Arrester
An arrester, specifically a surge arrester or lightning arrester, is a passive protection device built with metal-oxide varistor (MOV) blocks that limits high transient voltages by diverting excess surge energy from a line or signal conductor to ground, reducing voltage amplitude across protected equipment to a safe value below its impulse withstand level (BIL).
In shop floor maintenance, arresters are installed in parallel with critical assets like transformers and switchgear at substations or transformer feeders. They exhibit high resistance at normal operating voltage, switching to low resistance during a surge to conduct heavy current to earth, then reverting to high resistance once voltage normalizes. This enables repeated operation per ANSI C62.11 standards, protecting equipment from transient overvoltages and ensuring operational continuity.
Why is MTBF inappropriate for surge arresters?
Arresters lack random or wear-out failures; failure occurs only when applied stress exceeds capability, making annual probability of failure (PoF/year) the correct reliability metric.
How does an arrester differ from a fuse?
A fuse is a current-limiting device protecting against fault currents; an arrester is a voltage-limiting device protecting against surge voltages.
What happens when an arrester experiences end-of-life?
It becomes a short circuit, conducting all available power-frequency fault current to earth, potentially causing significant pressure build-up requiring pressure relief.