Grounded Wye - Grounded Wye VT Question 1

[charz]

What are the implications of primary neutral of a VT not connected to the ground in both the ungrounded and grounded system?
The configuration of VTs are three separate single phase VTs connected grounded wye - grounded wye fashion?

 

[Mbrooke]

If you leave the primary floating, you will get all sorts of eronius secondary voltages. Primary must be grounded for protective relaying to function correctly and measurements to be correct.

 

[RRaghunath]

In ungrounded and high resistance grounded systems, grounding of star points on both primary and secondary could cause maloperation of earth fault detection system for faults on secondary of VT.
Hence, earthing of secondary star point is avoided and y-phase is grounded instead.
This is the practice in generator systems.

Rompicherla Raghunath