How do ring main units achieve the core functions of "fault isolation and uninterrupted power supply" in urban power distribution networks?
Publish Time: 2025-12-26
In modern urban power distribution networks, power supply continuity and rapid fault response capabilities are directly related to residents' lives, commercial operations, and even public safety. As a key node device in the 10kV medium-voltage distribution network, the ring main unit is a crucial carrier for achieving this core objective of "fault isolation and uninterrupted power supply." With its unique ring topology and highly integrated intelligent protection system, the ring main unit can accurately identify and isolate faulty sections within milliseconds, while simultaneously ensuring continuous power supply to non-faulty areas, truly embodying the distribution concept of "local faults, global peace of mind."1. Ring Topology: Dual Power Supply Paths Construct Power RedundancyUrban power distribution networks commonly adopt a "daily daisy-chain" ring network structure, where multiple ring main units are connected end-to-end by cables to form a closed loop, powered by two different substations or different busbars of the same substation. During normal operation, a switch at a certain point in the loop is in the open state. However, if a short circuit or ground fault occurs in a section of the line or a user transformer, the protection device of the upstream ring main unit quickly activates, tripping the circuit breaker on the fault side. Simultaneously, the dispatching system or automation terminal can remotely/automatically close the tie switch, allowing the load to continue receiving power from the other direction. This "dual-path, single-operation, fault self-healing" mode fundamentally avoids the drawbacks of traditional radial networks where "a single fault causes a complete power outage," greatly improving power supply reliability.2. Intelligent Protection System: Millisecond-Level Precise ResponseTaking a typical outgoing switchgear as an example—its rated current is 630A, and its rated short-circuit breaking current is 25kA, which can cover most urban power distribution scenarios. The core of the switchgear is a vacuum circuit breaker, which, thanks to its excellent arc-extinguishing performance and long lifespan, can reliably break circuits under a 25kA short-circuit current. Combined with a high-precision current transformer, it collects three-phase current signals in real time; the integrated protection device performs millisecond-level judgments based on preset logic, and immediately issues a trip command once an anomaly is detected. Meanwhile, the grounding switch ensures personal safety during maintenance, the surge arrester suppresses lightning overvoltage, and the real-time display shows key data such as voltage, current, and switch status locally or uploads them to the main station. The entire system meets the "five protections" requirements, eliminating human error at the operational level.3. Fully Enclosed Design: High Reliability Supports Maintenance-Free OperationThe ring main unit adopts a fully enclosed indoor high-voltage structure with an IP4X or higher protection rating. Internal components are sealed in an SF6 gas or dry air insulating cavity, effectively isolating dust, moisture, and corrosive gases. This fully insulated and sealed design not only improves electrical clearance safety but also significantly reduces the impact of the external environment on equipment performance, achieving a maintenance-free operation cycle of up to 20-30 years. For ring main units deployed in underground utility tunnels, commercial complexes, or old residential area renovation projects, this high reliability translates to lower operation and maintenance costs and higher availability.Although compact in size, the ring main unit is a microcosm of the intelligent and reliable urban power distribution network. It perfectly unifies the seemingly contradictory requirements of "fault isolation" and "continuous power supply" by integrating topological redundancy, fast protection, and closed structure.
