The fully insulated and fully sealed ring main unit (RMU) is a critical component in the distribution network. If an arc fault occurs during operation due to insulation aging or component failure, it can instantly release high-temperature, high-pressure energy. This can not only burn internal components but also damage the cabinet, leak hazardous gases, and even threaten the safety of nearby personnel. The arc suppression structure of the fully insulated and sealed RMU is a multi-layered protection system designed to address these risks. Rather than a single component, it utilizes multiple mechanisms to comprehensively mitigate the hazards of arc faults, from limiting arc propagation and reducing arc energy to rapidly extinguishing the arc, ensuring stable operation of both equipment and the grid.
The arc suppression structure of the RMU first utilizes physical barriers to limit the spread of the arc fault. Because the RMU is inherently sealed, its arc suppression structure further strengthens internal compartmentalization, for example by installing insulating partitions or metal shielding in critical areas such as the busbar compartment and circuit breaker compartment. When an arc fault occurs, these structures prevent the arc from spreading to other areas, preventing it from directly impacting adjacent insulating components or sealing structures. Furthermore, the fully sealed enclosure withstands the instantaneous pressure generated by the arc, preventing the enclosure from rupturing due to the sudden pressure rise. This, in turn, prevents the leakage of high-temperature arcs or toxic gases, minimizing indirect hazards to personnel and surrounding equipment.
The directional guidance design of the arc channel is a key component of the arc suppression structure of the fully insulated and fully sealed ring main unit. This type of ring main unit incorporates a pre-defined arc-shaped or linear arc diversion channel, the inner wall of which is constructed of high-temperature and arc-resistant materials. When an arc fault occurs, the diversion channel utilizes electric field distribution or magnetic control principles to "guide" the chaotic arc into a pre-defined arc extinguishing chamber or pressure relief area, preventing the arc from randomly impacting critical components such as transformers and insulated busbars within the enclosure. This directional guidance not only reduces direct arc burns on core components, but also creates centralized and controlled conditions for subsequent arc extinguishing operations, minimizing damage caused by the arc. The arc suppression structure of a fully insulated and fully sealed ring main unit (RMU) also works synergistically with the insulating medium to rapidly weaken and extinguish the arc. Most such RMUs use either gas or solid insulating materials as both the insulating and arc-extinguishing medium. If a gas dielectric is used, when an arc occurs, the high temperature causes the gas to decompose into ionic species with strong arc-extinguishing capabilities. These species quickly absorb free electrons in the arc, weakening the arc's conductivity. Furthermore, the internal gas chamber design of the RMU allows for convection circulation, rapidly dissipating arc heat and accelerating arc cooling. If solid insulation is used, the arc suppression structure leverages the high-temperature resistance of the solid material to prevent arc burning, while also utilizing the dielectric loss characteristics of the solid dielectric to absorb arc energy and prevent continued arc combustion.
Rapid interruption and energy dissipation are key to minimizing the hazards associated with the arc suppression structure of a fully insulated and fully sealed ring main unit (RMU). The arc suppression structure of this type of ring main unit typically works in conjunction with internal components such as circuit breakers and fuses. Upon detecting an arc fault, the circuit breaker rapidly disconnects the circuit, severing the arc's energy source. Simultaneously, the energy-dissipating components within the arc suppression structure quickly switch on to absorb the remaining energy released by the arc, preventing the overvoltage caused by the sudden current interruption from re-igniting the arc. This combination of "rapid current interruption and energy dissipation" quickly weakens the arc's energy base, preventing problems such as component overheating and insulation breakdown caused by prolonged arcing, significantly reducing the severity of the fault.
The arc suppression structure of the fully insulated and fully sealed ring main unit is also designed to withstand arc wear, minimizing permanent damage to the arc itself and surrounding components. The high temperature of the arc fault can burn and corrode contacting materials. If the structure itself is not resistant to wear, its protective capabilities may be lost after a single fault. To this end, key parts of the arc suppression structure are coated with arc-resistant coatings or composite materials. These materials form a stable oxide film under the action of high-temperature arcs, preventing further burning. Furthermore, some components are designed as removable "wearing parts." After troubleshooting, only the components need to be replaced, eliminating the need to completely replace the ring main unit. This reduces maintenance costs and avoids long-term safety hazards caused by structural damage.
The coordinated design of pressure relief and cooling is a crucial complement to the arc suppression structure of the fully insulated and fully sealed ring main unit to mitigate the hazards of high voltage and high temperature caused by arc faults. If the instantaneous high pressure generated by the fault arc cannot be released in a timely manner, it may cause deformation of the cabinet structure; high temperatures may accelerate the aging of insulation materials. To this end, the arc suppression structure is equipped with a pressure relief valve or pressure relief duct in the cabinet. When the pressure reaches a safe threshold, it automatically opens and slowly releases the internal pressure to prevent the cabinet from bursting. Furthermore, a cooling device is installed in the pressure relief duct to quickly cool the high-temperature gas as it passes through, preventing burns to personnel or ignition of surrounding objects during discharge. The coordinated effects of pressure relief and cooling balance the internal pressure of the switchgear while mitigating the indirect hazards of high temperatures, forming a complete safety protection chain.
From a grid operation perspective, the arc suppression structure of the fully insulated and fully sealed ring main unit (RMU) improves the reliability of the distribution network by reducing the hazards of arc faults. Without effective arc suppression, a single arc fault can cause a long-term outage in the RMU, disrupting power supply to an entire area. However, the arc suppression structure quickly controls the fault scope, minimizing equipment damage and shortening repair time. It also prevents secondary accidents such as fires and gas pollution caused by arcing, reducing grid safety risks. This allows the fully insulated and fully sealed RMU to continue to perform its role in stable power distribution within the distribution network, meeting the requirements of modern distribution networks for safe and reliable operation.
