Delta Wye Transformer HV line current analysis for LV faults

[arrehman1]

Hello everyone,

I was reviewing through faults on the LV side of a non-standard delta wye transformer connection. My intention was to understand how the HV line currents would flow based on the type of secondary through fault…

The Delta side of the transformer would be connected non-standard ANSI connection with DAC on the HV side. LV side would be connected in Wye with the neutral solidly grounded.

This effectively makes it a Dyn11 transformer connection. Therefore, the secondary reference voltage LEADS the primary reference voltage by 30 degrees. Or in other words, the secondary reference voltage LAGs the primary reference voltage by 330 degrees - hence the non-standard connection. See this YouTube video for this transformer connection: [URL unfurl="true"]https://youtu.be/jwvGStgPANE?list=PLqJ0Y2s60r-5TG3jkbk9Er5OPI50i37kh[/url]

Anyway, as I was searching the internet and found an SKM article (attached) which shows the transformer connection in DAC but the flow of HV line current does not match my analysis. In fact, there are many inconsistencies in the article itself.

I wanted to get some feedback from this forum to ensure that my analysis is the correct way of thinking about it. Apologies for squiggly lines… Made this in a hurry.

Thanks!

 

[arrehman1]

My analysis is attached... Thank you for your feedback!

 

[ijl]

I tried to study your networks, but it is difficult without the parameters (voltages, impedances).

 

[jghrist]

I haven't taken the time to completely check your analysis, but it looks like your approach is correct. You don't need the voltages and impedances unless you are wanting to calculate the fault currents. Your approach is good for just determining the relationship among the currents. A useful addition would be to calculate the sequence currents, I0, I1, I2.