AC drive causes nearby DC drive problems

[redwine47]

When my AB 1336 AC drive runs it causes instrumentation problems with my dc drive analog output current. The output current raises 30% whenever the AC drive operates. As soon as the drive turns off the DC current immediately drops to its 'correct' level. We have tried the normal noise reduction techniques the AB drive manual says to use but the problem persists. Any help here is appreciated. Thanks for taking the time to read my post.

 

[dpc]

It could be a lot of things. You haven't provided many details on what mitigation measures are being used.

One common problem is the main output feeder from the VFD to the motor. It is a powerful source of RFI, so it is runs close to the DC drive, it is a likely suspect, especially if not enclosed in its own steel conduit.

 

[zappedagain]

There are many potential solutions. You may have ground loops throwing off your measurement, so isolating the measurement may be the first thing. Can you run your current meter from a battery to isolate it? If you get the correct readings all the time then you need to work on a grounding issue. If you need an isolator check out Dataforth (SCM5B41-01 is a good starting point if it meets your signal requirements).

You may also have noise coupling, either radiated or conducted. That takes other solutions that I won't get into until you give more information on your installation.

What equipment is generating your "dc drive analog output current"?
How is the system wired?
What are you using to measure the DC current?

John D

 

[redwine47]

Thanks for the help so far. I will let you know after I see the drive this week.

 

[jraef]

One thing you may run into that is not the "typical" experience:

On larger sizes of the 1336, A-B used a phase angle controlled SCR based front-end converter instead of a typical diode rectifier. This produces line noise that most VFDs with diode front ends do not, so if your "noise reduction" techniques were based on a typical diode rectifier it may not be adequate.


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