Unbalanced Faults using Symmetrical Components

[Elysium87]

For a line to ground fault with a delta star load transformer, solidly earthed. I am having trouble dealing with the source reactance, do I consider this for positive and negative sequence but ignore for zero?

Does solidly earthed mean that I do not need to include earth fault loop impedance in my calcs?

 

[davidbeach]

You need a good reference. Any Power System Analysis text should help, Blackburn's Symmetrical Components book or Anderson's Analysis of Faulted Power Systems would also be good sources.

 

[rcw retired EE]

What David said. But here's a quick answer.

"For a line to ground fault with a delta star load transformer, solidly earthed.... the source reactance, do I consider this for positive and negative sequence but ignore for zero?" Correct. The source IMPEDANCE does not appear in the zero sequence network.


"Does solidly earthed mean that I do not need to include earth fault loop impedance in my calcs?" Incorrect - you need to include the earth fault loop.

Do some more research to make sure you understand the reasons for these answers. Blackburn's book is a great resource.

 

[Elysium87]

Thanks for the response, OK so solidly earthed per se does not mean ignore effects of earth fault loop impedance, however, the problem does not specify a value for Zn, we are given no impedance nor is it mentioned in the question. I am just trying to understand how I would know if I had to include this. if we are given no value of Zn, then it is assumed to be negligible?