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Old 06-06-2013, 10:02 PM   #1
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Default am I missing something on sizeing a step up transformer

Do you still use the same math when figuring a step up transformer

I am looking at stepping up 230v 3 phase to 480v 3 phase

with a 175kva transformer

the way I did the math

primary side 230v needs a 500 amp breaker

the secondary side 480v 300 amp


does this seem right or did I miss something
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Old 06-06-2013, 10:06 PM   #2
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Quote:
Originally Posted by joelowrider View Post
Do you still use the same math when figuring a step up transformer

I am looking at stepping up 230v 3 phase to 480v 3 phase

with a 175kva transformer

the way I did the math

primary side 230v needs a 500 amp breaker

the secondary side 480v 300 amp


does this seem right or did I miss something
Huh
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Old 06-06-2013, 10:34 PM   #3
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You can possibly go up to 250% on both primary and secondary overcurrent protection. Check 450.3(B) note 3
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Old 06-06-2013, 11:02 PM   #4
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Originally Posted by bkmichael65 View Post
You can possibly go up to 250% on both primary and secondary overcurrent protection. Check 450.3(B) note 3

I will have to look when I get to work Friday

basically I guy I do work for needs 150amp 480v at a mach

he has 230v 3 phase

I has a 175kv transformer laying around I was trying size it in my head I think it is way 2 big

he has a 200 amp breaker with 3/0 running to the machine that was prior in its spot
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Old 06-06-2013, 11:06 PM   #5
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I rattle when I am at home sorry.

I really just need to find the cheapest way to get 150amp 480v.

When all I have is 200amp 230v, with a spare 175kva transformer, I will look in the morning but I think the primary side (230) will need 500 amp service
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Old 06-06-2013, 11:14 PM   #6
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If it just has primary overcurrent protection only use 125%- will give you over around 550 amps, so you can use 500 or go up to the next size to 600.
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Old 06-06-2013, 11:20 PM   #7
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Quote:
Originally Posted by bkmichael65 View Post
If it just has primary overcurrent protection only use 125%- will give you over around 550 amps, so you can use 500 or go up to the next size to 600.

Crap so my numbers are right not what I was wanting to hear.

I think am going to get a new drive for the machine so I can just wire it at 230v and use the original wire
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Old 06-06-2013, 11:44 PM   #8
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The 480 current on a 175KVA transformer would be 211 amps, the 230 volt current would be 440 amps.

To get 150 amps at 480, you'll need 314 amps at 230 volts, and at least a 125KVA transformer.
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Old 06-07-2013, 12:06 AM   #9
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Originally Posted by micromind View Post
The 480 current on a 175KVA transformer would be 211 amps, the 230 volt current would be 440 amps.

To get 150 amps at 480, you'll need 314 amps at 230 volts, and at least a 125KVA transformer.
Ya but my issue is only having 200amps at 230v so I can't use the 175kva we have setting around
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