Lightning Arrester
Lightning Arrester: Complete Guide (Working, Types, Installation & Maintenance)
Short summary: A lightning arrester (LA) protects electrical systems from high-voltage surges caused by lightning or switching operations. It diverts surge energy safely to earth without affecting normal operation—safeguarding transformers, panels, equipment, and electronics.
Lightning Arrester vs. Lightning Rod
| Aspect | Lightning Rod | Lightning Arrester |
|---|---|---|
| Primary purpose | Intercepts (attracts) a strike and sends it to ground via down conductors. | Limits overvoltage inside electrical circuits by diverting surge current to ground. |
| Location | On top of structures (roof level) as part of an external lightning protection system. | Within the electrical system (service entrance, panels, transformer terminals, switchgear). |
| Operation | Provides a preferred strike point and grounding path. | Non-linear device: high resistance in normal conditions, very low resistance during surges. |
What Is a Lightning Arrester?
A lightning arrester is connected between a live conductor (phase) and earth. Under normal voltage it is effectively insulating; when a surge occurs, it becomes conductive and diverts the surge current safely to ground, thereby limiting the voltage seen by equipment.
Main Components
- Spark gap / internal gap (if present): Blocks normal voltage; breaks down at a defined surge level.
- Non-linear resistor (ZnO/MOV or SiC): High resistance at normal voltage; very low resistance during surges.
- Housing: Porcelain or polymer (silicone rubber) weatherproof body.
- Ground terminal: Low-impedance path to earth.
How a Lightning Arrester Works
- Normal operation: The arrester presents a very high resistance; no current flows to ground.
- Surge event: When voltage exceeds the arrester’s spark-over/breakdown level, its resistance collapses and surge current is conducted to earth.
- After the surge: Voltage returns to normal; the device recovers to high resistance and normal service continues.
Types of Lightning Arresters
- Rod Gap Arrester: Two rods separated by an air gap. Pros: simple, low cost. Cons: less precise, slower, mostly legacy/low-voltage use.
- Metal-Oxide Varistor (MOV/ZnO) Arrester (Gapless): Modern standard for LV–HV; very fast, reliable response.
- Valve-Type Arrester (gapped MOV/Silicon Carbide): Series of spark gaps + non-linear resistors; used historically in HV systems.
- Expulsion-Type Arrester: Arc produces gas that helps extinguish it; common in distribution networks (outdoor).
- Polymer-Housed Arresters: Same internals as above with lightweight, hydrophobic polymer housing—good for polluted/coastal environments.
Selection Criteria
- System Voltage & Arrester Class: Ensure the continuous operating voltage (Uc) and maximum continuous operating voltage (MCOV) match the system.
- Protection Level / Residual Voltage: Choose a protection level lower than the insulation withstand of equipment.
- Energy Capability & Discharge Class: Ability to handle specified surge current (e.g., 5–20 kA for LV SPDs; higher for MV/HV).
- Environment: Pollution level, UV, altitude, temperature—consider polymer housings for harsh sites.
- Standards Compliance: Reference IEC 62305 (lightning protection), UL 96A / NFPA 780 (US), and relevant IEC/IEEE arrester standards for your voltage class.
Installation Best Practices
- Install as close as possible to the equipment being protected (service entrance, main panel, transformer HV/LV bushings, motor control centers).
- Provide a low-resistance, low-inductance earth path: short, straight conductors; minimum bends; no sharp loops.
- Target earth resistance < 10 Ω (site-dependent)—lower is better. Bond all grounds to a common earth.
- Match arrester Uc/MCOV and temporary overvoltage (TOV) withstand to the system.
- For panels, place arresters on each phase to neutral/earth; for MV/HV, mount at line terminations and equipment terminals.
- Respect clearances/creepage and torque values; follow manufacturer installation manuals and local codes.
Maintenance & Testing
- Visual inspection: Look for cracking, tracking, contamination, chipped housings, or flashover marks.
- Cleaning: Periodically clean in dusty/salty areas to prevent surface leakage paths.
- Leakage current monitoring: Trending of resistive leakage (esp. for ZnO) helps detect ageing/moisture ingress.
- Thermography: Infrared scans reveal hot spots due to poor connections or internal faults.
- Ground testing: Measure earth resistance regularly; repair corroded lugs and loose bonds.
- Replacement: Replace any arrester showing physical damage, abnormal leakage, or that has operated beyond rated energy.
Benefits
- Protects expensive equipment and electronics from surge damage.
- Improves system reliability; reduces unplanned outages and downtime.
- Lowers repair/replacement costs and improves safety.
Applications
- Power generation plants, transmission and distribution substations.
- Industrial facilities, PLC/SCADA, drives, motors, VFDs.
- Commercial and residential main panels and sensitive electronics.
- Renewables (solar arrays, wind turbines) and telecom sites.
Safety Tips
- Isolate circuits and apply LOTO before work; verify absence of voltage.
- Use appropriate PPE for the voltage level.
- Never install an arrester without a verified, bonded grounding system.
- Test before lightning season; replace suspect units promptly.
Conclusion
Lightning arresters are essential for modern electrical safety. Selecting the right type, installing it correctly with a robust earthing system, and maintaining it routinely will significantly enhance protection, uptime, and safety for homes, businesses, and utility networks.
Quick FAQ
Q1: Do lightning arresters attract lightning?
A: No. They do not attract lightning. They limit overvoltage inside the electrical system after a surge occurs.
Q2: Where should I install an arrester?
A: At service entrances, main panels, and directly at sensitive/load equipment or transformer terminals—always with short, straight earth conductors.
Q3: What standards should I look for?
A: IEC 62305 for lightning protection; UL 96A and NFPA 780 in the US; and the applicable IEC/IEEE arrester product standard for your voltage class.
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