Sf6 Gas

Sf6 Gas

Introduction

SF6 is a gas that is used in electrical power equipment. It is colourless, odourless, non-flammable and chemically stable. This means that at room temperature it does not react with any other substance. Stability comes from the symmetrical arrangement of the six fluorine atoms around the central sulphur atom. And this stability is just what makes the gas useful in electric equipment. SF6 is a very good electrical insulator and can effectively extinguish arcs, which makes high and medium voltage apparatus filled with SF6 highly popular. SF6 can be found in millions of electric apparatus all over the world; electrical equipment containing SF6 is a large export article.

SF6 is formed by a chemical reaction between molten sulphur and fluorine. Fluorine is obtained by the electrolysis of hydrofluoric acid (HF). Pure SF6 is not poisonous. The gas is not dangerous to inhale, provided the oxygen content is high enough. In principle you can inhale a mixture of 20% oxygen and 80% SF6 without danger. SF6 is about 6 times heavier than air. That means that it may collect in cable ducts or at the bottom of tanks. The gas is not dangerous to inhale but if it does accumulate where people work, there is a risk of suffocation due to the lack of oxygen. SF6 is a non-flammable gas that is used in electrical apparatus. SF6 is not poisonous.

The most common use for SF6, both domestically and internationally, is as an electrical insulator in high voltage equipment that transmits and distributes electricity. Since the 1950’s the U.S. electric power industry has used SF6 widely in circuit breakers, gas-insulated substations, and other switchgear used in the transmission system to manage the high voltages carried between generating stations and customer load centers.

Several factors affect SF6 emissions from electric power systems, such as the type and age of the SF6 containing equipment (e.g. older circuit breakers can contain up to 2,000 pounds of SF6, while modern breakers usually contain less than 100 pounds), and the handling and maintenance procedures practiced by electric utilities. Because of its long life span and high GWP potency, even a relatively small amount of SF6 can have a significant impact on our climate.

The SF6 Emission Reduction Partnership is one of EPA’s voluntary industry programs aimed at reducing greenhouse gas emissions. The Partnership’s primary objective is to reduce SF6 emissions via cost-effective technologies and practices. Through improvements in the leak rate of new equipment, refurbishing of older equipment, and the use of more efficient operation and maintenance techniques, utilities often find economical solutions to reduce SF6 emissions.

Emissions

The electric power industry uses roughly 80% of all SF6 produced worldwide. Ideally, none of this gas would be emitted into the atmosphere. In reality significant leaks occur from aging equipment, and gas losses occur during equipment maintenance and servicing. With a global warming potential 23,900 times greater than CO2 and an atmospheric life of 3,200, one pound of SF6 has the same global warming impact of 11 tons of CO2. In 2002, U.S. SF6 emissions from the electric power industry were estimated to be 14.9 Tg CO2 Eq. For more information on the U.S.

Opportunities for Electric Power Systems

The electric power industry has an enormous opportunity to help reduce the nation’s SF6 emissions through cost-effective operational improvements and equipment upgrades. With an average cost of $9.00 per pound, the SF6 emission reduction of partner companies from 1999-2002 totals $2.5 million dollars.

EPA works to share information on best management practices and technical issues that can help reduce emissions. EPA also sponsors SF6 conferences where partners and others from the industry can stay informed of the latest developments in this area. The most promising and cost effective options to reduce SF6 emissions are:

Leak Detection and Repair

EPA estimates that if consistently and aggressively implemented in the U.S., SF6 emissions could be reduced by 20%.

Use of Recycling Equipment

EPA estimates that SF6 recycling could eliminate 10% of total related emissions from the U.S. electric industry.

Employee Education/Training

Making employees aware of the environmental impact of these emissions and establishing a corporate policy for managing SF6 is critical. “You can’t manage what you don’t measure!”

Where and How Is SF6 Used?

SF6 is used as an insulating gas in substations, as an insulating and cooling medium in transformers and as an insulating and arc quenching medium in switchgear for high and medium voltage applications. These are all closed systems which are extremely safe and unlikely to leak.

In electrical power systems, high and medium voltage switchgear is required to cut off the power in case of a fault, in order to protect people and equipment. When power is switched, an electric arc strikes between the circuit-breaker contacts. Breakers filled with SF6 are electrically insulating and effectively control arcing. Gas isolated substations are mainly found in urban areas where you want them to take up as little room as possible and often integrate them into buildings. These substations reduce the magnetic field and remove the electrical field completely. This is a real advantage for installers, maintenance personnel and people who live in the vicinity of substations.

SF6 also is used in other ways. Mixed with argon, it can be used in insulated windows. SF6 is used in the metal industry, for example, when casting magnesium. Eye surgeons use SF6 as a cooling agent in operations. SF6 can also be used as a fire extinguishing agent because it is non-flammable and cooling. In electrical applications, SF6 is only used in sealed and safe systems which under normal circumstances do not leak gas. SF6 is collected and recycled if a piece of equipment or a substation needs to be opened.