# Medium Voltage Switchgear Selection: Air-Insulated (AIS) vs Gas-Insulated (GIS)

> Technical comparison covering IEC 62271-200 LSC2B-PM metal-clad AIS, SF6 and Clean-Air GIS, up to 70% footprint reduction, Internal Arc Classification (IAC AFLR 25 kA 1s), and life-cycle maintenance.

- **Category:** Medium Voltage Switchgear
- **Author:** Voltformer Medium Voltage Switchgear Engineering
- **Publication Date:** 2026-08-05
- **Reading Time:** 8 min read
- **Key Tags:** #MV Switchgear, #AIS, #GIS, #IEC 62271-200, #IAC AFLR
- **Canonical URL:** https://voltformer.com/articles/air-insulated-vs-gas-insulated-mv-switchgear-ais-vs-gis-selection
- **Markdown Source:** https://voltformer.com/articles/air-insulated-vs-gas-insulated-mv-switchgear-ais-vs-gis-selection.md

### 1. Medium Voltage Switchgear Architecture

Selecting medium-voltage switchgear (12 kV to 36 kV) requires evaluating civil room space costs, ambient harshness (humidity, dust, chemical pollution), and maintenance access.

### 2. Comparative Engineering Evaluation Matrix

| Engineering Parameter | Air-Insulated Metal-Clad AIS (IEC 62271-200) | Gas-Insulated Switchgear GIS (SF6 / Clean Air) |
|---|---|---|
| **Insulation Medium** | Ambient Air (Phase clearance: 120-220 mm) | $SF_6$ / Synthetic Air ($1.3 - 1.5\text{ bar abs}$) |
| **Footprint per Feeder (36 kV)** | $1000\text{ mm width} \times 2250\text{ mm depth}$ | **$600\text{ mm width} \times 1100\text{ mm depth}$ (-65% to -70%)** |
| **Loss of Service Continuity** | **LSC2B-PM (Partition Class Metallic)** | LSC2A / LSC2B sealed tank |
| **Internal Arc Withstand** | IAC AFLR 25 kA / 31.5 kA 1.0 s | IAC AFLR 25 kA / 31.5 kA 1.0 s |
| **Environmental Immunity** | Sensitive to condensation, dust, marine salt | **100% Hermetically Sealed (IP65 stainless steel tank)** |
| **Cable Termination System** | Air bushings with heat-shrink boots | Outer cone / Inner cone plug-in bushings (EN 50181) |
| **Maintenance Interval** | 3-5 years visual inspection & busbar torquing | **Maintenance-free primary circuit for 30+ years** |

### 3. Internal Arc Classification (IAC AFLR)

Per **IEC 62271-200**, switchgear must pass internal arc testing to protect personnel:
- **A:** Authorized personnel access only.
- **F, L, R:** Front, Lateral, and Rear protection.
- **25 kA / 31.5 kA 1.0 s:** Fault current magnitude and duration.

### 4. Eco-Friendly Clean-Air GIS Trends

Modern regulations phase out greenhouse gas $SF_6$ in favor of Clean-Air ($80\% N_2 + 20\% O_2$) with vacuum interrupters, achieving **Global Warming Potential ($GWP$) $< 1$**.

*Reference: IEC 62271-200:2021; IEEE Std C37.20.2-2022; CIGRE TB 740.*

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