Faultströmmen

Faultströmmen, or fault current, is the instantaneous electric current that flows through an electrical power system when a fault creates a low-impedance path, such as a short circuit. Common fault types include single-line-to-ground, line-to-line, double-line-to-ground, and three-phase faults. The fault current is typically much larger than normal operating current because the impedance seen by the sources drops significantly at the fault location. The exact magnitude depends on the Thevenin equivalent source behind the fault and the impedance of the network between the source and the fault.

Calculation and modelling of fault currents are essential for protection and equipment design. Short-circuit currents are estimated with network models using Thevenin or impedance methods. For simple cases, I_fault ≈ V_th / Z_th; unbalanced faults require analysis with symmetrical components. Short-circuit studies determine maximum fault currents and help set protection ratings and coordination, ensuring devices trip correctly and selectively.

Protection and operation play a central role in handling fault currents. Protective relays and circuit breakers are designed to interrupt fault current quickly to minimize damage and maintain system stability. Protection schemes are coordinated so that the device closest to the fault clears the fault with the appropriate operating time, while other parts of the network remain supplied when possible.

Implications and safety concerns include potential insulation damage, overheating, mechanical stress, arc flash, and service interruptions. Mitigation measures involve adequate protection settings, proper network design, insulation coordination, and planned generation or load shedding during faults to limit the impact on the system.