ABB ACS 800 Speed Limit In Torque Mode

jrexrode

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Join Date
Mar 2005
Location
Upstate, South Carolina
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106
Does any one know if there is a parameter within the ACS 800 drive that will limit the drive speed while in torque mode. We occasionally have web breaks that result in the drive "running away" that creates an unsafe situation. Parameter 20.02 (Max Speed) has no effect while in torque mode.

I know I can do this externally by detecting the run away condition and switching the drive to speed mode, just wondering if there was another way of handling this all within the drive.
 
I'm not all that familiar with the ACS 800's, but in general, on an AC Vector drive, if I need to command torque, but limit speed, I set the drive up as a normal speed regulator, and just control it's torque limits. Then I keep the speed loop saturated by always sending a speed command of whatever I think it should be + 10 or 20%.

This doesn't work though for dynamic applications that have to reverse torque though, for them I use a direct torque command, and kill the drive in the case of a web break.
 
You can detect a web break by monitoring for an UNDER LOAD condition and shut down. Torque control by definition eschews speed limitations, that's the entire difference. You NEED torque control for a web application, but when the web breaks, the drive tries to "find" the motor load by increasing the speed. So by triggerring on Under Load, the drive is constantly looking at the load and comparing it to a profile you entered, in which you TELL it what the motor load looks like with no web. If it sees that, it trips.

In the ACS800, that begins at parameter 30.31
 
Diameter is changing,load change

speed depend on product grade,

web weight depend on product grade

how the drive determine this
 
Could someone please explain "web break" as l am unfamiliar with this term.

Commonly used to describe a circumstance in offset "web" printing, the web is a long continuous roll of paper on which the printing takes place, after which it is cut. So imagine the images you may have seen in old movies when someone yells "Stop the presses!", the press they are referring to is a web press. The end of the toll is loaded into the machine and pulled through as images are printed on it at various stages. If the paper, or "web" breaks, it's a bad situation. It's not only web presses, the same term is used when describing any long roll of paper product being process, invluding converting (turning paper into cardboard) or even making the paper in the first place.
 
I would have expected Para. 20.02 to limit speed in Torque Control mode. If it doesn't, my next move would be a phone call to ABB Tech Service. There has to be a max speed parameter somewhere just like there is a max torque parameter in speed mode.
 
I would have expected Para. 20.02 to limit speed in Torque Control mode. If it doesn't, my next move would be a phone call to ABB Tech Service. There has to be a max speed parameter somewhere just like there is a max torque parameter in speed mode.
Dick,
You know more about the ABB drives than I do of course, but although I never used this with the ACS800, you can do it (albeit without DTC) in the ACS550 as well, which I have done. The motor won't necessarily run away completely, but when Torque Control is selected, the Over Frequency Trip will not activate until you are 50Hz over the maximum speed you set it at (in the ACS550 it was 120% of the Max Speed setting, so the ACS800 is different). That means for the most part, Torque Control takes precedence over the speed limits, so it will increase speed with no load, up to 50Hz over the 20.02 limit setting. That's why you implement Load Loss detection when using Torque Control.
 
P20.02 settings are not functional when the drive is running in Scalar Control Mode [Torque Control with Speed(frequency) Reference].
It makes you wonder why using an ACS800 in any other control mode than DTC?
I would look into P60.03(WINDOW SEL ON); this parameter, in conjunction with P60.02, P60.04 and P60.05 supervises the speed error values generated when within load loss conditions.
 
Last edited:
The preferred way to do torque control is to buy the Web Process firmware which sets up a speed window within which torque control operates. I don't know that I've ever used the Torque Control macro in raw form as the OP is attempting to do.

jraef, I don't doubt your observations about the max frequency and max speed but I'd be on the phone to Tech Service in a hurry if it was anything like 50hz over the max frequency parameter. There isn't a hint (that I know of) anywhere in the manual about that much headroom on overspeed.
 

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