480v to 600v sanity check

mobil1syn

mobil1syn

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need to run a 600v motor. I have a 480v soft start and step up transformer. is there any reason i cant put the soft start BEFORE the transformer?

my simpleton brain says, the transformer doesnt care where its at, its taking what you give it and moving it along the line.
 
My gut says if it’s a old school analog soft start you should be fine. A brand new one with a thousand safeties on if probably not. Should you do it that’s another question?


What size motor are you talking about?
 
I was told no by an electrician that had passed my question on to Eaton and got a response of "won't work properly". I wanted to use a soft start to ease the inrush current of a 550kVa 480-600v delta wye transformer that I'm frequently energizing and was told the inrush current of the transformer would be too high. That didn't really make sense to me, but I never pursued it further to get the details on why.
 
larboc said:
I was told no. I wanted to use a soft start to ease the inrush current of a 400kVa 480-600v delta wye transformer that I'm frequently energizing and was told the inrush current of the transformer would be too high. That didn't really make sense to me, but I never pursued it further.
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That can’t be any worse than the start up current of a 400 hp motor. The amp gauge gets buried when I hit that button. She’s a 1500 amp gauge :lmao:
 
ThePanzerFuhrer said:
My gut says if it’s a old school analog soft start you should be fine. A brand new one with a thousand safeties on if probably not. Should you do it that’s another question?


What size motor are you talking about?
Click to expand...

90kw

we backed ourselves into a corner and have to do a run test that is outside the normal scope of things, on motor voltage and size so im trying to come up with creative solutions to avoid have to rent a generator for a month.
 
ThePanzerFuhrer said:
That can’t be any worse than the start up current of a 400 hp motor. The amp gauge gets buried when I hit that button. She’s a 1500 amp gauge :lmao:
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i wonder if its because you are doubling up the startup between the two unless i put a knife switch in between the two allowing me to 'charge' the transformer before starting the motor
 
I’m thinking if you have the transformer as that’s the expensive part, a couple thousand dollar 600 volt soft start would be cheaper than renting a genset.
 
I always thought putting a knife switch on the output of vfd or soft start was always bad news. Like let the magic smoke out bad
 
ThePanzerFuhrer said:
That can’t be any worse than the start up current of a 400 hp motor. The amp gauge gets buried when I hit that button. She’s a 1500 amp gauge :lmao:
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Edited my post, it's actually 550kva and I've got a few of them. My main breaker is 3000 amps but that's the long term trip. I want to say the inrush current on one of these energizing is in the neighborhood 5000 amps. The estimate is that it the $10k smart breakers feeding them will start them about 2000 times before failing. I'm not sure what "failing" means but guessing it's bright.
 
ThePanzerFuhrer said:
I’m thinking if you have the transformer as that’s the expensive part, a couple thousand dollar 600 volt soft start would be cheaper than renting a genset.
Click to expand...

monthly rates
150kw generator - 4100
150kva transformer - 1000
200hp vfd - 2835

plus close to a 2500 in delivery/drop off fees

this is the first time ive had to run 600v, so buying a 600v soft start/vfd is a on time purchase. for a host of reasons, the less stuff we have in the building the better. they already collect enough crap

ThePanzerFuhrer said:
I always thought putting a knife switch on the output of vfd or soft start was always bad news. Like let the magic smoke out bad
Click to expand...

no idea, thats why im asking the question.
 
larboc said:
Edited my post, it's actually 550kva and I've got a few of them. My main breaker is 3000 amps but that's the long term trip. I want to say the inrush current on one of these energizing is in the neighborhood 5000 amps. The estimate is that it the $10k smart breakers feeding them will start them about 2000 times before failing. I'm not sure what "failing" means but guessing it's bright.
Click to expand...
There’s your problem smart breaker :lmao: I’m a big fan of the old school square d nema ****. That stuff is made for applications like this:lmao:
 
larboc said:
Maybe an obvious question, but are you sure the soft start you have isn't rated for 600V?
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dont have one yet. from my quick googling most are rated 208-480 and then jump to 575-600v, as does the pricing.

still looking if i can track down a 208-600v one for a reasonable cost in stock or short lead time ( this is the other problem, need to do this in late march/early april)
 
Another thing, have you considered just using an oversized contactor between the transformer and motor, maybe even an ebay special, and minimizing starts? 200hp isn't all that big to be line starting.
 
