Circuit Breakers - AC

A circuit breaker (CB) refers to a mechanical switching device, capable of making, carrying and breaking currents under normal circuit conditions as well as making, carrying for a specified time and breaking currents under specified abnormal circuit conditions, such as those of short-circuit.

Technology Types

The technology types of common new CBs can be defined as follows:

  • The arc-quenching medium:

    • for EHV - SF6, Oil
    • for HV - SF6, SF6-free, Oil, vacuum
  • Arc-quenching principle:

    • blast
    • Self-blast
    • Double motion self-blast
  • Drive type

  • Hydraulic
  • Spring
  • Number of series breaking units (1,2 or 4), grading capacitors or energisation resistors
  • Design:

    • Life tank (Interrupter is inside an enclosure that is insulated from ground potential.)
    • Dead tank (Interrupter is situated inside a grounded metallic enclosure filled with insulation gas. The Interrupter is connected via bushings to the AIS busbar. Typically, the current transformer is also attached to this module.)
    • GIS circuit breaker – Interrupter is located in a grounded pipe filled in with insulating gas. CB is connected with other GIS components such as disconnectors, voltage transformers and earthing switches in GIS technology.

Components & enablers


Advantages & field of application

The CBs enable the power flow to be controlled by connecting or disconnecting components from HV grid and switching ff the disturbances. Hence, they are essential for a reliable operation transmission system.

The choice of circuit breaker technology for specific application depends on required switching capabilities (e.g. 63 kA or 80 kA) and available space (e.g. life tank or dead tank). For special application (e.g. switching of currents without zero crossings) old technologies (hydraulic drive, blast principle, 4 interrupting chambers with grading capacitors) are still in use.

Due to very high switching performance requirements in the EHV grid, only SF6 gas is used. The latter has very high global warming potential. Hence, many new developments of SF6 free CB in HV networks have recently been observed. Nevertheless, there are no examples in EHV yet.

Technology Readiness Level

HV/EHV SF6 2020: TRL 9 – AIS & GIS circuit breaker

HV SF6-free 2020: TRL 7 – AIS & GIS circuit breaker

EHV SF6-free 2020: TRL 3 – AIS & GIS circuit breaker

Research & Development

Current fields of research: Higher switching performance (e.g. 80 kA in GIS); models and diagnosis methods for end of life prediction; increasing the reliability of devices; replacement of SF6.

Best practice performance

Rated nominal current: 4,000 A

Rated short circuit current: 80 kA

Maximum operating Voltage: 420 kV

Insulating medium: SF6

Number of breaking units per pole: 4

Speciality: very high arc resistance needed for switching of currents without zero crossing

Expected lifetime: > 50 years

Best practice application

Oerlikon, Switzerland


First pilot project of a distribution system operator using non SF6 gasses for HV circuit breakers, was initiated in Oerlikon, Switzerland.

3x50-MVA transformer station with 170 kV and 24 kV switching panels using non SF6 gas.

Fault-free operation since August 2015. No measurable decomposition of fluorine ketones to date.

Nördlingen, Germany


First installation of a GIS using a vacuum-interruption technology in circuit breakers with a rating of up to 145 kV.

The vacuum-interruption and clean-air insulation technology for a rated voltage of 145 kV, a rated short circuit-breaking current of up to 40 kiloamperes (kA), a rated current up to 3,150 A, and operating temperatures between -55° Celsius and +55° Celsius.

No published results yet – expected to provide same performance and reliability while avoiding greenhouse gases such as SF6 or other fluorids.

Obermooweiler, Germany

Expected 2021 for new construction; 2026 for modification.

The world’s first 380 kV gas-insulated switchgear (GIS) will be installed, which uses SF6 alternative gas mix (fluorine ketones).

Detailed planning in process for a new construction as well as an extension/modification of an existing switchgear.

No results yet – gain experience and reduce greenhouse effect by 99%.


[1] Ecofys, ETH Zürich. Concept for SF6-free transmission and distribution of electrical energy. [Link]

[2] Siemens. Clean-Air (Blue) GIS. [Link]

[3] Siemens. First use in the high-voltage grid: SF6-free circuit breaker from Siemens for Netze BW. [Link]

[4] PG&E SF6 Free HV GIS and Breakers. [Link]

[5] IEEE. AC High-Voltage Circuit Breakers. [Link]

[6] Saitoh,H., Matsui, Y. et al. Research and development on 145 kV/40 kA one break vacuum circuit breaker. [Link]

[7] Seeger, M. et al. Recent Trends in Development of High Voltage Circuit Breakers with SF6 Alternative Gases. [Link]

[8] ABB. Gas-insulated switchgear ELK-5 up to 1200 kV. [Link]

[9] ABB. ABB wins $40 million order for eco-efficient substation in Germany. [Link]

[10] T & D Europe. Technical Report on Alternatives to SF6 Gas. [Link]