Top 10 Ring Main Unit Brand & Manufacturers

What is a Ring Main Unit?

A Ring Main Unit (RMU) is a compact, factory - assembled, metal - enclosed set of switchgear used for medium - voltage power distribution. It is typically designed to operate at voltages ranging from 11 kV to 36 kV. The RMU provides a means to distribute power in a ring - shaped network configuration, allowing for more reliable power supply as power can be fed from multiple directions. It contains components such as switches, circuit breakers, and fuses that are used to control and protect the distribution of electricity to various loads.

History of Ring Main Unit

• Early Developments: The concept of ring - shaped power distribution networks and the need for a compact, efficient distribution unit led to the development of the Ring Main Unit. As urban and industrial power - distribution systems grew in complexity, traditional distribution methods faced challenges such as space constraints and reliability issues. The RMU emerged as a solution to these problems, with early designs focusing on simplifying the distribution process and improving the availability of power.
• Technological Advancements: With the progress of switchgear technology, RMUs evolved to incorporate more advanced components. The development of vacuum - interrupter - based circuit breakers and sulfur hexafluoride (SF?) - insulated switches improved the performance and reliability of RMUs. These technological improvements allowed for better arc - quenching capabilities, reduced maintenance requirements, and increased safety.
• Modern Developments: In modern times, Ring Main Units have become more intelligent and integrated. They now often come with advanced monitoring and control systems that can provide real - time data on power parameters such as voltage, current, and temperature. Additionally, there is a growing emphasis on making RMUs more environmentally friendly and energy - efficient through the use of better - insulated materials and optimized component designs.

Purpose of Ring Main Unit

• Power Distribution: The primary purpose of an RMU is to distribute medium - voltage power in a ring - network configuration. This allows for a more flexible and reliable power - supply system. In a ring - main network, power can flow in either direction, and if a fault occurs in one section of the network, power can still be supplied to the affected area from the other direction, minimizing power outages.
• Load Connection and Protection: RMUs provide a connection point for various medium - voltage loads such as industrial equipment, commercial buildings, and residential complexes. They also incorporate protection devices like circuit breakers and fuses to protect the connected loads from over - current conditions such as short - circuits and overloads.
• System Segmentation and Isolation: The RMU allows for the segmentation of the power - distribution network. In case of maintenance or a fault, specific sections of the network can be isolated without affecting the entire system. This helps in efficient fault - location and repair, as well as in the planned maintenance of the distribution infrastructure.

Principle of Ring Main Unit

• Ring - Network Configuration: The RMU is designed to be part of a ring - shaped power - distribution network. Power enters the RMU from one or more feeders and is then distributed to the various output connections. The ring - network principle allows for alternative power paths, and the RMU's switches and other components are used to manage the flow of power through these paths.
• Switching and Protection Mechanisms: Inside the RMU, switches (such as load - break switches and isolators) and protection devices (circuit breakers and fuses) work together. When a fault occurs, the protection devices quickly detect the over - current condition and trip to interrupt the current flow. The switches can then be used to isolate the faulty section and reconfigure the network to maintain power supply to other parts.
• Insulation and Dielectric Strength: The RMU's enclosure and internal components are designed with appropriate insulation to withstand the medium - voltage levels. The use of insulating materials such as SF? gas or solid - dielectric materials provides the necessary dielectric strength to prevent electrical breakdown and ensure the safety and reliability of the power - distribution process.

Features of Ring Main Unit

• Compact Design: RMUs have a compact and space - efficient design. Their factory - assembled nature and modular construction make them suitable for installation in areas with limited space, such as urban substations, underground vaults, or industrial complexes where space is at a premium.
• High - Reliability Components:[!--empirenews.page--] They are equipped with high - quality switches, circuit breakers, and other components that have high - reliability and long - service - life characteristics. The use of advanced technologies like vacuum interrupters and SF? - insulated equipment reduces the likelihood of component failures and the need for frequent maintenance.
• Multiple - Function Integration: RMUs integrate various functions such as power distribution, switching, and protection in a single unit. This simplifies the overall power - distribution system and reduces the need for multiple separate devices, saving space and potentially reducing installation and maintenance costs.
• Monitoring and Diagnostic Capabilities: Many modern RMUs come with built - in monitoring and diagnostic systems. These can provide real - time information about the unit's performance, including voltage, current, temperature, and the status of switches and protection devices. This data can be used for preventive maintenance and to quickly identify and address any potential issues.
• Environmental Adaptability: RMUs are designed to operate in a wide range of environmental conditions. They are often sealed to protect against dust, moisture, and other contaminants. Some models are also designed to withstand extreme temperatures and other harsh environmental factors.

