# VMX 1250A Softstart Setup 900hp



## Darylbnet22 (May 9, 2007)

Anyone familiar with a MotorTronics VMX 1250A soft start, I have one installed starting a 900 HP GE motor at 888amps, 480v, we basically have it setup at the factory settings, and the thing kills our poor Gens at 800kw each parallel...

We replaced the original kick start setup, which used x3 1200amp breakers, Start,Y,Run, which hits the gens. hard, but no where near 
the 2500 instant from the soft start, motor runs at 270-280 online...

We were spending too much to repair the old GE breakers, 
and replacements are obsolete...

If anyone can help I have all the input data on the setup...
Thanks... D...


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## Big John (May 23, 2010)

Silly question: Have you tried disconnecting the motor and just powering the soft start alone? It definitely shouldn't be drawing instantaneous current like that, and I wonder if this thing has a big DC bus with a damaged pre-loading circuit: Uncontrolled inrush on large capacitors can look like a short circuit.


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## Darylbnet22 (May 9, 2007)

I am offshore, going off shift, I will be back online tomorrow morning, for any replies, D...


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## Darylbnet22 (May 9, 2007)

The motor is connected to x2 DC shunt motors for a DC Gen/Motor drive setup, the bearings are free rolling, so free that it can be turned by hand almost...
Un-coupling the motors is not a simple task, lol,,, 
I am looking for any changes that I can tune, to ramp this motor smoother, or even use the kick start feature of the unit, if the kick won't knock one of my Gen's offline...
As a novice at this setup, we know changing the initial voltage, will change the force, but as the unit is working, we are hesitant to make changes... 
Currently we have it on a Ramp1 Voltage ramp at 60% with 5sec. ramp time, FLA set at 900A and Current limit at 320% 
We have started the motor approx. 10 to 12 +times, successfully...


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## micromind (Aug 11, 2007)

Some observations.....

1) Do the gens have any other electronic loads on them? VFDs, other soft-starts? I ask because if the gens are anything other than 2/3 pitch, they won't handle electronic stuff very well. 

2) Since the driven load has considerable inertia, the ramp time is too short. I'd go at least 10 seconds if the driven load can handle it. Even longer would be better. 

3) If it'll allow the motor to accelerate, I'd set the current limit lower. like maybe 200%. If 320% almost starts it then a bit lower will load the gens less. 

4) Don't use the kick-start. it'll place almost an across-the-lines load on the gens. 

In reference to (1) above, does starting the motor lug the gens engine or does it trip out on some sort of fault? Often, if the gen is not 2/3 pitch, the non-sineusodal waveform from electronic equipment (the soft-start) will confuse the regulator and it'll either lose its field or just trip. 

What brand is the alternator end of the gen? If it's Marathon or Stamford-Newage, it's very likely 2/3 pitch. If it's Caterpillar, especially an older one, it's likely 3/4 or even 4/5 pitch and it won't handle much of an electronic load. 

Rob.


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## Darylbnet22 (May 9, 2007)

LoL, Umm ok lets see,,, 
1. No other VFDs or any electronic starts...
2. We have tried a longer ramp with a Toshiba we have on our crane gen's and the longer ramp caused the initial rotation/amp load to trip out the voltage regulator card... It would not damage the vreg. but the 10sec max load would trip and we had to cold restart it, to get it back online each time, now that Vreg is Stamford SX421... The Vreg on our main gens are Basler SR8A, we have not had an issue of them tripping or blowing a fuse, but if not properly paralleled with each Gen, one will drop and sometimes this drop of the load off to the other Gen cause the other breaker to drop, as they have cycle limits that will drop the breaker... We have been very persistent on our load sharing setup, so they will handle the surge... 

3. I will monitor the next start-up more, and see how this ramp is moving the motor, at the start, to verify what force it is actually giving it...

4. As stated our other two motors are still setup on the kick start breakers, but yes, the 6 lead motor on those are split out to bump the leads to get it moving before bringing them back in the run mode. We have been reading over the ss manual which is available online I am think, and these new units have a lot of ramp/kick variations, so we were looking at a possible half or full V. kick for 1 maybe 2 sec. then bring the ramp on... On our Toshiba F11, Initial voltage at 60%, we ended up increasing this to 70% to reduce the starting amperage... 

x Our Main Gen's are Columbia Electric ones, state of the art, true gen's, lol,,, 800kw, 1000kva, so my guess is they will be 3/4 or 4/5 pitch, but they are holding long enough to get it started and running, #1 gen hits 1500a and #2 pegs 2000a on our sweep gauges... 

Thanks Rob, for your input...


