Low-Cost, Low-Loss DC Arc-Free Circuit Breaker Solution for Rail Transit

I. Solution Overview
This solution addresses the protection needs of DC systems (particularly rail transit traction power supply) against short-circuit faults by proposing a DC circuit breaker solution based on optimized mechanical breaker structure. It achieves arc-free interruption through capacitor voltage control, combining low on-state loss and high reliability, making it suitable for frequent operation scenarios.

II. Core Principle
Utilizes a fast mechanical switch topology combined with pre-charged capacitors and arresters:

1. Steady-State Operation: Current flows through the mechanical switch (main circuit), with on-state resistance at the micro-ohm level, resulting in extremely low loss.

2. Fault Interruption:
   • Upon detecting a short-circuit fault, the mechanical switch is triggered to open rapidly.
   • The capacitor module is engaged, controlling the voltage across the mechanical switch to remain below the arc ignition threshold, enabling arc-free interruption.
   • The short-circuit current is diverted to the parallel capacitor and arrester loop, where the arrester absorbs energy and suppresses overvoltage.

III. Technical Parameters

IV. Applicable Scenarios
• Rail transit traction power supply systems: Meets requirements for frequent switching and low loss.
• Urban DC distribution networks: Medium and low-voltage DC system fault protection.
• Industrial DC power systems: Applications demanding high reliability.

V. Advantages and Limitations
Advantages:

1. Low On-State Loss: Mechanical switch remains conductive during normal operation, avoiding semiconductor heating issues.

2. Controlled Cost: No need for all-solid-state switching devices, making it more cost-effective than hybrid circuit breakers.

3. Arc-Free Interruption: Active arc suppression via capacitor voltage control extends switch lifespan.

Limitations:

1. Capacitance Requirements: High-voltage capacitor modules are bulky, requiring optimized design based on system voltage.

2. Current Transfer Time: Relies on arrester energy consumption, resulting in slightly slower short-circuit current transfer compared to all-solid-state solutions.

3. Maintenance Needs: Mechanical components require periodic maintenance, though less frequently than traditional circuit breakers.

VI. Implementation Recommendations

1. Capacitor Selection: Use multi-module parallel capacitor groups to balance voltage control precision and size constraints.

2. Drive Optimization: Equip with high-speed actuation mechanisms (e.g., electromagnetic repulsion mechanisms) to ensure interruption response <2 ms.

3. Arrester Configuration: Select nonlinear resistors (MOVs) with energy absorption capacity calculated based on system short-circuit capacity.

VII. Summary
This solution combines mechanical structure innovation with capacitor voltage control to achieve low cost, low loss, and arc-free interruption in DC circuit breakers. It is particularly suitable for high-frequency operation scenarios like rail transit, providing a reliable path for fault protection in medium and low-voltage DC systems.