Indoor Circuit Breaker Ring Main Unit

Built for modern secondary distribution networks, the indoor circuit breaker ring main unit delivers robust load switching and fault interruption within a fully insulated, compact assembly. The design draws from the proven principles of Indoor Vacuum Breaker RMU Switchgear, utilizing vacuum bottles sealed for life to eliminate arc chute maintenance and reduce dielectric degradation over time. Each panel integrates a stainless steel sealed pressure relief system that vents downward into a dedicated arc duct, keeping operator safety at the forefront during internal arc events. Busbars are sleeved with premium epoxy insulation and arranged in a compact horizontal layout, allowing side-by-side extensibility without rear access clearance. The ring main topology supports multiple incoming and outgoing feeders, with motorized or manual load break switches and circuit breaker combinations configured to match site-specific automation requirements. Cable compartments are front accessible, fitted with capacitive voltage indicators, and sized to terminate XLPE or PILC cables up to 630mm² through standard air-insulated bushings. With an ingress protection rating of IP4X for the enclosure and IP2X for internal compartments, the unit withstands humid, dusty, and mildly corrosive indoor environments while maintaining operational integrity across a temperature range of -15°C to +45°C.

The Indoor Circuit Breaker Ring Main Unit separates each functional zone through earthed metallic partitions classified as PM class per IEC 62271-200, ensuring continued operator protection even when one compartment is opened for inspection. Vacuum interrupters seated inside epoxy resin poles mechanically latch in the open or closed position, with a clearly visible position indicator and padlockable operating handle. Auxiliary contacts relay status signals to remote terminal units, supporting SCADA integration through MODBUS, DNP3, or IEC 61850 protocols via a dedicated low-voltage compartment. Current transformers and voltage sensors installed within the bushing turrets feed protection relays and multifunction meters without exposing cores to ambient moisture. Earthing switches on cable and busbar sides carry full short-circuit making capacity, tested at 63kA peak, and interlock mechanically with the main switching device to prevent unsafe grounding sequences. Partial discharge levels remain below 5pC at 1.2 times rated voltage, confirmed through routine testing on every panel before dispatch. The enclosure receives a multi-layer powder coating over a phosphating pretreatment, achieving C3 corrosion class durability, while silicone gaskets on all removable covers maintain the enclosure's thermal and contamination sealing throughout a 30-year design life under normal indoor conditions.

Technical Specifications and Ratings

• Rated voltage: 12kV / 17.5kV / 24kV
• Power frequency withstand voltage: 28kV rms / 42kV rms / 50kV rms
• Lightning impulse withstand voltage: 75kVp / 95kVp / 125kVp
• Rated main busbar current: 630A / 1250A
• Rated feeder current: 630A (load break switch) / 630A-1250A (circuit breaker)
• Rated short-circuit breaking current: 20kA / 25kA / 31.5kA
• Rated short-time withstand current (3s): 20kA / 25kA / 31.5kA rms
• Rated peak withstand current: 50kA / 63kA / 80kA
• Internal arc classification: IAC AFLR 20kA 1s / AFLR 25kA 1s
• Insulating medium: Vacuum interruption + air insulation
• Frequency: 50Hz / 60Hz
• Enclosure protection degree: IP4X (housing), IP2X (internal partitions)
• Mechanical endurance: 10,000 CO operations (load break switch), 10,000 CO operations (circuit breaker)
• Ambient temperature range: -15°C to +45°C
• Humidity tolerance: Up to 95% relative humidity non-condensing