EMT Energy Maintenance Technologies | EMT Americas

Assero Testing & Maintenance

Sulphur Hexafluoride (SF6) gas has been utilised in High Voltage Gas Insulated Switchgear (GIS) and Circuit Breaker applications for over 50 years.

Over the years, earlier installations have started to show signs of the SF6 breaking down and decomposing due to high temperature arcing and leakage. These "arc" breakdown or decomposition products are difficult to measure and have various Health and Safety problems associated with their ongoing use.

These issues coupled with the fact that SF6 is a major greenhouse gas, more than 23,900 times more damaging to the Ozone layer than C02 means that measuring, monitoring and capturing SF6 is a very important step in the on going protection and maintenance programmes for sub-station personnel going forward.

These decomposition byproducts include lower fluorides of sulphur, which are hydrolyzable, yielding HF (Hydrofluoric Acid) and SO2 (Sulphur Dioxide). Moisture and oxygen will react with SF6 decomposition products in the presence of an electrical discharge to form a variety of compounds which are extremely toxic and very difficult to measure.

It is very important to measure the SF6 decomposition products and there are various IEC/CIGRE and ASTM methods which provide a guide to their use, handling and measurement.

Quality SF6 analysis and maintenance is very helpful at all stages of equipment life time, i.e. before equipment service, during equipment service (periodically or occasionally), and at the end of the equipment life.

Quality SF6 analysis serves three main purposes:

• To ensure that the initial conditions for the intended equipment service at the time of commissioning (or at any other moment of manipulation with the SF6 filling) are correct.
• To diagnose deteriorated conditions of any SF6 filled equipment during its service.
• To ensure proper environmental-friendly handling and consequent disposal with used SF6 gas.

All three purposes are very important and crucial to protection of SF6 plant and personnel. The key question is how do you select the right moment for internal intervention, i.e. how to prevent a violent failure and simultaneously how to avoid unnecessary internal inspections. This aspect is becoming more and more important as utilities are forced to avoid unplanned as well as planned outages and to cut preventive as well as corrective maintenance expenditures.

Condition based predictive maintenance activities thus provide optimum solutions and many utilities are changing their maintenance strategies towards this principle (CBM), and EMT Americas are leaders in this field.