Purely for informational purposes. As was mentioned a project like this outside the classroom is a large project that requires knowledge in several areas. Nothing that can be covered in a single forum. There are commercially available units made for this but for educational purposes we will break things down.
Starting with the mains power delivered to the sub station, in this case 3 phase 11 KV WYE power. We want to measure voltage on all 3 phases as well as current so we start with a "sensor" device for voltage. Yes, the device of choice is the Potential Transformer which is in simple terms no more than a very accurate ratiometric voltage device. For this case 11 KV is considered medium voltage. I suggest you find out the ranges for low, medium and high voltage. Get familiar with
potential transformers especially how they are fused and why some use double versus single fuse based on WYE or DELTA applications. Also get familiar with oil and air cooled.
Read this link and that is the transformer we will use. Our sub station is indoors!
Run to the store and buy 3 of model PTG5-1-110-1442F from the link. Now 0 to 14,400 VAC is equal to 0 to 120 VAC in a 120:1 ratio.
Now we need to do something with our 0 to 120 VAC. While you are at the store buy 3 of
these AC Voltage Transducers. You want the 0 to 150 VAC input with a 0 to 5 volt output versions.
The scaling is now 0 to 15,000 VAC is 0 to 5 volts DC. Scale it, chart it, record it and do whatever you wish with it. Feed the 0 to 5 volts into a data acquisition device and write the software.
That was a very brief idea of how this is done. There is much, much more to it.
The same would be done for current. The current transformers would be selected for the current at 11 KV.
Again, there is considerably more to all this.
Ron