![]() ![]() This is what elec calc™ software does in order to get as close as possible to the real phenomenon. The accurate calculation of the let-through energy must, therefore, integrate a chronological cumulation of the energies produced by each source. The protections associated with these different sources may not react at the same time to the short circuit current that they generate. Multiple sources: a fault can be supplied by several sources, each contributing to the short circuit current. It is then advisable to calculate an equivalent thermal current which replaces in the formulas the current Ik.Įlec calc™ takes into account the influence of this continuous component when the standard used requires it. It depends on the disconnection time and the value of the X / R ratio of the circuit at the fault point. The influence of this continuous component is especially noticeable when the point of fault is close to the sources. If we want to be more accurate, we must take into account the DC component of the fault current. Taking into account the DC component: in the formulas mentioned above, we have considered that the value of Ik is the RMS value of the AC component of the prospective fault current. It is this limited value which must be compared with the admissible thermal stress of the conductors. To operate Q1 (or Q2) in active mode: VCMmax VBE + VEEMAX VBE + VC -VCE,SAT VC+ 0.7 0.3 VCC - (II2)RC + 0.4 VCMmax 2.5 - (0.4I2)5 + 0.4 1.9 V.
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