1、 Core selection considerations
Voltage level and insulation coordination
Basic parameters: This is the starting point for selection, determining the basic number of required insulator strings. It is necessary to calculate and determine the small creepage distance and structural height that meet the requirements of power frequency voltage, operating overvoltage, and lightning overvoltage based on the high operating voltage of the system, the pollution level of the area, and the altitude.
Altitude correction: For every 100 meters increase in altitude, the air insulation strength decreases by about 1%. In high-altitude areas, it is necessary to increase the number of panels or choose products with higher climbing distances.
Mechanical load
Rated mechanical failure load (SML): This is the core mechanical indicator of insulators, such as U70BP, U100BP, U120BP, U160BP, U210BP, etc. The number represents the rated load (kN). It is necessary to choose based on the high tension or safety coefficient requirements in the line design, and consider extreme working conditions such as wind, ice, and wire breakage. The commonly selected Enron coefficient (rated load/large service load) should not be lower than 2.5-3.0.
Triple/double joint: For important lines or large spans, double or even multiple joint arrangements are often used to provide high mechanical integrity or redundancy.
Environmental conditions (one of the determining factors)
Pollution level: This is a key external factor that affects the performance of insulators. The national standard divides pollution levels into five levels: a (very light), b (light), c (medium), d (heavy), and e (very heavy).
Clean area (a, b): Standard type can be selected.
Medium and above polluted areas (c, d, e): anti fouling type, such as U × × BP type, needs to be selected. Its creepage distance is much greater than the standard type, and it adopts optimized umbrella shapes such as aerodynamic type and large umbrella to enhance self-cleaning and anti flashover capabilities.
Coastal areas, industrial zones, and saline alkali land are usually heavily polluted areas, and products with enhanced anti pollution or aerodynamic properties (such as U XXX BP - XXX M) should be selected.
Meteorological conditions: Special consideration should be given to areas with frequent winds, thunderstorms, and snow and ice.
Strong wind/typhoon zone: Aerodynamic insulators can be considered, whose streamlined design can reduce wind resistance and wind noise, improve wind deflection resistance and anti flutter ability.
Multiple lightning zones: Confirm that the lightning impulse withstand voltage of the insulator string meets the requirements, and sometimes consider installing arcing angles.
Heavy ice area: The umbrella skirt structure should not be prone to ice accumulation, or the problem of ice flash should be considered in the design.
Types and characteristics of insulators
Standard type: used in clean areas, with good economy.
Anti pollution type: used in polluted areas, with large climbing distance and complex umbrella shape.
Aerodynamic type: Upgraded from the anti fouling type, the umbrella shaped wind tunnel optimization combines excellent anti fouling and wind resistance performance, suitable for important power lines and harsh environments.
Large diameter insulator: sometimes used to prevent bird damage and flashover.
2、 Suggestions for selection process
Collect basic data: clarify the voltage level, meteorological zoning, pollution distribution map, wire model, tower design load, altitude, etc. of the line.
Determine pollution level: Based on the new distribution map of pollution areas and combined with on-site survey, determine the accurate pollution level of each section.
Electrical calculation: Calculate the required single piece creepage distance and minimum number of pieces based on voltage level, pollution level, and altitude. Verify its lightning and operational shock tolerance level.
Mechanical verification: Based on the comprehensive load of the wire, calculate the small rated mechanical load of the required insulator and select the corresponding grade of product (such as U120BP).
Model selection: Based on the above results, select specific models from the product series that meet electrical and mechanical requirements (such as U120BP-146D, U160BP-170M, etc.).
Technical and economic comparison:
Single string scheme vs. double string scheme: better in terms of cost-effectiveness and tower head size.
Products from different manufacturers: Compare their specific technical parameters (such as actual climbing distance, size, weight), type test reports, operating history, and prices.
Full life cycle cost: The initial investment of glass insulators may be slightly higher, but their characteristics of "zero value self explosion", zero value free testing, and long service life can significantly reduce the cost of later inspection and maintenance. Evaluation should be conducted from a long-term operational perspective.
Final determination: Formulate technical specifications, clarify models, quantities, technical standards, and acceptance requirements.
3、 Trustworthy advantages considerations for selecting glass insulators
When comparing with other materials such as porcelain and composite insulators, it is important to emphasize the following characteristics of glass insulators, which are also important additional items in the selection decision:
Zero value self explosion ", no need to measure zero value: Insulators that fail during operation will automatically break and fall off, making it easy to detect on the ground and saving a lot of manual and cost inspection on towers. The operation and maintenance advantages are enormous.
Long lifespan and anti-aging performance: Tempered glass material is stable, and electrical and mechanical properties do not deteriorate throughout the entire lifecycle.
Good dimensional consistency: easy to install accessories such as pressure equalization rings and optimize electric field distribution.
