Wye-Wye Transformer on Low Resistance Grounded System

[T247]

We have a 4160 V system that is low resistance grounded. The transformer supplying the 4.16 kV system is a 10 MVA, 13.8 kV Delta-Wye with a 12 Ohm neutral ground resistor. There is a temporary feeder being installed to supply some 480 V equipment along with a 4160-480 V transformer, however, the transformer that is being provided is a Wye-Wye transformer. My questions are:

1. What is the effect on the 4.16 kV system, specifically the ground fault protection, if the transformer is installed and the Wye-Wye transformer is solidly grounded on both the primary and secondary? Can this transfomer feed only three-phase loads?
2. What happens if the neutrals of both the primary and secondary are left floating? I know that there are the typical issues that occur when a system is left ungrounded and that some form of ground detection on the 480 V system would be requireded, but are there any other limitations?

 

[waross]

The 4.16 kV to 480 V transformer.
Primary; Do not ground, connect to the XO of the 13.8 kV:4.16 kV transformer.
Secondary; This is a separately derived system. The secondary XO may be grounded to safely supply line to neutral loads. (277V)

 

[T247]

We can't access the X0 bushing to the 13.8-4.16 kV transformer since the equipment is energized.