Circuit breakers or air circuit breakers are used in a DC circuit on railway vehicles. Other examples may be tramways or trolley buses. For example, such high speed DC circuit breakers may switch direct nominal currents with more than 5000 Ampere and at a voltage level of more than 900 Volt.
For example, when disconnecting a first switch contact from a second switch contact, gases between the switch contacts can quickly become conductive because of air ionisation and a plasma may appear. Further, a back re-ignition phenomena can occur at relatively high currents, for example, for currents greater than 15 kA. Thus, the circuit breaker capability can be decreased. Further, at certain current levels, the arc between the first contact and the second switch contact may not climb inside the arc chute.
In arc chute assemblies of DC-circuit breakers, plastic frames and metal plates are alternating stacked upon each other, wherein the metal plates are disposed on the plastic frames. The plastic frames form dielectric layers between the metal plates. The plastic frames have a cut out such that an arc may be built up between two adjacent metal plates. The plastic frames can be used to generate gas, such that the heat in the arc can be quickly blown out of the arc chute and to increase the arc voltage by a change of the chemical composition of the air between the metal plates.
The arc can move on the metal plates, and can be within the cut out. However, the arc can stay at a corner of the cut out. Thus, the metal of the metal plates can get very hot at these corners and may start melting. For example, adjacent metal plates can be connected to each other by melted metal.
This leads to a short lifetime of the arc chutes and a big structural dimension due to an increased distance between the metal plates to avoid a connection between two adjacent metal plates due to melted metal, and the increased number of the metal plates and plastic frames.
Known arc chutes can be heavy and have a high height. Further, the wear can be important at high currents, for example, at currents greater than 1 kA. The wear depends on the number of operations, the current density and the arcing time (time constant). Thus, the wear of the arc chute is not predictable. Hence, maintenance operations are difficult to plan but are nevertheless indispensable. For example, the metal or steel plates may be often checked and replaced. Further, the plastic frames may be checked as well and sometimes even replaced. In addition, there is a risk of steel drop minimum between the plates, such that less voltage is built up. For example, the circuit breaker may not be able to cut the circuit the next time. Further, more than 120 components may have to be assembled and the clearance distance is increased.
In EP0299460A2, a circuit breaker with a single arc chute stack having substantially parallel and U-shaped metal plates is disclosed. Two insulating plates are aligned in vertical direction of the stack and positioned inside of the two leg portions formed by the U-shaped metal plates in order to assist the arc extinction. The switching contacts of the breaker are arranged in between the two insulating plates.
WO 94/11894A1 discloses a single pole breaker unit with 30 Ampere nominal current rating, having an operating handle and a single stack of arc chute plates for extinction of the electric arc. To assist the arc extinction the arc chute is made of a thermoplastic cradle member with slots in which the arc chute plates inserted and which cradle member emits gas upon attack by the arc.
DE3247681A1 discloses a miniature circuit breaker having a single arc chute stack of a plurality of metal sheets. The arc extinction is assisted by a layer surface of a gas emitting material coated on each of the metal sheets. At least one switching contact is connected to an arc horn. The moving direction of the switching contacts is perpendicular to the gas emitting layer surface.
In U.S. Pat. No. 2,236,580, a circuit breaker with a hand operating lever is disclosed having a single arc chute stack of a plurality of metal plates arranged in non-parallel manner to each other. To assist the arc extinction, the side wall members of the arc chute are coated with boric acid.
USPTO Backgrounds
USPTO Backgrounds