Motor Contribution Through Delta/Star Transformer

The delta side of the transformer, having no direct connection to ground (no Neutral or Wye point connected to ground) has no path for a ground fault current to flow. If no path, then no current. When the first fault to ground occurs on a phase of the primary, all that happens is that it establishes a voltage reference for all the phases, based on that one being at ground potential. It's only a second fault to ground that then completes a circuit and you have a REAL ground fault. Note that this assumes that nowhere on the delta primary feeding the transformer is there a connection to ground in the first place (such as a wye secondary on the upstream transformer feeding the delta on yours)! Otherwise the first ground would complete a circuit and fault current would flow.

That's the principle used in delta distribution systems, usually in older industrial plants. There was no direct ground connection, so the first short to ground wouldn't bring all the motors, etc., to a halt. There would be a ground detection system that lights a flasher, rings a bell, sounds a horn, or something, so that maintenance people could track down the fault before a second one happened (and the smoke came out!).