Selection Parameters: Eight Core Factors
There are eight core parameters for selecting a ring main unit (RMU): voltage class, rated current, breaking capacity, insulation medium, enclosure type, protection class, arc-fault rating, and ring network scheme.
Industry experts advise checking against this parameter list to ensure accurate selection: voltage (10kV/24kV), current (630A/1250A), breaking capacity (20kA/25kA), medium (air/gas-insulated/eco-friendly), enclosure type (common tank/compartmentalized), protection (IP rating), arc-fault rating (internal arc test), and scheme (load-break switch/circuit breaker combination).
The Eight Parameters
- Voltage class: 10kV/24kV (system voltage), matched to the power grid;
- Rated current: 630A/1250A (load current), matched parameters;
- Breaking capacity: Short-circuit breaking (20kA/25kA), short-circuit level;
- Insulation medium: Air/Gas-insulated (SF6/eco-friendly gas), eco-friendly selection;
- Enclosure type: Common tank/Compartmentalized (structure), selected based on application;
- Protection class: IP3X–IP54 (environmental protection), determined by the environment;
- Arc-fault rating: Internal arc test (IAC), safety rating;
- Ring network scheme: Load-break switch/circuit breaker combination (configuration), selected based on reliability requirements.
Selection Highlights
First, prioritize environmental friendliness.
Prioritize eco-friendly gas-insulated switchgear (SF6-free) to align with environmental regulations and new project requirements.
Second, verify arc-fault performance;
check the Internal Arc Classification (IAC) rating to ensure personnel safety.
Third, ensure compliance through type testing (per GB/T 3906), specifically regarding breaking capacity and arc-fault performance.
Fourth, match the configuration to the application: choose between load-break switches (cost-effective) and circuit breakers (high reliability) based on the criticality of the load.
Pitfalls to Avoid
First, “insufficient breaking capacity”: verify short-circuit breaking ratings to avoid operational risks.
Second, “lack of arc-fault testing”: check for IAC ratings to prevent safety hazards associated with internal arcing.
Third, “gas leakage”: inspect sealing integrity to prevent insulation degradation caused by gas leaks.
Trends and Recommendations
Ring Main Units (RMUs) are shifting towards eco-friendliness—adopting SF6-free gas insulation—and intelligence (online monitoring).
For specifiers, the recommendation is to verify eight key parameters, prioritize environmental sustainability, and confirm arc-fault performance.
Accurate parameter selection ensures reliable power distribution.
