480 to 600 Transformer help - for testing a system

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Electric-Light

Electric-Light

Senior Member
emiller233 said:
this machine is fairly basic, it is a 'Test Bench' for testing an Air Compressor off of a train.
this transformer will power up a 480V 3-phase air conditioner (3.4FLA) and a large 330VDC Power supply (30KW) http://www.signaltestinc.com/product-p/sga 330-91.htm. Off the top of my head, this thing takes around 41A (I'd have to double check that #). so i need about 50A total

the control circuits are thru a separate 120VAC feed...

we looked into a mobile generator, and are willing to do this (that was priced into the job). the only thing is we may need to keep it much longer than we thought so the price would be quite a bit higher. that's why we are looking into using a transformer (that we could also use in the future if needed)
Click to expand...

The power supply alone takes around 78A at rated load.

The AC is likely around 30A with locked rotor which is what is relevant when you're comparing line sag during start up.

Transformers look plentiful if you can source from Canada. There's a 112.5 kVA 2% z available now. If you can sort out freight and getting it through customs.

https://www.kijiji.ca/b-ontario/600-480-transformer/k0l9004
 
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emiller233

Senior Member
Location
pittsburgh, pa
Electric-Light said:
The power supply alone takes around 78A at rated load.

The AC is likely around 30A with locked rotor which is what is relevant when you're comparing line sag during start up.

Transformers look plentiful if you can source from Canada. There's a 112.5 kVA 2% z available now. If you can sort out freight and getting it through customs.

https://www.kijiji.ca/b-ontario/600-480-transformer/k0l9004
Click to expand...

Here is the response i got from Ametek, and the calculations i did are below that.
If they do not look accurate, please advise!


Manufacturer's response:
almost there with the calculation but not quite. The formula is correct. The numbers are depended on worse case scenario which is full load at low line condition. So instead of nominal 480V we will would be looking at 396V as low line condition. Applying the formula gets us to 56A which is exactly what we already have stated on page 29 of the manual under the PFC section for Maximum AC current rating for this 30KW unit with the 480V nominal input. Please see Table 2-1 for reference in the manual.

Sizing the breaker at 125% of 56A gets us to around 70A breaker to use.


my calculations:
Efficiency = 0.87
Power factor = 0.9
AC amps = (30,000W)/(Vac x 1.732 x PF x Efficiency)
AC amps = (330VDC x 91Amp)/(Vac x 1.732 x PF x Efficiency)

Amps = 30,000/(1.732 x 480 x 0.9 x 0.87) = 46.086 Amp (at 480VAC supply)

----------------------------------------------------

this unit is then being powered thru a transformer.
Power source is 600VAC (Canada)
75KVA transformer is a 600V to 480V delta-WYE


this big power supply should never be maxed out either (customer couldn't provide accurate data for the VFD that it powers direct to the DC bus)
the customer also wouldn't accept the calculations using 396VAC input voltage to that power supply since it will actually be powered by 480VAC
 
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Electric-Light

Electric-Light

Senior Member
Power factor:
>0.69 typical for 440/480 VAC input (40V, 60V - 800V models, 0.9 available with modification “PF”)

I used 0.69. The value you use depends on if your rig was ordered with the modification they mentioned

For the AC, 30A is around the appropriate value to use for voltage drop. The voltage available with 30A added is what's available for motor while starting which isn't a big deal.

Initially you didn't give much details so my comments didn't exclude the possibility about something like a 40 hp motor that must start across the line under full load where the transformer impedance becomes a big deal.
 
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emiller233

Senior Member
Location
pittsburgh, pa
Electric-Light said:
Power factor:
>0.69 typical for 440/480 VAC input (40V, 60V - 800V models, 0.9 available with modification “PF”)

I used 0.69. The value you use depends on if your rig was ordered with the modification they mentioned

For the AC, 30A is around the appropriate value to use for voltage drop. The voltage available with 30A added is what's available for motor while starting which isn't a big deal.

Initially you didn't give much details so my comments didn't exclude the possibility about something like a 40 hp motor that must start across the line under full load where the transformer impedance becomes a big deal.
Click to expand...

it was ordered with the PF mod.

do we need to be concerned with voltage drop, the transformer is like 10 feet away from this power supply

sorry about that, i didn't know it was relevant or i would have! I'm still getting my feet wet with details such as these involving transformers.
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
emiller233 said:
is there a difference between a autotransformer, and a wye-wye autotransformer? or is it the same thing (which i believe it is)
Click to expand...

An autotransformer has a _single_ tapped coil circuit, an 'isolating' transformer has two separate coil circuits, primary and secondary.

wye-wye would imply two circuits.
 

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emiller233

Senior Member
Location
pittsburgh, pa
winnie said:
An autotransformer has a _single_ tapped coil circuit, an 'isolating' transformer has two separate coil circuits, primary and secondary.

wye-wye would imply two circuits.
Click to expand...

makes sense now that i see it!
The Hammond Power rep said they only have Wye-Wye Autotransformers, is he just using the wrong wording?
 
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emiller233

Senior Member
Location
pittsburgh, pa
Hammond power has found me a Y075PKCN3L0U (LINK) in stock.

It looks like what i need but i was unsure of whether or not I'd want to order the 'Neutral Kit' for it?

I've attached the schematics for the system that this transformer would be powering (just the 480VAC portion)

View attachment _XFMR help.pdf


the Hammond Power rep that I'm talking to is not really willing to give me any guidance...
 
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winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
The Y075PKCN3L0U doesn't get connected to the neutral, and your load doesn't require a neutral.

You bring three phases 480V plus egc (PE in your drawing) to this transformer, and three phases 600V plus egc to your load.

-Jon
 
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emiller233

Senior Member
Location
pittsburgh, pa
winnie said:
The Y075PKCN3L0U doesn't get connected to the neutral, and your load doesn't require a neutral.

You bring three phases 480V plus egc (PE in your drawing) to this transformer, and three phases 600V plus egc to your load.

-Jon
Click to expand...

thank you!, just wanted to verify...

are there typically lugs in these big transformers for the EGC's to land?
 
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