VSD Overspeed on Stacker Hoist

Dear Friends,



I have the following situation which I find very strange with an ABB VSD that we are using on a hoist. The situation is as follows the hoist basically stacks plates into different bays..



Now the VSD that control the hoist motor was actually working fine till the following happened.. When the hoist move upwards everything is fine and it controls at the required RPM .. The problem is when I move downwards the unit just accelerates over the Maximum RPM and then Trips on Overspeed Even when adjusting my Maximum Speed Down to 600RPM the motor accelerates over 1500 RPM.



When I manually release the brake the unit starts moving downwards slowly which means my Gearbox is obviously not maintaining the weight of the hoist



Question

• What could cause this to happen.. No Parameters were changed on the VSD. Could it be a Hardware issue, or a faulty VSD

• Would changing the GearBox ratio help with the effect that Gravity has on the hoist and limit the acceleration.

Any advise would be well appreciated.



Kind Regards

Very strange.

Your VFD has an available torgue for accellerating or decellerating a load. With a reducer that allows the load torque to drive the motor when the brake is released, you are relying on this VFD torgue to overcome the load torque. If the motor starts to overspeed and gains momentum the drive will not be able to overcome it.

DickDV will be able to expand or correct me if I am mistaken.

1. What is the time between brake release and start signal to VFD when lowering. (should be zero)
2. Has the load attached to the hoist increased?
3. Does the same thing occur with no load?

Some types of reducers/gearboxes allow back turning and some do not.

More enlightening posts are soon to follow I am sure.

Good Luck,

Brian.

Typically on hoisting applications, the run command is given and up to as much as 40% motor torque is applied prior to allowing the mechanical brakes to release.

Most hoisting applications actually drive the motor in the lowering direction. The potential for the load to overhaul or overspeed the motor is always there.

What is being described leads me to believe the motor may not be getting powered by the vfd in the lowering direction and the brake is still being released. Getting the overspeed trip says the drive is getting powered, but maybe the speed reference is too low. On hoisting, the speed is usually applied to the digital inputs and preset speeds are programmed into the drive to correspont with the operator controls.

With NO load on the hoist, raise it to the highest point. Then have an operator sequence the lower speeds. Monitor the drive to make sure all speeds are getting to the drive input(s). See if the empty hoisting runs at normal speed(s) or does it seem to fall too.

Additionally, make sure the torque proving functions are working. If you do not get the torque built up before releasing the mechanical brake, you many NEVER get the motor to control the load.

While going up, the drive will provide additional amps to produce the correct amount of torque to lift. While going down, less power is required.

BTW, is the drive a normal VFD or a VECTOR control?

I strongly suspect that the DC Bus overvoltage control parameter 2005 is ON allowing the drive to alter the braking torque and decel ramp if the DC bus rises too high. This parameter must be OFF.

The drive must have snubber braking installed. With the above parameter changed to OFF, the snubber will see the rising DC bus and apply the braking energy to the resistor. The expected braking torque and decel ramp will be enforced up to the current limit of the drive.

If that doesn't do it, come back to the BBS and we'll try to help again. I am very familiar with this drive and can likely get to the problem with a little information exchange and trial and error.

Thank you

Thank you for your replies, i hav found the problem to be on the external dynamic breaking kit, the external chopper circuit was never removed by the supplier the drive already caters for this circuitry.

Thanks again

So what changed?

Sliver,Dick

NOthing really changed,that i am aware of. The unit is only a prototype thus far and was also not used excesively, We now removed the External chopper cicuit with only the resistor remaining as requested by the supplier, the problem remains though.

The fault that i am getting is a DC OVervoltage fault... when

When enabling parameter 2005 OverVolt control i get the fault VSD Overspeed Fault

Do i activate flux breaking ?? Would that help??

The system is now as follows, i use the internal breaking facility of the drive and have an external resistor connected to it..

Any ideas,

Thanks again

Rheinhardt