Busduct shortcircuit protection

[toxx1065]

Hi, In a project i am working on i have a 1000A plugin busduct fed from MDB (main distribution board) in low voltage distribution network

and the shortcircuit level on busduct is about 45kA and according to catalogues from different manufacturers the 1 second
short-circuit withstandtime of 1000A busduct is about 35KA and there is 3 cycle withstand is about 100KA. I need to know how long is the standard time of a shortcircuit for busduct as per IEC.

thank in advance.

 

[GoldDigger]

I need to know how long is the standard time of a shortcircuit for busduct as per IEC.

That will be determined entirely by the overcurrent protection device. It is not a characteristic of the bus duct itself.

 

[ron]

Hi, In a project i am working on i have a 1000A plugin busduct fed from MDB (main distribution board) in low voltage distribution network

and the shortcircuit level on busduct is about 45kA and according to catalogues from different manufacturers the 1 second
short-circuit withstandtime of 1000A busduct is about 35KA and there is 3 cycle withstand is about 100KA. I need to know how long is the standard time of a shortcircuit for busduct as per IEC.

thank in advance.

What was the calculation of 45kA? Was it RMS symetrical, which is usually the 3 cycle calculated value? You need to "compare apples and apples".

If the 45kA was a 3 cycle calculation, and the busway rating is 100kA at 3 cycles, you are ok.

 

[Julius Right]

According to IEC 60865-1 Short-circuit currents ?Calculation of effects ch.3.2.2 Calculation of thermal equivalent short-time current:
Ith=I"k*sqrt(m+n)
k=1.02 + 0.98*(exp(-3R/X))
Factor m for the time dependent heat effect of the d.c. component of the short-circuit current
and factor n for the time-dependent heat effect of the a.c. component of the short-circuit current
n is a I"k/Ik function .If the installation is located far from the power station n=1 [very close could be 0.2].
m depends on R/X of the short-circuit circuitry. A medium value is 0.08-0.2.
for R/X=0.08 k=1.8 and m=0.1 for 1 sec[50 Hz] Fig.12a
Average Ith=I"k*sqrt(1+0.1)=1.05*I"k
For 3 cycles [0.06 sec] n=1[I"k/Ik=1] but m=1.08 [the same R/X=0.08].
Then Ith=I"k*sqrt(1.08+1)=1.4422*I"k
If for 1 sec Ith=35 kA then I"k=35/1.05=33.33 kA
and for 3 cycle Ith=33.33*1.4422=48.07 kA.