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SLG Fault current flowing back to Primary of the transformer with no load

Client's Question:

 I modeled a cable, a YG-delta transformer on the primary, and no load on the secondary. When I run the fault study on the transformer primary bus, it shows a 51A SLG contribution from the secondary. Where is the 51A contribution coming from if there is nothing on the secondary?


Solution:

When you have a YG-D configuration for the transformer,  it creates a path for zero sequence current to flow back. Hence, you see the program reports a small SLG fault current flowing back to the primary even when you don't have any kind of load connected to the secondary of the transformer.

Please see the snap shot below  where the faulted bus is BUS-0002 and there is a 51A SLG current flowing back to the primary of the transformer. 

 



Please refer to the attached project and the word document for detailed calculations.





Creation date: 9/8/2020 10:35 AM (talha.hussaini)      Updated: 9/8/2020 10:35 AM ()
Files   
DataImage9.png
108.6 KB resend
Single Line to Ground Fault Calcultion on Transformer Primary Bus.doc
257.5 KB resend
Transformer_SC current.zip
1.7 MB resend