PT Connection

Clearly that's not a PT but an isolation transformer.

A PT has a high impedance and the self capacity between windings and the tank and the parallel insulation resistance is lower. So since 400 V system is usually grounded the circuit is closed through the grounding.

the winding is on phase A and C ,both of which are not connected at 400V(primary) side. so how is this a PT? in ur scheme , the PT primary is just bolted short circuit of the bus to ground.

Coolyaar, your post is Reason #248 why you should go into horticulture or some other safe occupation that does not involve lethal quantities of energy. You're a danger to yourself and others, and your posts have shown this beyond all reasonable doubt.

Yep, electricity is a field with no second chances, and guess work is fatal work, singular in its frequency of occurrence. In common terms - - if your concern for safety ceases, you become an endangered species.

If you are too broke to pay attention, you can't afford to work around electricity.

It seems to me I did not understand the o.p. I thought fig.no.2 as a part of the schematic when it was simply a wrong interpretation. I was sure it is about a derangement.

According to one line diagram-I hope it is actually- the PT is V-V-in Europe or Open_delta in USA, indeed.

I was myself a young engineer specialist in electrical machines and not in electric power and transmission domain. It is not the same profession. You have to collect another theory and experience in this field. This forum cannot help you to overcome this gap in your knowledge.