You should not use protective earth to power anything.
The secondary of a transformer is "floating":
not related to any of the phases, neutral or protective earth.
You can use it, loading the network in an unbalanced way (hard not to with a single phase load), and there will be a phase difference of at least 30° in each of the phase wires even with a resistive load:
Power factor ≤ 0.866.
It does not give you a neutral potential.
If you have access to a neutral potential as well as to at least one phase of a three-phase network with a line-to-line voltage of 415 V nominal, you could
- connect a 230 V load to one of the phases if its voltage tolerance is high enough: Line-to neutral is 240 V nominal.
- use a 240:230 V step-down transformer.
There are grounding transformers capable to get a neutral potential from all three phases of an "ungrounded" symmetrical three-phase system.
Answer to revision 1:
Using a transformer to get a neutral potential from just two of the phases of a network at least somewhat commonly used for power distribution will work only when those are the phases in a "high leg" network that are not the high leg.
And in that case, the transformer needs to be 1:1.