Medium Voltage Switchgear: Components and Selection

A clear medium voltage switchgear decision begins with the approved network design, not an isolated catalog specification. This guide keeps the article focused on the project questions that determine a workable scope and directs narrower decisions to related technical articles.

Part 1. Use the one-line diagram to define the duty

Medium-voltage switchgear is an assembly that switches, protects, isolates, and controls circuits above low-voltage distribution levels. Selection starts with the system voltage, earthing method, continuous current, prospective short-circuit current, feeder roles, and operating philosophy. A voltage label alone does not establish the required assembly duty.

Part 2. Understand the components as one coordinated system

Typical sections combine busbars, circuit breakers or load-break switches, disconnecting and earthing functions, instrument transformers, protection relays, cable compartments, and interlocks. Their ratings and clearances must be coordinated. The equipment schedule should state what is included in each incomer, feeder, bus section, and metering panel.

Part 3. Choose the insulation and construction for the installation

Air-insulated, gas-insulated, and metal-clad designs solve different footprint, environmental, and maintenance problems. Indoor rooms require attention to access, cable routing, ventilation, and safety clearances. Outdoor or compact installations add enclosure and environmental considerations. Confirm the actual construction in approved drawings rather than inferring it from a generic category name.

Part 4. Separate protection design from hardware selection

Relays, CTs, VTs, breaker operating times, and the protection philosophy must be aligned with the network study. Protection settings are not universal values that can be copied between projects. Coordinate them with upstream utility equipment and downstream transformers or feeders before commissioning.

Part 5. Make factory and handover records part of procurement

Ask for approved GA drawings, wiring diagrams, nameplate information, routine-test records, relay documentation, and operation instructions. Factory tests should be witnessed or reviewed according to the contract. Site commissioning then verifies cable identification, interlocks, earthing, protection logic, and the latest settings file.

Part 6. Use the product page for initial scope alignment

For 12kV or 24kV project discussions, the published KYN28-12 medium voltage switchgear can provide a catalog starting point. Product recommendation boundary: fault duty, internal-arc requirements, relay scheme, and utility interfaces must be confirmed by project engineering.

For related detailed reading, see KYN28 Gas Insulated Switchgear Buyer Guide and Ring Main Unit Selection Guide and 11kV Vacuum Circuit Breaker Selection. Review the wider Shenheng Power category when comparing catalog families, and send the approved project inputs through Contact Shenheng Power for an engineering discussion.

FAQ

What does medium voltage switchgear do?

It switches, protects, isolates, and controls medium-voltage circuits according to the system design.

What should be defined before requesting a quotation?

Provide voltage, current, fault duty, insulation level, feeder schedule, protection requirements, site conditions, and required documentation.

How are AIS and GIS selection decisions made?

Compare footprint, environment, maintenance approach, project standards, and the required electrical duty rather than choosing by label alone.

Why are interlocks important?

They support safe operating sequences, but the required interlock scheme must match the approved single-line diagram and operating procedure.

What documents are needed before commissioning?

Use the approved drawings, test records, relay settings, cable schedule, manuals, and commissioning procedure.

When should an RMU be considered instead of a larger lineup?

Use the network layout, feeder functions, protection needs, and site constraints to determine whether an RMU is appropriate.

References

• IEC publications
• IEEE Standards Association