Talk:TN system - Earth-fault current calculation

Archives of past discussions

• Flow archive

Método de composición y Convencional

Hola: al mencionar el uso del método de composición para el cortocicuito bifàsico..¿no habría que mencionar que la resistencia de los cables se debe calcular a 70/90 ºC (PVC/XLPE) ? Porque en definitiva es el caso del valor mínimo de cortocircuito. Y, como es para el valor mínimo, ..¿no habría que mencionar que la tensión Uo debe ser multiplicada por 0.95?

Y para el método Convencional..¿no habría que mencionar que la tensión Uo debe ser multiplicada por 0.95?

Gracias Albertouy (talk) 02:49, 20 April 2026 (UTC)

Hi, thank you for asking your question on the Wiki.

Here is the answer to your question #1: The output of the composition method is the calculation of the maximum short-circuit current at the extremity of the circuit. The original composition method of calculation does not apply any reduction factor on the voltage. Taking just U0 in the formula maximises the result, while multiplying by 0.95 would lower the result. And we cannot recommend “changing” the initial calculation method. The composition method is an approximative method and gives no specific indication regarding the temperature of calculation of the impedance.

Regarding your question #2, the answer is no. The conventional method presumes that in the event of a short circuit, the upstream voltage (at the origin of the circuit) equals 80% of the rated voltage (which justifies the 0.8 factor applied to Uo). This is a practical estimate taking into account the upstream impedances.

Don't hesitate to reply in case you need additional information. Maria Vallet (talk) 14:49, 7 October 2026 (UTC)