VT how does it work, DIN mount, and voltages

Hi all,
another thread got me thinking (yes it’s dangerous, just ask my wife :stuck_out_tongue:)
So First question is how does the VT input work?
Is the frequency important or the voltage (or both). I.e. can i use a power supply or does it need to be an unfiltered transformer? As in theory a power supply can regulate the output in terms of voltage and some even the frequency removing any variance which is what the device may be monitoring.

Next, Is there an easy way to make it so the reference voltage is 24v ac rather than 9-12vac as the range of 24v DIN mount supplies out there is far greater. If you can use a DIN mount It means that instead of power points needing to be installed next to your switchboard, the VT can become part of your switchboard.

Lastly, has anybody done this?