What Voltage-Level Ring Main Unit Should Be Selected for Distribution EPC Projects?

In various distribution EPC general-contracting projects, the Ring Main Unit (RMU) acts as the core high-voltage component of package substations and box-type substations. The selection of its voltage level directly determines the stability, compliance and project cost of the whole power distribution solution, and it is also a key technical concern for EPC procurement engineers at the preliminary design stage. Many EPC general contractors raise a question at the early inquiry stage: What voltage-level ring main unit should be selected for distribution EPC projects?

Located in Yueqing, Zhejiang, Zhejiang Deyan Electric Co., Ltd. specializes in the R&D and manufacturing of medium-voltage power distribution equipment. We supply IEC-compliant SF6 gas-insulated and eco-friendly solid-insulated ring main units, European-style package box substations, prefabricated cabin-type substations and a full range of power distribution equipment. We have long served global EPC general-contracting clients and provide customized RMU selection solutions for different distribution projects.

Reference for Mainstream Ring-Main-Unit Voltage-level Selection in Distribution EPC Projects

12 kV (10 kV system)

The 12 kV ring main unit is the mainstream model widely adopted in global distribution EPC projects. It is extensively applied in urban distribution network renovation, industrial-park power distribution, PV & energy-storage grid-connection, and small-to-medium-size package substations. Featuring high modularity and controllable costs, this RMU fits most conventional ring power supply architectures, with short-circuit withstand current options of 20 kA / 25 kA. It is also the most frequently-inquired specification for EPC projects.

24 kV

24 kV ring main units are mostly used for industrial zones with larger loads and longer power-transmission distances, as well as new-energy collection stations. Compared with the 12 kV solution, it reduces line losses and lowers investment on cable cross-sections, making it suitable for large-capacity EPC general-contracting projects. It requires higher equipment insulation grades and reinforced cabinet structural design, and its overall cost is higher than that of a 12 kV ring main unit.

36 kV (33 kV system)

36 kV ring main units are deployed for long-distance suburban distribution networks, large-scale mining areas and long-distance power-supply EPC works. Falling into the medium-high-voltage distribution category, they are generally used together with large-capacity package substations, and impose higher requirements on insulation, internal arc protection and factory acceptance test (FAT).

Core Selection Principle: The rated voltage of the ring main unit shall be determined according to the nominal system voltage of the project, rather than merely based on transformer capacity. EPC clients shall first confirm local grid standards, system short-circuit parameters, project altitude, ambient temperature and humidity conditions before finalizing the rated voltage of the ring main unit.

Additional Considerations for EPC-project Equipment Selection

Apart from voltage level, EPC general contractors shall also pay attention to product standards, environmental adaptability and complete-set delivery capability when purchasing ring main units:

Certification Requirements: Products shall comply with the IEC 62271 series international standards. Full sets of type-test reports and CE certificates shall be available to support project drawing review and Factory Acceptance Test.

Environmental Adaptability: Customization is available for outdoor IP54 protection rating, anti-condensation temperature-control systems and anti-corrosion coatings for coastal areas, to adapt to complex operating conditions such as high temperature, high humidity and high altitude.

Complete-set Supporting Solutions: Deyan Electric can supply standalone ring main units, as well as turnkey solutions of integrated package substations combining RMUs, transformers and low-voltage cabinets. One-stop delivery cuts communication costs for EPC clients arising from multi-party procurement and coordination for commissioning.

Intelligent Upgrade: FTU intelligent terminals are optional to realize fault location and remote monitoring functions, suitable for EPC projects of smart distribution networks and new-energy grid-connection.

Conclusion

Voltage-level selection is the primary step for ring-main-unit specification definition. Improper selection may trigger severe risks such as failed grid acceptance, equipment overload and project delay. Boasting a professional electrical-engineering technical team, Zhejiang Deyan Electric Co., Ltd. can deliver ring-main-unit voltage-selection services and primary-scheme design based on EPC project drawings and local grid specifications. ODM customization is supported to deliver stable and reliable medium-voltage power-distribution solutions for global distribution EPC projects.