Circuit breaker

A circuit breaker comprises a latching plate rotatably coupled to a moveable plate, and tensile type latching springs, each latching spring having two ends fixed to the latching plate and the moveable plate, respectively. Time taken for a moveable contact to be lifted up from a contact time point between the moveable contact and a fixed contact may be shortened, and thus a time duration for which an accident current flows may be reduced. Accordingly, the amount of energy applied to the circuit breaker may be reduced, and a breaking function of the circuit breaker may be enhanced. Furthermore, since a contact pressure between the moveable contact and the fixed contact has a constant change, a reliability on a conductive state of the moveable contact and the fixed contact may be enhanced.

CROSS-REFERENCE TO A RELATED APPLICATION

Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2010-0004491, filed on Jan. 18, 2010, the content of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit breaker capable of performing a breaking operation for line protection or for opening and closing a load, or when an overload and a short circuit have occurred, and particularly, to a circuit breaker having a shaft unit, the circuit breaker capable of minimizing damages due to an accident current by rapidly performing a tripping operation when an accident current has occurred.

2. Background of the Invention

Generally, a circuit breaker normally maintains a conductive status when a rated current flows, but performs a breaking operation when an accident current occurs. More concretely, a fixed contact and a moveable contact maintain a closed status when a normal current flows. However, when an accident current has occurred, the fixed contact and the moveable contact are separated from each other to break the accident current as a trip unit detects the accident current and transmits a signal to a switching mechanism. Then, the switching mechanism is released.

Here, it takes several minutes for the switching mechanism to be released. The shorter the time, the more a breaking function of the circuit breaker is maximized. While the accident current is applied to the fixed contact and the moveable contact, an electromagnetic repulsive force is generated between the fixed contact and the moveable contact. As a result, the fixed contact and the moveable contact are separated from each other.

Once the moveable contact has been separated from the fixed contact by the electromagnetic repulsive force, the trip unit detects the accident current to limit the accident current before the switching mechanism is released. This may reduce the amount of energy applied to the circuit breaker to prevent damages of the circuit breaker, thereby maximizing a breaking function of the circuit breaker.

FIG. 1is a sectional view of a circuit breaker having a shaft assembly in accordance with the conventional art, andFIG. 2is a disassembled perspective view of a latch unit and a moveable plate unit of the shaft assembly inFIG. 1.

As shown, the conventional circuit breaker comprises a trip unit1configured to detect an accident current, a switching mechanism2configured to separate a moveable contact21afrom a fixed contact5aby receiving a signal indicating the occurrence of an accident current from the trip unit1, and a shaft assembly3configured to perform a closing or tripping operation by the switching mechanism2.

The shaft assembly3includes a shaft10, a moveable plate unit20having the moveable contact21adetachably mounted to the fixed contact5afixed to the circuit breaker, and rotatably coupled to the shaft10, and a latch unit30disposed between the shaft10and the moveable plate unit20so that the moveable plate unit can maintain a closed or tripped status.

The moveable plate unit20consists of a moveable plate21having the moveable contact21awelded at one end thereof, and having a pin forcibly inserted at another end thereof, a connecting plate22coupled to the shaft10and having the moveable plate21rotatably coupled thereto, a connecting pin23configured to couple the moveable plate21and the connecting plate22to each other, connecting springs24configured to generate a contact pressure by pushing the moveable plate21and the connecting plate22from two sides, and washers25configured to prevent separation of the connecting springs24.

The latch unit30consists of a limit latch31supported by the shaft10and the moveable plate21, a latch spring32implemented as a compression spring so as to elastically support the limit latch31, and a limit pin33penetratingly formed at the shaft10and the limit latch31and configured to rotatably support the limit latch31by the shaft10.

Unexplained reference numeral5denotes a fixed plate,11denotes a pin groove, and21bdenotes a moveable plate pin.

The operation of the conventional shaft assembly will be explained.

As shown inFIG. 3, a compression force of the limit spring32assembled to the shaft10is transmitted to a moveable plate pin21bforcibly inserted into the moveable plate21through the limit latch31. As a result, the moveable plate21maintains an OFF status.

