PT Connection

The individuals who drew, reviewed and approved the installation for construction should be in the various boxes in the corner of the drawing. These would be the best people to ask.

http://electrical-engineering-portal.com/star-delta-transformer-connection-overview

The drawing are not drawn professionally really can see which is primary winding and which is secondary winding

The question has already been answered for you on another website.

1. PT secondarys are always earthed - as part of keeping xxxkV from LV equipment and you. Capacitance coupling to unearthed secondary from HV primary is enough to be lethal, particularly since current in normal conditions could exceed "let-go" hand potential. Which phase is earthed would be just convention.

2. The neutral has a separate PT. My opinion is that the interconnection of the 4 PT secondaries is a) the same as that of primaries, plus it gives "zero sequence" voltage, "positive & negative sequence" voltage and 3 line voltages to earth separately in LV circuit.

3. the lower secondary of the 0-X0 PT primary may be because the PTs have two secondaries any how; opposite polarity might be required - note obvious cross-over of secondary connection; or maybe diffferent voltage required.

4. As has been commented, the manufacturer or the protection relay drawings and types or maintenance manual may help.