PowerFlex 400 Will Not Come Up To Speed

JKS

Member
Join Date
Dec 2014
Location
Portsmouth, NH
Posts
56
Gentlemen;

Have a bit of an odd one - a customer has a PF400 running a vacuum pump motor. They said they changed the motor out 3 months ago, and then at some point, the drive died.

They then changed out the drive with a brand new PF400, and it ran fine for about a month, at which point it would not reach the commanded speed, and in fact would only get to about 4-6 Hz.

They pulled that drive and sent it back for analysis/repair as it was still under warranty, and put in a re-manned from AB.

This drive is doing the same thing - it will not get above 4-6Hz, yet pulls about 80A. Here are the specs:
PF400: 22C-088A: 60Hp, 480VAC, 90.0A
Motor: 60Hp, 460VAC,65.1FLA, 3560rpm

Notes:
- It behaves the same in manual as it does in Auto; ie, won't ramp past 6 Hz
- It does not sit at that speed but rather bounces around between 3-6Hz
- The speed of the motor is 3560rpm (per nameplate) but they had it in the parameters as a 4 pole motor (fixed, obviously)
- A170 was left as Default; when I tried to run some boost to it, (via either a Custom V/Hz curve or a pre-set boost curve), the drive would trip out on Overcurrent immediately on start. Fault current was 162.5A.
- The motor seemed to megger fine: insulation tests from each phase to ground were in the 40Meg range (40 @ 1000V; 45 @ 500V).
- the motor did, however, feel hot and smelled burnt, but that could simply be from running at a low speed (it is a TEFC motor).
- The motor bearings are grounded.
- You can spin the coupling by hand, in both directions, with no effort.
- They tried to run the motor de-coupled and everything acted the same way.
- I ran the drive with the motor leads disconnected and the drive acted Ok; ie, it ran up to the commanded speed.
- Whether in manual or auto, the commanded speed is correct.
- There were no other errors to the parameters that I could see. They had good documentation that included a list of non-default parameters, and it all checked.

Anyone with any good ideas here? We dealing with some odd gremlin in the drive, or a bad rebuild on that motor? I'm open to anything at this point!

Thanks!
- Jeff
 
Megger the motor, motor leads... I'm betting on it being one of those.

Sounds like the VFD is in current limit. Check what that is set at.
 
Current limiting so check for any obstructions in the line that are working against the pump. Is there anyway to not restrict the pump to where its just rotating? When you do that you can isolate if its the pump motor or the mechanicals around it causing a restriction.
 
Current limiting so check for any obstructions in the line that are working against the pump. Is there anyway to not restrict the pump to where its just rotating? When you do that you can isolate if its the pump motor or the mechanicals around it causing a restriction.

Restriction in a vacuum line? Wouldn't that just allow you to reach vacuum sooner (less atmosphere) or am I not following correctly?

And the customer said that they ran the motor un-coupled from the vac pump and still got the same results.

Current limiting: I've seen this multiple times in my research; am I to understand this as the drive is protecting itself by limiting it's output because there is a mechanical overload?
 
Did you check continuity on the motor leads from the VFD to the disconnect, disconnect to the motor? I don't remember how a single phased motor acts on a VFD.
 
This drive is doing the same thing - it will not get above 4-6Hz, yet pulls about 80A.

Are you measuring at the infeed to the VFD or at the motor leads?

- The speed of the motor is 3560rpm (per nameplate) but they had it in the parameters as a 4 pole motor

Was the original motor a 3560 rpm unit?

- the motor did, however, feel hot and smelled burnt,

Not a good sign, I have had motors that smelled ok but would not run. But every motor that I had identified as burnt has failed.

They tried to run the motor de-coupled and everything acted the same way.
- I ran the drive with the motor leads disconnected and the drive acted Ok;

What you are describing sounds like a "first turn short". See if you can find a motor shop with a surge tester. Your motor sounds like it's around 60 hp, can you round up a good motor somewhere in the 20 to 60 hp range and temporarily hook it to test (no mechanical load) the VFD?

I'm open to anything at this point!

Thanks!
- Jeff
 
You need to do a surge test as well as perform a polarization index test on the motor. Also a dielectric absorption ratio test would be helpful. A spot check to ground only tells us that there's not a ground short. It doesn't tell us much about the integrity of the winding insulation.
 
I would quickly wire up another motor right at the drive to see if it will run it. Cut out the existing motor circuit and just prove that the drive will ramp on on any other motor/motor leads.
I had a similar situation a few weeks back with a powerflex70. Motor occasionally, but more often than not, would hang at 17HZ but draw big amperage, even tripped the shear pin fault a few times. It was when I decided to connect another motor at the drive when I noticed a terribly loose connection on two of the drives output terminals. The wires were barely in the terminals at all. Tightened, problem solved!
You are describing very similar symptoms to what my situation had.

Check connections, and motor lead!
 
How is the motor wired? Delta or Wye? When using a vfd if i remember correctly it needs to be wired for Delta. Ive been in plants that had the motors connected in wye(start) configuration to a vfd and the motors were scorching hot and burnt out prematurely. Id probably start there especially since you said the drive behaved correctly with motor disconnected.
 

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