The XGN series ring main units (box-type, fixed‑type metal‑enclosed switchgear) are a widely used cabinet type in 10 kV distribution systems, extensively applied in ring‑network power supply and terminal distribution scenarios. Unlike the KYN28 center‑mounted switchgear, the XGN ring main unit adopts… Fixed structure The core switching components are permanently mounted inside the cabinet and cannot be removed. Their internal structure features a unique design in terms of compactness, modularity, and insulation. This article will guide you through “opening” the XGN ring‑main unit to take a closer look at its interior.
I. Overview: Four Major Functional Zones
The cabinet body of an XGN ring main unit typically adopts Aluminum-zinc coated steel sheet It is assembled after CNC bending. Along the vertical and depth directions, the cabinet is divided into four core functional zones:
| Functional Area | Location | Core equipment | Main Features |
|---|---|---|---|
| Busbar Room | Upper part of the cabinet | Main busbar, branch busbar | Implement power collection and distribution among cabinets. |
| Main Switchgear Room | Middle (or rear) of the cabinet body | Load switch/circuit breaker, arc-extinguishing chamber | Circuit On/Off Control and Protection |
| Cable Room | Lower part of the cabinet | Cables, current transformers, surge arresters, grounding switches | Incoming and outgoing line connections and installation of protective devices |
| Low-Voltage Room (Control Room) | Front upper part of the cabinet body | Operating mechanism, interlocking device, secondary components | Switching Operations, Control, and Signal Processing |
These four compartments are typically separated from one another by metal partitions, ensuring that an internal fault in one compartment does not propagate to adjacent compartments.
II. Busbar Compartment: The “Energy Highway” on the Top of the Cabinet
The busbar compartment is located within the cabinet. Upper part The main busbar runs horizontally along the entire row of switchgear, connecting all cabinets into a complete power distribution system.
Main internal components ：
Main busbar : Copper or aluminum busbars, horizontally arranged, carrying the system’s total current.
Branch busbar : Drawn from the main busbar and connected to the main switchgear room.
Insulating support component : Secure the busbar and ensure insulation from ground.
Structural features ：
The top of the busbar compartment is usually equipped with Pressure relief channel When an internal fault arc occurs, the pressure can be vented upward, ensuring the safety of operating personnel.
Adopting a modular design, the cabinet can be easily expanded laterally as needed.
III. Main Switchgear Room: The Core Control Hub
The main switchgear room is part of the XGN ring main unit. Heart , whose core component is Load switch or Vacuum circuit breaker . Depending on the type of insulating medium, the internal structure of the main switchgear compartment is mainly classified into the following types:
1. SF6 Gas-Insulated Type (XGN15-12)
This is the most common type. The main switch is Three-position SF6 load switch The enclosure is encapsulated with epoxy resin, and the interior is filled with SF6 gas, which serves as both an insulating and arc-quenching medium.
Internal structure ：
Three-position switch It features three operating positions—closed, open, and grounded—and its integrated design saves space.
SF6 gas chamber : Sealed arc-extinguishing chamber; gas pressure can be monitored via the front of the cabinet. Barometer Real-time monitoring
Transparent observation window : Located at the lead-out end of the operating shaft, the actual position of the switch contacts can be directly observed through the end cover.
Functional Advantages of the Three-Position Switch ：
| Location | Functionality | Status Description |
|---|---|---|
| Close the switch | Circuit is closed | The load switch is closed, supplying normal power to the load. |
| Open circuit breaker | Circuit isolation | The main circuit is open, but the incoming line side remains energized. |
| Grounding | Safety grounding | Ground the outgoing side to ensure the safety of maintenance personnel. |
2. Solid Insulation Type
Epoxy resin solid material is used as the primary insulating medium, and all live parts and switches are fully enclosed within an epoxy resin housing, eliminating the need for gas charging.
Internal structure ：
Insulating tube : Made from imported epoxy resin, with a thickness of not less than 12 mm.
Vacuum arc-extinguishing chamber : Built into the insulating cylinder, it is responsible for interrupting the circuit.
