About the Lightning Arrester Selection
Lightning arrester (surge arrester) selection determines the appropriate discharge class, maximum continuous operating voltage (MCOV), and energy capability of metal oxide varistors (MOV) used to protect solar plant equipment from direct lightning strikes and induced switching surges.
How to calculate it
- 1For LT equipment (inverter AC output, ACDB): Type II SPD (IEC 61643-11), discharge current Imax ≥ 20 kA, voltage protection level Up ≤ 1.5 kV for 230/415 V systems.
- 2For HT equipment (11 kV or 33 kV bus): station class or distribution class MOV arrester. Select MCOV ≥ system phase-to-earth voltage × 1.05.
- 3For 11 kV system: MCOV = 11,000 ÷ √3 × 1.05 = 6,660 V → use 9 kV MCOV arrester (standard: 9 kV, 12 kV or 18 kV MCOV for 11 kV system).
- 4For DC side (DCDB): DC-specific SPD, rated for system DC voltage × 1.25.
- 5Location: install as close as possible to the protected equipment terminals. The effectiveness of an arrester degrades with distance from the equipment.
Worked example
An 11 kV solar plant in a high-lightning-density area (Keruntung, Odisha — IKL > 50). HT bus: 9 kV MCOV station-class MOV arrester on each phase. LT ACDB: Type II SPD 40 kA on each phase. DC DCDB: Type II DC SPD rated 1,200 V DC, 20 kA. Earthing of arrester body directly to the plant's main earthing grid (< 1 Ω path).
What you can calculate
- Rated voltage
- SPL/TOV
- Energy class
- IEC 60099-4
Standards & references
Frequently asked questions
Does a solar plant need lightning protection beyond surge arresters?
Surge arresters protect equipment from conducted surges (traveling on cables). For direct lightning strikes to the plant, a separate lightning protection system (LPS) per IS 2309 / IEC 62305 is required: air terminals (rods) at high points, down conductors, and an earth termination network. For ground-mount plants, the metal structure frames are often used as natural down conductors. A combined approach — LPS for direct strikes and SPDs for conducted surges — is the complete solution.
How do I know if a surge arrester has been damaged by a lightning strike?
MOV surge arresters can degrade gradually from repeated small surges or fail abruptly from a major strike. Signs of failure: (1) the arrester's built-in fault indicator shows red (many modern arresters have a visual indicator); (2) leakage current through the arrester increases — measure with a milliammeter; (3) physical cracks or carbon tracking on the housing. Damaged arresters should be replaced immediately — a failed arrester may fail short-circuit (connecting the phase to earth continuously) and must be isolated.
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