Varistor Voltage Behavior of Metal Oxide Varistors Stressed by Electromagnetic Pulse

This paper describes degradation characteristics of Metal-oxide-varistors (MOVs) stressed by electromagnetic pulses (EMPs). Degradation characteristics under sub-microsecond pulses such as $1/100\mathrm{~ns}$ (TLP), $5/50\mathrm{~ns}$ (EFT/B) and $25/500\mathrm{~ns}$ are confirmed and compared with a lightning impulse current of $8/20\mu\mathrm{s}$. The varistor voltage $V_{0.01\mathrm{~ms}}$ at current 0.01 mA changes asymmetrically dependent on the direction of measurement current under repetitive sub-microsecond shots, similar to $V_{\text{lmA}}$ in the case of application of $8/20\mu\mathrm{s}$ impulses. Degradation of $V_{\operatorname{lmA}}$ is also observed, however, the change of voltage $V_{0.01\mathrm{~mA}}$ is much more sensitive. The degradation of voltages $V_{0.01\mathrm{~mA}}$ and $V_{1\mathrm{~mA}}$ progressed by repetitive sub-microsecond pulse applications, though, the failure of the tested varistor of $4\mathrm{~mm}$ in diameter and $1\mathrm{~mm}$ in thickness did not occur by application of 650 shots of $300-\mathrm{A}$ sub-microsecond pulses with 25/500 ns waveform.