Carson,
Based upon the thread so far and your forum profile, I presume that your question has been judged 'not DIY'. However your questions suggest to me that you do not yet have the background necessary to complete the installation you are considering. I'm going to bring a truth over from a DIY forum: electrical installations are all about the details, and we have no way of knowing which details that you do not understand, and which questions you don't even know enough to ask. We do not see what you are looking at, and have no way of pointing out 'got-yas' that would be obvious in person. The only thing that we can do is answer the questions that you present to us, maybe through in personal experience that we _guess_ is related, and hopefully give you enough pointers that you can go and fill in the holes in your own knowledge.
A coil in a transformer operates as a single phase device. It interacts with the alternating magnetic field of the core, and produces a single phase voltage between its two terminals. If connected in a closed circuit, current may flow through the coil. The 'primary' and 'secondary' coils do exactly the same thing; they are simply windings which interact with a magnetic field. The direction of current flow in the windings, and power flow through the transformer depends upon what is externally connected to the coils.
If you connect a source of power to the coil with more turns, and a load to the coil with fewer turns, then you have 'step down' transformer action. Connect the power to the coil with fewer turns, and the load to the coil with more turns, and you have 'step up' transformer action.
Three phase transformers are actually combinations of single phase transformers, connected together in different ways to provide the desired three phase voltage set.
The 'delta' connection means a set of three phase coils connected so that the schematic diagram looks like a triangle.
The 'wye' connection means a set of three phase coils connected so that the schematic diagram looks like a capital 'Y'.
The angles of the coils in the diagrams are not just to make the pictures, but actually to conceptually represent the phase angle of the voltage applied to the winding. This is of course, only approximate and representative, but it should help give you the idea of what is going on.
With a delta connected transformer set, there is no neutral for the three phase terminal voltages. _Some_ delta transformers will have a center tap on one of the coils, providing a neutral for the two terminals that share that coil.
With a wye connected transformer set, the 'common terminal' where all three coils are connected _is_ a neutral between all of the phase terminal voltages.
When a service is described as 'wye' or 'delta', that simply means the type of transformer connection in the secondary providing the service.
For reasons which I do not entirely understand, it is generally preferable that the transformer primary be delta connected. Wye connected primaries can be (and are) used, but delta primaries are preferred.
For reasons of safety and insulation system protection, it is generally preferable to use a _grounded_ secondary. This means that one of the terminals of the transformer set is intentionally connected to ground. In theory, _any_ terminal of the secondary could be grounded, but electrical code requires selecting the terminal which would minimize the voltage to ground of the other terminals. This means the neutral or the terminal closest to neutral.
Wye secondaries are desirable because they provide a nice solid neutral point for grounding. With a grounded wye system, all of the phase to ground voltages are the same, and minimized for a given voltage. However delta secondaries can certainly be used, and one of the 'phase' terminals of the secondary could even be grounded. This is called 'corner grounded delta', and is a safe and known approach to grounding. However it is uncommon enough to be confusing.
Non-standard grounding may cause issues with protective relays or with surge protective devices, and adjustment may be needed to do this.
'Ungrounded' systems may be used, however these present risks of insulation failure and undetected ground faults. Ungrounded systems are commonly used on entire plants, so that ground faults will not shut the process down. There are special code rules dedicated to ungrounded systems, and IMHO you should not use this for a single machine.
While it is entirely possible to have a 240V wye system, this would be _very_ uncommon. It is much more likely that you have a 240V delta service, possibly with a grounded center tap on one of the coils. The reason for this is to provide for 120V single phase loads. 240V with a center tapped coil provides this 120V as the voltage between the phase and center tap. This system is sometimes called 'high leg' delta, because the third phase terminal (the one that doesn't share the center tapped coil) ends up at 208V to ground. A true 240V wye service would not have 120V available anywhere, and instead would have 139V to ground.
The common 200V class wye service is 120/208, where you have three 120V coils connected 'wye' to provide 120V phase to ground, and 208V phase to phase.
Strangely, while 240V wye is very uncommon, 480V wye is quite common. This is provided with three 277V coils connected in wye, with 480V phase to phase. 277V lighting is quite common with these services. So you could either see 480V delta, or 480V wye.
A _very_ common transformer has a 480V delta connection as the primary input, and a 120/208V wye connection as the secondary output. These transformers are so common that they are often used 'in reverse' to provide 480V to a machine tool. However there are several problems with this arrangement. 1) The input doesn't have 'taps' to correctly adjust the input voltage. 2) The output doesn't have a nice neutral point to ground.
For your system, you could use a 480V delta to 240V delta transformer. This would again have the problem of no voltage adjustment taps, and no neutral on the secondary. For the loads that you describe, a neutral is not required, and you could presumably use a 480V corner grounded delta. Corner grounded delta requires that your circuit breakers and components all be rated for the full 480V to ground, which might make these components more expensive. As I said above, you probably don't want to deal with the issues of an ungrounded system.
Ideally you would get a 240V delta to 277/480V wye transformer, with voltage adjustment taps on the 240V side. This would provide a neutral point for grounding, and permit you to use normal 277/480V breakers.
You could not use a common 480V to 120/208V transformer in reverse. The supply voltage would be too high, saturating the core and leading to excessive heating, and with no taps you could not adjust for this.
-Jon
