Surge arresters are critical components in electrical systems, designed to protect equipment from overvoltage events caused by lightning strikes, switching operations, or other transient surges. However, like all protective devices, surge arresters can fail. Understanding their failure modes is essential for proper maintenance and system reliability. Here are the primary failure modes for surge arresters:
1. Thermal Runaway
Cause: Occurs when the surge arrester experiences excessive continuous overvoltage or degradation of the metal-oxide varistor (MOV) blocks, leading to heat generation.
Effect: Increased heat causes further degradation, leading to a self-sustaining cycle of heat buildup and eventual catastrophic failure.
Detection: Temperature rise, visible bulging, or discoloration.
2. Electrical Overstress (EOS)
Cause: Surge arresters can be subjected to electrical stresses beyond their energy absorption capacity, such as direct lightning strikes or power frequency overvoltages exceeding their design limits.
Effect: Internal damage to MOV blocks or insulation breakdown, leading to failure of surge protection.
Detection: High leakage current, insulation breakdown, or permanent voltage rise across the arrester.
3. Moisture Ingress
Cause: Compromised sealing, cracks in the housing, or poor manufacturing leading to water entering the arrester.
Effect: Moisture can lead to insulation degradation, increased leakage current, corrosion, and electrical flashover.
Detection: Visible moisture, corrosion, increased leakage current, and partial discharge activity.
4. Aging and Wear-Out Failure
Cause: Long-term exposure to transient surges, continuous minor overvoltages, or environmental stresses can degrade the MOV blocks over time.
Effect: Reduced energy absorption capacity, increased leakage current, and eventual insulation failure.
Detection: Periodic performance tests indicating reduced energy absorption capacity or increased leakage current.
5. Partial Discharge and Insulation Breakdown
Cause: Insulation defects, contamination, or moisture ingress can lead to partial discharges within the arrester housing.
Effect: Progressive degradation of insulation leading to complete dielectric breakdown and failure.
Detection: Partial discharge measurements and insulation resistance testing.
6. Mechanical Damage
Cause: Physical impacts during transportation, installation errors, or external mechanical stress (e.g., wind, ice load).
Effect: Cracks in the arrester housing, compromised sealing, or damage to internal components.
Detection: Visual inspection, cracks, or structural deformation.
7. Poor Installation and Handling Errors
Cause: Improper installation, over-tightening of connections, or mounting in unsuitable environments.
Effect: Mechanical stress, poor grounding, or insufficient clearance leading to reduced performance or immediate failure.
Detection: Visual inspection, improper clearances, or grounding deficiencies.
8. Material Defects and Manufacturing Errors
Cause: Defects during manufacturing, such as improper MOV block sintering, poor quality control, or substandard materials.
Effect: Premature failure due to insufficient voltage handling capacity or insulation weakness.
Detection: Quality testing and initial commissioning tests.
Preventive Measures and Mitigation:
Routine Testing: Regular insulation resistance tests, leakage current measurements, and thermal imaging can detect early warning signs.
Proper Installation: Ensure correct grounding, positioning, and handling during installation.
Environmental Protection: Use surge arresters suited for environmental conditions (e.g., UV protection, moisture-resistant designs).
Quality Control: Select arresters from reputable manufacturers and verify compliance with standards (e.g., IEC 60099).
By understanding these failure modes, surge arrester reliability can be significantly improved, preventing equipment damage and enhancing power system protection.
