AB VFD 700H Speed Control
AB VFD 700H Speed Control
(OP)
Good Day all:
A mechie coming over for some help.
We have two identical AB 700H VFD controlling 300hp motors operating in parallel in our material flow. I would like to reduce the speed, one will allow the change and the other will not. Is there a way to merge the good "modifiable" settings file to the other VFD drive?
Thanks
Mike
A mechie coming over for some help.
We have two identical AB 700H VFD controlling 300hp motors operating in parallel in our material flow. I would like to reduce the speed, one will allow the change and the other will not. Is there a way to merge the good "modifiable" settings file to the other VFD drive?
Thanks
Mike





RE: AB VFD 700H Speed Control
Keith Cress
kcress - http://www.flaminsystems.com
RE: AB VFD 700H Speed Control
Are the motors "stuck" running full speed or something else? What controls that on the one you can change?
RE: AB VFD 700H Speed Control
As far as I know the speed is being controlled by frequency selection on the HIM. Currently the speed is set at 60Hz on both, one can go up and down but the other one cannot be changed.
We have a PLC that can reverse the motors direction but it does not control the speed; too much variation for the guys in the plant will cause chaos.
itsmoked: Can you tell me the parameter number of the "prevents tampering" setting?
Thanks
Mike
RE: AB VFD 700H Speed Control
For example, you said "material flow" without any further explanation, which could mean any number of technologies. But let's say it is a conveyor belt with two 350HP motors at each end. It could very well be that one is allowed to vary the speed, the second one follows the first one strictly by using a torque reference sent out by the first. This is a very common application and if you mess with it, you end up with the two drives trying to fight the stretching of the belt, it will start to act like a rubber band and you will have chaos!
Get to the engineer that designed the system and ask ask ask...
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: AB VFD 700H Speed Control
Thanks for your concern but I am an experienced mechanical engineer and I mentioned that the two motors operate in parallel but without any feedback or closed loop controls.
Slowing down the motors is a valid process control parameter that has frustrated management for a little while now. Also the designing engineer is no longer available for questions.
Mike
RE: AB VFD 700H Speed Control
I would take a look at the analog inputs to see if there are any wires connected there. If there are, I suspect that that is where the drive is looking for its speed signal. Now, the challenge is to discover where those wires come from. Knowing that, you will probably know where the speed control resides and can probably deduce how to change it.
However, as jraef wisely cautions, if the speed signals are from two different places, it is likely that some kind of linkage or logic with something else is involved. At these horsepowers, you will need to acquire the "big picture" before making any changes.
Don't you just love it when you inherit a system with no documentation or reference people to consult!!
RE: AB VFD 700H Speed Control
The two motor conveyor application that you referenced is a very interesting one. With the 1 motor controlling the speed does the drive of the first motor control the speed and aquire a torque feedback using this torque feedback to send a torque reference to the second motor to pick up the slack of the remaining torque required to turn the conveyor? How does the first drive know how much additional torque is required?
In this application are there typically two VFD's one for each motor, or does on VFD handle each motor?
RE: AB VFD 700H Speed Control
When the helper motor is so configured, the drives automatically divide the load torque between the two of them and you have "load sharing".
RE: AB VFD 700H Speed Control
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies