Softstarter in Conveyors

[Freshsurfer]

Hi, I'm working on a conveyor belt specification where the client is asking to use a softstarter for its motor.

Even a softstarter have the option to set 2 starts mode; 1 with low load and 1 full load, I'm not sure if working with the full load start mode will stress the mechanical components of the conveyor.

Somebody have more experience in this kind of configuration?

 

[ScottyUK]

Is the conveyor required to start in a laden condition, or light?

 

[GroovyGuy]

Hi FreshSurfer,
How large is the motor expected to be(ie in hp or kW)? Is there a fluid coupling on the mechanical drive train?
Why does your Client want to install a RVSS-starter? (ie so as to not beat-up the drive system, or to limit inrush current due to Utility concerns?). Seeing that he has asked you to provide a RVSS starter for this particular application, I assume that he has done this sort of thing successfully before, correct?

A RVSS may, or may not, be the best solution for a conveyor, depending on the size of the conveyor. A fluid-coupling or a VFD might be a better solution.
I have seen lots of failures of conveyors that have stalled out (ie failure to accelerate due to insufficient torque being developed by the motor). Note; I have seen these failures on systems with VFDs and fluid-couplings as well as RVSS systems).

Scotty: I have never seen a conveyor application where the drive was not called on (from time to time) to accelerate a fully-loaded conveyor.

Regards,
GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[Freshsurfer]

Thanks GroovyGuy,this conveyor doesn't have a fluid-coupling, its a 150hp in LV motor.

I believe that the client wants to save money by using a softstarter instead a fluid-coupling.

My concern is on the acceleration time of the motor, how the motor acceleration time is affected when using a softstarter?

Scotty: Yes, the conveyor might start on a full load condition.

 

[LionelHutz]

how the motor acceleration time is affected when using a softstarter?

The time will be longer if you limit the motor current or reduce the motor voltage. What is possible and how much of an effect happens can't be answered without the motor and conveyor data.

With a directly connected motor, the conveyor (or any other load) will not start if the motor is not capable of producing enough torque to accelerate it. This applies regardless of the motor starting method.

A good soft-starter can limit the torque between the motor maximum possible torque down to a level that is too low to be useful. So, a good soft-starter is able to start it the same as a full-voltage starter, if full-voltage actually is required. The maximum torque I'm referring to comes from the torque vs speed curve the motor manufacturer should have given you. You have to adjust it for the actual available voltage during the motor start when the current is high.

 

[ScottyUK]

GG - I've seen enough folks with shovels unloading a conveyor that wouldn't re-start to ask the question. ;-)

 

[davidbeach]

You have to assume that's the fate of every conveyor at some point in its life.

 

[waross]

The worst case I saw;
A waste sawdust conveyor was overloaded to the point that it stalled.
A millwright took the guard off of the coupling between the motor and the reduction gearbox.
He proceeded to spin the coupling backwards with his foot until he took up all the back-lash.
Then he hit the start button. The motor came up to speed and started the conveyor moving. It went about three feet until it stalled.
The process was repeated. I was called by the maintenance super and told to get up there with a spare 10 HP motor and all tools needed for a quick motor swap.
I don't remember but we were probably using an air hose to keep the overload heaters cool.
The millwright was able to clear the conveyor, three feet at a time, and get the mill back into production without the motor failing.
Oh how I miss the old "U" frame motors.
In the debriefing, the Super explained that the cost of downtime was so high that the time saved by abusing the motor more than made up for the possible cost of a 10 HP motor.
That was a long long ago.

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

 

[GroovyGuy]

Yes Scotty, that was me shovelling off a 9000TPH coal conveyor after it was overloaded and couldn't re-start (and it was equipped with a VFD). Apparently one of the mechanical engineers forgot to adjust the apron feeder.

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[edison123]

Never understood the 'cost cutting' concept behind such critical machines.

Muthu

http://www.edison.co.in

 

[ScottyUK]

davidbeach,

I agree that a conveyor should be capable of restart in a laden state. Experience suggests it isn't the reality, or at least the assumptions about conveyor loading made during design aren't accurate.

GG -