In known systems electrical transmission lines leading from a power source such as a generator, to consumers are protected against insulation failure or overload by at least one circuit breaker. In certain instances the circuit breaker includes mechanical switching devices having a pair of conductor terminals and a bridging member for opening and closing the gap in between said terminals. Because it is not possible to interrupt a high voltage or a large electrical current instantaneously, the electric arc emerging in the expanding gap upon pulling the conductor terminals apart is often spread and broken in an insulation gas environment, such as pressurized air or sulfur hexafluoride for example. The high voltage circuit breaker market is increasingly dominated by self-blast technology.
FR 2575594 discloses a representative of such a self-blast-type circuit breaker (GCB) using SF6 as an extinguishing agent. The arrangement includes movable and immovable electrical contacts located in an arcing zone such that an electric arc is generated in the arcing zone. A pressure chamber arrangement is connected by channels to the SF6-filled arcing zone for enhancing the breaking quality by preventing the electric arc from becoming revitalized after an initial extinction.
In known systems, the highest short-line fault ratings (SLF) are covered by puffer type gas circuit breakers such as tank SF6 puffer circuit breakers for example. If limits above 50 kA, 245/300 kV are to be achieved by employing such puffer type circuit breakers expensive line to ground or grading capacitances are specified.
There have also been attempts in scaling-up known self-blast technology puffer breakers to withstand ratings of 63 kA at 300 kV, in a 60 Hz environment having 450 Ohm without a delay in time.
Known GCB features a quenching chamber, also known as interruption chamber, which is filled with an insulating gas. The chamber extends along a longitudinal axis and is designed to be radially symmetric, (e.g., rotationally symmetric about said longitudinal axis. The quenching chamber further includes at least two separable arcing contact pieces coaxially arranged and facing each other as well as an arcing zone formed in between the at least two arcing contact pieces. An electric arc burns between the at least two arcing contact pieces during a disconnection/interruption process and heats up the isolating gas in the arcing zone when the contact pieces are separated. The heat causes an increase of the pressure of the insulating gas in the arcing zone of the GCB. The pressurized gas escapes through at least one dedicated annular gap between an arcing contact piece and the quenching chamber and through cavities arranged proximal to the longitudinal axis in the contact pieces, if any, such that each emerging flow path constitutes an optimal gas nozzle. Thus, in the context of the present disclosure, the term nozzle describes a functional flow rather than a physical component.
Known attempts to achieve the above ratings with scaled-up self-blast technology puffer breakers failed because higher pressure values are expected which lead to mechanical failure of the material of the GCB and an undesired reduction of the dielectric withstand of the insulating gas due to the associated high temperature of above 2000K.
There are two situations under which a high-voltage circuit breaker, in particular a high-voltage alternating current circuit breaker, should endure. The first situation is known as a short line fault (SLF) and the second situation is known as a terminal fault (T100a).
In a GCB, the pressure in the arcing zone should be comparatively high for extinguishing the electric arc in a reliable manner in case of a short line fault. One drawback, however, is that a high pressure raises the thermal load to the structure of a circuit breaker. With respect to a terminal fault, the current pressure values in the arcing zone exceed the pressure values that are specified for reliably extinguishing the electric arc, which are comparatively low. Hence, in case of a GCB, the gas nozzle should be able to bear the pressure in the arcing zone in the SLF situation, as well as withstand T100a conditions.
In “Investigation of Technology for Developing Large Capacity and Compact Size GCB” disclosed in the IEEE Transactions on Power Delivery, Vol. 12, No. 2 dated April 1997, a different solution for achieving the above-mentioned ratings by employing different nozzle geometry is proposed. This nozzle is different from other known GCB applications because of an inner nozzle that is assigned to a movable arcing contact wherein said inner nozzle contributes to the establishment of local higher gas pressures specified for the thermal interruption at a SLF without only increasing the pressure in a dedicated puffer chamber of a GCB.
There remains the drawback, that high gas pressures are known to cause high temperatures which in turn are undesired for dielectric interruption since the gas becomes conductive above 2000 Kelvin such that it can not be employed sensibly for breaking an electric arc in case of SF6 gas employed as the extinguishing agent in a GCB.