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Unbalanced Faults using Symmetrical Components

Unbalanced Faults using Symmetrical Components

Unbalanced Faults using Symmetrical Components

(OP)
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?

RE: Unbalanced Faults using Symmetrical Components

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.

RE: Unbalanced Faults using Symmetrical Components


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.

RE: Unbalanced Faults using Symmetrical Components

(OP)
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?

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