Pure SF6 is an excellent insulator in electric switchgears, but humidity in the gas decreases its insulating ability and can also result in very harmful decomposition products for humans, machinery, and the environment. Created in partnership with a European utility company, WIKA’s revolutionary GAD-2000 not only removes humidity from SF6 gas and dehydrates the compartment itself, but it does so while all the equipment is still online.
Sulfur hexafluoride (SF6) is an excellent dielectric insulator, commonly found in medium- and high-voltage electric switchgear. The non-flammable gas is a potent arc quencher: In the high-heat environment of an electrical discharge, the six fluorine atoms split from the sulfur atom to capture an electron. After the discharge is quenched, the molecule quickly recombines. In addition, SF6 gas is non-toxic.
However, humidity in the gas causes severe operational and safety issues. Water is an impurity that, by its very presence, lowers the overall system dielectric strength. H2O also prevents sulfur and fluoride from recombining fully. When SF6 doesn’t “self-heal” completely after each electrical arc, there’s less and less of it. What’s more, separated sulfur and fluorine can combine with the oxygen molecules in water to create toxic byproducts: thionyl tetrafluoride (SOF4), thionyl fluoride (SOF2), sulfuryl fluoride (SO2F2), and sulfur dioxide (SO2). This acidic, corrosive environment damages equipment, leading to leaks that can endanger personnel and the environment (SF6 is a potent greenhouse gas).
To maintain proper insulation and to avoid corrosion and critical conditions, operators routinely remove moisture from the gas to keep humidity below the water saturation point. Up until recently, the only way to dehydrate SF6 has been to take the gas-insulated switchgear (GIS) offline, evacuate the gas, pass it through a gas handling unit with dehydration filters, refill the GIS with the dried gas, and then put the system back online. This can be a time-consuming process that requires power plant downtime.
Online Removal of Moisture from SF6 Gas
A utility company in Europe needed a device that could dry out SF6 gas while all the equipment was still online. It even had a patent for such a unit. What it didn’t have was the resources to actually develop and manufacture it.
Knowing that WIKA is a leader in the power transmission and distribution industry, the utility company contacted our SF6 experts for help. The result is the GAD-2000.
This revolutionary gas dehydrator removes a portion of the SF6 from the GIS, runs the gas through a series of oil-free compressors and two water-absorbing filters, and then returns the dried gas to the GIS. This process is repeated until the water level in the gas is below the saturation point or reaches a desired value. Since the GAD-2000 automatically dehydrates the gas while the GIS is still online, there is little to no downtime, nor much demand for human intervention. When a technician needs to interact with the gas dehydrator, the 7-inch touchscreen is easy and intuitive to use.
Plant Safety: A Priority in SF6 Gas Handling
Because SF6 is such a potentially harmful gas and a critical system component, it requires a robust safety system and extremely careful handling. The GAD-2000 has an automatic gas compartment that isolates the SF6 in a safety module during extraction and refilling, in case an error occurs. The unit can, optionally, continuously check the monitoring instrumentation from the gas compartment, and it has an additionally implemented SIL2 safety control.
What’s more, the GAD-2000 can be optionally equipped with a GSM (Global System for Mobile communications) module to transfer data directly to a mobile device. Once installed, the operator can leave the unit running automatically and remotely receive information about:
- Current humidity level in the gas compartment
- Filter conditions
- Job concluded
The GAD-2000 is a highly efficient and effective gas dehydrating unit that allows a power plant to keep operating normally while maintaining safe humidity levels of the SF6 gas in switchgears. To find out more about the GAD-2000 and other SF6 gas cleaning, handling, and servicing equipment by WIKA, contact our specialists in power transmission and distribution.