Temporary service shortcoming 120kW VFD

[itsmoked]

I'm assisting a small start-up company. They failed to give proper consideration to the power demands of a 160HP extruder. It's driven by a BIG Schneider VFD.

They're working on getting 480V service brought in but in typical PG&E service land it may take a year or more to happen. They're hoping they can modify their process so they can limp-along with only about half the full power requirement available.

They'll only have about 80kW for a while. This is a screw extruder that spews starchy foam.

The questions are:

1) Do you think they can start the motor and run the completely "unloaded" (empty) extruder?

2) Anyone have any gut feeling for if they could process anything at all? (I know - a long-shot guess but maybe someone has been in the same sort of boat.)

Keith Cress
kcress -

http://www.flaminsystems.com

 

[RedSnake]

To know, you/we need the data sheet, manual on the 160HP extruder.

"starchy foam" hmm.. chees doodles.. big ones mmm mums..

Best Regards A


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[LionelHutz]

The VFD is a power converter, near zero speed there is very little shaft power so the power draw from the source will also be very little. What's the no load shaft power draw as it accelerates? That's what you'll draw from the utility. Most likely, not much with it unloaded.

 

[Gr8blu]

There should be no issue with starting the unloaded extruder - as long as there is sufficient voltage at the motor terminals. Output torque is going to be proportional to the square of the terminal voltage (in per unit terms). What that really means is the volt/hz has to match up to develop the right amount of torque. On a drive, low frequency corresponds to low voltage, with current being regulated to some appreciable portion of full load. Therefore, the motor should be able to bump the driven load into motion and keep it going - as long as the extruder remains "empty". Whether the extruder will properly cool without material throughput is another can of beans.

Usually, the extruder load is related to the "thickness" of the material being processed. Heavier/sludgier (is sludgier even a word?) material means more load on the screw, hence more power from the drive motor. Sou ds to me like they have a specific consistency for their material, which would require something like 125-150 hp to "properly" create the end product. They could - assuming the motor is constructed correctly - operate at reduced frequency and therefore speed. This means it takes longer to process a specific amount of raw material. Will it be moving so slowly it will solidify again before it gets out the other end? If so, they're further behind than when they started since they'll have to clean out the extruder and start again. If it won't get too sticky and bind up the works, they might be able to operate at about half speed or so for some (shorter rather than longer) period. They might also have to run some shifts and not others (meaning it won't be a 24/7 operation which is what I think they were originally intending).

If the motor was not intended for operating at reduced speed for extended periods, then the user is going to be stuck until they get the correct infrastructure.

Converting energy to motion for more than half a century

 

[itsmoked]

Red; The manual is in Chinese..

Lionel; Thanks for confirming my expectations just about exactly.

Gr8blu; Thanks for the info. Seems things to especially look for are::

A motor that can actually run not at nearly full speed and not flame-out due to cubed fan laws. Means I need to check for aux cooling.

I could see things kind of piling up somewhere in the extruder until maybe the string is packed up enough to force things further thru. Sort of self-requiring high torque for anything to make it out the end. This extruder chain is about 20 feet long. Could be you could dribble stuff into the input and nothing ever comes out the end until the whole thing loads up and crams everything out the nozzle. They could see 40kW, 40kW, 45kW, 45kW, 100kW suddenly spewing finally. I better have more talks with them about the details of their process.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[RedSnake]

Red; The manual is in Chinese..

I could always use google translate.. LOL

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[waross]

They could see 40kW, 40kW, 45kW, 45kW, 100kW suddenly spewing finally.

Keith, with restricted input power, wouldn't that be:
1760 RPM, 1760 RPM, 1760 RPM, 1720 RPM, 1100 RPM, 900 RPM?
Lightly loaded, the machine will run full speed.
As the machine loads up, the RPM will drop until the torque output equals the load demands.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Pud]

Is the screw not driven with a hydraulic motor? All extruders (for plastic/rubber) I've seen have such.
I know direct drive for injection moulding machines are quite common.



Politicians like to panic, they need activity. It is their substitute for achievement.

 

[jraef]

(is sludgier even a word?)

Higher viscosity...

I agree with Gr8blu, starting it with the VFD will likely be no problem, but running it might be the real issue. You can program most VFDs to Current Limit, so in this case set the CL to your supply capacity, and most motors will start up unloaded with a VFD at 10-30% of FLA. I have started 1a 100HP unloaded motor with a 10HP drive on one occasion. But what the VFD will do under load to keep the current down is to limit the output frequency (and with it, voltage), giving you full torque capability but at some severely limited speed. Whether or not that works for your foam extruder is not something that is electrically determinable.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

You might be right Bill!

Pud; That's what I tend to see too, but my experience mostly with injection molding. Big time screw followed by a major hydraulic shove.

In this case it's a trashcan size motor right into a trashcan size gearbox that mates with a 20 foot long 5 inch diameter screw that runs thru about 14 heating /injection stations and out a 2" x 4" machined 1/2" thick screen.

Jeff; Thanks for that confirmation and the current-limit point. That parameter will help a lot.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[FacEngrPE]

Keith you might also want to try power limiting.
The Max Amps setting usually limits motor amps, not line draw.
Power limiting would limit input kW, and if voltage is constant, current would then be limited.

Schneider likely publishes the VFD Manual in English.
Try looking here

https://www.se.com/us/en/download/

 

[itsmoked]

FacEngrPE; Very good point and definitely different then a current limit. Thanks for that tip.

Keith Cress
kcress -

http://www.flaminsystems.com