Understanding Progressive Failure Of Surge Arresters: Key Signs, Risks, And Solutions For 11kv And 15kv Systems
A lightning surge arrester is designed to protect electrical equipment from transient overvoltages. However, surge arresters do not fail instantly in most cases. Instead, they undergo a gradual degradation process known as progressive failure. Recognizing this pattern helps maintenance teams prevent unexpected downtime and transformer damage.
What Is Progressive Failure in Surge Arresters?
Progressive failure refers to the stepwise deterioration of a surge arrester’s internal metal-oxide varistors (MOV) due to repeated or prolonged electrical stress. Each surge event causes microscopic damage that accumulates over time, leading to increased leakage current, reduced clamping voltage, and eventual thermal runaway.
Common Causes of Gradual Degradation
Multiple factors contribute to progressive failure in field installations:
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Repeated lightning strikes – Each surge slightly degrades the non-linear resistance of the MOV blocks.
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Temporary overvoltages – Sustained overvoltage from system faults accelerates aging.
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Moisture ingress – Failed housing seals allow humidity to contaminate internal components.
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Pollution on housing – Surface leakage currents create uneven thermal stress.
For example, an 11kv lightning arrester installed in a coastal area may develop progressive failure within 5–7 years due to salt pollution and frequent minor surges, whereas the same model in a dry inland zone could last 15 years.
Identifying Failure Stages in Surge Arresters
| Failure Stage | Observable Symptoms | Recommended Action |
|---|---|---|
| Initial degradation | Slightly increased leakage current (<0.5 mA) | Schedule annual thermography |
| Moderate degradation | Leakage current 0.5–1.0 mA; warm spots on housing | Plan replacement within 6 months |
| Advanced degradation | Leakage >1.0 mA; audible noise; discoloration | Immediate replacement |
| Imminent failure | Thermal runaway; cracked housing; blown fuse | Isolate and replace urgently |
Impact on Transformer Protection
A failed lightning arrester in transformer applications no longer clamps overvoltages, leaving the transformer winding exposed to full surge energy. This is particularly critical for distribution transformers protected by a 15kv lightning arrester. When the arrester progressively fails, its leakage current may also increase system losses and cause nuisance fuse blowing. Regular monitoring of surge arresters – including periodic leakage current measurement and infrared inspection – is the most effective way to detect progressive failure before it leads to transformer damage or unplanned outages.
For technicians, tracking the service history of each lightning surge arrester and replacing units after a defined number of surge events (or based on manufacturer’s aging curves) ensures system reliability across 11kv and 15kv networks.