No risk of gas leakage, Maintenance-free , and is unaffected by the external environment
3. Environmentally Friendly Gas-Insulated Type (Dry Air)
Dry air is used as the insulating medium in place of SF6, and all live parts and switchgear are enclosed within a stainless-steel gas compartment.
Internal structure ：
Three-position isolator switch + vacuum circuit breaker/load switch Combination, vertically arranged
Fracture surface visible : After the isolating switch is opened, the contact gap can be directly observed.
Environmentally friendly with no greenhouse effect : In line with the current trend toward environmentally friendly distribution equipment
4. Cable Chamber: A spacious space for incoming and outgoing cable connections.
The cable chamber is located at the lower part of the cabinet and is a component of the XGN ring main unit. It accounts for the largest share of space. The compartment occupies approximately 75% of the cabinet’s internal space.
Main internal components ：
Cable termination At the point where single-core or three-core cables are connected, a non‑shielded cable termination may be used for a simple connection.
Current transformer : Used for current measurement and protection sampling
Lightning arrester Overvoltage protection
Lower grounding switch (Partial models): Further ensures safety during cable-side maintenance.
Structural features ：
Ample workspace : Facilitates cable termination, securing, and phase switching.
The base plate is detachable. The cable chamber floor and the door frame can be removed, facilitating cable entry and installation.
Sealed design The base plate is equipped with a rubber sealing cover to prevent moisture from the cable trench from entering the cabinet.
Bottom pressure relief passage : When an internal arc fault occurs in the cable compartment, pressure can be relieved through the bottom.
V. Low-Voltage Room (Mechanism Room): The Brain of Operation and Control
The low-voltage compartment is located within the cabinet. Anterior upper part , completely isolated from high-pressure areas, serves as the “control panel” of the XGN ring main unit.
Main internal components ：
Spring-operated mechanism : Operates the load switch to open and close, with a position indicator.
Mechanical interlocking device : Implement mandatory interlocking for the “five protections” to prevent misoperations.
Auxiliary contact : Output switch status signal
Live display indicator : Indicates whether the high-voltage circuit is energized.
Electric operating device (Optional): Supports remote closing and opening of circuit breakers.
Trip coil, emergency trip mechanism (When equipped with a circuit breaker)
Structural features ：
The 750 mm-wide cabinet model is equipped with Two identical low-pressure chambers , can accommodate more attachments
The control panel features a clear layout, with switch positions and power‑on status readily apparent at a glance.
VI. Comparison between XGN Ring Main Units and KYN28 Center‑Mounted Switchgear
By comparing the internal structures, we can gain a clearer understanding of the XGN ring main unit’s positioning:
| Comparison dimension | XGN ring main unit | KYN28 Center-mounted Cabinet |
|---|---|---|
| Switch type | Fixed installation | Center-mounted handcart type, withdrawable |
| Main Switch Type | The load switch is the primary component (with a fuse), and a circuit breaker can also be optionally installed. | Vacuum circuit breaker |
| Insulation method | SF6, solids, dry air, and various others | Air insulation (composite insulation) |
| Space utilization rate | Compact and small in size | Relatively large in size |
| Maintenance convenience | Fixed type; power outage required for maintenance. | Handcart interchangeability for convenient maintenance. |
| Applicable Scenarios | Ring network power supply, terminal distribution, and packaged substations | Power plants, substations, and high-capacity distribution systems |
| Typical dimensions (width × depth × height) | 375/500×750/1000×1600mm | 800/1000×1500×2300mm |
XGN ring main units, with their Compact structure, modular design, reliable operation Its distinctive features make it an ideal choice for urban distribution networks, residential communities, industrial and mining enterprises, and box-type substations. Internally, the three‑position load switch—available with SF6, solid‑state, or environmentally friendly gas insulation—is a key component, while the well‑planned arrangement of the busbar compartment and cable compartment ensures both electrical safety and ease of installation.
Hunan Electrical Appliance Co., Ltd. As a professional manufacturer of complete electrical switchgear, we possess independent R&D, production, and supply capabilities for the XGN series ring main units, offering you a comprehensive turnkey solution—from system design to on-site services. For technical consultation or product selection assistance, please feel free to contact us at any time.
