GB2147146A

GB2147146A - Contact mechanism for a circuit breaker

Info

Publication number: GB2147146A
Application number: GB08422432A
Authority: GB
Inventors: Kazuhiko Sato; Shuzo Oizumi; Tsuneo Honma; Eiichi Matsumoto
Original assignee: Fuji Electric Co Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 1983-09-26
Filing date: 1984-09-05
Publication date: 1985-05-01
Also published as: KR890001472B1; JPH0155738B2; KR850002653A; GB2147146B; JPS6070626A; GB8422432D0

Abstract

A support member 4 is pivotally mounted at 4c and carries a contact 3. A spring 5 urges one end of the contact 3 away from the member 4 with a force component such as to maintain engagement between shoulders 3c and the member 4. Closing of the contacts causes engagement surfaces 4d to move around the pivot axis through 4c and move the support 3 laterally as well as downwardly giving a sliding, self-cleaning action between the contacts 2a, 3a. <IMAGE>

Description

SPECIFICATION Contact mechanism for a circuit breaker The present invention relates to a contact mechanism for a circuit breaker such as a nofuse circuit breaker or an earth leakage breaker.

The contact mechanism in a circuit breaker is an important component for switching on and off a load current and breaking a shortcircuiting current or overload current. It is necessary for the contact mechanism to present a low and stable contact resistance while a current flows under normal condition, to undergo minimal temperature rise, and not to undergo fusing of the contacts where a large current is to be interrupted.

In Fig. 1 of the accompanying drawings there is shown a contact mechanism in a conventional circuit breaker by way of example, the contact mechanism including a fixed contact member 2 having a fixed contact 2a and secured to a case 1. The contact mechanism also includes a movable contact member 3 having a movable contact 3a projecting on one side at one end and a projection 3b on the other side positioned intermediate the two ends of the member 3. The opposite end of the member 3 is supported in the case 1. A movable contact support 4 has a through bore 4a and a projection 4b on an upper side of the through bore 4a, with the movable contact member 3 extending through the bore 4a. A contact spring 5 is disposed between the movable contact member 3 and said upper side of the through bore 4a and is held in place by means of the projections 3b, 4b. Designated at 6 is a lead wire.

In operation, the movable contact support 4 is moved by means of an actuator (not shown) in a direction (in the direction of the arrows P,Q) substantially perpendicular to the plane of the fixed contact member 2 in order to move the movable contact member 3 in an arc to bring the movable contact 3a into or out of contact with the fixed contact 2a, thus opening or closing the circuit breaker. To bring the contact mechanism from an open position as shown in Fig. 1 into a closed position, the movable contact support 4 is moved in the direction of the arrow Ct to cause the contact spring 5 to push the movable contact member 3, which is therefore turned counterclockwise about the end supported in the case 1 until the contacts 2a, 3a contact each other as shown in Fig. 2.When the movable contact support 4 is moved further in the direction of the arrow 0, the contact spring 5 is compressed as shown in Fig. 3 to increase the pressure of contact between the contacts 2a, 3a.

With the above contact mechanism, the pivot point or fulcrum of the movable contact member 3 remains the same at all times during an interval following the instant when the contacts 2a,3a have come into contact with each other and while they are pressed against each other under an increased pressure. Therefore, the contacts 2a,3a are kept in contact with each other always over the same contact surfaces. If dirt is deposited or an oxidized film is produced on the surfaces on the contacts at the time they are disengaged, then the dirt deposit or oxidized film will be sandwiched between the contacts when they next contact each other, resulting in an increased and unstable contact ohmic resistance which gives rise to a temperature rise.

When the contacts are subjected to high temperatures, they tend to fuse when a large current is to be cut off, and so the contact mechanism becomes poor in reliability. Since the movable contact member is moved arcu ately about the fulcrum on the case 1 at all times, powdery particles are ground off due to frictional engagement between the movable contact member and the case, a disadvantage which is partly responsible for making the above-mentioned problems worse.

It is an object of the present invention to provide a contact mechanism for a circuit breaker which can ameliorate the above-mentioned shortcomings, and which can have a low and stable contact resistance, can reduce the risk of contact fusing, and be reliable in operation.

According to the present invention there is provided a contact mechanism for a circuit breaker and comprising a fixed contact fixed to a case, a movable contact support pivotally supported in said case, a movable contact member having a movable contact on one end in confronting relation to said fixed contact, said movable contact member being carried by said movable contact support and having its opposite end engaging said movable contact support at a position spaced from the pivot axis of the movable contact support, and means for providing resilient bias between said movable contact member and said one end of said movable contact support, said movable contact being movable into and out of contact with said fixed contact while in sliding contact therewith in response to pivotal movement of said movable contact support.

An embodiment of the present invention will now be described, by way of example, with reference to Figs. 4 to 6 of the accompanying drawings in which: Figures 1 to 3 are sectional side elevational views of a contact mechanism for a conventional circuit breaker and illustrating respective positions in the operation of the mechanism; Figures 4 to 6 are sectional side elevational views, corresponding to those of Figs. 1 to 3, of a contact mechanism for a circuit breaker embodying the present invention.

