URT
URT
Power Dissipation - P V The power dissipation (or power loss) of fuse links is calculated by multiplying the rated current by the value of the voltage drop measured over the fuse link after loading with rated current up to a final the steady state temperature under the conditions described above. Initial Short Circuit Alternating Current - I K" The effective value of the short circuit current at the beginning of the short circuit which would flow if the short circuit would occur directly behind the fuse link and if the fuse link would be replaced by a member of negligible impedance. Cut-Off Current - I D Peak of the short circuit current limited by the fuse. The highest momentary value of the current during the breaking process. Melting Time - t S Period between the start of the fault current and the melting of all elements. Arcing Time or Extinguishing Time - t L Period between the melting of the elements and the definite arc extinction. Operating Time - t A Total sum of the melting time t s and the arcing time t L . Switching Voltage or Arcing Voltage - U L Maximum value (peak value) of the voltage occurring at the terminals of the fuse link during the breaking process. Melting Integral - s Integral of the current squared over the melting time. The value of the melting integral depends, amongst other things, on the construction of the fuse elements and the ambient temperature.
t s
I 2 t
I 2 dt
=
s
t 0
Arc Integral - L Integral of the current squared over the arcing time. The value of the arc integral depends on the system voltage, the short circuit current or respectively current rise rate di/dt and the short circuit impedances R K and Z K .
t a
I 2 t
I 2 dt
=
L
t s
Operating integral A
Total sum of the melting integral and the arc integral I 2 t A = I 2 t s + I 2 t L
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