VFD Output Motor Cable Number of Cores
VFD Output Motor Cable Number of Cores
(OP)
I observed that all VFD motor cables are 3core construction. I would like to understand why a 3 x 1c VFD output cable cannot be used.
I have a medium voltage VFD controlling a 1000kW, 4kV induction motor. I am insisting to use 3 core but our client is looking on single core arrangement because that is what their previous consultant recommended. In this regard your expert opinion or reference will bemush appreciated.
I have a medium voltage VFD controlling a 1000kW, 4kV induction motor. I am insisting to use 3 core but our client is looking on single core arrangement because that is what their previous consultant recommended. In this regard your expert opinion or reference will bemush appreciated.






RE: VFD Output Motor Cable Number of Cores
3 x 1/c configuration will work fine to run the motor, but the radiated energy coming out of the feeder can wreak havoc on any nearby low-level circuits.
Tell him it's the standard of the industry. Check any VFD installation manual.
David Castor
www.cvoes.com
RE: VFD Output Motor Cable Number of Cores
Just thinking out loud on what client may respond with.
Thanks you.
RE: VFD Output Motor Cable Number of Cores
There are different types of MV VFDs. The Robicon (now Siemens) seems to be 'nicer' than most other, but I would still be very hesitant to use single core cables. Some very large rolling mill motors have to use single core cables simply because there are no three-phase cables available for those currents and voltages. But that is an exception.
For 1 MW, I would definitely go with three-phase cables.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
Technically, i did not see any different.I have experience to lay VFD to 800kW (6.6kV) induction motor.
RE: VFD Output Motor Cable Number of Cores
RE: VFD Output Motor Cable Number of Cores
EMC issues with VFDs
thread237-303429: EMC issues with VFDs
You may decide that there is a difference.
Bill
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"Why not the best?"
Jimmy Carter
RE: VFD Output Motor Cable Number of Cores
The operating conditions that was based for testing did not mentioned any discrimination of 3 core or single core arrangment.
I am into the opinion that if I use singe core, 3.6/1kV, screened copper cables arranged in trefoil formation plus grounding cable and they are properly clamped together and their screens are bonded together at both terminations using EMC glands, they will offer the same like a 3 core screened cable.
I am not pretty sure though if single core screened, EPR cables are available at 3.6/1kV nominal? Any ideas?
RE: VFD Output Motor Cable Number of Cores
It would help if you told us what VFD you will be using. A lot depends on that.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
Based on proposals, it would be more likely to be an ABB ACS1000.
I also have a strong belief that there is a significant difference. However, I am trying to get some technical information to explain it or better yet any technical literature that I could refer to understand and effectively explain and convince them to use 3 core, 3.6/6kV cables instead of the single core equivalent. I can't deal with the vendor at the moment because there is P.O. placed yet but we might pre-order the cables that is why I have some concerns.
RE: VFD Output Motor Cable Number of Cores
I am afraid that wasn't much help
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
David Castor
www.cvoes.com
RE: VFD Output Motor Cable Number of Cores
1 - The transposition reduces magnetic field radiation. It is similar benefit to twisted shielded pair for signal cables (except for signal cables the concern is acting as magnetic receiver vs transmitter)
2 -With 3 cables in one shield, the fields should cancel resulting in very little shield current. In contrast 3 individually shielded 1/c cables would each have current in their shields. That shield current itself can be a source of emi.
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(2B)+(2B)' ?
RE: VFD Output Motor Cable Number of Cores
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
Am I right with this opinion? In a 3 core cable, the separation between the 3 conductors are dependent on the thickness of insulation that surrounds each copper conductor and the overall screen will tend to trap any stray voltages.
On the 1 x 3core on the other hand, this separation will be dependent on the thickness of insulation+jacket+air gap due to a probable imperfect installation (trefoil) in the field.
However, will this difference cause significant EMI to cause a problem?
RE: VFD Output Motor Cable Number of Cores
It is here: http:
Putting cores in different screens is a bad idea. High currents are capacitively coupled into the screens and that will cause lots of problems.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
I am doing my further research to get a close answer to this but would help a lot if you throw me your thoughts further. Appeciate your comments much...
RE: VFD Output Motor Cable Number of Cores
For other inverters with PWM output, there are very good papers on the web. Just google +PWM +"motor cable" and variations thereof.
Those pictures were started so you can visualize the difference between a symmetrical three-core cable with a common screen and other configurations where current is coupled from the separate cores to the respective screens.
That current now has to flow along the cable screen to ground and will produce HF emission and HF voltage drop in the screen. That is not what you want. But, as I said, no probs with the ACS 1000.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: VFD Output Motor Cable Number of Cores
To all, thank you for your assistance. I'll take it from here.
RE: VFD Output Motor Cable Number of Cores
The cable type and reformation from the manufacturer varies significantly in accordance with the VFD design parameter, number of pulses, filters, etc.
During the bid process, some manufacturers recommended using three single shielded cables installed in metallic conduit. If triplex cable was used, it must have three symmetrical grounds.
For EMI reasons, the project in concurrence with the VFD manufacturer decided to use triplex cable in cable tray.
RE: VFD Output Motor Cable Number of Cores