After a storm or switching surge, plants ask whether the arrester “did its job.” The harder question is whether the arrester is still fit for the next event. Polymer or porcelain housings can look fine while internal moisture or cumulative energy has raised resistive leakage toward failure—or left the unit short of protective margin.
Underground cable ampacity and busduct joint IR are adjacent electrical stories. Vacuum breaker timing and transformer PD are different craft. This note is medium-voltage surge arrester condition—leakage, counters, and replacement discipline.
Arresters clamp overvoltage by conducting when voltage exceeds their protective level. Age, sealing leaks, and repeated high-energy operations degrade the metal-oxide blocks. Symptoms include rising leakage current, hotter housings under IR, or surge counters that rack up without a matching investigation. A unit that failed short is a permanent ground; one that failed open leaves the feeder unprotected. Neither failure announces itself with a friendly HMI banner.
Practical monitoring
Trend leakage (where instrumented) and surge counts against weather and switching logs. IR survey arresters with the rest of the yard—hot spots relative to sisters matter. After a known severe surge or near-fault, inspect and test per the utility or OEM criteria rather than assuming survival. Replace on leakage/count/age rules written before storm season, not on “it still looks white.”
Pretty housings do not equal protective capability. Plants that watch leakage and counters retire arresters before the next transient writes the outage report.