How to tell if a transformer is wye or delta

[pyro214]

I'm going through a list of 12 transformers and trying to determine if they are wye or delta. The schematics I have come across are for power engineering and don't go into too much detail other than the following:

The transformers step down ~400V 60Hz AC (three-phase) to ~120V 60Hz AC (single or three-phase) with one of the two schematic configurations:

1 - http://s8.postimage.org/66olvudat/transformer.png
2 - http://s8.postimage.org/edglnf3dh/transformer_4.png

I'm familiar with the first schematic drawing with two circles however this is my first time seeing four circles to represent a transformer; any ideas?

Thanks!

 

[Studiot]

 

[hisham.i]

The transformers step down 440V 60Hz AC (three-phase) to 115V 60Hz AC (single or three-phase), 24V 60Hz AC (single-phase)

How can 3 phase transformer step down voltage to single phase voltage?
3 phase transformer steps down 3 phase voltage to 3 phase voltage, the connection may be different between the primary and the secondary.

First you have to be sure that the transformer is 3 phase transformer.
Else if i didn't understand your point please correct for me what do you mean 440 v three phase to 24 v single phase.

I'm familiar with the first schematic drawing with two circles however this is my first time seeing four circles to represent a transformer

I think the four circles means that:
First circle -> input winding
The other 3 circles means there are 3 different outputs the transformer can give.

Do you have transformers and want to know there connections or you just have a schematic and want to know the connections?

 

[Studiot]

How can 3 phase transformer step down voltage to single phase voltage?

Very easily, there are several ways.

The 'step down' bit refers to the change of voltage magnitude.

Plucking a single phase froma multiphase transformer involves
either a single winding (which has two ends and therefore a single phase)
or using the interphase voltage which is done to supply higher power devices in electricity supply.

 

[hisham.i]

So where you put the iron core of the single phase?
3 phase to 1 phase -> same secondary core will make the flux of the 3 primary windings path in the same core of the secondary resulting in 0 flux -> 0 voltage on the output.
BUT if you place the core of the secondary on one phase of the primary you will get an output but in this case you will have single phase transformer not 3 phase to 1 phase

 

[skeptic2]

I'm not a power engineer and I don't "know" the answer but it seems to me delta is normally used on the high voltage side of the transformer to avoid the expense of running a fourth cable. Wye is usually used on the low voltage side of the transformer in order to have a ground connection. This would be particularly important with a single phase output in order to avoid a floating circuit.