GB2517972A - Circuit breaker - Google Patents

Abstract

A circuit breaker, for example a vacuum interrupter, has a contact 4 that is movable in a contact direction between a position where it abuts a fixed contact 3 and a position where the contacts are spaced apart. A mass 10 is arranged with play to the first contact, and is movable in the contact direction relative to the movable contact 4. The mass can be guided by a switching rod 6 having end stops 11,12 to restrict it s movement. End stops 11,12 can be adjustable The mass can be movable in a cavity (fig 3, 21) of the switching rod. A damper such as a spring or shock absorber can be arranged between the moving contact and the mass to prevent it bouncing. The mass can be solid and cylindrical or liquid having damping characteristics. Movement of the mass lags and overshoots that of the contact and its kinetic energy, when transferred to the rod, reduces contact bounce.

Description

Circuit breaker The invention relates to a circuit breaker, for example a vacuum interrupter, having a first contact and a second contact, wherein the first contact is movable in a contact direction between a contact position, in which the first contact abuts the second contact, and a second position, in which the first contact is spaced apart from the second contact.

Such circuit breakers are typically used for interrupting a medium or high voltage circuit by moving the first and second contact away from each other. However, when the circuit has to be taken into operation, the first and second contacts need to be brought in contact with each other, such that a current can flow through the circuit. If the two contacts are brought together too slow, arcing will occur between the contacts before the contacts abut. This arcing will cause damage to the contacts, such as damage to the surface of contacts. Such damage could results in additional resistance in the circuit breaker, which could cause overheating, damaging the circuit breaker.

Arcing bctween the contacts also leads to temporary heating of the surfaces of the contacts resulting in welding together the contacts. If the contacts are welded together, it is no longer possible to brcak a circuit, leading to a dangerous situation, when the power needs to be interrupted.

Therefor circuit breakers are designed to bring the contacts quickly into contact with each other, for example by a solenoid moving one of the contacts or a cam on a rotating rod and a push rod operating the movement of one of the contacts. However, such mechanisms need to have a compensation for differences in dimensions caused by heat expansion of the circuit breaker parts or wear of the parts. So, typically a contact spring is integrated into the mechanism, which moves one of the contacts.

If with such an arrangement, the contacts are brought together quickly, the contacts will bounce away upon impact due to the integrated contact spring, similar to a marble falling on a solid surface. This bounce effect or chattering also could lead to welding of the contacts and therefor it is required to minimize this chattering time.

US 20080047819 describes a circuit breaker wherein both a moveable contact and a stationary contact are placed in a housing. The housing is supported by a supporting unit comprising a layered structure of a plurality of plates. The mechanism fin displacing the moveable contact is also supported on this supporting unit. This mechanism is a drive rod operated by a solenoid, which drive rod is connected to the movable contact. If a bouncing effect occurs in this circuit breaker, kinetic energy is absorbed by friction between the plurality of plates, such that the chattcring timc is reduced.

A disadvantage of this prior art embodiment, is that the use of a plurality of plates requires a substantial change in the structure of common circuit breakers. It is therefor difficult to apply this method of bounce reduction on already existing circuit breakers.

EP1 367616 also discloses a circuit breaker. To reduce the bounce effect, a hydraulic damping system is arranged at the end of the drive rod. This hydraulic system comprises two chambcrs and a channel between them with a cross sectional area selected ibr the purpose. The hydraulic system influences the damping function of the contact spring when the stationary and moveable contact are driven against each othet A disadvantage of this prior art embodiment is that the hydraulic system counter acts the contact spring, If the contacts are brought together quickly and the movement of the rod is larger, than the distance between the contacts, generally the contact spring would compensate ibr this difference. However, it could occur, that the fluid in the damping system cannot flow quick enough from the first to the second chamber through the channel, which would block the compression of the spring. As the spring could not be compressed over the required distance, this could lead to mechanical damage of the drive rod, the operating mechanism or the contacts.

It is an object of the invention to reduce the above mentioned disadvantages.

This object is achieved by a circuit breaker according to the preamble, which circuit breaker is characterized in that a mass is arranged with play to the first contact, whcrein the mass is movable in the contact direction relative to the first contact.

When, starting from the second position, the first contact is accelerated towards the second contact, the mass will lag. As soon the first contact hits the second contact and comes to a stop, the mass will catch up and overshoot because of the play between the mass and the first contact. However, if the first contact bounces upon contact with the second contact, the first contact will be accelerated in the opposite direction and the mass will again lag. As the mass 1 0 was still overshooting and catching up with thc carlicr lag, thc mass will rcducc thc acceleration in the opposite direction, such that the bouncing is reduced or even stopped.

An embodiment of the circuit breaker according to the invention further comprises a switching rod connected to the first contact for moving the first contact between the contact position and the second position.

In a further embodiment of the circuit breaker according to the invention the relative movement of the mass is guided by the switching rod.

The mass can easily be guided by the switching rod, which is already used for operating the movcmcnt of thc first circuit. It would even be possible to provide already existing circuit breakers having a switching rod with a mass according to the invention. This will provide a cost effective embodiment.

In a preferred embodiment of the circuit breaker according to the invention, the mass is guided on the switching rod and two stops are arranged on the switching rod on opposite sides of the mass to restrict the movement of the mass.

The mass could for example have a cylindrical shape and the switching rod could extend 3 0 through the mass. The stops ensure that the mass is taken along with the movement of the switching rod. The two stops on opposite sides of the mass ensure that the mass is arranged with play to the first contact.

