Motor gradually goes to overcurrent on drive 1

[quickee]

We have 5-5hp, 480v, 3ph, motors each running a vacuum pump. Each motor is controllers by an ABB drive, all identical. All 5 pumps work together, that is, each pump is connected in parallel, so if one pump/motor fails, the other 4 carry the load.

Generally all motors are running at 16% as indicated on the drives, except #3. It starts at 16% then gradually climbs to 60% and finally goes into overcurrent and shuts down after about 30 minutes. At present we are running 4 motor-pumps with no problems.

We have replaced the motor (kept the old one as a spare), replaced the pump, replaced the lovejoy (thinking major misalignment), and will now swap drives from one of the known working motor-pumps. (we plan on doing this in the next day or two).

The control work we designed and installed will increase the motor speed when more vacuum is called for in the ovens. Presently these controls are disabled.

We have had the vacuum lines checked for obstructions but none were found.

4 of 5 motor-pumps work fine and within parameters.

Thanks for any assistance.

Is there something we are missing? Have you seen or heard of anything like this in other applications?

 

[crthompson]

Have you tried reading the voltage and current on all three phases of the motor? If you have a single phase condition, the motor will gradually heat up until it goes out on thermal. When you said all motors are running at 16% did you mean 16% of thermal capacity?

 

[quickee]

Thanks! Yes we checked for single-phasing. 16% is rated current of motor.

 

[crthompson]

How long was this application in service before you started having issues?

 

[waross]

I would interchange two motors. That is swap the leads from the drives to the motors. That should differentiate between a motor/pump problem and a drive problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gattie]

Check all connections between Drive & Motor.
Could be a poor joint/connection heating up over time.

 

[ScusaMe]

..... Or it could be a 'process related' problem.


H-m-m-m-m-m-m.

 

[jraef]

SWAG#3

It almost sounds as though you have a PID loop controlling that drive separately from the others, i.e. someone may have programmed the INTERNAL PID loop inside of that drive (most likely it has one). If you take waross' suggestion and isolate the problem between the drive and the load, and it turns out to follow the drive, I would check into that.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[jraef]

By the way for future reference, no VFD that I know of would continue to operate the motor if one of the outputs was not connected, or even with unbalanced current. That is something that all modern drives protect against.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[quickee]

Here's a follow up to the original post.

We swapped output leads from a know good VFD to the motor and vice versa. The same thing happened leading us to believe the motor was bad.
This was a replacement motor and was new as in Feb 2012.

The VFD worked fine no problems on the motor it was temporary connected to.

When the technician removed the motor the lovejoy fell apart. We now suspect improper alignment, loose motor mounting and a host of mechanical problems.

Will update when new parts arrive and are installed.

Thanks for the help!

Tim

 

[itsmoked]

Thanks for the update.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[quickee]

We replaced the lovejoy, aligned the motor and pump shaft and secured every nut & bolt. The vaccum pump has functioned on and off for the past 4+ months. Some days it works fine others it goes into overcurrent. This is one of 5 pumps for a system. the system runs well enough on 4 of 5 so there was no major hurry to discover the real problem (customer did not want to spend the money).
Customer called a week ago. I called a pump friend of mine and we all met at the job site.

The pumps are designed to be run at 1070 rpm not 440 rpm as they are now. We closed off 3 of the pumps on the manifold, and increased the rpm on 2 motors to 1070 rpm. The 7.5hp motors amperage decreased, the vaccum increased slightly and everyting seems to be normal. We are monitoring the system but have found no problems since increasing the motor rpms.

This is a system we inherited.

Just thought I would let you know where we were with this.

Thanks!

 

[Compositepro]

Do you even need the VFD's? They may be using more energy than no VFD. The energy used by most vacuum pumps depends on the flow through them, which depends on your process. If no vapor goes through the pump then the motor is basically under no load at full speed. This explains your recent observations.

 

[LionelHutz]

Hmmm, sounds like someone got the bright idea that running 5 pumps at a slow speed would take less energy than running the 2 pumps at the designed speed.