Transformer current calculation help for In-rush and current consumption

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emiller233

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Location
pittsburgh, pa
GoldDigger said:
I agree. (Depending, of course, for what purpose the DC supply is intended.).
Click to expand...
Powers a VFD for a motor (see details below)

Ingenieur said:
Rated dc v is +/- 0.01% of full scale
for 330 vdc +/- 33 mV
that is tight
better be for $20k lol
Click to expand...
^^^^ i was thinking the same thing haha


I probably should have mentioned this as part of my original post so everyone had all details...!!!

these components that we are talking about are part of a 'Test Bench' for Bombardier's train which they will use here in the US and Canada, hence the reason this needs to run off of 600VAC or 480VAC (depending where they currently are using it)

i attached my Preliminary schematics (PDF) for the XFMR and Power supply section (breaker/wire sizes will change once we nail down the currents for everything...)

here is a diagram since i like visuals to help understand things...
NOTE: the way they drew the XFMR and Inverter(Power Supply) is not 100% accurate! The 330VDC Power Supply is 480VAC powered, not 240 as pictured
Test Bench Diagram.jpg

If they are in Canada, they will use the 600delta to 480/277WYE transformer to get the 480VAC.
If they are in the USA, they just use the shop supplied 480VAC,

either way the 480VAC supplies the power to this 'interesting' Power supply that we've been talking about that creates the CONSTANT VOLTAGE 330VDC output (which replicates voltage that they tell me is used ON THE TRAIN)

this 330VDC supplies power to a Yaskawa V1000 VFD. but it does so directly to the DC BUS of the VFD, not to the Line Side terminals that you typically use (I've never seen this before?). But at any rate, the output current (constant 330VDC voltage) of the 330VDC power supply will change with the demands of the VFD

the VFD produces a 208VAC that runs the 3-phase motor of a air compressor, which is used for just the braking system of the train

this 'Test Bench' will test all components of their Air Compressor's functionality (including the VFD that powers it). we can also bypass the VFD (for testing) and use their shop supplied 208VAC to verify the Air Compressor motor is functional

the 120VAC and the 110VDC on the diagram are the control voltages being used



so are we all on a agreement that the input amperage to the Power Supply @480VAC is 60.11 Amps? so i can calculate the current consumption as well as the inrush current to the 600VAC Transformer (when being used)

Transformer OUTPUT current (VA) = 60.11A x 1.732 x 480V = 50,713VA

Transformer INPUT current (A) = 50,713VA / (600V x 1.732) =


if my Transformer input current is 48.8A at 600VAC, what is the inrush current? Just from doing googling, it looks lke i should use 10x - 14x the current consumption, which would be an inrush current of: 488A - 683.2A

am i heading down the right path here...?
 

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Jraef

Jraef

Moderator, OTD
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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
So I have a question about your setup in general. You are feeding a VFD with the DC supply. Why? The VFD can have its own rectifier built in, so all you would need is a transformer ahead of it on the test bench to be able to feed it 208VAC from whatever your line source is. This seems overly complicated to me. In fact you could probably get away with using one transformer, sized for a 480V input, then when you feed it 600V, the secondary would be 260VAC feeding to the drive, which is well within the drive input voltage tolerances. Then you have the drive programmed to output 208VAC to the motor regardless of the input voltage.

And, by the way, you WOULD use a 208VAC input to that drive if you want a 208VAC output. Your 330VDC bus would be correct if the output was 230VAC, but for 208VAC output you only need 295VDC. Even so, you don't need a 480VAC input to a regulated DC supply to achieve that. The caps in the converter will hold it to 330VDC from a 240VAC input (or 295VDC from 208VAC).
 
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emiller233

Senior Member
Location
pittsburgh, pa
Jraef said:
So I have a question about your setup in general. You are feeding a VFD with the DC supply. Why? The VFD can have its own rectifier built in, so all you would need is a transformer ahead of it on the test bench to be able to feed it 208VAC from whatever your line source is. This seems overly complicated to me. In fact you could probably get away with using one transformer, sized for a 480V input, then when you feed it 600V, the secondary would be 260VAC feeding to the drive, which is well within the drive input voltage tolerances. Then you have the drive programmed to output 208VAC to the motor regardless of the input voltage.
Click to expand...

