Medium Voltage Switchgear Selection Guide: Key Parameters and Standards
A comprehensive guide for selecting medium voltage switchgear (1kV-36kV). Covers type selection, rating calculation, standards compliance, and installation requirements.
本文为中文技术阅读版本，工程参数、标准和项目边界仍应以正式图纸、技术协议和书面报价为准。
Medium Voltage Switchgear Types
Air-insulated switchgear (AIS): Traditional, cheaper, needs more space, requires more maintenance.
Gas-insulated switchgear (GIS): Compact, sealed, low maintenance, expensive, suitable for urban areas.
Hybrid switchgear: Combination of AIS and GIS, balance of cost and space.
RMU (Ring Main Unit): For distribution networks, compact, sealed, maintenance-free.
Key Parameters to Consider
Rated voltage: 12kV, 24kV, 36kV (IEC) or 15kV, 27kV, 38kV (IEEE).
Rated current: 630A, 1250A, 1600A, 2000A, 2500A, 3150A.
Short-circuit withstand: 20kA, 25kA, 31.5kA, 40kA for 1-3 seconds.
Insulation level: Power frequency withstand (28kV, 50kV, 70kV), lightning impulse (75kV, 125kV, 170kV).
Standards Compliance
IEC 62271-200: AC metal-enclosed switchgear for rated voltages above 1kV and up to 52kV.
IEC 62271-203: Gas-insulated switchgear for rated voltages above 52kV.
IEEE C37.20: Switchgear assemblies including metal-enclosed interrupter switches.
Buyers should specify which standard to comply with in RFQ.
Circuit Breaker Types
Vacuum circuit breaker (VCB): Most common for 12-36kV, maintenance-free, long life.
SF6 circuit breaker: For higher voltages (>36kV), but environmental concerns.
Air circuit breaker (ACB): For low voltage, not medium voltage.
Recommendation: Use VCB for 12-36kV applications.
Installation Considerations
Clearance: 1.5m in front, 1m behind (IEC 62271-200).
Ventilation: For indoor installation, 10-15 air changes/hour.
Cable termination: Top or bottom entry, prefabricated cable terminations preferred.
Protection: IP4X minimum for indoor, IP54 for outdoor or dusty environment.
Common Specification Mistakes
1. Undersizing short-circuit withstand (breaker fails during fault)
2. Wrong insulation level (fails dielectric test)
3. No maintenance access (cannot maintain circuit breaker)
4. Ignoring ambient temperature (breaker derates at high temperature)
5. No CT/PT provision (cannot add metering later)