NB/T 31056-2014 in English
VALIDTechnical specification for earthing for wind turbine genarator systems
- Issued on:2014-10-15
- Implemented on:2015-03-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$204.00
Introduction
Analysis of the core content of the standard
| Grounding type | Resistance requirements | Key formulas | Special condition processing |
|---|---|---|---|
| System grounding | Star connection neutral point direct grounding | - | High voltage units can use resonant grounding |
| Protective grounding | ≤2000/IG(low resistance system) | Formula (1) | Special protection is required when the ground potential rises ≤5000V |
| Lightning protection grounding | Impact resistance ≤10Ω | GB/T 50065 | Radial grounding in areas with high soil resistivity |
Key technical points
1. Grounding system design
According to clauses 4.1-4.3 of the standard, the three-in-one grounding system must meet the following requirements:
- The resistance of the common grounding device shall take the minimum value required for each functional grounding
- Lightning protection grounding must meet the standards under dry soil conditions during the thunderstorm season
- Contact potential difference calculation formula: Ut=(174+0.17ρsCs)/√ts
2. Material Specifications
Article 5.1 of the standard stipulates the minimum size of grounding materials:
Typical application case: A wind farm uses copper-clad steel stranded wire (diameter 10mm) as a horizontal grounding electrode. In the area with ρ=800Ω·m, six 60m radial electrodes are added to reduce the power frequency grounding resistance from 5.2Ω to 3.8Ω.
Special geological solutions
| Geological type | Recommended measures | Technical parameters |
|---|---|---|
| Permafrost | Deeply drilled grounding electrode | Depth ≥5m below the frozen soil layer |
| High resistivity | Underwater grounding grid | Connection line ≥15m |
| Moving sand | Increase vertical grounding electrodes | Spacing ≥2 times the length |
Implementation recommendations
- Construction phase: Video records of foundation reinforcement connection points must be kept (standard 8.1.b)
- Acceptance focus: Check ≥3 connection points of equipotential terminal board (standard 7.3.1)
- Maintenance cycle: Measure power frequency characteristic parameters every year (standard 9.2)
Typical problem handling: A 2MW unit in the ρ=1500Ω·m area, by laying 80m radial poles + adding resistance reduction agent, the impulse grounding resistance was reduced from 12Ω to 8Ω, meeting the requirements of standard 4.3.1.
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