As shown inFIG. 4, when the circuit breaker is in a closed (ON) status by the switching mechanism2, the shaft assembly3is rotated to allow the moveable contact21aof the moveable plate21to come in contact with the fixed contact5aof the fixed plate5. Here, the compression force of the limit spring32is transmitted to the moveable plate pin21bforcibly inserted into the moveable plate21through the limit latch31. As a result, a contact pressure is generated between the fixed contact5aand the moveable contact21a.

As shown inFIG. 5, in the occurrence of an accident current, a contact repulsive force is generated between the fixed contact5aof the fixed plate5and the moveable contact21aof the moveable plate21. As a result, the moveable plate21is lifted up. Here, the moveable plate pin21bmoves along an operation surface (outer surface) of the limit latch31, which is located on positions different from the operation surface of the limit latch31shown inFIGS. 3 and 4. Then, the compression force of the limit spring32assembled to the shaft10is transmitted to the moveable plate pin21bforcibly inserted into the moveable plate21through the limit latch31. As a result, the moveable plate21is lifted up (current limiting status).

However, the conventional shaft assembly consecutively operated as shown inFIGS. 3 to 5may have the following problems.

Referring toFIG. 6, a contact pressure generated between the fixed contact5aof the fixed plate5and the moveable contact21aof the moveable plate21will be explained. It takes about 17 seconds for the moveable contact21ato be lifted up from a contact time point between the fixed contact5aand the moveable contact21a. A contact pressure when the circuit breaker in an ‘ON’ state is in the range of 2.5˜2.7. More concretely, it takes a long time from the contact time point between the fixed contact5aand the moveable contact21ato the time point when the moveable contact21is lifted up. This may cause a time duration for which an accident current flows to be long. Accordingly, the amount of energy applied to the circuit breaker is increased to degrade a breaking function of the circuit breaker. Furthermore, reliability on a conductive state between the fixed contact5aand the moveable contact21amay be lowered due to a large change of the contact pressure.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a circuit breaker capable of having a maximized breaking function by reducing the amount of energy applied thereto, and capable of reducing a time duration for which an accident current flows by rapidly generating an electromagnetic repulsive force between a moveable contact and a fixed contact.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a circuit breaker, comprising: a trip unit configured to detect an accident current; a switching mechanism configured to separate a moveable contact from a fixed contact by receiving a signal indicating the occurrence of an accident current from the trip unit; a shaft rotated by the switching mechanism; a connecting plate fixedly-coupled to the shaft; a moveable plate rotatably coupled to the connecting plate, and having the moveable contact contacting or separated from the fixed contact; a latching plate rotatably coupled to the moveable plate; and a latching spring formed as an elastic spring so as to receive an elastic force in a direction that the moveable contact is spacing from the fixed contact, and having both ends fixed to the latching plate and the moveable plate, respectively.

According to another aspect of the present invention, there is provided a circuit breaker, comprising: a trip unit configured to detect an accident current; a switching mechanism configured to separate a moveable contact from a fixed contact by receiving a signal indicating the occurrence of an accident current from the trip unit; a shaft rotated by the switching mechanism; a moveable plate rotatably coupled to the shaft, and having the moveable contact contacting or separated from the fixed contact; a latching plate rotatably coupled to the moveable plate; and a latching spring formed as an elastic spring so as to receive an elastic force in a direction that the moveable contact is spacing from the fixed contact, and having both ends fixed to the latching plate and the moveable plate, respectively, wherein a first latching pin for fixing one end of the latching spring is coupled to one end of the latching plate, a second latching pin for fixing another end of the latching spring is coupled to one end of the moveable plate, a latching pin hole for inserting the first latching pin is formed at the latching plate, and the latching pin hole is positioned farther than a rotation center of the moveable plate based on the moveable contact.

DETAILED DESCRIPTION OF THE INVENTION

Description will now be given in detail of the present invention, with reference to the accompanying drawings.

For the sake of brief description with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and description thereof will not be repeated.

Hereinafter, a circuit breaker according to the present invention will be explained in more detail with reference to the attached drawings.

