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Fault current through different transformers

Fault current through different transformers

Fault current through different transformers

(OP)
Hi guys,

Hope somebody will be able to help me to understand something I'm struggling at the moment :)

I'm trying to understand how fault refers thorough different transformer vector group.

The one we have is Dzn0 but I want to fully understand how for example phase to phase fault on the lower side will refer to the higher. Our transformer is 33/11kV but again that's not important as I get really interested in fully understand how that works, but unfortunately never dealt with the protection of the transformer itself.

Anyway I have spent lots of time on internet and my old book and notes.

I know what turn ratio I have got and what a different transformers have (Dy= √3N, Yz=3N etc).
The problem I have I unfortunately can't find it anywhere! Is how will phase to phase (or phase to earth) refer through transformer. I have found that for the Dy it is 2:1:1.

However can't find anything for different groups and what important I cannot find explanation how to get to the answer. I would like to get my head around and understand how to get that current distribution for different transformers so I don't have to struggle every time we have to supply different transformer.

I would be grateful for any advice.
 

RE: Fault current through different transformers

Draw out the winding connection diagram.  Show the relevant current in the secondary winding and the directly coupled primary winding, multiplied (or divided) by the turns ratio.  Add the primary currents vectorially at connection points to determine the line currents.
 

RE: Fault current through different transformers

Where this Dzn0 connection is used?Any specific reason for selecting this connection?

RE: Fault current through different transformers

Hi prc,

Typically they are used as an earthing transformer for 3-wire systems with no neutral.

They also sometimes turn up in power electronic systems such as UPS output stages where they can aid in suppression of triplen harmonics.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Fault current through different transformers

Scotty, I am afraid something more is there in it. If only earthing, it can be just zing-zang winding only as earthing transformer. If they wanted to cater to a secondary load,then it can be simply Dy1 or Dy11.But if they want same vector position as primary then DZn0 is the only solution.Then why somebody wants such a requirement?

I have seen YNzn11( Mumbai,India)and YNzN5( Surinam) connection in some parts of the world.Then I understood that it is to avoid stabilising tertiary winding eventhough Z winding will have 15 % more copper than equivalent voltage Y winding.

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