VFD)

[ALEVIN]

SEVERAL VFD MANUFACTURERS HAVE MENTIONED IN THEIR SPECS THAT THE MOTOR LOAD SHOULD NOT BE LOCATED BEYOND A SPECIFIC DISTANCE FROM THE VFD.

WHAT IS THE TECHNICAL REASON FOR THE DISTANCE LIMITATION BETWEEN THE VFD AND ITS MOTOR LOAD?

IF IT IS A VOLTAGE DROP CONCERN , THE CONDUCTORS TO THE MOTOR CAN BE INCREASED IN SIZE.

 

[jbartos]

Suggestion: See

http://www.ab.com/drives/techpapers/ieee/ieee.html

for the following papers (in *.pdf format):
1) D. Leggate, J. Pankau, D. Schlegel, R. Kerkman, and G. Skibinski, Reflected Waves and Their Associated Current, IEEE Industry Application Society Conference, St. Louis, MO, October 12-16, 1998, pp. 789-798 and IEEE Transactions on Industry Applications, Vol. 35, No. 6, pp.1383-1392, November/December 1999.
2) G. Skibinski, R. Kerkman, D. Leggate, J. Pankau, and D. Schlegel, Reflected Wave Modeling Techniques for PWM AC Motor Drives, IEEE Applied Power Electronics Conference, Anaheim, CA, February 15-19, 1998, pp. 1021 - 1029.
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Essentially, fast switching IGBT devices create high frequency (due to sharp rise, dv/dt) currents and voltages (common mode and differential mode) which are traveling in the motor feeder cable (behaving as a transmission line) and reflect at the cable end at the motor terminals, then traveling back to the source terminal where they reflect back to the motor terminals, etc. The reflected waves can built up in its magnitude to have negative impact on insulation and votage sensitive devices. The longer cables (or transmission lines) usually have a higher attenuation of traveling waves; therefore, they possess the mitigating effect of traveling wave magnitude build-up.