TechTopics No. 54

Interrupter switch technology comparison - type SIMOSEC SF6 switch - conventional air switch

In TechTopics No. 53, the characteristics of SF6 (sulfur hexafluoride) gas that make it advantageous for use in mediumand high-voltage electrical equipment were discussed. This issue of the TechTopics series will discuss this issue further by comparing the features of conventional, medium-voltage loadinterrupter switches operating in air with those operating in an SF6 gas environment.


The table on the next page shows some of the major characteristics of medium-voltage 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 (15 kV 600 A) switch, and the dimensions for a 27 kV switch are significantly greater. Even though typical data is used for the air switch, the table is considered valid for an overall understanding.


From the data in the table, these observations can be made:

  • Endurance: The switching endurance of the type 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 type SIMOSEC SF6 switch is isolated from the atmosphere.
  • Size: The type SIMOSEC SF6 switch (without operator) is over 90 percent smaller than the basic air switch, allowing for a great reduction in space for the overall type SIMOSEC switchgear installation.
  • Maintenance: Maintenance required for the switch itself is essentially eliminated.

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

Table 1
Type SIMOSEC SF6 switch
Medium-voltage air switches
Switching life:

● Mechanical

● Electrical
● 1,000 operations

Very high:
● 100 operations at 600 A
Low – ANSI C37.22 requires:
● 500 operations up to 15 kV
● 350 operations at 27 kV

Low – ANSI C37.22 requires:
● 50 operations up to 4.76 kV
● 30 operations for 4.8 to 15 kV
● 10 operations for over 15 to 27 kV
Welded, stainless steel switch enclosure, sealedfor-life, isolated from contaminants
Switch in air, exposed to contaminants, corrosive influences, dust, dirt
Very small:
● Basic 600 A switch module for up to 27.6 kV (without enclosure) is about 14"D x 8"W x 9"H (0.6 cubic feet)
● Basic 600 A switch module for up to 15 kV 600 A (without enclosure) is about 28"D x 25"W x 26"H (10.5 cubic feet)
Visible isolation 
● Large viewing window for verification of position (CLOSED – OPEN – GROUNDED)
● Integrated fault-making (make-proof) grounding for outgoing feeder cables

● Inherently prevents simultaneous CLOSED and GROUNDED positions
No integral grounding capability 
Operation means 
● Manual spring operator (standard)
● Motorized spring operator (optional)
● Motorized spring stored-energy operator (optional)
● Manual spring operator (standard)
● Motorized spring stored-energy operator (optional)
Mechanism force 
Very low:
● Small moving mass
● Short travel distance
● Easier operation
● Increased reliability
● High moving mass
● Long travel distance
● Harder operation
● Lower reliability
Gas handling 
● Switch enclosure sealed-for-life
● No gas handling during maintenance 
Not applicable 
Gas leakage 
Less than 0.1% per year:
● Welded, stainless steel gas enclosure
● Switch enclosure sealed-for-life
● Bushings welded to enclosure
● No sliding or rotating seals
Not applicable 
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
● Switch operates in air
● Switch needs adjustment, inspection
● Operating mechanism requires lubrication
● Arcing contacts subject to erosion
● Arc chutes subject to degradation

Should you have any questions about this issue of TechTopics or any of our products, solutions, or services, please contact your local Siemens sales representative for more information.

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