airinsulated

Air-insulated equipment (AIS) refers to electrical apparatus in which air acts as the primary dielectric between energized conductors and other potentials. The term is most often used for high-voltage switchgear and substations, where components such as circuit breakers, disconnectors, busbars, and current transformers are mounted in outdoor or indoor structures and insulated by the surrounding air rather than enclosed gas or oil.

In AIS designs, insulators are typically porcelain or polymer and are used to span gaps and support conductors. The operating voltage, required creepage and clearance distances, and environmental conditions determine the geometry and layout. AIS equipment is commonly installed in outdoor substations or protected buildings, with weatherproof housings or enclosures.

Advantages include lower capital cost for many voltages, straightforward maintenance, and the absence of gas handling. AIS can be easier to inspect and repair and avoids issues related to gas leakage. Disadvantages include a larger footprint due to air clearance requirements, sensitivity to pollution and weather, arcing and tracking risks in contaminated environments, and higher insulation coordination demands for very high voltages.

Compared with gas-insulated switchgear (GIS), AIS uses free air instead of a sealed gas-filled enclosure. GIS offers a compact, protected layout and a smaller footprint but raises concerns about gas leakage and greenhouse effects. AIS remains common in outdoor substations and at voltages where space is less constrained.

Standards governing AIS fall within the IEC 62271 series for high-voltage switchgear and controlgear, with parts addressing air-insulated equipment and insulation coordination. Design and maintenance address thermal performance, clearances, and fire safety.