Phase to Ground Fault

Good morning,

In three phase, three wire ungorunded or resistance grounding sytem,

During phase to ground fault; voltage level of faulty phase is zero,

but voltage-to-ground of the other phases rises by 73 percent.

However phase to phase voltage remains the same and only phase to ground voltage

in two healthy phases increases.

What is the reason of this in technicaly?

What is the main advatages and disadvantages of using 11 kV or 22 kV instead of 33 kV according to the phase to ground fault.

Best Regards,

Musa UÇAN