SF6 Gas Circuit Breaker: Uses and Gas Handling Recommendations

What is an SF₆ Gas Circuit Breaker?

Circuit breakers protect electrical power stations and distribution systems by interrupting electric currents when tripped by a protective relay. SF₆ gas circuit breakers use sulfur hexafluoride as an arc-quenching insulating medium. Transmission substations transfer high voltage power to distribution substations, which subsequently disperse the incoming electricity to lower voltages suitable for consumers on power grids. Both transmission and distribution circuit breakers are vulnerable to arcing events, which can be triggered by power surges, partial discharges, and lightning strikes.

SF₆ gas is inert, non-flammable, non-toxic, thermally stable, and has unmatched arc-quenching capabilities. It is more effective at dissipating heat than air, nitrogen, or other dielectrics. SF₆ requires a lot of heat to break down the bonds between the molecules. When the heat source is removed the atoms begin to recombine immediately.  The chemical properties of SF₆ make it ideal for use within circuit breakers and switchgear. SF₆ gas has excellent thermal transfer characteristics, so it works to absorb the energy of the arc. This creates resistance across the arcing contacts and eventually extinguishes the arc. Once the arc is extinguished, the SF₆ gas begins to regenerate almost immediately. 

The introduction of SF₆ gas circuit breakers offered several benefits to the electrical industry. For example, oil circuit breakers popular in the 1990’s required frequent upkeep as the medium became polluted and caused a potential fire hazard. The introduction of sulfur hexafluoride gas breakers offered a non-flammable solution. SF₆ gas breakers also allow for a smaller footprint compared to breakers made to handle other insulating mediums. The dielectric strength of SF₆ increases with pressure, therefore smaller breakers can be used at higher voltages.

SF₆ Gas Circuit Breaker Testing

Circuit breakers are designed to clear faults to protect electrical power stations; however, in normal conditions these breakers are only in operation for a matter of minutes of their entire 20 plus year lifespan. Over time, moving parts on circuit breakers wear, alignments and clearances change, and critical functions can be negatively affected. How can you ensure that a SF₆ gas circuit breaker will work when you need it to? That’s where “Doble testing”, or power factor testing comes into play. The Doble test detects the presence of contamination or deterioration of the breakers insulating system.

The Doble test can detect issues including:

·       Moisture contamination

·       Corrosion of insulating components

·       Damage of components like operating rods and interrupters

Circuit breaker testing reveals these and other changes, in advance of a failure. If any problems are found, corrective action can be taken to safeguard the reliability of the breaker.

Gas Handling Recommendations for SF₆ Circuit Breakers

During routine maintenance of an SF₆ gas circuit breaker or in the event of a failure, the gas insulated equipment may need to be opened. This requires SF₆ gas handling to remove as much gas as possible and place the breaker into the vacuum to avoid SF₆ emissions. In its pure form, SF₆ gas is inert and non-toxic; however, dangerous SF₆ by-products form when the gas is exposed to a fault. By-products such as SO₂ can also form when SF₆ circuit breakers are in service for a long time and exposed to high heat and moisture.

We always recommend checking the quality of SF₆ gas with an analyzer before beginning any handling procedures as by-products of SF₆ are extremely hazardous to human health. In addition, by-products will damage gas handling equipment and accessories. Special PPE must be worn, and best-practices must be followed to ensure the safety of technicians. You can learn more by watching our free webinar: Emergent By-Product Cleanup Services. 

In addition to being aware of the gas quality and knowing how to handle SF₆ by-products correctly, users must also take great care to avoid producing any SF₆ emissions. SF₆ gas has the highest Global Warming Potential of any gas known to man. Ideally, SF₆ should be handled in a closed-loop system. Proper training and emission-free SF₆ gas handling equipment is very important to prevent emissions.

SF₆ Safety & Handling and Circuit Breaker Testing Fundamentals Training

Are you interested in learning more about SF₆ gas handling and circuit breaker testing? You’re in luck! DILO and Doble have joined forces to offer a special 4-day training focusing on both topics. This IACET accredited course focuses both on theoretical aspects as well as in-depth hands-on training. The next SF₆ Safety & Handling and Circuit Breaker Testing Fundamentals Training is taking place July 18-21 at DILO Company in Odessa, FL.
 

The first two days focus on SF₆ gas theory and practical equipment demonstrations to provide technicians with vital knowledge for optimizing SF₆ gas handling practices, safety procedures, and regulations/reporting.

In partnership with Doble, the second two days will cover circuit breaker testing. An introduction of various mechanism types, interrupters and testing methodologies will be discussed. For each test, there will be an in-depth discussion of each measurement, setup and test methodology, and acceptance criteria. A Vanguard specialist will provide training to decipher and review apparatus test results so that they are clear and easy to understand. Test results will be used for reporting and maintenance purposes and used for historical data samples to improve maintenance schedules.

Learning Objectives

 Upon completion of this course, the participant will be able to:

 ·       Describe characteristics of SF₆, including history, properties, and contaminants

·       Compare and contrast virgin and reconditioned SF₆ gas

·       Use an emission-free approach for SF₆ gas analysis

·       Employ best safety practices for hands-on SF₆ gas handling and safety methods

·       Create and apply a zero-emissions approach to SF₆ gas handling, including recovery, filling, and evacuation

·       Identify current environmental standards at a local and federal level

·       Discuss important DOT/transportation and certification requirements and considerations for SF₆ gas cylinders

·       Understand the operation of circuit breakers, when to perform routine circuit breaker tests

·       Interpret test results, case studies, and numerous field examples

·       Effectively create test plans using the manufacturer’s circuit breaker specifications

·       Confidently use Vanguard circuit breaker analyzers and VCBA S2 software to perform routine circuit breaker tests and manage test plans and test results

If you have any questions or wish to schedule a custom training at your facility, please contact us.

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