220/127 volt transformer

[lowvoltman]

I was wondering if anyone has come across this issue before.
We need a 480v to 220/127 volt transformer. instead of having a custom one built, does anyone see a problem with just tapping the h.v. side to 455v but bringing 480 v to it to boost the l.v. side up to about 220 volts? your input would be appreciated. thanks!

 

[broadgage]

It should be OK for a short time, for example to test something, but not for permanent use.
If a transformer winding (or a part of a multi tapped transformer winding) is subjected to greater than the design voltage, then this leads to extra magnetizing current, and therefore extra losses.
This may cause the transformer to overheat even when not loaded, and will certainly reduce the load that can be supplied.
In this case it is proposed to supply 480 volts to that part of the winding intended for only 455 volts, and remember that the nominal 480 volt utility supply might be on the high side at perhaps 500 volts.

 

[don_resqcapt19]

That may not be a custom transformer. Look at a "drive isolation" transformer. Some of them have a 220Y/127 secondary.

 

[Electric-Light]

Check into Mexico. i believe their power grid is derived from 220Y/127v

 

[kingpb]

I was wondering if anyone has come across this issue before.
We need a 480v to 220/127 volt transformer. instead of having a custom one built, does anyone see a problem with just tapping the h.v. side to 455v but bringing 480 v to it to boost the l.v. side up to about 220 volts? your input would be appreciated. thanks!

Yes, you absolutely can use the taps to get the voltage you want. I don't know what KVA rating your talking about but if it's a standard dry type, they are usually good for full KVA rating at all tap positions up to 10% voltage above nominal tap. Above that you can still operate, it's just that efficiency drops off.
Check with supplier.

So, for a 208V tap you could increase to 228V and run forever. The -5% tap will get you 218V on the LV side. If it has a -7.5% tap then you can get to 223V.

 

[templdl]

For drives having a 220Y/127 is good because you have 127v to ground. The 127v is not otherwise a usable voltage that I have ever found a use for.

 

[lowvoltman]

thanks

thanks

This is to be used in mexico. It's a 112.5 kva transformer run from generator for temporary construction purposes. so I believe it would be used intermittantly.
thanks for all your input.