Voltage Transformer Primary star point no eartth Secondary White phase earthed ?

[CraigMW]

Good day Gents,

Durring the pre-commissioning testing of a 11KV mobile modular (11KV switcgear & associated equipment).
Found the Voltage Transformer connected to the 11KV Trf. Circuit Breaker has the middle phase(White phase) earthed reference and the primary side star point floating (no earth). Opened VT covers to asses if it would be possible to install a primary star point earth (Grounded star point), but the primary winding is encapsulated(Moulded), no access to primary star point.
VT- Star/Star
Voltage - 11KV/110V

Question 1 -Why earth the blue phase on the secondary and not the starpoint neutral?

Question 2 - Why is the primary star point floating?
Thanks
CraigM

 

[scottf]

I don't follow your comments about the primary neutral point not being accessible.

The neutral end of the primary winding of the VT must exist the unit somewhere OR is internally grounded/connected to the base - assuming these are single-phase VTs. If they are 3-phase VTs and the primaries are connected in WYE, then the neutral point is either grounded/connected to the based or it comes out to a terminal somewhere on the unit. It would not be left "floating" inside the unit.

 

[ScottyUK]

This configuration is common on older British gear. The 'B' phase of an A-B-C group, also referred to as the 'yellow' phase in British parlance, is frequently earthed to the frame. It saves a VT conductor in a three-wire distribution system, or that was the apparent logic of the time. The star point is generally accessible somewhere even if it isn't brought out.