IEEE 141 and Short-circuit calculations

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NickBSi

New member
Location
MA
Hello to all,

In the IEEE 141 chapter 4.5.2 (collect and convert impedance data).
For calculations of maximum short-circuit currents, the IEEE 141 recommend to use a "Hot" or rated load resistance values for these calculations. Now, for the short-circuit calculations at reduced temperature here is the IEEE suggestion:

"For industrial plant office buildings, and for other facilities with largely non-motor loads, full load
might be applied without delay at start-up and calculations should account for pre-start-up
temperatures of components and their resistances. For a low-voltage short circuit at the end of
a feeder from a substation to a non-motor load, where the resistance of the feeder circuit is
significant in determining short-circuit current magnitude, it may be appropriate to assume a
no-load feeder conductor temperature and resistance to calculate a maximum current."

What IEEE means by "no-load-feeder conductor temperature"?

Thanks,
Nick
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
In my opinion it is similar to IEC 60909-0 ch.2.4 Maximum short-circuit currents:
When calculating maximum short-circuit currents, it is necessary to introduce the following conditions:
..............
-resistance RL of lines (overhead lines and cables) are to be introduced at a temperature of 20 oC.
 

JDBrown

Senior Member
Location
California
Occupation
Electrical Engineer
"No-load-feeder conductor temperature" is going to be the same as ambient/room temperature. It's the temperature of the conductors when no current is flowing. Once current starts to flow, the I2R losses in the copper (or aluminum) cause the conductor to heat up, which increases the conductor's resistance. This increase in resistance decreases the available fault current. So, for a worst-case fault current calculation, you need to use the resistance/impedance of the feeder at room temperature.
 
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