I have seen a recent increase in amplitude at 2 x line frequency on several dc drives recently. The amplitude at 7200 cpm is sidebanded by what appears to be 2 x the output speed of the gearbox (150 cpm). The resolution of the readings is not a fine as I would like (12000 cpm fmax/400 lor) and I plan to collect some better data. Even so, there is nothing else that might vibrate at or near 7200 cpm.

There are no significant amplitudes at scr frequency or other harmonics of line frequency that would indicate a drive problem.

These are small motors and probably permanent magnet and I think shunt wound.

BTW these motors are c-faced (hollow input shaft) to right angle worm drives that are shaft-mounted to machine rolls.

I'll post some spectra in a few minutes.

Any ideas what might be going on here?

This message has been edited. Last edited by: Danny Harvey,

crdrive.doc (48 Kb, 26 downloads)

Danny:

Have you taken previous spectra on these machines? Or, is this the first time?

Are these half-wave rectifiers? And, is it fed by single or three phase power?

Yes, I have seen these type of signatures before, both in vibration and ESA.

Howard

Howard,

You must have replied while I was posting the spectra. Please take another look.

Previous spectra show no real significant changes over the last few years in the acceleration spectra to 120000 cpm fmax. The amplitude at 7200 cpm has been a gradual increase from .03 ips to about .3 ips in about 2 years. That trend has accelerated recently.

I believe that these are full wave rectifiers with 6 scr's. That is not positive and although I have asked that question in several different forms, I'm still not sure that my client understands the difference.

Thanks again,

Danny

Danny

If the motor is less than 5hp and is PM (must be either PM or shunt not both) it is likely a 1ph drive, I am pretty sure there would not be 6 SCRs. What make is the drive?

One possibility that may be easy to check is for loose connections on the AC side of the drive, if it is one of those small drives (looks like a circuit board) and the connections look OK, and they have spares, swap the the drive out and see what happens. Make sure all of the drive settings are the same. In the meantime also see if the commutation is OK.

Alan

Alan,

I think you are probably right, but my client says it is a 480vdc (sic) input. I got the same response when I asked the if it was a full or half wave rectifier and how many scr's-"Huh?"

I'm almost sure about it being a pm motor and they have lots of Fincor drives, so I suspect it is something like the 2300 if I recall their nomenclature correctly.

Danny

According to Fincor's Website a 2300 series drive is 1ph (120 or 240) and is non regen.

Is it spring in your neck of the woods yet?

Regards,
Alan

Alan,

That is what I am telling them, but they insist that it is 480 volts direct current. Have you ever seen 480 vdc?

For now it is spring. It is about 70 deg and the crocuses are bloomed today, but calling for highs in the low 30's this weekend. I suspect you may have some more winter?

Danny

Danny

Anything is possible, but most small (FHP-PM)drives have 1ph AC input. Normally over 5hp they go to 3ph which could be 240/3/60 or 480/3/60 input (AC Side). Check the motor nameplate, if the armature is 90VDC then the drive is normally 120/1/60, If the armature is 180VDC the drive is usually 240/1/60. If the armature is 240 or 500VDC then the input is likely 240/3/60 or 480/3/60 (respectively), If the input is 3 phase then the fields are likely wound.

Spring (variable but still more pleasant than winter) is at least another month away.

Regards,
Alan

ALan,

That agrees with my recollection from my days in drive sales.

These folks are being stubborn about getting the real info on the drive. I guess they just aren't really that interested in an accurate analysis

I'm getting to the point where I have tried all I'm going to with these folks. If they will give me real answers, I will give them a real analysis.

Oh well. 45 minutes until it's beer thirty on the clock.

Cheers,

Danny

It seems to me very likely there is a problem on the power/supply or drive creating unusual ripple on the voltage.

I don't think there are any faults in the motor that can cause this (especially if you are sure the frequency is harmonics of line frequency).

Pete,

Let's say fairly sure it is 2 x line frequency. I need 12000 cpm/1600 lor and 120000 cpm/3200 lor velocity spectra, but don't have them right now. There are no other defect frequencies any where near there.

They might be able to change the drives out quicker than they can tell me what they are.

Any ideas as to what is a typical spectrum for the small drives like Alan is talking about? I had a hand in selecting some of the original drives in this plant in the '80's and there was really nothing special about any of them. I think the the Fincor 2300 series is correct.

I'll look further into them and see what I can find out.

As much as I'd like to, I just can't walk away, even from a client who shows no interest on their own part. It's a curse I'm afraid is shared by many of us here.

Thanks and have a good weekend,

Danny