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The Core Value and Applications of Ring Main Unit Switchgear in Urban Power Grids

Release time:

2025-11-20

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Abstract

As the "nerve endings" of urban power grids, ring main unit switchgear—thanks to their unique ring-shaped power distribution architecture and intelligent design—are reshaping the fundamental principles of modern urban electricity delivery. Beyond their core benefits, such as enhancing power supply reliability and optimizing space utilization, these devices are also playing a pivotal role in driving the city's energy transition, thanks to their seamless integration with emerging applications like renewable energy and electric vehicles.

I. Ring Architecture: Building a Highly Resilient Power Supply Network

The core design concept of the ring network switchgear lies in achieving "dual-path power supply" by closing the ring-shaped power distribution network. Take, for instance, a central business district in a major city—this area employs a "hand-in-hand" ring network structure, consisting of six ring network switchgear units that form a circular power supply unit. Each cabinet can operate independently while simultaneously being interconnected via busbars, creating redundant power pathways. When one of the lines is interrupted due to construction or a fault, the system automatically switches to the backup path within 0.3 seconds, reducing the power restoration time by 80% compared to the conventional radial grid. As a result, the annual average outage duration in the commercial district has been slashed from 12 hours to just 1.5 hours, with power supply reliability soaring to 99.995%.

In terms of fault isolation, the "three-position load switch" technology in ring main units plays a critical role. Take SF6 gas-insulated ring main units as an example—these units integrate three key functions: interrupting load current, isolating circuits, and providing reliable grounding. Paired with high-voltage fuses, they form a robust "load switch + fuse" protection combination. When a transformer experiences a short circuit, the fuse blows within 0.02 seconds, while the load switch simultaneously disconnects the faulty section, ensuring that other equipment remains unaffected. This hierarchical protection mechanism significantly reduces the scope of fault impact—from an entire line under traditional schemes down to just a single distribution unit.

II. The Spatial Revolution: Compact Design Solves Urban Land-Use Challenges

Facing the growing challenge of increasingly scarce urban land resources, ring main units achieve a qualitative leap in space utilization through modular design. Take, for instance, a distribution project in a high-rise residential community: while traditional switchgear required 120 square meters of ground space, deploying solid-insulated ring main units now only demands 15 square meters of underground space. This compact design is made possible by three major technological breakthroughs:

1. Revolutionary Insulation Medium: The solid-insulated ring main unit utilizes epoxy resin casting technology to completely encapsulate live components, reducing the insulation distance by 60% compared to air-insulated models.

2. Structural Optimization: Adopting a common-box design, the incoming line, outgoing line, and transformer compartments are integrated into a single gas-insulated enclosure, reducing the overall volume by 45% compared to the modular design.

3. Intelligent Integration: Built-in microcomputer protection device integrates relay protection, measuring instruments, and communication modules—traditionally requiring separate installations—into a control unit just 100mm thick.

In Shenzhen's Qianhai Free Trade Zone, the outdoor ring main units achieve an IP67 protection rating, allowing them to operate safely even when briefly submerged in water—effectively addressing the issue of salt-spray corrosion common in coastal regions. Additionally, their stainless steel laser-welded gas-tight enclosure technology ensures an annual leakage rate of less than 0.1%, making them 10 times more reliable than conventional designs that rely on traditional sealing gaskets.

III. Intelligent Evolution: From Devices to Energy Internet Nodes

With the upgrade of distribution automation, ring main units are transitioning from passive devices into proactive, intelligent terminals capable of sensing their environment. In the demonstration project at Hangzhou’s “Future Science City,” 200 smart ring main units equipped with DTUs (Distributed Terminal Units) have been deployed to deliver three key intelligent functionalities:

1. Comprehensive Status Awareness: Utilizing built-in voltage/current transformers, the system collects 12 types of operational data in real time, with a sampling rate of up to 100 times per second.

2. Autonomous Decision-Making Control: When line overload is detected, automatically adjust the load distribution strategy to prevent tripping.

3. Cloud-edge collaborative operations: Leveraging 5G communication to upload data to the distribution automation master station, combined with AI algorithms to achieve a fault prediction accuracy rate exceeding 90%.

In new energy integration scenarios, the bidirectional power metering function of ring main units supports the "self-generation for self-consumption, with surplus power fed back to the grid" model for distributed photovoltaic power generation. For instance, in Suzhou Industrial Park, 3,000 photovoltaic connection points utilize ring main units to achieve grid-connected control, boosting the PV self-consumption rate from 75% to 98%. Additionally, to address the impact of surge loads from electric vehicle charging stations, the new-generation ring main units are equipped with dynamic reactive power compensation devices, increasing the power factor from 0.7 to 0.95 and significantly enhancing power quality.

IV. Technological Iteration: The Path Forward Toward Future Evolution

Currently, ring main unit technology development is showing three major trends:

1. Eco-friendly transformation: Solid insulation technology is gradually replacing SF6 gas, and an environmentally friendly ring main unit developed by a certain company has already achieved a 60% reduction in its carbon footprint over its entire lifecycle.

2. Standardization: The State Grid has implemented the “Primary-Secondary Integration” standard, unifying interface protocols and data models to enable seamless interoperability among equipment from different manufacturers.

3. Digitalization: Digital twin technology is applied to the full lifecycle management of ring main units, enabling real-time assessment of equipment status and optimization of operation and maintenance strategies through virtual mapping.

In the construction of the "Digital Grid" in Xiong'an New Area, a digital twin system for ring main units based on BIM technology has already been put into operation. This system can simulate how equipment responds under scenarios such as extreme weather conditions or external damage, enabling proactive development of emergency plans and reducing the average fault-handling time by 40%.

From enhancing power supply reliability to supporting the energy transition, ring main unit switchgear is redefining the boundaries of urban power grids through technological innovation. As the construction of next-generation power systems advances, this "compact yet high-capacity" equipment will continue to evolve, ultimately becoming the cornerstone for building smart city energy networks.

Key words:

Advantages of box-type substations (box-type transformers): Rapid deployment and small footprint

The importance of detailed relay protection configuration in distribution cabinets

Hunan Chengyuan Electrical CO.,LTD

The Core Value and Applications of Ring Main Unit Switchgear in Urban Power Grids