Calcolatore Protezione da Sovratensione
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Short Circuit Current
12,028 A
Short Circuit Current vs Transformer Rating
Formula
## Estimating Short Circuit Current The maximum short-circuit current at a transformer secondary determines the required interrupting capacity of protective devices. ### Formula **I_sc = I_fla / (Z% / 100)** Where I_fla is the transformer full-load secondary current and Z% is the transformer impedance. **I_fla (3-phase) = kVA x 1000 / (sqrt(3) x V_secondary)** This gives the maximum available fault current at the transformer terminals. Downstream cable impedance reduces the fault current at the load.
Esempio Risolto
500 kVA transformer, 5% impedance, 480 V secondary.
- 01FLA: 500,000 / (1.732 x 480) = 601.4 A
- 02I_sc: 601.4 / 0.05 = 12,029 A = 12.0 kA
- 03Available SC kVA: 500 / 0.05 = 10,000 kVA
Domande Frequenti
Why is short-circuit current important?
All protective devices (breakers, fuses, switches) must be rated to safely interrupt the available fault current. Under-rated devices can explode.
Does this include utility contribution?
This calculation assumes the utility source has infinite capacity (worst case at transformer). In practice, utility impedance slightly reduces the fault current.
How does cable length reduce fault current?
Cable impedance adds to the transformer impedance, reducing the fault current at downstream points. Longer cables mean lower fault currents.
Impara