[Big John]

The primary low side is protected by the feeder breaker and is most likely fed from a grounded system already.

The secondary high side you want to protect should have one phase grounded. This will give you 600V-to-ground on the remaining two phases. And you'll have what's called a corner-grounded delta.

You need to be careful about how you treat your grounded phase. I don't have the Good Book in front of me, but for one thing, you can't use fuses in your secondary overcurrent protection because your grounded-phase overcurrent protection needs to open all the remaining phases.

 

[SteveBayshore]

Or ground detection equipment on secondary side.

 

[butcher733]

Or ground detection equipment on secondary side.

would that shunt trip the primary breaker?

 

[Tsmil]

iGard makes ground fault detection equipment that does this.