Circuit breakers and SF6

Circuit breakers are used in high voltage DC and AC applications for swithcing of powerlines, transformers, reactors and capacitors. One phase and three phase operations up to 800kV, 63kA.

There is a wide variety of HV circuit breaker designs and configurations in existence. They can be classified in various ways, but the most common classifications are described in the figure to the right.

A circuit breaker has several main functions:

• Conduct rated currents when closed

• Maintain rated insulation withstand across its contacts when open

• Close its circuit always and only on command

• Open or interrupt its circuit always and only on command, according to its ratings

From air-blast and oil to SF6 and springs

From a historical perspective, oil and air-blast interrupters are the oldest designs and essentially have been superceded by SF6 interrupters since the mid-1980's. There has also been an increasing trend towards the use of spring operating mechanisms from the early 1990's, following from the results of the second CIGRÉ enquiry into the reliability of HV breakers.

Service and testing of circuit breakers evolve around the electrical and mechanical functions in order to ensure a secure and steady elcetrical power flow. Non working breakers is an expensive event for utilities, power companies and manufacturers. As you can see in the conclusions below the criterias for analysing the SF6 gas is obvious.

CIGRÉ report 13-202 draws some important general conclusions regarding the most common problems with breakers, including:

• Operating mechanisms are the sub-assembly with the most failures – further work was suggested to "simplify the electrical and mechanical control process".

• While only 7% of major failures in SF6 breakers were attributed to loss of gas, approximately 40% of minor failures were due to this problem, leading to the conclusion that additional effort was needed (in the early 1990's) to address SF6 gas pole sealing and monitoring.

• Additional type testing for mechanical endurance, climate testing and life cycle assessment were recommended (see later discussion on impacts on revisions to IEC breaker standards).

• Encouragement was made for the use of "common definitions for reliability studies and maintenance techniques".

Environment

The need for testing of the SF6 gas is not only to protect the electric power equipment but maybe more importantly in order to protect our environment.

A high productive circuit breaker factory for live tank air insulated breakers consumes approximately 50 tons of SF6 gas each year. A deadtank circuit breaker factory consumes 10 times that amount.

A single live tank air insulated circuit breaker contains somewhere from e few kilos up to a few tens of kilos. While a deadtank breaker, as stated previously, consists of tens times as much.

And as you may all be aware, a GIS substation can contain several tons of Sulphur Hexaflouride.

Even though the SF6 insulated switchgear development has managed to produce compact designs that reduces space reduction up to 98% compared to air insulated switchgear and has reduced the SF6 volume up to 75% with leakage rates down to 0,5% per compartment and year.

Air insulated breakers is still considered to be the best choice for our environment.

Air insulated breaker (HPL)

This page is part of the Elcon International Group.
Circuit breaker test equipment for the generation, transmission and distribution industry.
Commissioning, service, manufacturing and on-line monitoring of high voltage circuit breakers.

Designed by Xpresso Publishing