Preferably, the distance between the two stops is adjustable, such that the bounce reduction by the mass can be adjusted to the specific conditions of the circuit breaker.

In another embodiment of the circuit breaker according to the invention, a cavity is provided in the switching rod and the mass is arranged movable in the cavity.

By providing the mass within the switching rod, it is ensured, that the moyement of the mass cannot be impaired by dirt, dust or other particles.

Yet another embodiment of the circuit breaker according to the invention comprises damping means arranged between the first contact and the mass.

With damping means it could be ensured that thc mass itsclf will not start bouncing bctween the stops, which could result, in extreme conditions, in that the first contact is moved away from the second contact.

Preferably the damping means comprise a spring and! or a shock absorber.

Although the most common application of a bounce reducing mass according to the invention would be with onc movable contact and one stationary contact, it would also bc possible to have two movable contacts, which arc cach providcd with a mass arranged with play.

The mass used in the invention would typically be a solid mass, but could also be a liquid mass. A fluid with high viscosity, for cxample arrangcd in a cavity in the switching rod, codd, similady to a solid mass, rcducc the bouncing of the contacts. An additional advantage of a fluid is that the fluid in itself comprising damping characteristics, which could contribute to avoiding bouncing of the mass between the stops.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a first embodiment of a circuit breaker according to the invention.

Figures 2A -2D show a schematic view of the circuit breaker according to figure 1 in different stages.

Figure 3 shows a second embodiment of a circuit breaker according to the invention.

Figure 1 shows a first embodiment I of a circuit breaker according to the invention. The circuit breaker I has a vacuum housing 2 with a stationary contact 3 and a movable contact 4.

The movable contact 4 has a contact rod 5, which extends out of the housing 2 and is connected to an isolation rod 6. A push plate 7 is arranged at the free end of the isolation rod 6, to push the movable contact 4 towards the stationary contact 3. A contact spring 8 is arranged bctwccn thc push plate 7 and the isolation rod 6 to compensate for differences between the movement of the push plate 7 and the distance between the contact 3, 4. A compensation spring 9 is furthermore provided to urge the push plat 7 hack into the position shown in figure 1, wherein the contacts 3, 4 are spaced apart.

A massive ring lOis arranged slidable around the isolation rod 6. The relative movement of the ring 10 is limited by stops 11, 12 arranged on either side of the ring 10.

Figurcs 2A -2D show a schcmatic view of thc circuit brcakcr 1 according to figure 1 in different stages.

When a push force is exerted onto thc push plate 7, the movable contact 4 will be moved towards the stationary contact 3. As a result of its inertia, the ring 10 will remain stationary until the stop 12 hits the ring 10 and takes the ring along. (see figure 2A) When the movable contact 4 hits the stationary contact 3 and comes to a halt, the ring 10 will 3 0 continue to move. (see figure 2B).

If the movable contact 4 bounces back from the stationary contact 3, as shown in figure 2C, the movable contact and connected isolation rod 6, will move in opposite direction away from the stationary contact, while the ring 10 still moves towards the stationary contact.

However, when the ring 10 hits the stop 11, the kinetic energy ofthe ring 10 will be transferred to the isolation rod 6 and stop the bounce movement of the movable contact 4.

(see figure 2D).

It is clear that the mass of the ring 10 and the distance between the stops 11, 12 has to be designed for a specific circuit breaker 1. This depends for example on the size and mass of the movable contact 4, the strength of the contact spring 8, and the speed with which the movable contact 4 is moved towards the stationary contact 3.

Figure 3 shows a second embodiment of a circuit breaker 20 according to the invention. This embodiment 20 corresponds largely with the embodiment of figure 1 and the same parts are designated with the same reference signs.

In this embodiment, the isolation rod 6 is not provided with a ring 10 slidable along the outside of the rod 6, but with an internal space 21. A massive pin 22 is arranged movable in this elongate space 21.

The combination of the internal space 21 and massive pin 22 functions similar to the ring 10 and stops 11, 12 of the embodiment according to figure 1. In this embodiment 20, the stops are provided bythe end walls of the elongate internal space 21.

Claims (8)

1. Claims 1. Circuit breaker, for example a vacuum interrupter, having a first contact and a second contact, wherein the first contact is movable in a contact direction between a contact position, in which the first contact abuts the second contact, and a second position, in which the first contact is spaced apart from the second contact, characterized in that a mass is arranged with play to the first contact, wherein the mass is movable in the contact direction relative to the first contact.
2. 2. Circuit brcakcr according to claim 1, further comprising a switching rod conncctcd to the first contact for moving the first contact between the contact position and the second position.
3. 3. Circuit breaker according to claim 2, wherein the relative movement of the mass is guided by the switching rod.
4. 4. Circuit breaker according to claim 3, wherein the mass is guided on the switching rod and wherein two stops are arranged on the switching rod on opposite sides of the mass to restrict the movement of the mass.
5. 5. Circuit breaker according to claim 4, wherein the distance between the two stops isadjustable.
6. 6. Circuit breaker according to claim 3, wherein a cavity is provided in the switching rod and the mass is arranged movable in the cavity.
7. 7. Circuit breaker according to any of the preceding claims, further comprising damping means arranged between the first contact and the mass.
8. 8. Circuit breaker according to claim 7, wherein the damping means comprise a spring and! 3 0 or a shock absorber.