Vector Group

Hai,

As per Mr. MS Suggesstions go head for TX 6.3/11 KV YNd 5,7 or YNyn0.

When U are synchronizing alternators and transforming to higher voltages, Ur talking about parallel operation of transformers. For transformers to be connected in parallel, they must meet the following requirements,

1) They must be of same primary and secondary voltages.

2) The same tape ratio.

3) The same percentage impedance.

4) Most belong to the same vector group.

The answer to Ur question is any transformer of the same vector group that meets with the condition for paralleling as specified above. If they are not of the same specification as above, the breakers will not close due to fault signals, as phase rotations, etc.

DICKSON.

KVA Rating of alternator seems wrong.

any way, It depends on type of system you are designing, earthed or Unearthed,

The secondary of transformer can be star or delta.

With star connected system neutral is available and can be grounded. where as delta system earthing transformer would be required to earth the system, the vector group of earthing transformer shall be Znyn11. The star connected secondary of earthing transformer can be 415 volts for auxiliary services

I suggest a Dyn11 Vector Group Transformer. (Please recall that the HV side or 11kV side is Delta and is denoted by a Capital Letter and the LV side or the 6.3kV side is Star and is denoted by a small letter. The brought out neutral on the LV side is represented by the small 'n').

The reasons are:

i) Generator side of the TRF has to be a grounded system to reduce high fault currents which could be harmful for the generator. So, you go for a Star connections with an earthed neutral (preferably a high resistance earthed system) at the generator side (6.3kV side).

ii) As the HV side is feeding a 11kV (3-wire) bus, you don't need a star connection at the 11 kV Side. You can go for a Delta Connection as you need only three wires for distribution.

iii) the following '11' denotes that the phase shift of the LV winding with respect to the HV winding is + 30 degrees. Now, as the LV side is the generator side, with reference to this generator voltage, the HV side voltage will be "lagging" by 30 degrees. You normally have the same Dyn11 Vector Group Transformers at the 11kV/433V level, whose LV side will have a + 30 degrees phase shift. Now, the 433 V at this transformer's LV side will be in phase with the generator voltage.