Dyn11yn11 50KVA Transformer

Do you mean you have one transformer provided with 2 identical secondaries, do you? And you intend to connect the secondaries in parallel- as far as I understood.

The supply voltage will be the same as it was on each terminal before and the total current will be the same-in my opinion.

None, assuming that you verify that: the windings are identical, they are both on the same tap, there is no voltage difference across like phases, the phase rotation is indeed the same, AND after making these checks, you make sure the connections are solidly made.

If any part of this is not understood, or you think that the output will double to 100kVA, then do not proceed except to get a qualified engineer to help you. Failure to do so WILL have a major impact on the transformer and the equipment fed by it.

With the reason being that your transformer actually splits that total of 50kVA between the two secondary windings (check the nameplate to see if it is equally divided or some other ratio). So if you connect the seondaries in parallel, you total the two and get 50kVA max capacity.

Input= 50 KVA, 132 KV, Vector Group= Dyn11yn11

Output 1= 25 KVA, 6.3 KV

Output 2= 25 KVA, 6.3 KV.

These 2 outputs from different winding feeding different feeders. And there is mechanical interlocking between feeders and two outputs of the transformer. We can't turn on both outputs of the transformer when these two feeders are connected.

What is the reason behind this scenario?

The reasoning is probably similar to your reason for not providing this additional information in your original posting; i.e., "We don't know".

You now need to go research the reason by going through the original design documentation until you find the logic behind that decision. All "we" can do is speculate until you provide another clue, you have already used up your "free pass" here.

If it is correctly protected, then either nothing or one of your protective devices will operate, switching the output off.

If it isn't, then it will becomean incendiary device.

This kind of arrangement is provided when there is need to limit the fault level in the secondary circuits. If you parallel the two windings, you are defeating the design objective.

After all, the designer could as well have provided one single secondary winding rated 50kVA.

Dear Raghun,

Thanks for your value able answer. Can you please tell me the per unit impedance of the three winding of the transformer?

per unit impedance

primary to secondary 1 ?

primary to secondary 2 ?

secondary 1 to secondary 2 ?

That's a matter of design.

Typically, the %impedance of two secondary windings with reference to the primary would be identical and that of one secondary with reference to the other secondary would be higher. This is because, one secondary is close to the core limb and the other is after the primary winding (i.e. outer-most).