The use of SF6-free gases for interruption and insulation of T&D equipment draws ample interest these days, on the wave of the increasing urge to replace the greenhouse gas SF6.
In this CIGRE webinar, the physical basis of arc interruption will be explained in engineering terms, first in SF6, then in its alternatives, in this case mainly mixtures of fluoronitriles with CO2 and O2 and mixtures of CO and O2 only.
First, after a general introduction on the working principle of AC circuit breakers, a detailed analysis is presented on the principal processes that govern the energy exchange processes in SF6, such as thermal conduction, convection, turbulence and radiation. It will be explained how the material properties of the SF6 plasma and gas impact the interruption in the critical" thermal" window and the early recovery period. It will be highlighted, how the arc shape, arc temperature profile and gas flow can be controlled by the design of the arcing chamber.
In the second part, the key material properties of the above mentioned SF6 alternatives will be compared to those of SF6, and how they affect the interruption process. The role of energy density in the mixture plasma will be discussed, along with the impact of related parameters like electrical conductivity, plasma composition, as well as arc geometry and temperature in the "new" mixtures.
Also, attention will be paid to the electric breakdown parameters and how these compare to SF6 regarding dielectric recovery after interruption. Concluding, it will be discussed how through generic design modifications of arcing chambers interruption performance comparable to SF6 can be achieved in spite of various differences in material parameters.
Speakers: Dr. Martin Seeger, prof. Joseph Yan, prof. Christian Franck.
Organization: Current Zero Club, International Research Group on Interruption Phenomena of Power Switching Devices (liaison organization of CIGRE SC A3)
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