MODELING A SINGLE-LINE TO GROUND FAULT

[burnt2x]

Can anybody help me on a specific problem?

I tried short-circuit simulation on an MV ungrounded system and I can't seem to arrive at good results on a SLG condition. How do you model an SLG?

Any comment/ tip is accepted

 

[davidbeach]

What did you get and what are you expecting?

 

[dpc]

Hint: Draw a circuit diagram showing the current path for a line-to-ground fault on an ungrounded system.

 

[EBAG]

You don't have fault current because the system is ungrounded.

Put a ground reference in your model whit moderate impedance to see some fault currents and voltages.

For example try including a reactor in your model whit very hig impedance.

Excuse my bad english.

 

[asekhar]

Ungrounded system will not have earth fault current.

Anand Sekhar

 

[slavag]

Hi Anand.
It's not exectly.
Earth fault current in ungrounded(isolated)systems are depend on the capacitance of the system. ( lenght of cables, number of cabels, voltages, etc.)
Possible current up to few amp's, I see also about ten amp's.

You can continue work with this fault.
Best Regards.
Slava

 

[asekhar]

Hi Slava,

I know that system capacitive currents exist & will depend on the size of the system & lenght of its cable network. The capacitive contibution is calculated & used for setting of earth fault protection alarm / directional earth fault protection trip for unearthed systems. But I am not sure whether the capacitive contribution is considered as fault current in fault calculations / modelling. That is what I meant.

Anand Sekhar

 

[slavag]

Hi Anand.
Yes, we talk about same.
I agree with you 100%.
Best Regards.
Slava

 

[burnt2x]

Thanks for the tips.

I tried inserting a single-phase load at the source generator. The load was set capacitive (I played around with values), but when I simulated an SLG fault on any bus, only the phase to ground voltages on rose to 1.73 times! I can't see the expected single-line to ground current!

 

[dpc]

You have to have ground path in your model. The model doesn't know about the capacitive coupling to ground.

It may not be possible to model it using whatever software you are using.

As painful as it might be to consider, it may be necessary to calculate it manually - and you might actually learn something in the process.