Fault current at 11KV 1

[lyledunn]

I am interested to know the typical line to earth fault level on the primary of an 11KV/400/230v D/S Trfmr, the type generally used on the UK public distribution network.
Where the tank earth and the secondary star-point earth connection are bonded the fault voltage appearing between the installations earthed parts connected via the faulted transformer and true earth would equate to the voltage drop across the tank earth electrode.
I know that the earth fault currents are often attenuated by LERs or similar devices located in sub-stations and I wonder what might be the typical magnitude and duration of these fault voltages.


Regards,

Lyledunn

 

[Zogzog]

KVA? %Z?

You need to know these, voltage alone tells us nothing

 

[davidbeach]

High side, transformer impedance won't have much impact. All you need to know is the source impedance, Z1 and Z0. Here it could vary over a wide range; across the pond I don't have a clue.

 

[lyledunn]

Sorry guys, I guess I wasnt too clear in my question. I am more interested in the typical magnitude of bolted earth fault currents on the 11KV network due to deliberate attempts to restrict them by LERs or other devices. For example, would it be usual to restrict earth fault currents to a certain manageable value of say 2KA?
The KVA, %Z and electrode resistances are obvious considerations but I am really only looking for typical values.
Many thanks.

Regards,

Lyledunn

 

[davidbeach]

No idea, since here systems at that level are all solidly grounded.

 

[Marmite]

Normal practice is to limit the earth fault current to the equivalent full load current of the 33/11kV transformer at the primary substation, so typically you are looking at 650-1000A. The thermal rating of the resistor is typically 10 secs, but you would expect the protection to operate and clear the fault much quicker than that.
Regards
Marmite

 

[ScottyUK]

UK industrial users with private MV networks typically have E/F levels similar to those Marmite has indicated or perhaps even a little lower, down to about 300A.


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