Secondary Circuit Design: A Six-Step Process
The design of secondary circuits for power distribution cabinets follows a six-step process: defining control requirements, creating schematic diagrams, configuring terminal blocks, selecting components, drafting wiring diagrams, and performing verification.
Industry experts note that the design should proceed as follows: control requirements (switching/signaling/protection), secondary schematics (control logic), terminal blocks (wiring allocation), component selection (relays/instruments/selector switches), wiring diagrams (routing), and verification (short-circuit/logic checks).
Crucially, the design must prevent “parasitic circuits” and logic errors.
The Six-Step Process
- Control Requirements: Switching, signaling, interlocking, and protection (functional requirements);
- Schematic Diagrams: Secondary principles (control logic and circuit numbering);
- Terminal Blocks: Terminal allocation (circuit mapping);
- Component Selection: Relays, instruments, and selector switches (parameter matching);
- Wiring Diagrams: Secondary wiring (routing and wire numbering);
- Verification: Logic checks (preventing parasitic circuits) and short-circuit checks (preventing unintended operation).
Key Design Points
First, ensure clear logic.
Control logic (interlocking/protection) must be clearly designed to prevent unintended operation.
Second, prevent parasitic circuits.
Check for parasitic circuits (cross-circuit leakage) to avoid malfunctions.
Third, standardize numbering.
Circuit and terminal numbering must be standardized (for organized management) to prevent wiring errors.
Fourth, ensure component compatibility.
Match parameters (voltage/contacts) for relays and instruments to prevent equipment failure.
Pitfalls to Avoid
First, “parasitic circuits” (cross-circuiting leading to unintended operation);
implement checks to prevent parasitic paths.
Second, “logic errors” (interlocking logic faults leading to safety incidents);
perform logic verification.
Third, “numbering confusion” (wiring errors);
ensure standardized numbering.
Trends and Reminders
Secondary circuits are moving towards “intelligence,” characterized by trends such as intelligent terminals (decentralized/local protection) and digital secondary systems (fiber-optic patching).
For designers, the recommended approach is a “six-step workflow” incorporating logic verification and parasitic circuit prevention.
Sound secondary system design ensures reliable control.
