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Fault level at the end of a cable run
2

Fault level at the end of a cable run

Fault level at the end of a cable run

(OP)
I am trying to determine the fault level at the end of a length of cable. What is the formula?

eg

at an MSB the fault level is 30kA. If the cable is 95mm² XLPE and the route length is 30m. What is the prospective F/L at the end of the cable?

Phill

RE: Fault level at the end of a cable run

The fault level at the gear is based on the source impedance to the gear.  Add the cable impedance and you will have the source impedance to the end of the cable.  Then make your fault.

RE: Fault level at the end of a cable run

V=IZ and Z=R+jX

Calculate source impedance from 30 kA and system voltage.
Add source impedance and cable impedance in series.
Divide source voltage with the total impedance.

You may have to assume source X/R ratio between 8 and 15. Use per phase values.

Look up any good book, like IEEE Red Book, on short circuit calculations for more formula and methods.

OR use a software. You may be able to find some free ones for simple calcs on the web, but you need to check their validity.

Rafiq Bulsara
http://www.srengineersct.com

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