Traverse City Light and Power (TCL&P) located in Traverse City, Michigan has installed circuit switchers that use clean dry air instead of traditional sulfur hexafluoride (SF6) insulating gas, making it the first utility in the United States to use the new technology.
The Blue Clean Air 72.5-kilovolt (kV) CPV2V Circuit Switcher was built by Siemens Energy in the company’s Richland, Mississippi plant and commissioned at TCL&P in October 2020.
The new switchers “provide more reliability to our customers and save maintenance costs along with being more environmentally friendly,” Tony Chartrand, system engineer at TCL&P, said In addition, SF6 will likely be outlawed at some point in the future – as many refrigerants have – and it is getting harder and harder to refill a bottle of SF6, he said.
TCL&P has set a goal of deriving 100% of its generation needs from renewable energy resources by 2040. The new switchers “match up with that goal by getting rid of devices that could leak greenhouse gases into the atmosphere,” Chartrand said.
Sulfur hexafluoride has a global warming potential 23,500 times that of carbon dioxide.
The clean air switchers use a vacuum tube to break the arc instead of SF6. The vacuum tube is surrounded by a normal air mixture that is dried and filtered in order to remove any possible contaminants that could cause an arc around the vacuum bottle. Clean air is readily available from industrial suppliers, but Siemens provided a G-size tank of air to fill the switchers that is expected to last as long as the switchers do. The new technology also eliminates the need to store and handle sulfur hexafluoride gas.
Siemens says its Blue Clean Air circuit switchers are capable of reliable short-circuit interruption at voltage levels above 69 kV and that it can in temperatures as low as -50° C (-58° F), thus eliminating the need for external heaters.
TCL&P has been upgrading its 69-kV distribution system. The two new switchers were installed to replace fuses that were protecting the transformers. It was the utility’s last substation that was still using transformer fuse protection, Chartrand said.
TCL&P has a number of other SF6 switchers, most of which are not even 20 years old and still have life in them, Chartrand said, adding that the utility is taking a phased approach to replacing them.
Eventually TCL&P plans to replace all its traditional SF6 switchers with clean air switchers, but they are more expensive, currently costing about 68% more than traditional technology, Chartrand said. On the other hand, the new switchers offer estimated life cycle cost savings of up to 40% over SF6 circuit switchers, and the new switchers have a longer expected operating life and have longer maintenance intervals. “We have no plan to buy any more SF6 devices; we plan to move exclusively to vacuum technology for all of our breakers and circuit switchers,” Chartrand said.