Ring Main Unit

Product Overview

Ring Main Unit is a set of electrical transmission and distribution equipment (high-voltage switching equipment) installed in a metal or non-metal insulated cabinet, or an electrical equipment made into an assembled and partitioned ring network power supply unit.
Ring network refers to a ring-shaped distribution network, that is, the power supply main line forms a closed ring. The power supply supplies power to this ring main line, and then distributes power from the main line through high-voltage switches all the way. The advantage of this is that each distribution branch can take power from the main line on its left side and the main line on its right side. When the left main line fails, it continues to receive power from the right main line, and when the right main line fails, it continues to receive power from the left main line. In this way, although the total power supply is a single-channel power supply, each distribution branch gets benefits similar to dual-channel power supply, thereby improving the reliability of the power supply.

Ring network power supply system diagram

Ring main unit features and applications

•The core part uses load switches, fuses, and circuit breakers, which have the advantages of simple structure, small size, low price, improved power supply parameters and performance, and safe power supply.

•It is widely used in distribution stations and box-type substations in AC 10kV power distribution systems such as urban residential areas, high-rise buildings, large public buildings, factories and enterprises.

Ring main unit type

•According to the insulation medium, it can be divided into solid insulation and gas insulation. Solid insulated ring network cabinet is commonly known as solid cabinet. Gas insulated ring main unit includes air insulated ring main unit and inflatable cabinet. Inflatable cabinets include N2 (or dry air) insulated ring network cabinets (commonly known as environmental protection cabinets) and SF6 insulated ring network cabinets.

•Epoxy resin is the main material for solid insulation. Solid cabinets have no risk of gas leakage and greenhouse effect, good environmental performance, and are maintenance-free; the fully sealed insulation structure of integrally cast epoxy resin has reliable insulation performance and strong environmental adaptability; modular design, small size, flexible products, and easy to assemble on site; for remote areas with poor road traffic conditions, they can be dismantled for transportation and then reassembled, diversifying transportation and installation methods; emerging products, high cost, incomplete supporting equipment; immature production technology, high scrap rate; immature intelligent monitoring technology, and the effectiveness of test results needs to be improved. Epoxy resin has little impact on the environment during use, but the impact on the environment during the production of epoxy products and the issues of later material recycling and processing still require further analysis and research.

•The insulating medium of environmentally friendly gas gas insulation is dry air or N2 gas. It has the advantages of relatively small size, reasonable structure, and good adaptability. It is currently the mainstream product of ring main unit and has a huge amount of bidding in the State Grid.

•The outstanding features of fully insulated ring network cabinets (including SF6 fully insulated ring network cabinets, solid cabinets, and environmentally friendly gas cabinets): excellent insulation performance.

During normal working

Fully insulated ring main unit

Common cabinet types

•The basic cabinet types of the ring network cabinet include load switch cabinet (C cabinet), circuit breaker cabinet (V cabinet), load switch-fuse combination electrical cabinet (F cabinet).

•The load switch cabinet is equipped with a load switch. The load switch has an arc extinguishing grid that can break and close the rated current (630A), but cannot break short-circuit current. It is generally used in incoming cabinets.

•The vacuum circuit breaker installed in the circuit breaker cabinet can not only break and close the rated current, but also break and close the short-circuit current. It is generally used in outlet cabinets.

•The combined electrical cabinet is equipped with load switches and high-voltage fuses with short-circuit protection function. It is generally used as the outlet cabinet for transformers with a capacity of 1600kVA and below.

•Based on the basic cabinet type, the cable lifting cabinet (B cabinet), voltage transformer cabinet (PT cabinet), metering cabinet (M cabinet), load switch contact cabinet (L(K) cabinet), circuit breaker contact cabinet (L(V) cabinet), transformer cabinet and other cabinet types have been expanded.

Basic cabinet type

Expansion cabinet type

•Voltage transformer cabinet: Built-in PT, providing AC220V power supply to the ring main unit or DTU, and some can perform both measurement and zero-sequence protection functions.

•Cable lifting cabinet: The air box is directly connected with copper bars and connected to the cable through the outlet casing. It is also called a direct connection cabinet. Metering cabinet: Measurement-grade CT, measurement-grade PT, and electric energy meter are installed in the cabinet for electric energy measurement.

•Load switch contact cabinet: Built-in load switch, no outlet bushing, with expansion ports on both sides, connected to the cabinets on both sides through bus couplers, serving as a contact cabinet.

•Circuit breaker contact cabinet: Built-in vacuum circuit breaker, no outlet bushing, with expansion ports on both sides, connected to the cabinets on both sides through bus couplers, serving as a contact cabinet.

• Transformer cabinet used: A 30-50kVA dry-type transformer is installed in the cabinet to convert the 10kV primary voltage into a 380V secondary voltage for use in the station's DC panel, control circuit, lighting, etc. It is also called a station transformer cabinet.

Expansion cabinet type primary diagram

Product structure

The ring main unit consists of a cable room, a mechanism room, a switch room, and a secondary chamber. Each compartment is separated by a steel plate to prevent faulty parts from affecting other compartments.

Main technical parameters

 The company has a diverse, high-performance product portfolio, backed by cutting-edge technology and stringent quality standards, to meet the needs of the domestic and international markets. The products include 12-72.5 kV gas insulated switchgear, 12-40.5 kV switchgear, Ring Main Units (RMUs), Mobile Substations, Column Mounted Switchgear and Integrated Primary and Secondary Switchgear. Its flagship products, such as the NISELA series of environmentally friendly gas-insulated RMUs and the GISELA series of SF6 gas-insulated RMUs, integrate cutting-edge technologies such as solid insulation, vacuum interrupting and modular plug-in design to ensure high reliability, environmental friendliness and adaptability to different scenarios (indoor/outdoor, basement, etc.). These products are widely used in urban power distribution networks, rail transportation, new energy and industry, etc. The market share of RMUs in China's railroad sector reaches 30%. The company prioritizes product innovation and continues to strengthen its R&D capabilities in 40.5kV environmentally friendly gas insulation, SF6 breaking technology and multi-field coupling simulation. This commitment ensures that our products not only meet current industry standards, but also lead the way in technological advancement, providing future-proof solutions for our customers. In addition, they products are exported to Singapore, South America, Southeast Asia, Korea, the Middle East and other international markets.

Huatou Power Equipment Group Co., Ltd. consistently adheres to the principle of ‘pursuing high quality and customer satisfaction,’ upholding the principles of ‘the most competitive prices, the most considerate service, and the most reliable product quality.’ The company focuses on long-term customer satisfaction, offering timely after-sales service, including on-site commissioning, maintenance guidance, and technical consultation. Its comprehensive logistics and response system ensures rapid access to spare parts and professional support. We welcome you to contact us.