everything about this project is overly complicated!!! You should see the controls portion of this, twice as bad as this power section! haha

basically this test bench needs to be abe to run off of 3 diffferent 'Shop Supply' voltages , depending on what they are testing. it coule be 600V or 480V depending what country they are in to power the Power Supply, or they can use the 208VAC to test the motor only

it will typically run on 480VAC(use the 600to 480 XFMR when in Canada) to power the 330VDC Power supply.

this 330VDC power is what they typically use on the train(so they tell me?) , and this i really what we are trying to replicate. they Transformer and 330VDC Power Supply are used offline in their shop (not on board the train)

the VFD and Air compressor are typically mounted onboard the train doing their job, that is until they malfunction and then they will bring it to this 'Test Bench' in their shop for testing of the VFD and/or Air compressor

The 330VDC (supplied by the train) powers the VFD which powers the air compressor motor

they are using the 330VDC directly to the DC Bus on the VFD b/c they simply do not have 3-phase power available to them to use onboard the train. I didn't even know this was possible but the VFD people tell me that this setup works, just not a typical installation obviously...?
 
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Besoeker

Besoeker

Senior Member
Location
UK
Ingenieur said:
smart man lol
I do the same
is there a friends and family discount? :D
Click to expand...

I can be bribed.....
A little off topic tale that might amuse - mods be kind...
I got a call from my son.
"Dad, would you like to have Sunday lunch with us?"
"OK. When did you have in mind?"
"This Sunday."
Check with wife.
"OK. That's good with us."

"What do you know about dimmers?"
"I might know something....."

The long and the short, we purchased the parts, I did the repair, and we had a superb lunch. I think we got the better side of the deal................:D
 
I

Ingenieur

Senior Member
Location
Earth
Besoeker said:
I can be bribed.....
A little off topic tale that might amuse - mods be kind...
I got a call from my son.
"Dad, would you like to have Sunday lunch with us?"
"OK. When did you have in mind?"
"This Sunday."
Check with wife.
"OK. That's good with us."

"What do you know about dimmers?"
"I might know something....."

The long and the short, we purchased the parts, I did the repair, and we had a superb lunch. I think we got the better side of the deal................:D
Click to expand...

Lol
That's what dads are for
especially when they have highly sought after and expensive skill sets :D

at least you got a good meal out of it lol
 
Besoeker

Besoeker

Senior Member
Location
UK
Ingenieur said:
Lol
That's what dads are for
especially when they have highly sought after and expensive skill sets :D

at least you got a good meal out of it lol
Click to expand...
Irish stew - his lady is Irish - but made with the best cut of steak.

I'll come back to the sqrt(2/3) once we have agreed a suitable stipend...................:p
 
T

topgone

Senior Member
emiller233 said:
everything about this project is overly complicated!!! You should see the controls portion of this, twice as bad as this power section! haha

basically this test bench needs to be abe to run off of 3 diffferent 'Shop Supply' voltages , depending on what they are testing. it coule be 600V or 480V depending what country they are in to power the Power Supply, or they can use the 208VAC to test the motor only

it will typically run on 480VAC(use the 600to 480 XFMR when in Canada) to power the 330VDC Power supply.

this 330VDC power is what they typically use on the train(so they tell me?) , and this i really what we are trying to replicate. they Transformer and 330VDC Power Supply are used offline in their shop (not on board the train)

the VFD and Air compressor are typically mounted onboard the train doing their job, that is until they malfunction and then they will bring it to this 'Test Bench' in their shop for testing of the VFD and/or Air compressor

The 330VDC (supplied by the train) powers the VFD which powers the air compressor motor

they are using the 330VDC directly to the DC Bus on the VFD b/c they simply do not have 3-phase power available to them to use onboard the train. I didn't even know this was possible but the VFD people tell me that this setup works, just not a typical installation obviously...?
Click to expand...
Take a simpler path solving things. Basically, your DC-fed inverter will have losses and the AC amps input will just be the VFD output plus losses translated into AC. The usual practice is to always use the least possible AC voltage you can get from your source, here, if it's 480 volts AC, use 480 x 0.95 = 456VAC.
Lemme try:
AC amps input = (91A x 330VDC)/(456 x 1.732 x 0.69pf x 0.87eff) = 63.34 amps AC. That's a 50kVA transformer, 3-phase for you, at a minimum.
 
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