Transformers from 480V - 415Y/240V

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fjrivera

Member
Greetings.

I need to step down from 480V three-phase to 415Y/240V using a 45KVA transformer. Since this kind of transformer is not common I will try to use three single phase transformers from 480V to 240V of 15KVA each and will create like a transformer bank with the input connected in Delta and the output connected in Wye for 415Y/240V with a total of 45KVA. Can anyone foresee any problem with this type of connection?
 

wirenut1980

Senior Member
Location
Plainfield, IN
Is the supply voltage 60 Hz (I assume it is). Is the equipment expecting 60 Hz voltage?

Also, I'm not sure about this, but I think you'll need to make sure the single phase transformers can be internally jumpered to be connected wye on the secondary.
 

bob

Senior Member
Location
Alabama
Greetings.

I need to step down from 480V three-phase to 415Y/240V using a 45KVA transformer. Since this kind of transformer is not common I will try to use three single phase transformers from 480V to 240V of 15KVA each and will create like a transformer bank with the input connected in Delta and the output connected in Wye for 415Y/240V with a total of 45KVA. Can anyone foresee any problem with this type of connection?

What voltage do you expect to get from this type of connection?
1. You are connecting a transformer rated for 415 V to 480 V. The
output at each transformer is 277 volts
2. The voltage phase to phase will be 480 volts.
You will be right back were you started.
This is not going to work for you.
 

Besoeker

Senior Member
Location
UK
Is the supply voltage 60 Hz (I assume it is). Is the equipment expecting 60 Hz voltage?
A valid point. A 415/240V system is generally 50Hz. Using transformers to get the right voltage is easy.
But that won't fix a frequency mismatch.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Greetings.

I need to step down from 480V three-phase to 415Y/240V using a 45KVA transformer. Since this kind of transformer is not common I will try to use three single phase transformers from 480V to 240V of 15KVA each and will create like a transformer bank with the input connected in Delta and the output connected in Wye for 415Y/240V with a total of 45KVA. Can anyone foresee any problem with this type of connection?
No problem at all, except maybe the frequency issue (as others have pointed out).
 

gmtt

Member
Aside from the frequency issue, if you have 3 single-phase transformers each of which is 480V/240V, configure primary to delta and secondary to Wye. You will then have 240V line-to-neutral and 415.69V line-to-line in the secondary.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Other than the frequency issue, I can't think of any issues. Xfmr manufacturers usually have configuration diagrams for getting whatever voltage you want from what you have. I have seen some wierd ones and the manufacturers always seem to have an answer.
 

fjrivera

Member
Yes. The working frequency of the equipment is 50 Hz. With other similar equipments I have not encountered any issue with frequency mismatch and the R&D team didn't foresee any problem. Most of the elements connected to the machine are marked for 50Hz/60Hz and the motors have inverters that can work also 50Hz/60Hz

The issue is that 415V three phase is needed for the inverters and a 60KVA three phase transformer 480V-415/240V may be not available on time. Don't know why since three phase transformer 480V- 415/240V is very similar to a three phase 480V-240V with 120V centertap only that the output need to be connected in Wye with no centertap.

Meybe I can use a three phase 480V-240V but I need to rearrange the internal connections.

That is why using 3 single phase transfromers are needed.
 

bob

Senior Member
Location
Alabama
Aside from the frequency issue, if you have 3 single-phase transformers each of which is 480V/240V, configure primary to delta and secondary to Wye. You will then have 240V line-to-neutral and 415.69V line-to-line in the secondary.

He does not have a 480/240V transformer. He has a 415/240V transformer.
If he applies 480 volts to this transformer the output will be 277 volts and not 240 volts.
 

fjrivera

Member
He does not have a 480/240V transformer. He has a 415/240V transformer.
If he applies 480 volts to this transformer the output will be 277 volts and not 240 volts.

I don't have a three phase 415V/240V transformer. That's what I want but isn't available. Thus, I will try to step down from three phase 480V using three single phase 240V transformer.
 

bob

Senior Member
Location
Alabama
I don't have a three phase 415V/240V transformer. That's what I want but isn't available. Thus, I will try to step down from three phase 480V using three single phase 240V transformer.

OK. I misunderstood you original post. I thought you were trying to apply 480 volts to the 415/240 volts transformer.
 

Besoeker

Senior Member
Location
UK
Yes. The working frequency of the equipment is 50 Hz. With other similar equipments I have not encountered any issue with frequency mismatch and the R&D team didn't foresee any problem. Most of the elements connected to the machine are marked for 50Hz/60Hz and the motors have inverters that can work also 50Hz/60Hz

The issue is that 415V three phase is needed for the inverters and a 60KVA three phase transformer 480V-415/240V may be not available on time. Don't know why since three phase transformer 480V- 415/240V is very similar to a three phase 480V-240V with 120V centertap only that the output need to be connected in Wye with no centertap.

Meybe I can use a three phase 480V-240V but I need to rearrange the internal connections.

That is why using 3 single phase transfromers are needed.
Are you sure you really need a transformer for the inverters?
I'm from UK and the standard three-phase supply here is nominally 400V, 50Hz. However, most of the inverters we use are rated for 380-500V input to accommodate both EU and North American supplies.
 

templdl

Senior Member
Location
Wisconsin
What you quoted for lead time on ordering the correct transformer? Did you look into it?
But I must admit that a Rube Goldberg arrangement is more fun though.
I also found the people loose precious lead time in delaying what should have been done correctly in the first place.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
IMHO a properly designed bank, consisting of 3 standard single phase transformers, is a probably better design than a custom 3 phase transformer.

The standard transformers will probably be cheaper, will have greater flexibility, have greater re-use potential, and have a greater re-sale value than the custom unit.

The set of 3 single phase units will probably weigh more than the three phase units.

Banking transformers is a standard and well known method of using transformers.

-Jon
 
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