SF6 gas handling

Frequently Asked Questions

What are the most important factors of quality criteria for SF6 gas in gas insulated switchgear (GIS)?

The following is of great importance: gas density, moisture concentration, decomposition products, gas purity (air concentration) which are determined by means of special SF6 measuring instruments as well as gas density controllers. DILO supplies the measuring devices required for the determination of the SF6 gas quality and for the verification of the switching points of density controllers.

Why is the SF6 quality in the GIS circuit breaker of great importance?

The gas quality is the decisive factor for the correct and reliable function of the switchgear. Moisture or toxic and corrosive decomposition products in circuit breakers might have a negative impact on the insulation properties and switching capacity.

When can SF6 be reused?

Reuse of SF6 is allowed if the previous measuring results of the switchgear comply with the limit values stipulated in the IEC 60480 regulation (air, moisture and SO2 concentration). But essentially the indications of the switchgear manufacturers regarding the minimum quality of SF6 gas are to be followed. 

What is to be observed when working with SF6 gas?

In accordance with the EC 517/2014 directive and by implementing the 2015/2066 regulation, only certified personnel is allowed to carry out SF6 gas handling in Europe. The 2015/2066 regulation stipulates the minimum requirements for the certification of personnel.

DILO is an accredited company and is therefore allowed to hold training courses for the acquisition of the permission to carry out the recovery of SF6 gas.

What is the function of a service cart?

A service cart enables the recovery of the SF6 gas from a gas compartment to a final vacuum of < 1 mbar. Thereby the gas flows automatically via dry and particle filters which effectively adsorb decomposition products and moisture from the gas. During the gas recovery process the SF6 is stored either in gaseous or in liquid form. Furthermore, the air is evacuated from gas compartments after maintenance works. Then, the gas compartments are refilled with SF6 to the desired operating pressure. The gas is led via filters and is purified once again while filling. 

What are the most important criteria when selecting a service cart?

The most important criteria are the volume of the gas compartment, filling pressure, gas volume to be stored, the desired time for the gas recovery, evacuation and filling processes as well as the final vacuum desired for the gas recovery process (< 5 or < 1 mbar). Our service cart selection tool allows for (pre-)selection of the appropriate service carts, taking your particular requirements into account.

How can SF6 gas be stored?

SF6 can be stored in gaseous form, and pressure liquefied depending on the temperature. Pressure liquefaction is achieved by means of compressors installed in the SF6 maintenance equipment. Thus, it is possible to store considerably higher gas quantities into pressure vessels.

What is the final vacuum that SF6 should be recovered to?

The IEC 62271-4 guideline stipulates a limit value of < 20 mbar. However DILO recommends a recovery down to < 1 mbar and therefore offers SF6 maintenance equipment allowing a recovery of < 1 mbar.

When should the SF6 gas quality be measured?

The SF6 gas quality must be checked prior to the recovery of SF6 from gas compartments, in particular with regard to possible reuse in accordance with the IEC 60480 directive. Also check whether a pre-filer unit should be used to protect the service cart or whether personal protective measure should be taken.

The key parameters here are the SF6 purity (%), the moisture content and the concentration of decomposition products. In general, the gas quality must always be checked if a decision regarding the reuse of the SF6 gas must be made or in the context of condition-based maintenance to prepare a trend analysis.

What must be done after having found gas contaminated with decomposition products in the circuit breaker?

In this case a pre-filter unit should be installed between the gas compartment and the service cart which adsorbs most of the decomposition products and moisture. This is to avoid contamination of the SF6 service cart and purifies the gas again during the recovery. In addition, personal protective measures should be taken before opening the gas compartment.

How can the gas quantity in the SF6-filled production equipment be determined?

Since the introduction of the first (EU) F-gas regulations, the SF6 gas quantity filled in the components must be indicated on the type plate. The SF6 gas quantity can be recorded during the gas recovery by means of a mass flow meter or cylinder scales at liquid storage. In case of old SF6 filled components please get in contact with the manufacturer.

Why must electrical production equipment be evacuated prior to SF6 filling?

Before filling with SF6 gas the air and moisture must be evacuated from the gas compartment to a final vacuum of < 1 mbar in order to prevent mixing with air and / or humidification. 

When are N2/SF6 gas mixtures or CF4/SF6 gas mixtures used?

These mixtures are used at low temperatures to avoid liquefaction of the gas at low temperatures. The same puncture strength as pure SF6 is achieved by higher system pressures.

Is it possible to separate SF6 by means of a SF6 maintenance device?

No it isn't possible. For this purpose special SF6/N2 separating units are necessary. After the separating process the gas complies with the quality criteria for reuse stipulated in the IEC 60480 directive. However, DILO separating units allow the SF6 gas mixture to be purified to the extent that it even meets the standards of IEC 60376 (directive for new SF6 gas technical quality) with regard to moisture, SF6 percentage and decomposition products (SO2).

However, the SF6 service cart can improve the quality of the gas regarding the decomposition products and humidity. You will find more detailed information on the preparation of used SF6 gas in the DILO Certified Gas section.

Which decomposition products may occur in case of failure in a GIS unit?

Toxic and corrosive decomposition products may occur. Corresponding measures for occupational health and safety in accordance with the local regulations DGUV Information 213-013 (= German social accident insurance concerning SF6 machinery and equipment) which are in effect in your country are to be taken. For this purpose a special working protection kit has been compiled. 

Which safety measures are to be taken if decomposition products are found in circuit breakers?

Please follow the local regulations for occupational health and safety DGUV Information 213-013 (= German social accident insurance concerning SF6 machinery and equipment) which are in effect in your country. 

What must be observed for the transportation of SF6 maintenance devices containing SF6 gas?

In accordance with the ADR guidelines applicable in Germany, SF6 may only be transported on roads under an exemption if the pressure of the gas in the maintenance device or storage tank is a maximum of 2 bar at a temperature of 20 °C. Further information on the transport regulations applicable in Germany can be found in the DILO Certified Gas/Transport Regulations section.

How can I reduce the pressure of a SF6 service cart to transport pressure?

In order to reach a transport pressure of max. 2 bar pe, a transport pressure reduction with pressure equalisation generally needs to be carried out in the device. Most DILO devices are equipped with a special function implemented in the control which automatically establishes this pressure equalisation.

What is meant by SF6 monitoring?

This means the stock management of SF6 gas. The aim is to record all incoming and outgoing SF6 gas in order to create a mass balance.

How can I detect an SF6 leak?

A drop in pressure or density, which can be read on the pressure/density monitors installed at the SF6 gas compartment, indicates a leakage. Room monitoring devices also trigger an alarm in the event of an SF6 leak.

What can I do with used SF6 gas? Can I reuse it?

If the limit values stipulated in the IEC 60480 regulation for SF6 purity (%), moisture content and concentration of decomposition products are met, the gas can be reused. Otherwise DILO offers the preparation of used SF6 gas. Further information can be found in the "DILO Certified Gas" section.