Single Phase Transformer Windings

[PhaseShift]

Have a 5kVA transformer with primary option of 480/240 and secondary option of 120/240. I see typically these transformers wired so that primary windings are in series so when 480V are applied each winding sees 240V. Can I connect these windings in parallel so that 480V is seen across each winding. Are these windings rated to handle this 480V across them.

I was thinking about using this transformer as an isolation transformer for 480V to 480V by paralleling primary windings at 480V and putting secondary windings in series to give 480V output.

 

[winnie]

Doing as you describe would swiftly destroy the transformer.

The coil _insulation_ is rated for well in excess of 480V, however the coils are magnetically designed for 240V. If you apply 480V then you will saturate the core and get excessive magnetizing current.

-Jon

 

[LarryFine]

Can I connect these windings in parallel so that 480V is seen across each winding. Are these windings rated to handle this 480V across them.

No and no.

 

[PhaseShift]

Doing as you describe would swiftly destroy the transformer.

The coil _insulation_ is rated for well in excess of 480V, however the coils are magnetically designed for 240V. If you apply 480V then you will saturate the core and get excessive magnetizing current.

-Jon

OK so I'm assuming that the same holds true on the secondary side and that the secondary coils are only designed to have 120V across each of them?

So the primary windings are only meant to be put in parallel for a 240V supply?

I have seen a european 480V to 230V (L-N) transformer with a similar arrangement with both of the primary windings in parallel with 480V across them. The secondary windings were also in parallel so I believe the transformer ratio was a 2:1 ratio. Why would this type of transformer allow 480V across the windings? Are these ratings usually listed on the unit?

 

[winnie]

I don't know why the European transformer that you describe was set up that way.

A transformer coil can be set up to give just about any desired voltage, simply by adjusting the number of turns of wire at the design stage. For whatever reason that European transformer was designed such that each coil could handle 480V.

The nameplate should show a connection diagram with voltage ratings for each connection. You can safely use a transformer at _lower_ than rated voltage, however this wastes material, because the effective KVA goes down.

-Jon