This study aims to determine the basic physical properties of varistor, which is a protective element in a surge protection device (SPD) used to prevent damage to electric and electronic equipment due to lightning. To do this, we conducted tests of insulation resistance, leakage current, heating characteristics, accelerated aging, impulse current, and operating duty according to temperature. To measure insulation resistance and leakage current, an S1-1568 insulation resistance tester was used. To measure the temperature rise according to a change in the external environment, a convection oven was employed. For the impulse current test, a surge current generator of a direct lightning strike, which was designed and manufactured according to the IEEE and UL standards, was used. We verified that the leakage current increased and the insulation resistance decreased as the voltage and outside temperature were applied to the varistor. This meant that heating and deterioration accelerated due to the leakage current, depending on the place where the SPD was applied. Heat accumulation due to constant heating could cause a change in the physical properties of a varistor and degradation of performance, leading to failure. The impulse current test results of the varistor through the operating duty test showed that changes in insulation resistance and leakage current did not occur significantly with an increase in the number of impulse applications when the less than the maximum surge currents. On the other hand, the maximum surge current was exceeded, the insulation resistance rapidly decreased, which also rapidly increased the leakage current.INDEX TERMS SPD, MOV, varistor, surge protection device.

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 0.1<i>Ω</i>/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.