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## Darylbnet22 (May 9, 2007)

And Yes, Rob, now you have me googling pitch, which I see makes a difference with our Gen's parallel factor, something we will have to watch for in finding a replacement for one of the Gen's we have down now, and setup of the 4th Gen, they want to add onboard...
Thanks Rob... 
Ps. on the info sheet I found from ABB.com library, it is a little confusing on what they mean by fully grounded, being on derrick barge, I would assume ours would be more to the not fully grounded type, would that be correct...?


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## Darylbnet22 (May 9, 2007)

Classic...


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## Darylbnet22 (May 9, 2007)

Main Gen Classic...


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## Darylbnet22 (May 9, 2007)

We are currently offshore working projects, but would like to do some adjustments in the coming months when we shut down for winter...


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## JRaef (Mar 23, 2009)

I actually know a lot about the VMX, I helped design it...

Screw the Kick Start, we put that in only because other mfrs had it and we had to match specs. It does nothing useful in 99% of the applications. Turn it off.

Do you know what amount of current your generators can handle? If so, set that as the Current Limit setting, then turn the ramp time to ZERO. Yes, that's right, zero (which is actually .1 second). The VMX will go into current limit and stay there until the motor accelerates and current drops naturally, or shut down after 30 seconds to protect the soft starter. If it accelerates in less than 30 seconds, close the door and leave it. If the starter trips off line at 30 seconds, wait and try it again at 350%, repeat until the starter doesn't trip. If after increasing it like this, the generator trips off line first, then you cannot start this motor with that generator and a soft starter. But given that you WERE starting it with a Y-Delta, that's going to be highly unlikely. If it accelerates in less than 5 seconds, you could try turning the Current Limit down to 250% and try again, but only if you want to.dont bother with less than 200%, that only works on totally uncoupled motors.

If you DON'T know what the genset can handle, start by using 300% of FLA and try it. If it works, leave it. Remember to wait 30 minutes between starts though, maybe longer if that motor has a low Starts-per-Hour rating.

The reason why you set the ramp time to Zero on this is because when using Current Limit, the ramp time represents a ramp INTO the current limit, which basically consumes thermal time without doing useful work in accelerating it. Ramp time is for when you need more mechanical softness, like on a pump to prevent pressure surges or a conveyor to keep product from falling over. None of that applies here, you don't need it. What you need is to maximize the acceleration within the limits you have in the generator and the soft starter.


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## Darylbnet22 (May 9, 2007)

Awesome information, we will definitely test these settings out...

As for the Max current on the gens, we have them paralleled with 600amp split, 300a each, then starting the soft start, it's display shows 2500 for 3-5 seconds of the ramp, so if this is not tripping my Gen breakers or Vr's, I am guessing the max is 3200a or very close to it...
The mains for the gen's are 1500 each...
I know the 2500 is very quick and isn't holding long enough to let the mains trip...

Will this .1 sec be long enough to amp the motor into rotation, guess all we can do is see...
On our ramp the voltage is set at 60% on F11, the factory rep kept telling us to leave that at 60%, on the Toshiba, and no matter what we did, we couldn't get the starting amps to come down, on a compressor, but also that compressor was trying to start loaded, which we later found out...
Is the 60% ok, or can we up that to reduce amps as well ?

THANKS for your assistance...


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## Darylbnet22 (May 9, 2007)

Also in forgot to ask, we are using F10 setting 1, for VR1 voltage ramp, would using a setting 2 CR1 current ramp be better at the same settings of 300 current limit ?
Factory on the Initial CR ramp is 200% ...


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## JRaef (Mar 23, 2009)

No, that is the Initial Torque setting IIRC, which just means the place where the voltage jumps to immediately. In a Current Limit start arrangement, that means next to nothing, so leave it alone too. For reference though, the way you set that is to find a level at which the motor shaft just BEGINS to move, because starting a ramp from any level less than that is again, just consuming thermal capacity with no useful work. Your motor can only handle so much heat, so if you are ramping, applying voltage to the motor without getting anything out of it is going to decrease the overall energy the motor can handle to accelerate the load. So you always want to BEGIN that process at the point where it has an immediate effect.

But again in this situation with no ramping, it's irrelevant.

Back to your settings though, 3200A is roughly 355% current. If it were me, I'd still try it at 300% first, it might work and if it does, it's going to be easier on everything.


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## Darylbnet22 (May 9, 2007)

Again, thanks for the knowledge, we will test out these changes...
We are online and operating offshore at the moment, 
but this incoming weather in the Gulf may give us the time soon, 
to shut it all down and try it out...


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## garfield (Jul 30, 2009)

As Jraef said we used current limit on a 200 hp rock crusher with a weg soft start instead of voltage ramp and it dramatically reduced inrush amps.


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