You may choose to ground the system, or to keep it ungrounded. Either way the transformer's frame will need to be grounded and I believe there needs to be a Grounding Electrode system for the transformer - even if the system is ungrounded. Need to verify this - I know ungrounded Delta services require a Grounding Electrode system.
You may want to choose to Ground the system, since the distance to the Motor is 1.5 Miles from the Transformer. This will help stabilize the voltage to ground [so it does not "Float" from 300 VAC upto 1000 VAC!!!], also will assist with Lightning Discharges and other imposed stuff on the Motor, branch circuit and overall system.
If you choose to Ground the system, physically bond any one of the three "Phases" to the newly created Grounding Electrode system for this Transformer. Do this as you would with 4 wire Wye Transformer's "X0" terminal, or with 1 phase 3 wire "Neutral" points - the typical X2-X3 jumper.
Bond one and only one "Phase" to the Grounding Electrode system. Verify which line this will be and identify it as a Grounded Conductor.
Also, do not fuse this conductor, nor re-ground it at any other point than at the Transformer.
Check NEC Article 250 [mostly the first 4-5 pages], and 450-10 for more information on the NEC requirements. Also verify with the AHJ as to their conserns.
Lastly, take a look at the Transformer Schematics which are located in the 'Electrical Theory and Applications' forum area. Select to "Search From Posts Made Over 6 Months", or even longer to find them.
The schematics should show Grounding Points clearer to you for better reference.
Good luck
Scott "SET"
