NB/T 11313-2023
Design regulations for 35kV ice-covered overhead transmission lines (English Version)
- Standard No.
- NB/T 11313-2023
- Language
- Chinese, Available in English version
- Release Date
- 2023
- Published By
- Professional Standard - Energy
- Latest
- NB/T 11313-2023
- Introduction
Analysis of the core content of the standard
This standard aims at the special working conditions of 35kV heavily iced overhead lines. On the basis of GB50061, it adds design specifications for medium ice area (10-20mm) and heavy ice area (≥20mm), and focuses on strengthening the following technical control points:
- Path selection needs to avoid micro-topography areas such as passes and wind ducts
- Conductor safety factor increased to 2.5 (arc sag point)
- Insulator mechanical strength safety factor up to 3.0
- Establish a dynamic calculation model for icing loads
Comparison of key technical parameters
Project Medium Ice Zone Heavy Ice Zone Length of Tension Section ≤5km ≤3km Wind Load Increase Factor B1 1.3 1.5-2.0 Unbalanced Tension (Tension Tower Conductor) 35-40% 40-45%
Typical Project Implementation Cases
Liangshan Ruki Wind Farm Accident: In 2016, the N9 tower collapsed under the designed ice thickness of 20mm, and the actual ice coverage reached 33mm. After the disaster, it was renovated according to the 30mm standard. Key lessons:
- The angle of the corner tower needs to be controlled within 60°
- The design level of the air outlet should be increased by one ice zone
- Square cross-section towers should be used to enhance torsional performance
Innovation requirements for insulation coordination
New formula for calculating the number of insulators under icing conditions:
$$ N_b = \frac{V_m}{(k_h \times V_w) \times H} $$
Where V_w needs to take into account the voltage gradient decrease effect of the insulator string after icing. It is recommended to use a correction factor of k_h=1.1-1.3 in Sichuan's high altitude areas.
Key points of load calculation
The standard value of icing wind load adopts a three-layer calculation system:
Conductor load $$ W_x = \alpha W_0 \mu_z \mu_{sc} B_1 d L_p \sin^2\theta $$ Insulator string load $$ W_I = W_0 \mu_z B_1 A_I $$ Tower load $$ W_s = W_0 \mu_z \mu_s \beta_z B_2 A_s $$ Note: class=instrument>B2 coefficient needs to be determined according to the ice thickness (15mm is 1.6, 20mm is 1.8, >20mm is 2.0-2.5)
NB/T 11313-2023 Referenced Document
- GB 50061 Code for design of overhead power lines of 66KV and below
NB/T 11313-2023 history
- 2023 NB/T 11313-2023 Design regulations for 35kV ice-covered overhead transmission lines
