VFD Cable length
VFD Cable length
(OP)
Hi,,,
I am researching about the max. allowed cable length from VFD to motor. I spoke to one of the vendors application engineers and his answer was that max. what he has seen is 100 ft. My requirements are 400 m. I was wondering, is there a way instead of just relying on vendor, I can make a decision my self as a consultant. It is for a ventilation fan 300 HP, 575 V in an undeground mining environment.
Is it true in all the situations, the cable used between VFD and motor has to be application specific ?
How do we decide, what cable to use ?
I would appreciate a word.
Thanks
I am researching about the max. allowed cable length from VFD to motor. I spoke to one of the vendors application engineers and his answer was that max. what he has seen is 100 ft. My requirements are 400 m. I was wondering, is there a way instead of just relying on vendor, I can make a decision my self as a consultant. It is for a ventilation fan 300 HP, 575 V in an undeground mining environment.
Is it true in all the situations, the cable used between VFD and motor has to be application specific ?
How do we decide, what cable to use ?
I would appreciate a word.
Thanks
RE: VFD Cable length
Four hundred meters is a lot. You may need a sine filter ro run such a long cable. And there are other issues, too. Like voltage drop and cable capacitance influencing the filter characteristics.
First advice: Do not listen to the salespersons.
Second advice: If you did. Do not believe what they say.
Third advice: Get a good consultant if you cannot do this by yourself.
I must say, though, that this vendor did not promise too much.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Cable length
RE: VFD Cable length
I very like advice 1 and 2 at your post.
Regards.
Slava
RE: VFD Cable length
Don
RE: VFD Cable length
RE: VFD Cable length
This is a very common problem with IGBTs and results in overvoltage at motor end so that ozone inception voltage is reached and ozone (O3) is produced. It accelerates insulation aging and should be avoided.
There is also the fact that cable capacitance needs to be charged and discharged on every edge of the PWM waveform. That heats the transistors and VFD manufacturers have tables where maximum cable length vs switching frequency, cable type and supply voltage can be read.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: VFD Cable length
Pursuant to Gunnar's advice, the problem is that one VFD is not like another VFD is not like another VFD etc. etc. No two designs are exactly alike; there is a core technology that is the same, but the topology of the components and feature selection is driven more often by marketing gimmicks than engineering sense. So what may be fine with one VFD might be a disaster with another.
One approach you might consider taking is to NOT specify exactly how long they can have for cables or how they solve the problems, but rather just state all the issues very clearly and insist that potential vendors must mitigate these issues with whatever package they feel is best. Then require that they support their approach with detailed engineering (not sales) documentation and have that proposal reviewed by an engineer with a good depth of drives experience.
RE: VFD Cable length
I guess there are few things I need to watch out as a consultant and solutions seems very traditional as well.
Two important issues:
1. Voltage stress on Motor insulation
2. Noise
I noticed that most of the vendors have these published tables that talk about distance issues.
In my case VFD the carrier freq is 2.2 KHz and Rise time 500 mic.v/Sec. Besides that I am gonna use a inverted duty rated motor. The application is 600 V and the motor insulation will be rated traditionally is 2.2 KV. besides that I can use a inverter duty rated teck cable and make sure that motor leads are in EMT conduit.
Besides that after 100 ft., I intend to use a dv/dt filter and a input line reactor. If the distance goes beyond 600 ft then probably a sin wave filter.
Skogsgurra,
Do you agree with me?
Just wondering on what basis Carrier freq. and rise time is decided.
Thanks
RE: VFD Cable length
RE: VFD Cable length