Help with a voltage monitoring system

I am building a Voltage monitoring system to monitor the AC phase voltages ( 3 phase , 4 wire, 115/230 V) using the arduino. Each phase voltage ( eg : Van = 115v, Vbn = 115 V, Vcn = 200V). I m unsure as to what transformer i should use in order to step down the voltages, what kind of 3 phase converter to use ( semi converter, dual or full ) in order to convert it to DC, and is the arduino capable of reading analog directly or would i have to use an ADC and read the data from that?

Very dangerous to be playing with this potential.
Fault currents can be massive.
Best advise is stay away from it.

Lol I have to do it as part of a final year project :~ Do you know any alternative methods to monitor the phase voltages?

bluejets I agree there is a risk, but it can be done safely, with careful attention to detail.

Since you have a 4th wire that I assume is the neutral, it seems to me that three separate single-winding transformers would allow you to monitor each phase separately with respect to neutral and do whatever fancy math is necessary to extract your desired information in software. (I don't know anything about multi-winding transformers, so I don't know if the voltages would get hopelessly muddled together).

If so, you should be able to use just about any transformer that comfortably exceeds the voltage rating on the primary side (as you know, peak is higher than RMS!). I would then connect each secondary winding to it's own separate a full-wave bridge rectifier, each of which in turn connects to it's own resistor divider to bring the voltage into the 0-5V range for the Arduino to measure. (Definitely add overvoltage protection diodes to the Arduino pins.) I recently saw a cleverly modified full-wave bridge rectifier circuit online that would also allow you to sense when the input was on the positive and negative half of each cycle, but darn it, I can't find it now.

The Arduino has a built-in ADC, which should be fast enough and (probably) accurate enough for this purpose.

I have to do it as part of a final year project

In what? If it's EE power electronics, you should have been paying more attention. If it's basket weaving, they have assigned a project WAY outside the scope of the course.

Have a look at this:

You will get some ideas how a multiphase power meter does this.

bluejets I agree there is a risk, but it can be done safely, with careful attention to detail.

Have to strongly disagree.
The reason being I doubt anyone in a teaching environment would assign something such as this that would endanger someone.
The OP has obviously zero experience or qualifications in and around such potential given the basis of the question, and it is in most countries considered as unlawful to attempt any such operation.
In endorsing such an action could also find the endorsee responsible in event of a mishap.
The OP did mention "building" this so I assume it would also be a temptation to "test" it as well, not just theory.