is this true?
is this true?
(OP)
Quote:
Voltage reflection, which can destroy a motor, may occur when the motor cable is longer than or equal to the critical length; lead lengths as short as 25 ft are sufficient for such an event . Thus, voltage reflection is a function of the lead length of the power cable between the drive and motor.
We can predict voltage reflection using the following equation:
Eq. 1: Lcritical=Vcable × tr
where, Lcritical is the critical cable length in feet.
Ive used more than 100 meters cables between VFDs and Motors !





RE: is this true?
For short cables this wave behavior does not apply. As cable gets longer we get into the region where it applies.
Here is a discussion "Riding the Reflected Wave"
http:/
The figure on top of page 6 shows this effect where rise time and cable length are independent variables. Motor impedance, cable type and shielding also affect the reflection/magnification.
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RE: is this true?
At the end of this thread, there is a discussion on overvoltage caused by VFD. There is also a link to a paper showing how cable length influences overvoltage. It increases first and then decreases as cables get above a certain length.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: is this true?
The curve on page 4 of the link shows a flattening of the max stress at high cable lengths, not a lessening... correct?
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RE: is this true?
The curves are withstand requirements.
The actual voltages measured are represented by the circles, squares and triangles. The do, as you can see, fall when cable length increases.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: is this true?
Now another thing is confusing me about that graph - it shows 2 different axes. Rise time across bottom for the envelope lines and cable length across top for the test result measured voltage squares, triangles circles. There is really no basis for plotting these on same graph, right? i.e. no specific correlation between a given cable length and given rise time.... so magnitude of circles and squares in relation to line has no meaning unless someone tells us rise time of those circles and squares so we can locate appropriate portion of the limit line (?)
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RE: is this true?
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RE: is this true?
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RE: is this true?
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