VFD Oscilloscope checks

Hello. I am performing research that will lead to developing a program to record Baseline oscilloscope readings on our VFDs. We will record drive values approximately 2 times a year. I am presently recording input and output voltages, DC bus voltages, power supply voltages, and speed references. I will record an oscilloscope waveform of the input and output voltages. We will use this data to compare and hopefully predict possible drive failures. Would anyone have suggestions on further readings to record? Any suggestions would be greatly appreciated.

Drive Temp might be one to watch as well.

I dont know which drive and size HP you are using but I know there are quite a few that have a small fan on the heatsink. You might want to make sure that is part of the check. Youd be surprised at the problems that are created if this fan stops working.

PaperMiller said:

Hello. I am performing research that will lead to developing a program to record Baseline oscilloscope readings on our VFDs. We will record drive values approximately 2 times a year. I am presently recording input and output voltages, DC bus voltages, power supply voltages, and speed references. I will record an oscilloscope waveform of the input and output voltages. We will use this data to compare and hopefully predict possible drive failures. Would anyone have suggestions on further readings to record? Any suggestions would be greatly appreciated.

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Recording drive output waveforms sound like a huge waste of time to me. I would think a candid conversation with the drive manufacturer on recommended maintenance practices would go a lot further and be a lot simpler.

Unless you are an expert on IGBT's and power diodes in parallel and the waveform behaviors that they exhibit when they age, there is little useful information that can be gained on the motor leads.

Also, if this is a 460V system, be sure your recording equipment is good to 1600VDC. Some of the pulses could go that high!

What's the point?

Either you systemically replace the drives or you wait for a failure...There is no in-between. I agree with DickDV, I don't think a scope is going to tell you much about a drive that is close to failure. Unless your an expert IGBT's and diodes don't wear, they fail. (for practical purposes)

I think the best thing you can do is when you go around to all the drives is the following:

1.) Make sure the manufacturer's installation specifications were adhered to when the drive was installed.

2.) Make sure cooling fins are dust free.

3.) As previously mentioned, ensure fans are working. (many drives can be set to fault or alarm if the fan fails.)

4.) Make sure lugs are torqued properly.

5.) Ensure the enclosure temperature is not too hot.

Greg

One utility you could use is the drive explorer for the series of drives you have this will allow you to get baselines on temperature and siome of them will allow trending on the amount of output current used during application. Cleaning the heatsinks regularly will also allow longer drive performance I would record the current usage as opposed to looking at the waveforms a large amount of drive failures is a result of a poor motor. Regularly clean all contacts in at the motor, junction boxes and at the drive itself. Also check the fault logs on the drive itself it will often indicate problems

I agree with mordred.
I took it that the scoping was to monitor motor condition, not drive condition. Doesn't matter, the point is the same. I'll be blunt - scoping sounds like a waste of time and resources.
To predict motor failure, you monitor current draw. Higher currents are caused by bearing wear, lube gets low, one winding is slowly burning up, etc.
All of this can be monitored and plotted by simply logging current feedback parameters from the VFD. My brain says current, but monitoring voltage may also work. Either way, a scope isn't needed.

here is a useful site that specializes in VFD/motor testing

http://www.pdma.com/oldart.html

there is some documents showing the various waveforms with types of problems you can see they also go extensively into spectrum analysis naturally they are trying to sell their products however it does contain lots of useful info