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Medium Voltage Solid Insulated Ring Main Unit
For many years, Cotenele has been committed to innovation and research and development of new products and technologies, and Medium Voltage Solid Insulated Ring Main Unit is one of our newly developed new products.Medium Voltage Solid Insulated Ring Main Unit represent an important direction in the evolution of intelligent and integrated technology for medium voltage switchgear. It has the core advantages of environmentally friendly insulation materials and better reliability. After continuously overcoming material and process challenges, it is gradually becoming an ideal choice in many key application scenarios.
Medium Voltage Solid Insulated Ring Main Unit is one of the main products of Cotenele,Medium Voltage Solid Insulated Ring Main Unit is a key piece of distribution equipment used for sectioning, coupling, and load tapping of cable lines in medium-voltage distribution networks. Based on the evolution of insulating media, Medium-voltage RMUs have progressed from air-insulated to SF₆ gas-insulated designs. The medium-voltage solid-insulated RMU is a fully insulated, fully sealed distribution device developed from SF₆ gas-filled medium-voltage RMUs.
The key concept is to encapsulate the switch and medium-voltage live parts entirely in epoxy resin or similar solid materials, replacing traditional gas insulation with solid media, thereby achieving a fully insulated, fully sealed, maintenance‑free distribution solution. Driven by China’s “carbon peak, carbon neutrality” strategy and the growing demand for smart distribution networks, the market for medium-voltage solid-insulated RMUs continues to expand. The global market size is expected to reach approximately US$2.4 billion by 2032, with a compound annual growth rate (CAGR) of about 6%.
The definition of the medium-voltage solid-insulated ring main unit:
A medium-voltage solid-insulated ring main unit is defined as an RMU that uses solid insulating materials as the primary insulation medium. The medium-voltage solid-insulated RMU is a fully insulated, fully sealed modular unit in which the vacuum interrupter and its conductive connections, disconnector, earthing switch, main busbar, branch busbar, and other main live circuit components (either individually or in combination) are encapsulated in a solid insulating material. The external surfaces that can be touched by personnel are coated with a conductive or semi‑conductive shielding layer and can be directly and reliably earthed.
Main technical parameters:
| Item | Unit | Value | ||
| Rated Voltage | kV | 12，24 | ||
| Rated Current | A | 630, 1250 | ||
| Rated Insulation Level | 1min Power Frequency Withstand Voltage | kV | 32 | |
| Lightning Impulse Withstand Voltage | kV | 60 | 75 | |
| Rated Frequency | Hz | 50 | ||
| Rated Short-circuit Breaking Current | kA | 20, 25 | ||
| Rated Short-time Withstand Current / Rated Short-circuit Duration | kA/s | 20, 25 | ||
| Rated Peak Withstand Current | kA | 50, 63 | ||
| Rated Short-circuit Making Current | kA | 50 | ||
| Degree of Protection | Switchgear Enclosure | IP4X | ||
| Cabinet Dimensions (W*D*H) | mm | 420 (450) * 912 * 1700 | ||
The product advantages:
1. Environmentally Friendly
Solid‑insulated RMUs completely eliminate the use of SF₆ gas. They use solid materials (epoxy resin, silicone rubber) as the insulating medium, emitting no toxic substances or greenhouse gases which ensured truly zero emissions and zero pollution.
2. Safety and Reliability
Solid insulation does not leak. This fundamentally eliminates the safety hazard of insulation failure caused by gas leakage from damaged or poorly sealed SF₆‑filled units, significantly improving safety. Phases are separated from each other, so even an internal fault does not cause a phase‑to‑phase short circuit. Comprehensive mechanical and electrical five‑prevention interlocking effectively prevents maloperation.
3. Strong Environmental Adaptability
Solid‑insulated RMUs are unaffected by external climate conditions and operate stably in harsh environments such as
Extremely cold environments，High altitudes area and Wet, salt‑fog, sandstorm, and other harsh environments.
4. Maintenance‑Free and Low Operating Cost
Because there is no risk of gas leakage, there is no need to periodically refill SF₆ or check gas pressure. The need for gas pressure monitoring is eliminated, greatly reducing maintenance, even achieving truly maintenance‑free operation.
