Air Insulated Ring Main Unit: A Classic and Reliable Medium-Voltage Power Distribution Solution

The air insulated ring main unit is a type of switchgear equipment that uses air (atmosphere) as the primary insulating medium, installing high-voltage live parts (such as busbars, isolating switches, circuit breakers, etc.) inside a metal cabinet and maintaining insulation through air gaps. Due to its intuitive structure, mature technology, and cost advantages, it has long dominated the power distribution network and is considered a classic and reliable solution.

I.Core Insulation Method: Semi-insulated/Semi-sealed Structure

Unlike fully insulated and fully sealed gas-insulated or solid-insulated cabinets, the air insulated ring main unit features a "semi-insulated" or "semi-sealed" structure. This means:

1.Primary Insulation Medium: Phase-to-phase and phase-to-ground main insulation relies on air (atmosphere). Insulation strength between live parts inside the cabinet and between live parts and the grounded enclosure is ensured through designed air gaps and creepage distances.

2.Visibility: Some models allow viewing of switch on/off status through observation windows while ensuring safety, providing clear and intuitive operation.

3.Requires Manual Intervention: Due to its non-fully sealed nature, the equipment's operating environment is greatly influenced by the installation location. It typically needs to be installed in a dedicated distribution room to avoid insulation degradation caused by external factors such as dust, humidity, condensation, and small animals, which could lead to failures.

II.Main Product Features

1.Simple Structure and Cost-Effective: No need for complex gas sealing systems or special solid casting processes; mature manufacturing technology and relatively low raw material costs provide significant price advantages in initial investment.

2.Intuitive Operation and Easy Maintenance: Relatively open internal structure with clear component layout. For experienced maintenance personnel, inspections, repairs, and part replacements are more direct and convenient.

3.Flexible Expansion: Modular design with flexible scheme combinations, facilitating later circuit expansion or addition of functional units based on load growth.

4.Mature Technology and Wide Application: As the switchgear with the longest development history, its technology is very mature, with rich operating experience, easy access to spare parts, and high familiarity among maintenance teams.

III.Challenges and Limitations

Despite the above advantages, with technological progress and increasing demands for power supply reliability, the inherent drawbacks of air insulated ring main units are becoming more prominent:

1.Highly Susceptible to Environmental Influences: Requires high cleanliness and dryness of the operating environment. In humid or heavily polluted areas, it is prone to flashover or phase-to-phase short circuits due to surface condensation or dust accumulation.

2.Bulky Volume: Due to the need for sufficient air insulation distances, phase-to-phase and ground distances are larger, resulting in a relatively large cabinet size and occupying more space in the distribution room.

3.Relatively Lower Safety: Risks of internal arc faults exist, and due to non-full sealing, high-temperature gases and splashes from arcs may harm personnel and adjacent equipment.

4.Requires Regular Maintenance: Needs periodic cleaning, dehumidification, and tightening of connection points, with higher maintenance workload and costs compared to fully insulated ring main units.

IV.Practical Application Scenarios

Given its characteristics, air insulated ring main units are currently mainly suitable for:

1.Indoor Distribution Rooms: Must be installed in spacious, controllable, clean, and tidy indoor environments.

2.Cost-Sensitive Projects: In projects with limited initial investment budgets and guaranteed good operating and maintenance conditions, it remains an economical and practical choice.

3.Transitional Solutions for Upgrades: In upgrades of some old distribution rooms, it is still considered due to good compatibility with early systems.