Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

VFD Help 1

Status
Not open for further replies.

xJAyx

Electrical
Oct 29, 2003
100
Hello everyone,
I am working on a project which I have been parachuted into. The electrical system is a mess as it was never properly designed and what design there was was not followed very closely. There is no separation of power/signal conductors in the cable tray and no cinsistency in the sheilding of the conductors. The system is powered by 3 synchronized gensets, 400/230 VAC, 50 Hz. My concern at the moment is the VFDs installed in the system. I do not know if they have any reactance installed in them, but I do know that while the design did call for sheilded cable the installation is inconsistent on this. Most of the VFDs are powering fractional hp motors, but two of them are powering 30 hp pumps.
My concern is noise and harmonics generated on the line side and EMF generated in the cable tray runs. I know that the larger vfd's will need to be dealt with, but do I have to worry about the smaller ones (there are about 4 of them) creating a larger problem as a whole than they would individually?
Does anyone know and good web resources or have any tips for me on this one?
 
Replies continue below

Recommended for you

A second question would be what regulations apply? Is this an EU installation?

The total harmonic current distortion caused by the VFDs is proportional to the total load power delivered by the VFDs compared to the overall total load power delivered at the utility metering point. The total voltage distortion is proportional to the total load power delivered by the VFDs compared to the capacity of the power source.

For additional information, start with the manufacturer's installation manuals for the VFDs. See if you can download them or otherwise obtain them if you don't have them. Read them carefully and obtain any additional material mentioned in them. Check the manufacturer's web sit for any additional material that might be available.
 
Answer #1 - the system is not up and running yet.
Answer #2 - this is a shipboard application, under DNV jurisdiction, which is based on and references the IEC code.

thanks for the quick replies so far.
 
You're worried about harmonics? on the operational point of view,as long as the cables and motors are not overheating then it COULD be acceptable,but of course there's limitation, however running this along or in bunch with signal cable is not acceptable. All our VFD cables vis-a-vis signal cables have minimum separation criteria of 150mm while some are running on a separate tray. For fractional horsepower motor with shielded cable->50mm is acceptable.(DNV approved!)
 
Oh believe me, if I had been around when this started everything would have been separated properly, or I would have died trying. I am sure it is going to cause no end of headaches once everything is up and running. But it is too late to separate everything now.
 
We have exactly the same problem in our acquired vessel in China and its 15 days before delivery (June 2006) until our company decided to send electrical surveyor. Our site Manager and YARD says its too late to make changes, however we stick to the requirement. Vessel was delivered a month and a half later until its correctly done. You're correct that it will cause headache once its up and running/delivered ....and its the OWNER's head. Mind you builder will definetely not minch nor bother to correct it once problem arises and the ship is at another part of the globe. Guarantee claims will file up while the builder sit tight and promise to correct it on the NEXT PORT!
 
What is the size of the gensets? Are all three operating in parallel all of the time?

Various manufacturers of drives and harmonic mitigation equipment have downloadable tools for estimating harmonic distortion. You may or may not need drive input reactors to avoid problems. The small drives probably don't need reactors unless there are a lot of them.

As difficult as it might be, you may need to put in shielded motor cable for all of the drives or figure out how to separate the motor cables from everything else.



 
Here are some links:

NEMA Application Guide for AC Adjustable Speed Drive Systems
(free download)

Shielded Motor Cable
Ölflex-Servo-FD 780 CP
MCCMK
295xx (eCatalog-Industrial-VFD Cable)

Reactors and Filters
TCI – Trans-Coil, Inc.
Hammond Power Solutions, Inc.
Mirus International, Inc.
MTE Corp.
Bonitron, Inc.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor