What Is A Medium Voltage Switchgear?

Medium voltage switchgear (MV switchgear) is a core hub in power systems connecting transmission networks and terminal loads, undertaking critical functions of control, protection, isolation, and monitoring. Its typical application voltage range is 1 kV to 52 kV (as defined by the IEC 62271-200 standard), and it is widely deployed in substations, industrial plants, data centers, new energy power plants, and urban power distribution networks.

What Are Medium-voltage Switchgear?

According to IEC 62271-200 and GB/T 3906 standards, medium-voltage switchgear is defined as:

“A combination of one or more switching devices (such as circuit breakers, load switches, disconnectors) and related control, measurement, protection and regulation equipment, all internal components of which are enclosed in a grounded metal enclosure, for the distribution and protection of electrical power in a medium-voltage AC system.”

Its core functions include:

• Normal operation: Connects/disconnects load current
• Fault protection: Quickly disconnects faulty sections in case of short circuit or overload
• Electrical isolation: Provides visible disconnection for safe maintenance
• Status monitoring: Integrates current/voltage transformers and intelligent terminals (IEDs), supporting SCADA/EMS systems

Core Architecture and Safety Classification of Medium Voltage Switchgear

Classification by insulation and structure（IEC 62271-200）

Type	Full Name	Key Characteristics	Typical Applications
AIS	Air-Insulated Switchgear	Air insulation; open structure; low cost	Outdoor substations; industrial sites with ample space
GIS	Gas-Insulated Switchgear	SF₆ gas insulation; highly compact design	Urban central substations, underground substations, islands, and other space-constrained locations
Solid Insulated	Solid-Insulated Switchgear	Epoxy resin encapsulation; SF₆-free design	Environmentally sensitive areas; small to medium distribution systems

Classification by degree of metal enclosure

Type	Full Name	Key Characteristics	EPC Considerations
Metal-Enclosed (ME)	Metal-Enclosed Switchgear	All live parts are enclosed within a grounded metal housing, but internal compartments are either absent or not fully segregated	Lower cost; suitable for general industrial applications
Metal-Clad (MC)	Metal-Clad Switchgear	Each functional unit is housed in an independent metal compartment (circuit breaker, busbar, cable, and low-voltage compartments), with full “five-interlock” safety features	Preferred for high-reliability applications such as hospitals, data centers, and petrochemical facilities

Key technical parameters

Core performance parameters

Parameter	Typical Values (12 kV Class)	Applicable Standard	Engineering Significance
Rated Voltage	12 kV / 24 kV / 40.5 kV	IEC 62271-200	Must be ≥ the system’s maximum operating voltage (Um)
Rated Current	630 A – 4000 A	—	Determines conductor sizing and allowable temperature rise
Rated Short-Circuit Breaking Current	20 kA – 40 kA / 3 s	—	Must be verified against the system’s maximum short-circuit level
Internal Arc Classification (IAC)	AFL / AFLR	IEC 62271-200 Annex AA	Ensures personnel safety (test pressure ≥ 1.5 bar)

Application scenarios

	Industry	Application Scenario	Recommended Configuration
	Energy	Wind and solar step-up substations	Outdoor compact AIS or GIS; IP54 enclosure; C5-M anti-corrosion protection
	Industrial	Steel, chemical, and mining facilities	Metal-clad (MC) switchgear; LSC-2B; IAC AFLR; full five-interlock safety system
	Infrastructure	Metro systems, airports, hospitals	MC switchgear with automatic transfer switch (ATS); high-availability design
	Commercial Buildings	Supertall buildings; data centers	Dry-type transformers paired with MC switchgear; low-noise operation (≤ 65 dB)

Conclusion

Medium-voltage switchgear acts as the “immune system” of the power system, operating silently under normal conditions and responding decisively to faults. For engineers and EPC teams, selecting the appropriate type (AIS/GIS/MC) and strictly controlling manufacturing standards (IEC 62271-200) are prerequisites for building inherently safe, highly available, and easy-to-maintain distribution networks.

Driven by the new power system and the “dual carbon” goal, medium-voltage switchgear is rapidly evolving towards intelligence, greenness, and compactness, becoming a key carrier for the digital transformation of energy infrastructure.

Appendix: Commonly Used Standards

• IEC 62271-200: AC metal-enclosed switchgear for rated voltages above 1 kV and up to 52 kV
• GB/T 3906:6 kV～40.5 kV AC metal-enclosed switchgear and control equipment
• DL/T 404: Technical specifications for ordering indoor AC high voltage switchgear

FAQ

1. What are the essential differences between Metal-Enclosed and Metal-Clad switchgear?

Metal-Clad is a higher form of Metal-Enclosed.

The MC type requires each functional unit (circuit breaker, busbar, cable) to be equipped with:

• Aremovable circuit breaker trolley
• Meeting LSC-2B service continuity requirements (single-bay maintenance does not affect other circuits)
• Possessing complete mechanical five-proof interlocking

2. What is the IAC internal arc rating? Why is it important?

IAC (Internal Arc Classification) is an internal arc test certification specified in IEC 62271-200, verifying whether equipment can:

• Limit the outward ejection of arc energy
• Ensure the safety of operators in designated positions (e.g., front, side)

The grade is represented by AFLR：

• A: Arc duration 0.5 s
• F: Test location includes front
• L: Includes side
• R: Includes rear

3. Is GIS necessarily superior to AIS?

This is not the case; a comprehensive assessment is required.

Dimension	AIS	GIS
Initial Cost	Low	High (approximately 2–3× that of AIS)
Footprint	Large	Extremely compact (about 10–20% of AIS)
Maintenance	Straightforward; easy on-site servicing	Requires specialized tools; SF₆ handling is complex
Environmental Impact	No greenhouse gases	SF₆ has a GWP of 23,500 and requires recovery and recycling

Recommendation: GIS is recommended for areas with limited space or environmental sensitivity; AIS is more economical for conventional industrial plant areas.

4. Can MV switchgear be directly connected to the generator outlet?

Yes, but it requires special design：

• The generator’s short-circuit current decays slowly (X”d is small), requiring verification of the circuit breaker’s DC component withstand capability
• Large voltage fluctuations necessitate enhanced insulation coordination
• It is recommended to use a generator-specific circuit breaker (such as ABB VD4G), which offers higher breaking capacity

5. How to verify the effectiveness of the “five-protection” functions of switchgear?

“five-protection”refer to：

• Prevent accidental opening/closing of circuit breakers
• Prevent operating disconnect switches under load
• Prevent connecting grounding wires while the circuit is energized
• Prevent closing switches with grounding wires connected
• Prevent accidental entry into energized compartments

Verification method：

• Simulate each operation item in the FAT (Factory Acceptance Test)
• Check whether the mechanical/electrical interlocks forcefully prevent unauthorized operations
• Require the supplier to provide a five-proof logic diagram and sign for confirmation

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