18 Pulse VFD w14% VTHD????
18 Pulse VFD w14% VTHD????
(OP)
I've spent the last 3 days collecting PQ data on a AB 7000 drive. 17th & 19th & 35th & 37th & 53rd & 55th harmonics all way above limits. The control is intermittently stopping/faulting and shutting down the drive. I don't have enough experience with these drives to begin to troubleshoot. Any thoughts?





RE: 18 Pulse VFD w14% VTHD????
The first question that I would ask, is what is the THDv when the drive is not running?
Secondly, where is the measurement made relative to the drive?
and third, what is the fault current and the drive rating?
Best regards,
Mark
Mark Empson
L M Photonics Ltd
RE: 18 Pulse VFD w14% VTHD????
THDv disappears when the drives are shutdown. Data was recorded at the xfmr 15kV feeder. Xfmer=13.8/2300 delta/delta-delta-delta. Also data recorded at the 480 bus. Same high harmonic content on the 480 gear. The 480 xfmr is a Y/D. One would expect some mitigation through the 480 xfmr. Not the case.
I assume that the distortion is sourced from the drives because the signatures are multiples of 18. I don't see the distortion coming from the 480 bus.
RE: 18 Pulse VFD w14% VTHD????
What is the fault code on VFD? Did you consult the drive mfr.?
Is this the only drive on this type and size? If not, compare the readings with the drives that do not have the problem.
I am sure you did some research before deciding to monitor the PQ.
Rafiq Bulsara
http://www.srengineersct.com
RE: 18 Pulse VFD w14% VTHD????
2 drives on the 15kV bus both suffering the same distortion. With one drive off the VTHD is half.
RE: 18 Pulse VFD w14% VTHD????
Rafiq Bulsara
http://www.srengineersct.com
RE: 18 Pulse VFD w14% VTHD????
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: 18 Pulse VFD w14% VTHD????
Neil
RE: 18 Pulse VFD w14% VTHD????
In most cases I've metered, a drive with 30% to 100%+ current distortion might only cause a few percent voltage distortion.
RE: 18 Pulse VFD w14% VTHD????
Balanced input voltages.
New equipment
Both drives fail.
RE: 18 Pulse VFD w14% VTHD????
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: 18 Pulse VFD w14% VTHD????
RE: 18 Pulse VFD w14% VTHD????
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(2B)+(2B)' ?
RE: 18 Pulse VFD w14% VTHD????
RE: 18 Pulse VFD w14% VTHD????
I am surprised to see that level of harmonic voltage coming from a VFD.
This suggests that the VFD has no reactors, either DC or AC and that the supply is very inductive.
The 18 pulse drive option will cancel some harmonics, but not all, however the higher order harmonic currents should not be high enough to create such high harmonic voltages.
I would check to see if there is either a DC bus choke fitted or AC line reactors. If they are not fitted, are they an option?
If you fit reactors, they must be balanced and equal on all rectifiers. You can have a DC bus choke in series with each rectifier, or a single reactor after the combined rectifier output. If AC reactors are used, they should be fitted at the input of each reactor.
With reactors fitted, I would expect the high order harmonic currents to be sufficiently attenuated to not cause any harmonic voltages of significance.
Best regards,
Mark.
Mark Empson
L M Photonics Ltd
RE: 18 Pulse VFD w14% VTHD????
Seeing the current and voltage harmonic spectrum would be more useful than those curves you posted.
RE: 18 Pulse VFD w14% VTHD????
Neil
RE: 18 Pulse VFD w14% VTHD????
Chris
RE: 18 Pulse VFD w14% VTHD????