The Effects of Long-Term Operation on the Insulation Resistance of Gas Discharge Tube

Gas discharge tube (GDT) protectors are widely used in low voltage system to provide protection from lightning and alternating current power faults. GDTs are designed to be insulating under operating voltage and current flow. Under large transient voltage, such as from lightning, the GDT becomes a conductor, essentially short circuiting the system and thus protecting the electrical components from overvoltage damage. However, after a long-term use and multiple discharges, the GDT has the risk of a short-circuit failure due to a decrease in insulation resistance. In this paper, through multiple discharge experiment platforms, the research on the evolution of the GDT life cycle insulation degradation and the failure samples were made. Then, the internal composition and structural changes of the cavity were compared and analyzed. The results show that during the last 10% of the life cycle, the insulation resistance value continues to drop by several orders of magnitude, and the insulation resistance value before failure is mostly below 1k Ω. During the entire life cycle, the breakdown voltage first increases and then decreases. In addition, by X-ray observation of the short-circuit failure samples after multiple discharges, it was found that two different anomalous substance growth conditions were present inside the cavity, such as interelectrode flocs and tube wall accumulation.