Necessity of Protective Coordination Systems According to Battery Capacity

As the capacity of lithium-based batteries rapidly is increasing, the number of applications using them is continuously increasing. However, this leads to the risk of fire and explosion, and thus, the number of accidents is increasing. To analyze the magnitude of short circuit currents according to the battery capacity and external circuit impedance and the necessity of protective coordination, this study conducted experiments using cylindrical batteries with capacities of 800, 2200, 3000, and 5000 mAh and cables with an impedance of 0.1Ω/m. Results indicated that as the battery capacity increased, the short circuit current increased and circuit-opening time decreased. However, as the circuit impedance increased, the short circuit current decreased and circuit-opening time increased. Based on these results, we reviewed protective systems applied to batteries and analyzed their problems. For protective systems designed considering the maximum short circuit current, if the state of charge is low or the impedance is high at the point of short circuit, the protective system does not operate when short circuit occurs, thus failing to block the circuit and potentially leading to fire. Therefore, while designing protective systems, it is appropriate to use multiple circuit breakers and fuses, considering the short circuit current according to the battery capacity and circuit impedance to enable protective coordination between devices.