Interrupter switch technology comparison / SIMOSEC SF6 switch-conventional air switches


In previous articles, we discussed the characteristics of SF6 (sulfur hexafluoride) gas which make it advantageous for use in medium- and high-voltage electrical equipment. Here we compare the features of conventional medium-voltage load interrupter switches operating in air with those of operating in an SF6 gas environment.


The table below displays some of the major characteristics of medium-voltage load interrupter switches that influence the application or the space required load interrupter switches that influence the application or the space required. Of course, the table data for air switches is generic, and the specific data for a particular vendor of air switches can vary significantly. The air switch dimensions shown are for the most common (15kV 66A) switch, and the dimensions for a 27kV switch are significantly greater. Even though typical data is used for the air switch, the data below is considered valid for an overall understanding.


From the data below, we can make these observations:

  • Endurance: the switching endurance of the SIMOSEC SF6 switch is significantly higher than that of an air switch that merely meets the ANSI C37.22 endurance requirements.

  • Environmental: the switching performance does not deteriorate in adverse environments since the SIMOSEC SF6 switch is isolated from the atmosphere.

  • Size: the SIMOSEC SF6 switch (without operator) is over 90% smaller than the basic air switch, allowing for a great reduction in space for the overall SIMOSEC switchgear installation.

  • Maintenance: maintenance required for the switch itself is essentially eliminated.

This comparison illustrates the superiority of the SIMOSEC SF6 load interrupter switch in comparison to traditional load interrupter air switches.


SIMOSEC SF6 switch


Mechanical - High 1000 - operations


Electrical -  Very high - 100 operations at 600A


Environmental - Welded stainless steel switch enclosure, sealed-for-life, isolated from contaminants


Very small - Basic 600A switch module for up to 27.6kV (without enclosure) is about 14"D x 8"W x 9"H (.6 cubic feet)


Visble isolation - Yes - Large viewing window for verification of position (closed - open - grounded)


Functionality - Integrated fault-making (make proof) grounding for outgoing feeder cables; Inherently prevents simultaneous CLOSED & GROUNDED positions.


Operation means - Manual spring operator (std); Motorized spring operator; Motorized spring stored energy-operator(opt);


Mechanism force - Very low - small moving mass; short travel distance; easier operation; increased reliability


Gas handling - None - Switch enclosure sealed-for-life; no gas handling during maintenance


Gas leakage - Less than .1% per year - welded stainless steel gas enclosure; switch enclosure sealed-for-life; bushings welded to enclosure; no sliding or rotating seals


Maintenance of switch module - Extremely low - switch enclosure sealed-for-life; no contact inspection or replacement; no lubrication for operating mechanism; insignificant contact erosion during switching; no arc chutes


Medium-voltage air switches


Mechanical - Low - ANSI C37.22 requires: 500 operations up to 15kV; 350 operations at 27kV


Electrical - Low - ANSI C37.22 requires: 50 operations up to 4.76kV; 30 operations for 4.8 - 15kV: 10 operations for 15-27kV


Environmental - Switch in air, exposed to contaminants, corrosive influences, dust, dirt


Size - Large - typical basic switch module (15kV 600A) without enclosure is about 28"D x 25"W x 26"H (10.5 cubic feet)


Visible isolation - Yes


Functionality - No integral grounding capability


Operation means - Manual spring operator (std); motorized spring stored-energy operator (opt)


Mechanism force - High - high moving mass; long travel distance; harder operation; Lower reliability


Gas handling - Not applicable


Gas leakage - Not applicable


Maintenance of switch module - High - switch operates in air; switch needs adjustment, inspection; operating mechanism requires lubrication; arcing contacts subject to erosion; arc chutes subject to degradation.

Mailing address

Siemens Industry, Inc.

7000 Siemens Road

Wendell, North Carolina 27591

United States