Motor Overload 1

[Paul2016]

Hi, im looking for some advice. The saw mill i work in has just been revamped and had new software installed, replacing the old company's program so all the inverter settings ect had been reprogrammed (all the motors have NOT been replaced). But we came across a problem with the stacking line motor. They have a high speed and low speed programmed which the new company have it running at.

High speed up - 60hz
High speed down - 40hz
Low speed up - 30hz
Low speed down 20hz

The speed of the motor seems to run ok (like before the revamp) but now with the new program while its stacking its suppose to stop at the sensor but when it stops it seems to drop 2-3 inchs after the brakes kicked in. The engineers and electricians are blaming the programmers set up, and the programmers are blaming the motor itself. The engineers have had it re-wound as it did have a ground fault and replaced the brake but it's still got the same problem. A new motor is being ordered but wont come until 3 weeks and may not even solve the problem. It ran with no problems before the revamp. Could the values be wrong? Is it possible the programmers have upped the values to much and damaged it when they tested it? Its suppose to hold the weight of at least 5 ton but it trips with an overload with not even 2 ton. The values have also been changed but still has the same problem

 

[waross]

If it trips on overload they may be using the VFD and a torque setting of zero RPM to hold the position.
" when it stops it seems to drop 2-3 inchs after the brakes kicked in."
You may have too much mechanical backlash.
Some mechanical brakes have a slight lag before applying. Thrusters were intentionally designed to have a lag and to apply slowly.
But if the brake worked before, it should work now.
If there is a delay in sending the brake signal, it is a programming issue.
If the VFD is used for holding, go back to the mechanical brake that used to work.
A pilot light (available in a wide range of voltages) across the brake terminals may help determine whether the problem is a slow setting brake or a late signal.
It worked and I changed it and now it doesn't work. It's not my fault.
How many variations of that have I heard? Let me count the ways!

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

 

[edison123]

Bill, indeed. And they burnt a working motor without even spending the money to get a VFD duty motor or at least getting the old motor rewound for VFD duty.

I am sure it was all done under the guise of 'increased productivity'.

To answer OP. It's not a motor problem, it's a control problem.

Muthu

http://www.edison.co.in

 

[jraef]

Hoisting applications with VFDs are not for the faint hearted. There are a lot of things about it that are unique to the application, including how it handles the setting of mechanical brakes. The VFD, used in the correct fashion, can be capable of 100% torque at zero speed, do that it can hold the load still until the brakes set. But to accomplish this feat, the VFD must use "Flux Vector Control". That then REQUIRES that the drive be able to accurately establish and maintain a mathematical model of the motor circuit. The model is established either manually by entering a lot of motor data that is often hard to find, or allowing the drive to "learn" the motor circuit information by testing, what's called an "auto-tune" procedure. If your drive was tuned to the motor, then the motor was rebuilt, the motor circuit is now different and if nobody re-performed the auto-tune procedure, the motor model is invalid now and the drive cannot perform as it used to. This is my first suspicion.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Paul2016]

what happened was on the monday everything was working ok just a few timing issues so the programmers stopped back to tweek them. Came in on the tuesday to a note saying 'elevator tripping please get an electrician to check it out' sparky came down and there was a ground fault. Engineers took off the motor sent it off to get recoiled, got it back then bam overload errors after a certain weight but when it does stack it drops 2-3 inchs passed where it should stop ready for the next layer to be stacked. Now the engineers and electricians have the 'they f**ked it, they mend it' attitude which i dont blame them but the programmers are wanting a new motor fitted. I'll mention the above to the programmers tomorrow. Cheers for the help lads.

 

[waross]

Nice Jeff. lps

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