Short-Circuit Fault Characteristics and Protection Devices for kt cloud AIDC UPS Power Equipment

When a short-circuit fault occurs in UPS power equipment, the asymmetric short-circuit current first spikes sharply, then converges to the symmetric short-circuit current over time. The initial current is larger due to the DC component, and it explains that this can expand up to 2.83 times.

Damage falls broadly into two types. Thermal burnout is explained by Joule's law (I²Rt) — the larger the current, the greater the resistance, and the longer the breaking time, the greater the heat generated. Mechanical damage occurs due to electromagnetic force between conductors, where currents in the same direction act as an attractive force and currents in opposite directions act as a repulsive force, deforming the conductors.

As a countermeasure, UPS Static Bypass is presented. It bypasses the fault current through the UPS's internal bypass, guiding the upstream breaker to trip only the faulted section while maintaining power to the healthy circuit.

Existing CBs operate at 3~8 cycles, around 50ms, which is too slow to block asymmetric fault current. Therefore, semiconductor breakers such as SSCB (Static state circuit breaker), which break within a few microseconds to 4ms, are introduced as a strong alternative for UPS protection.

Ultimately, as AI workloads increase UPS capacity and lower system impedance, fault current becomes even greater. Data center power design must now go beyond supply and consider a defense-centered optimal protection configuration that combines CB, Static Bypass, and SSCB.