OVERVOLTAGE DURING SINGLE LINE FAULT

[JAMartinezB]

Hi, I would like to know the cause of the overvoltage in non-faulted phases during a single line fault of a three phase system. What interaction in the generator or system impedance causes this?

Regards.

 

[Robert789]

My understanding of it is that it is caused by a shift in the voltage of the neutral with respect to remote earth.

If a bolted fault occurs on one phase of a distribution feeder, the voltage across the fault is essentially zero, but the voltage at the substation is still pretty close to the normal line to neutral voltage.

The path of fault current is from the source, along the phase conductor, through the fault, and back to the source through the neutral/earth return path.

If the line voltage is 7.2 kv, and the phase conductor has 2 times the impedance of the earth/neutral return path, then the voltage from neutral to remote earth at the fault location is about 2.4 kv. This results in an increase of the line to neutral voltage for the unfaulted phases near the fault location.

 

[ScottyUK]

It mainly happens in impedance or resistance grounded systems and in ungrounded systems because the neutral voltage is able to rise above earth potential by the line-neutral voltage of the faulted phase.


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If we learn from our mistakes I'm getting a great education!

 

[JAMartinezB]

Thank you all. Very logical.

Regards.