Voltage During SLG and DLG faults

[reynal74]

I was wondering if it is possible for the voltage of the healthy phase to a double line to ground fault to be higher than the voltage of the healthy phases to a single line to ground fault. The fault is considered to happen on the low voltage side of a transformer feeding a grid.

 

[magoo2]

Yes it is.

There's a series of curves of maximum voltage to ground for arrester application. These are plotted as a function of X0/X1 and R0/X1. The values (voltage on unfaulted phase) are based on both a single line-to-ground fault as well as a double line-to-ground. The double line to ground fault does influence a portion but not the majority of the curve.

I'll try to post a copy of one of the curves if someone else doesn't do it.

 

[reynal74]

Thanks for the reply. The curves will be a great help. I simulated faults on the high voltage side on the transformer and the voltage of the healthy phase to a double line to ground fault were lower than the voltage of the healthy phases to a single line to ground fault, this was expected. However, when I simulated faults on the secondary, results were confusing (as explained in the post). Thank you again, I will be waiting for the curves.

Regards,

Reynaldo Salcedo

 

[cuky2000]

Yes, it is possible for the voltage of the healthy phase for a LLG is larger than the voltage for a SLG fault.

If the sequence impedance parameters could be available, the maximum voltage could be calculated after determine the coefficient of grounding (Eath Fault Factor for the IEC marketplaces).

Check this post:

http://www.eng-tips.com/viewthread.cfm?qid=237503

 

[magoo2]

Here's the curve that I had from the Transmission & Distribution Reference Book by Westinghouse/ABB. It has a separate curve for varying amounts of R1.

For the most part, you can come pretty close to this curve if you base it on a single line-to-ground fault. However, there is a small area where a double line-to-ground fault is more limiting.

This is really the same curve that cuky referred to.

 

[magoo2]

One more time

 

[reynal74]

Thanks a lot for the help, I also found some information stating that over-voltages from DLG can be larger than over-voltages from SLG in the book Electric power distribution handbook by Tom Short pg 654-658 (just in case someone needs to cite it sometime in the future). Also, IEEE Std C.62.92.1 and C62.92.4 are of great use in the topic. I will proceed on making calculations as per this documents and revise if simulation match the info provided. Some of the curve that magoo2 posted are not downloadable, can you please revise it?

Regards,

Reynaldo Salcedo