The effect of Short-Circuit Current in Cables

A short circuit occurs when two points with different potentials are improperly connected directly or by a conductor with very low impedance (or resistance) in a normal circuit. Short circuits generate very large currents, often damaging electrical equipment or causing fires. In power systems, abnormal connections (short circuits) between phases or between a phase and ground (or neutral line) can result in extremely large currents flowing through them. These currents are much greater than the rated current and depend on the electrical distance between the short-circuit point and the power source. For example, when a short circuit occurs at the generator terminal, the maximum instantaneous short-circuit current flowing through the generator can reach 10 to 15 times the rated current. In large-capacity power systems, short-circuit currents can reach tens of thousands of amperes. This can have serious impacts and consequences on the normal operation of the power system.

Key Impacts on Cables
Although this current exists for a short time, it generates enormous heat instantaneously. If the cable cross-section is insufficient or the protection system fails, it will lead to:

1. Thermal Stability Degradation: Insulation melting, conductor burning, and even fire.   
2. Electrodynamic shock: The mechanical stress generated by a huge current may cause conductor deformation or joint damage.

Selection constraints: When selecting cables, their short-circuit thermal stability cross-section must be verified to ensure that they can withstand the expected short-circuit current without damage. In short, it is the maximum instantaneous current index that the cable must withstand under fault conditions, and it is an important basis for verifying the cable's thermal stability and selecting protection equipment.