In Fig. 4, a fixed contact member 2 has a fixed contact 2a and is fixed to a case 1. A movable contact support 4 has a through bore 4a substantially in the form of a rectangular parallelepiped having a rectangular cross section.

The movable contact support 4 has an arm projecting from a side portion adjacent one end of the through bore 4a and serving as a spring seat, the arm having a projection 4b on its inner surface.

The movable contact support 4 also has projections 4c extending laterally outwardly from side portions in the vicinity of the opposite end of the through bore 4a, the side portions lying perpendicularly to the side portion from which the spring-seat arm projects.

The movable contact support 4 is pivotally supported, by means of the projections 4c, in the case 1.

The movable contact member 3 has at one end a movable contact 3a and a projection 3b on a surface opposite the movable contact 3a, and a locking portion 3c at the opposite end of the member 3 where the latter is of increased width.

The movable contact member 3 extends through the bore 4a in the movable contact support 4 and is disposed in confronting relationship with the fixed contact member 2.

A contact spring 5 is disposed between the end of the movable contact member 3 and the spring seat of the movable contact support 4 and held in position by means of the projections 3b, 4b which are inserted into the opposite ends of the spring 5. The movable contact member 3 is prevented from moving to the left in the drawing because the locking portion 3c is held in engagement with opening edges 4d of the through bore 4a that are spaced from the pivot axis of the projections 4c. The contact spring 5 normally urges the movable contact member 3 leftward as shown to be held back by the movable contact support 4. The movable contact member 3 at the time the contact mechanism closes is pushed to the right by the opening edges 4d. Denoted at 6 is a lead wire.

In operation, the movable contact support 4 is moved arcuately about the projections 4c by means of an actuator (not shown) to bring the contacts 2a, 3a of the fixed and movable contact members 2,3 into or out of contact with each other in order thereby to open or close the circuit breaker.

When moving the contact mechanism from the open position shown in Fig. 4 to a closed position, the movable contact support 4 is turned counterclockwise to move the movable contact member 3 arcuately with the movable contact support 4 until the contact 3a is brought into contact with the contact 2a as illustrated in Fig. 5. As the movable contact support 4 is turned further in the same direction, the contact spring 5 is compressed as shown in Fig. 6 to load the movable contact member 3 to increase the pressure of contact between the contacts 2a, 3a.

While the movable contact support 4 is moved counterclockwise about the projections 4c, the opening edges 4d move the locking portion 3c to the right with the distance between the locking portion 3c and the pivot axis of the projections 4c serving to provide a moment. As a result, the movable contact 3a is moved to the right with respect to the fixed contact 2a giving sliding engagement between the contacts 2a, 3a. Since the movable contact member 3 is not moved about a single fulcrum, it is not as liable to the production of powdery particles due to the grinding action between the movable contact member and its fulcrum.

With the contact mechanism for a circuit breaker as described above, the movable contact support is movably supported in the case, and the movable contact member is carried by the movable contact support. The movable contact member is supported such that when the movable contact member is moved into a closed position, it is restrained from moving in undesired directions.

When the movable contact support is turned further in the same direction after the movable contact has contacted the fixed contact, the movable contact member is pushed by the movable contact support to cause the contacts to slide against each other, tending to remove any dirt, ground particles or oxidized film which has been trapped between the contacts upon their contacting each other.

The electrical contact between the contacts is thus rendered substantially complete, and the contact resistance between them is low and stable, with the result that the contacts are not unduly susceptible to heating to a high temperature when a current flows through them so that they are relatively free from the risk of fusing when cutting off a large current.

Since there is little frictional movement where the movable contact member is supported by the movable contact member, substantially no ground-off powder will be produced which might find its way between the contacts, an advantage which helps to avoid an unwanted contact failure between the contacts.

Claims

1. A contact mechanism for a circuit breaker and comprising a fixed contact fixed to a case, a movable contact support pivotally supported in said case, a movable contact member having a movable contact on one end in confronting relation to said fixed contact, said movable contact member being carried by said movable contact support and having its opposite end engaging said movable contact support at a position spaced from the pivot axis of the movable contact support, and means for providing resilient bias between said movable contact member and said one end of said movable contact support, said movable contact being movable into and out of contact with said fixed contact while in sliding contact therewith in response to pivotal movement of said movable contact support.

2. A contact mechanism according to claim 1 wherein said engagement between the movable contact support and the movable contact member is arranged to provide a force causing said sliding of the movable contact relative to the fixed contact, said force being in opposition to a force provided by means of said resilient biassing means.

3. A contact mechanism according to claim 1 or claim 2 wherein said resilient biassing means comprises a compression spring between the movable contact member and the movable contact support.

4. A contact mechanism according to any one of the preceding claims wherein said opposite end of the contact member provides shoulders on which bear laterally extending portions of the contact support which extends through a bore in the contact member.

5. A contact mechanism for a circuit breaker and substantially as described herein with reference to Figs. 4 to 6 of the accompanying drawings.

6. A circuit breaker including a contact mechanism according to any one of the preceding claims.