Transformer vector connection

[prc]

In generator transformers used in power stations, the vector group connection is YNd1 in IEEE areas and YNd11 in IEC areas. Some countries YNd5 is also seen.It is understood that delta connection on LV side is to avoid the zerosequence current entering in to generator stator windings during an LG fault on HV lines.
1) What is the reason for Yd5 connection.Any advantage over Yd1 or Yd11 or juast a convention?

In case of Wind power stations and solar power panels, the transformer connection is Dyn5 or Dyn11 with collector transformer having a connection of Dyn11 ie D of turbine transformer connected to yn of step up transformer.
2) Logic for above connections and how in this case zerosequence currents are filtered out of the stator windings.

 

[slavag]

I think, I asked such Q's before one or two years.
No answers, I found only, that Yd5 or Dy5 its German standard.

 

[waross]

If a ground fault hits a wye:wye generator step up transformer on A phase, A phase of the generator must supply the entire current.
If a ground fault hits a wye:delta generator step up transformer on A phase, A phase of the generator must supply one half of the current and B and C phases, acting as an open delta (broken delta in IEC speak) will supply one half of the current.
The delta is on the generator side.

Bill
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