What Is The Environmentally Friendly Load Switch Air-Insulated Ring Main Unit?

12kV Air-Insulated Secondary Switchgear - Ring Main Unit

The Schneider Electric SM AirSeT utilizes a load switch with parallel vacuum interrupter technology. The interrupter is cast into the upper section of the traditional gas-filled chamber. During the opening operation of the three-position switch, the electric arc is extinguished by this vacuum interrupter chamber.

AirSeT uses compressed air-sourced directly from the ambient environment-as its insulating and interrupting medium. This eliminates concerns regarding greenhouse gas emissions, as the gas is non-toxic and harmless. There are no safety risks for maintenance personnel in the event of a gas leak. The medium offers excellent insulation performance.

Key Specifications:

Rated Voltage: 12kV

Rated Current: 1250A

Short-Circuit Withstanding Current: 31.5kA

Dimensions: 600mm (width) x 1050mm (depth) x 2220mm (height)

Filling Pressure: 0.14 MPa

By using parallel vacuum interrupter technology, Siemens also provides gas-insulated load switches like the SM6, enabling SF6-free operation in air-insulated ring main units and thus avoiding this greenhouse gas.

Air-insulated ring main units typically use separate fixed or withdrawable circuit breakers, though some designs integrate the switch and circuit breaker into a single unit, similar to solid-insulated switchgear. The UniSec AirPlus HBC utilizes a conventional three-position switch combined with a vacuum interrupter, both cast inside an epoxy resin enclosure. While the breaking gap of the traditional three-position switch relied on SF6 for insulation, ABB's new insulating gas, AirPlus, offers comparable dielectric strength. AirPlus is a groundbreaking eco-friendly hybrid gas, a mixture of 3M's C5 and air, which reduces the global warming potential (GWP) by 99.99% compared to SF6.

Key Specifications for UniSec AirPlus HBC:

Rated Voltage: 24 kV

Rated Current: 1250 A

Short-Circuit Withstanding Current: 25 kA

Dimensions: 500 mm (width) × 1070 mm (depth) × 2000 mm (height)

Filling Pressure: 0.14 MPa

Technical Features of AirPlus

AirPlus is an environmentally friendly alternative to SF6 gas. This new hybrid gas, used in medium-voltage GIS for both insulation and interruption, comprises fluoro-ketone, nitrogen, and oxygen. It is based on the C5-perfluoroketone molecule.

To maintain the C5-FK in a gaseous state, it is mixed with dry air at a concentration of approximately 8%. The air-insulated, medium-voltage UniSec switchgear is an SF6-free solution rated for voltages up to 24kV. Its key innovation lies in using AirPlus as the insulating medium, which reduces the global warming potential by 99.99% compared to SF6. The Hysec AirPlus model further integrates the functions of a circuit breaker, disconnector, and earthing switch.

The HySec AirPlus consists of two main sections. The upper epoxy resin section ensures the required insulation level, while the lower stainless steel part provides a metal-enclosed compartment, achieving a partition type of class PM. This design is widely adopted in solid-insulated switchgear in China, where the busbar, three-position switch, vacuum interrupter, and operating mechanism are fully sealed within the epoxy resin cast enclosure. This ensures complete insulation and shielding, with a protection rating of IP67. The outgoing line bushings comply with the DIN 47636 standard, and cables are connected via cable connectors to these bushings.

Inside the enclosure, the breaking gap of the three-position switch is insulated by air. Unlike the initial SF6-based design of ABB's HySec AirPlus, this air-insulated switch requires a significantly larger air clearance distance and also faces the challenge of a "non-isolated" or "pseudo" breaking gap.