System Diagram Design: A Five-Step Process
The design of a primary system diagram for switchgear follows a five-step process: load analysis → main connection scheme → equipment selection → short-circuit calculation → drawing preparation. Industry experts note that the design should proceed as follows: load analysis (circuits/capacity), main connection scheme (single busbar/double busbar/ring main unit), equipment selection (circuit breakers/CTs/surge arresters), short-circuit calculation (breaking capacity/dynamic and thermal stability verification), and drawing preparation (standard symbols/circuit numbering).
The design must adhere to standards (using GB/T 4728 symbols) and undergo proper verification.
Five-Step Process
- Load Analysis: Analyze and summarize the load (capacity/current) for each circuit;
- Main Connection Scheme: Determine the scheme based on reliability requirements (e.g., single busbar for economy vs. double busbar for reliability);
- Equipment Selection: Select equipment (circuit breakers/instrument transformers/surge arresters) based on parameter matching;
- Short-Circuit Calculation: Calculate short-circuit currents and verify breaking capacity as well as dynamic and thermal stability;
- Drawing Preparation: Create the diagram using standard symbols (GB/T 4728), circuit numbering, and parameter annotations.
Key Design Points
First, ensure a rational scheme.
Select the main connection scheme based on reliability requirements (balancing the cost-effectiveness of single busbars against the reliability of double busbars).
Second, verify equipment selection.
Check equipment specifications (breaking capacity/current ratings) against short-circuit calculations to prevent under-specification.
Third, use standardized symbols. Draw using standard symbols (GB/T 4728) to avoid misinterpretation.
Fourth, ensure consistent numbering.
Standardize circuit and equipment numbering (across both the design and the bill of materials) to facilitate management.
Pitfalls to Avoid
First, “over-engineering” of schemes: Avoid excessive use of double-busbar configurations (which entail high costs) and instead select single-busbar setups based on actual needs.
Second, “inadequate equipment selection”: Insufficient breaking capacity poses short-circuit risks;
always perform short-circuit verification.
Third, “inconsistent symbols”: Non-standard symbols lead to misunderstandings;
use standardized symbols.
Trends and Recommendations
System diagram design is moving toward “digitalization”: CAD electrical design (utilizing intelligent symbols) and digital twins (3D system modeling) enhance efficiency.
Designers are advised to follow a “five-step process, standardize symbols, and verify equipment selection.”
A well-designed system diagram ensures the reliability of switchgear.