Types of Ring Main Unit

• SF? - Insulated Ring Main Unit: These RMUs use sulfur hexafluoride (SF?) gas as the insulating medium. SF? has excellent dielectric and arc - quenching properties. The gas - insulated design provides a compact and reliable solution for medium - voltage power distribution. SF? - insulated RMUs are widely used due to their high performance and relatively low maintenance requirements.
• Vacuum - Insulated Ring Main Unit: Vacuum - insulated RMUs use vacuum - interrupter - based technology for switching and protection. The vacuum provides excellent insulation and arc - quenching characteristics. These units are becoming more popular due to their environmental - friendliness (as they do not use SF? gas) and their ability to handle high - current interruptions effectively.
• Hybrid Ring Main Unit: A hybrid RMU combines different insulation and switching technologies. For example, it may use SF? for some components and vacuum - interrupter technology for others. This type of RMU aims to take advantage of the benefits of different technologies to provide a more optimized and flexible power - distribution solution.

Precautions for using Ring Main Unit

• Proper Installation: The RMU must be installed according to the manufacturer's instructions and relevant electrical codes. This includes proper alignment, connection of power cables, and grounding. Incorrect installation can lead to performance issues, safety hazards, and reduced equipment lifespan.
• Gas - Monitoring (for SF? - Insulated Units): If the RMU is SF? - insulated, regular monitoring of the SF? gas pressure and quality is essential. Any leakage of SF? gas can affect the unit's insulation and arc - quenching capabilities and has environmental implications due to SF?'s high global - warming potential.
• Regular Maintenance: Conduct regular maintenance of the RMU, including inspection of switches, circuit breakers, and other components. Check for signs of wear, damage, or abnormal operation. Maintenance activities may include cleaning, tightening of connections, and replacement of worn - out parts.
• Over - Voltage and Over - Current Protection: Ensure that the RMU's protection devices (circuit breakers and fuses) are properly sized and set to protect against over - voltage and over - current conditions. Regularly test and calibrate these protection devices to ensure their effectiveness.
• Environmental Protection: Consider the environmental conditions where the RMU is installed. Protect the unit from extreme temperatures, humidity, and corrosive substances. In outdoor installations, provide appropriate enclosures or shelters to safeguard the RMU from the elements.

Things to consider when purchasing Ring Main Unit

• Voltage and Current Ratings: Determine the maximum voltage and current that the RMU will need to handle in your power - distribution network. Choose a unit with appropriate voltage and current - handling capabilities, with some margin for safety and future expansion of the system.
• Type of RMU: Select the most suitable type of RMU based on your specific requirements. Consider factors such as the insulation type (SF? - insulated, vacuum - insulated, or hybrid), the application environment, and the expected performance and maintenance requirements. Each type has its own advantages and disadvantages in terms of cost, reliability, and environmental impact.[!--empirenews.page--]
• Monitoring and Control Features: Look for an RMU with advanced monitoring and control capabilities. The ability to monitor real - time power parameters and the status of the unit's components can greatly assist in maintenance and operation. Some RMUs may also offer remote - monitoring and - control options, which can be beneficial for larger - scale power - distribution systems.
• Space and Installation Requirements: Consider the physical size and installation requirements of the RMU. Ensure that it can fit into the available space in your substation or distribution - network layout. Also, take into account any special installation requirements such as ventilation (for SF? - insulated units) or access for maintenance.
• Cost: Establish a budget for the RMU purchase. The cost can vary depending on the voltage and current ratings, type, and features of the unit. Consider not only the initial purchase price but also the long - term costs, such as maintenance, gas - replacement (for SF? - insulated units), and potential replacement costs. A more expensive, high - quality RMU may be a more cost - effective choice in the long run if it offers better performance and reliability.
• Brand and Reputation: Choose a reputable brand with a good track - record in manufacturing Ring Main Units. Read customer reviews and ask for recommendations from other power - distribution professionals to assess the quality, reliability, and performance of different models. A well - known brand is more likely to provide reliable customer service and replacement parts.

Terms of Ring Main Unit

• Interrupting Capacity: The maximum current that the RMU's circuit breakers can interrupt under specific conditions. It is a crucial parameter for determining the unit's ability to protect the power - distribution network from short - circuit currents.
• Dielectric Withstand Voltage: The maximum voltage that the RMU's insulation can withstand without breakdown. It is usually specified for both AC and DC voltages and is an important factor in ensuring the safety and reliability of the unit in medium - voltage applications.
• Gas - Insulation Pressure (for SF? - Insulated Units): The pressure of the SF? gas inside the RMU is a critical parameter. Maintaining the correct gas pressure is essential for the proper functioning of the insulation and arc - quenching mechanisms. Deviations from the recommended pressure can lead to performance degradation and safety risks.
• Load - Break Capacity: The maximum load current that the RMU's switches can break without causing excessive arcing or damage. It determines the ability of the unit to safely disconnect loads during normal operation or in case of a fault.
• Monitoring Parameters: These are the electrical and physical parameters that the RMU's monitoring system can measure and report. Common monitoring parameters include voltage, current, temperature, and the status of switches and protection devices. Understanding these parameters and how they are used for maintenance and operation is important for effective use of the RMU.