EXPLANATORY INFORMATION - Surgetek

Example of Calculation:Given:Load breaking capacity S aShort-circuit duration T kI k"kA400300200100A = 1000 mm²800To be determined: Required cross section A of cable or barA remote short circuit is assumed.S aThree-phase current I k " = I k = I a = ———√ 3 • U N5040302010600500400300200S aSingle-phase ac current I k " = I k = I a = ——U NThe required cross-section of the cable or bar can now be calculated from the aboveequations or taken from the diagrams using I k ".The permissible rated current time of an earthing and short-circuiting device isexpressed by the cross-section shown on the short-circuiting cables or bars.Notes– Earthing and short-circuiting devices are designed for loading only once at thepermissible rated current time!– Short-circuiting cables of multi-pole earthing and short-circuiting devices must havethe same cross sections.– The cable lengths of earthing and short-circuiting devices have to be at least 1.2times the distance between two connection points. Neither should cable lengths beunnecessarily long, since cables deflect strongly in the event of a short circuits.– The following conditions must be observed for earthing and short-circuiting devicesconnected to cables in parallel to achieve certain total cable cross sections:1. identical cable lengths and cross-sections,2. identical connections and connection points,3. devices fitted close to each other with parallel cable routing,4. the permissible rating per cable has to be reduced to 75 % of the rating forcable cross section.Note:Devices may be fully loaded if it is ensured that arthing and short-circuiting devicesconnected in parallel are only loaded once with the short circuit current (no shortinterruption).This applies generally to systems with nominal voltages above 110 kV.Cross section Max. permissible short circuit current I k , shown for aof copper duration ofcablemm² 10 s 5 s 2 s 1 s ≤ 0.5 s16 1 000 1 400 2 200 3 200 4 50025 1 600 2 200 3 500 4 900 7 00035 2 200 3 100 4 900 6 900 10 00050 3 100 4 400 7 000 9 900 14 00070 4 400 6 200 9 800 13 800 19 50095 5 900 8 400 13 200 18 700 26 500120 7 500 10 600 16 700 23 700 33 500150 9 400 13 200 20 900 29 600 42 00021Current Rating of Short-Circuiting Bars ofE-Cu F 20Initial temperatureFinal temperaturefor bars of E-Cu F 20:A = 5.54 I k " √T k50.1 0.2 0.5 1 2 3 5 10 s20° C250° Cfor bars of E-Al Mg Si 0.5 F17:A = 8.79 I k " √T kT kfor T k ≥ 0.2 sfor T k ≥ 0.2 sA bar cross-section in mm²I k" maximum initial ac short circuitcurrent in kA in accordancewith DIN VDE 0102T k short-circuit duration in sI k"kA4003002001005040302010A = 1000 mm²80060050040030020050.1 0.2 0.5 1 2 3 5 10 sT kCurrent Rating of Short-Circuiting Bars ofE-Al Mg Si 0.5 F17