Response of Metal-Oxide Varistors Excited by Consecutive Early-Time and Intermediate-Time HEMP Conducted Currents

High-altitude electromagnetic pulse (HEMP) can be divided into three parts: 1) early-time HEMP (E1); 2) intermediate-time HEMP (E2); and 3) late-time HEMP (E3). Most studies focus on E1 alone, as E2 and E3 pose lower peak value, especially E2, which is considered less severe than lightning. However, E2 coexists with E1 and affects victim equipment simultaneously, which may result in different effects than E1 or E2 alone. As the most widely used surge protection device, the behavior of metal-oxide varistors (MOVs) under the consecutive E1 and E2 should be investigated and compared with those under E1 or E2 alone. Based on a pulse current injection platform, the voltage, current, susceptibility, and nonuniformity behavior of two types of MOVs under the separate E1, E2, and consecutive E1 and E2 disturbances are investigated and compared. The peak residual voltages of the MOV samples under consecutive E1 and E2 disturbances reach 15 kV, which is the same as that under the E1 disturbance and much higher than that under the E2 disturbance (1.5 kV). The MOV samples are more sensitive to the consecutive E1 and E2 disturbance, particularly those with a higher nonuniformity. Finally, the response process is discussed based on the microstructural nonuniformity of MOVs.