5. Compact Structure
The dielectric strength of solid insulation is about 3 ~ 5 times that of SF₆ gas, significantly reducing the required insulation distance, thus reducing equipment volume and footprint, this can meet miniaturisation requirements.
6. Intelligence Compatibility
Solid‑insulated RMUs are easily integrated with intelligent distribution terminals. By adding intelligent measurement and control units (compliant with IEC 61850) and 5G/fibre optic communication modules, real‑time parameters such as switch status, load current, and internal temperature/humidity can be uploaded.
Core components And Structure of the Medium-voltage Solid-insulated Ring Main Unit:
| Category | Components | Description |
| Primary circuit components | Vacuum interrupter | Opens and closes the circuit(core switching function).Uses vacuumas the arc-quenching medium. |
| Three-position switch(disconnector/earthing switch) | Isolates the circuit and provides earthing.Some products use vacuum insulation;others use air insulated designs with visible break. | |
| Main busbar/branch busbar | Provides electrical connection between units.External insulation uses silicone rubber,manufactured by vacuum casting. | |
| Incoming/outgoing bushings | Connect the unit to the external cable system.The design is consistent with SF₆gas-filled RMUs for compatibility. | |
| Operating mechanisms | Circuit breaker operatingmechanism | Provides opening/closing power for the vacuum switch,typically a spring mechanism. |
| Disconnector operating mechanism | Operates the three-position switch Interlocking with the breaker mechanism is critical for safety. | |
| Auxiliary components | Instrument transformers(CT/PT) | For current/voltage measurementand protection signal sampling. |
| Controller(DTU/ intelligent unit) | Enables distribution automation, supports remote communication, fault detection and location. | |
| Surge arrester | Overvoltage protection. |
Core components
| Compartment | Description |
| Instrument compartment(secondary compartment) | Located in the upper part;houses secondary equipment such as microcomputer protection devices,intelligent controllers,and communication modules for distribution automation and remote monitoring. |
| Mechanism compartment(operating mechanism compartment) | Located below the instrument compartment or to the side of the primary section;contains dedicated spring operating mechanisms for opening/closing the circuit breaker. |
| Primary part compartment(main circuit compartment) | The core of the unit.Key components such as the switch,interrupter,and connecting conductors are fully encapsulated in epoxy resin using the APG (Automatic Pressure Gelation)process,achieving full insulation and sealing. |
| Cable compartment(incoming/outgoing compartment) | Located in the lower part;used for cable incoming and outgoing connections.Ample space is reserved for cable termination and installation. |
Structure layout
Gas-insulated ring main unit vs Solid-insulated ring main unit:
| Feature | Solid Insulated Switchgear | Gas-Insulated Switchgear(SF₆) |
| Insulation medium | Solid material(e.g.,epoxy resin) | Gas(e.g.,SF₆,dry air) |
| Environmental friendliness | Zero greenhouse effect,highly eco-friendly | SF₆ has a GWP 25,000 times that of CO₂, with leakage risk |
| Low-temperature performance | Excellent,unaffected by low temperatures | Poor,gas may liquefy at low temperatures |
| Maintenance cost | Maintenance-free,minimal lifecycle maintenance | Requires regular leak checking and gas refilling,some maintenance needed |
| Size | Compact | Compact |
| Cost | Relatively higher | Relatively lower |
Main Function Units For Environmentally Friendly Ring Main Unit
| Unit Code | Function | Description |
| V-unit | Circuit breaker unit | Uses a vacuum circuit breaker;provides short-circuit and overload protection.Suitable for critical loads(e.g.,hospitals,data centres). |
| C-unit | Load switch unit | Uses a load switch;capable of switching normal load current but not short-circuit current. |
| F-unit | Switch-fuse combination unit | Uses a load switch +fuse.The fuse quickly clears short-circuit currents.Suitable for transformer protection. |
| M-unit | Metering unit | Houses energy metering devices(PT/CT)for consumption monitoring and remote meter reading. |
| PT-unit | Voltage transformer unit | Provides voltage signals for measurement and protection. |
| Coupling unit | Bus tie unit | Connects two ring circuits for dual-power backup,improving supply reliability. |
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