![]() Resistances and reactances that make up the loop. Zsc: total impedance of the fault loop at the point in question this is the vectorial sum of the.U0: phase-to-neutral voltage of the installation.c: voltage factor taken as being 0.90 for minimum short-circuits and 1.1 for maximum short.Resistances and reactances of the fault loop It is possible to determine the value of a short-circuit atĪny point in the installation by adding together the We need first the value of the short circuit current! The mechanical stress withstand capacity of the cable: The thermal stress withstand capacity of the cableĢ. Via Marconi 5, 24044 Dalmine (BG) – Italyįor the rating to withstand the effects of short-circuit currentsġ. This course provides practical overview of short circuit performance of a cable.Ĭable sizing to withstand short-circuit current - ExampleĪngelo Baggini, Bergamo University - Engineering Department It is expected, however, that a cable installation will remain safe in operation and that any deformation remains within tolerable limits even after several short circuits. The short circuit strength of a cable system is not quantitatively defined with regard to permissible number of repeated short circuits, degree of deformation or destruction or impairment quality. With single-core cables however the mechanical effect - related to the magnitude of the peak short-circuit current - is of such significance that, next to the thermal, the mechanical strength of both cable and its supports should be investigated.Īlso accessories must be rated with respect to thermal and mechanical short-circuit stresses. For multi-core cables in most instances the thermal effect - related to the magnitude of fault current and clearance time - is the critical parameter, since the cable will normally have enough mechanical strength. The thermo-mechanical effects of the current shall also be considered.įor the given short-circuit condition the short-circuit capacity of a cable should be investigated with respect to all these parameters. and should be limited to a permissible short-circuit temperature. The temperature rise is important for its effect on ageing, heat pressure characteristics etc. Indirectly the temperature of adjoining insulation and protective covers also increases,Įlectro-magnetic forces between the current-carrying components. A short circuit causes very extreme stresses in a cable which are proportional to the square of the current:Ī temperature rise in the conducting components such as conductor, screen, metal sheath, armour. ![]()
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