ThePanzerFuhrer said:
I always thought putting a knife switch on the output of vfd or soft start was always bad news. Like let the magic smoke out bad
Click to expand...
not sure on the soft start as its just regulating voltage, but the VFD will have a PWM output and those arent keen to being shut off improperly. weve done it, but definitely not in this circumstance.
 
mobil1syn said:
need to run a 600v motor. I have a 480v soft start and step up transformer. is there any reason i cant put the soft start BEFORE the transformer?

my simpleton brain says, the transformer doesnt care where its at, its taking what you give it and moving it along the line.
Click to expand...
simple answer is yes.

problem is, youre fighting the transformer inrush AND the motor inrush and the SSS might not push enough torque to initially operate the load.

can you start unloaded?
 
larboc said:
Another thing, have you considered just using an oversized contactor between the transformer and motor, maybe even an ebay special, and minimizing starts? 200hp isn't all that big to be line starting.
Click to expand...

trying to manage only 60amp breakers at the panel. the panel feed is 200amp i could go mickey mouse and tap the main but i dont want to be cast member at disneyland, because if you do it once do mickey here it becomes the way we do things
 
mobil1syn said:
trying to manage only 60amp breakers at the panel. the panel feed is 200amp i could go mickey mouse and tap the main but i dont want to be cast member at disneyland, because if you do it once do mickey here it becomes the way we do things
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60 amp breaker @ 480 volts is like 50hp, I'm confused?
 
larboc said:
60 amp breaker @ 480 volts is like 50hp, I'm confused?
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youre not confused, the math doesnt add up. im trying to make magic happen with grinding dust for management.

i suspect what is going to happen is i will have to find a refurb'd 100amp breaker for an outdate panel and wire up a disconnect to feed that weg soft starter. if i had time and could afford the downtime i would just replace the entire panel to something more modern and patched together.
 
Transformer is going to have inrush current and reactance the same way a motor would. Not sure how the soft start would play with the combination of both. Might work, might not, might be a pretty explosion. Would need to get detailed specs on everything and have someone with electrical background look at it.
 
mobil1syn said:
youre not confused, the math doesnt add up. im trying to make magic happen with grinding dust for management.

i suspect what is going to happen is i will have to find a refurb'd 100amp breaker for an outdate panel and wire up a disconnect to feed that weg soft starter. if i had time and could afford the downtime i would just replace the entire panel to something more modern and patched together.
Click to expand...
Still doesn't add up to me, to feed a 200hp motor via a 480-600 xformer you're going to need a 250 amp 480 feed unless it doesn't need deliver rated power and is going to start unloaded. Seems to me you may have trouble starting and running it on a 100 amp breaker unless you're using a VFD. Unloaded it's still going to be pulling close to 100 amps. Using a VFD would correct the power factor at light loads and might allow you to run it up to 75hp of shaft power on a 100 amp breaker with a 200hp nameplate.
 
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Another note, if you're going to be running quite a bit under rated power, why not just run the 600 volt motor on 480?

About twice the price of the soft start, but I would be strongly considering a vfd and derating the motor hp, which it sounds like your feed can't supply anyway.
www.ebay.com

Variable Frequency Drive VFD VT 200HP 132kW 264AMPS 480V IP20 w/ NEMA 1 KIT H100 | eBay

IP20 with NEMA 1 Kit. LS Electric H100 Series Drive. Variable Frequency Drive Chassis. Variable Torque / Normal Duty. Key Pad Included. EMC Filter Constant Torque Specifications (de-rated) horsepower, rated kilowatts and.
www.ebay.com
 
larboc said:
Still doesn't add up to me, to feed a 200hp motor via a 480-600 xformer you're going to need a 250 amp 480 feed unless it doesn't need deliver rated power and is going to start unloaded. Seems to me you may have trouble starting and running it on a 100 amp breaker unless you're using a VFD. Unloaded it's still going to be pulling close to 100 amps. Using a VFD would correct the power factor at light loads and might allow you to run it up to 75hp of shaft power on a 100 amp breaker with a 200hp nameplate.
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90kw - so around 120hp

200hp was just the option the rental company offered, so i ran with it for price comparison shopping. its overkill, but its in stock. 130 is in stock as well so i may save a few bucks and go that route.

1645639671953.png


larboc said:
Another note, if you're going to be running quite a bit under rated power, why not just run the 600 volt motor on 480?
Click to expand...

short answer is that we are duplicating a factory test on a piece of equipment, they did it at 600 so we have to do it at 600 to avoid a huge headache
 
Ahh, okay. That's making more sense. Line start the transformer with a 150amp+ breaker or tap the feed, and then line start the motor with a fused disconnect from the transformer. That little guy will be fine line starting unless you've got a massive load on the shaft, in which case it should be getting a VFD or soft start anyway.
Sure seems like you could buy a used dry transformer for the price of renting one for a month.
 
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so after laying out the options and cost there has been a change in plans. more information is starting to trickle out the project engineer.

turns out the pump has a 30 BkW rating, the 90kw motor was the smallest that would fit the job spec. so with the new information we are going to be running the test at 480v and the search is on for a budget VFD. anyone have experience with delta or galt vfds?
 
mobil1syn said:
so after laying out the options and cost there has been a change in plans. more information is starting to trickle out the project engineer.

turns out the pump has a 30 BkW rating, the 90kw motor was the smallest that would fit the job spec. so with the new information we are going to be running the test at 480v and the search is on for a budget VFD. anyone have experience with delta or galt vfds?
Click to expand...
No, but I did let the smoke out of a "FU9000" one time and it was spectacular. In hindsight I think one of the input legs was loose and I don't think the alibama specials have nearly the safety's or functions of a brand name, but if you make sure everything is tight, and are only running it in hand anyway you should be fine.
 
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