LV Generator Line To Neutral Fault

[healyx]

Hi,

For a LV generator (400V output) that feeds a TNC-S earthing system where 4 cables leave the generator (3 phases and 1 PEN (combined Protective earth and Neutral)). The neutral on the generator is also bonded to the earth electrode.
Is it correct to say that Line to Neutral faults in the installation will involve the zero sequence impedance of the generator? I was reading some literature that said only a Line to Ground fault involved the zero sequence impedance, which just didn't seem right to me.

Can anyone confirm this?

The main point to my question is that I always thought Line to Neutral and Line to Ground faults are usually higher for generators than 3 phase faults. If a line to neutral fault no longer involved the zero sequence impedance, this would no longer hold (for L-N anyway).

 

[ScottyUK]

Most MV applications have a 3-phase, 3-wire configuration with the neutral earthed through a resistance or transformer + resistor. Loads are connected line-line or in delta. In this type of installation only earth faults have a zero sequence component.

For a 4-wire system with a neutral then the neutral will include the zero sequence component. Line-ground faults do generally result in higher fault levels than line-line faults.

 

[waross]

A line to neutral fault will include the zero sequence impedance.
A line to ground fault with an impedance grounding system will have one zero sequence impedance for line to ground and another zero sequence impedance for line to neutral.
Some groups use the terms neutral and ground interchangeably on higher voltages.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jghrist]

Both a line-neutral and a line-earth fault will include the zero-sequence impedance of the generator. A line-neutral fault at the end of a TN-C-S circuit would have a different zero-sequence impedance for the line than would a line-earth fault because of the lack of earth return to the generator point were the neutral and earth are bonded. There would still be a zero-sequence impedance for the line, but it would be different without the earth return.