FIG. 7is a sectional view of a circuit breaker having a shaft assembly according to the present invention,FIG. 8is a perspective view of the shaft assembly ofFIG. 7, andFIG. 9is a disassembled perspective view of the shaft assembly ofFIG. 8.

As shown, a circuit breaker having a shaft assembly according to the present invention comprises a trip unit101configured to detect an accident current, a switching mechanism102configured to separate a moveable contact121afrom a fixed contact5aby receiving a signal indicating the occurrence of an accident current from the trip unit101, and a shaft assembly103closed or tripped by the switching mechanism102.

The shaft assembly103includes a plurality of shafts110, a moveable plate unit120having the moveable contact121adetachably mounted to the fixed contact5afixed to the circuit breaker, and rotatably coupled to the plurality of shafts110, and a latch unit130coupled to the moveable plate unit120so that the moveable plate unit120can maintain a closed or tripped status.

The moveable plate unit120consists of a moveable plate121having the moveable contact121aat one end thereof, a connecting plate122fixedly-coupled to the shaft110and having the moveable plate121rotatably coupled thereto, a connecting pin123forcibly inserted into the shaft110by penetratingly-coupling the moveable plate121and the connecting plate122to each other, connecting springs124disposed on outer surfaces of two sides of a latching plate131to be later explained, and configured to generate a contact pressure by pushing the latching plate131, the connecting plate122, and the moveable plate121from two sides, and washers125configured to prevent separation of the connecting springs124.

The moveable plate121is formed in ashape, and the moveable contact121ais coupled to one end of the moveable plate121by welding. To another end of the moveable contact121a, a sliding recess121bhaving a slit shape so as to couple a second latching pin133to be later explained thereto is formed in a direction of a pin hole to be later explained. A pin hole121cfor passing the connecting pin123therethrough is formed at an intermediate portion of the moveable plate121, i.e., at a bent portion between two ends. A limit hole121dhaving a circular arc shape and configured to restrict a relative motion of the latching plate131with respect to the moveable plate121is formed at one side of the pin hole121c.

A body portion122aof the connecting plate122is insertion-fixed to the shaft110, and a coupling portion122bhaving a ‘U’ shape is formed at an upper end of the body portion122aso that the moveable plate121can be rotatably inserted thereinto. A hinge hole122cfor passing the connecting pin123therethrough is formed at one end of the coupling portion122b. At another end of the coupling portion122b, a first stop surface122dwith a step are formed so as to restrict a rotation of the latching plate131by locking a first latching pin132to be later explained.

The latch unit130consists of a latching plate131disposed between the coupling portion122bof the connecting plate122and the connecting spring124so as to plane-contact outer surfaces of two sides of the connecting plate122, a first latching pin132coupled to the latching plate131, a second latching pin133coupled to the sliding recess121bof the moveable plate121, and a plurality of latching springs134each having both ends coupled to the first latching pin132and the second latching pin133, respectively, and configured to elastically support the moveable plate121so that the moveable plate121can maintain a closed status and a tripped status.

The latching plate131is formed in a non-linear shape having at least three protrusions, and a latching pin hole131afor inserting the first latching pin132is formed on one protrusion. A cam surface131bfor slidably supporting the second latching pin133is formed on another protrusion linearly or in the form of a minute curved surface. A second stop surface with a step131cprotruding from the end of the cam surface131bwith a predetermined stagger angle is linearly formed on still another protrusion so as to restrict a sliding motion of the second latching pin133. A pin through hole131dfor passing the connecting pin123therethrough is formed between two protrusions of the latching plate131. A pin coupling hole131efor coupling a limit pin135coupled to the limit hole121dof the moveable plate121is formed at one side of the pin through hole131d.

In a case that the sliding recess121bof the moveable plate121is formed in a direction of the pin hole, the latching pin hole131aof the latching plate131is preferably positioned farther than the pin through hole131dbased on the moveable contact121a. The reason is because the moveable plate121can be moved by a proper electromagnetic contact force.

The plurality of latching springs134are implemented as tensile type coil springs each having a predetermined tensile force. As aforementioned, each of the latching springs134has both ends fixedly-coupled to the first latching pin132and the second latching pin133, respectively.

Assembly processes of the shaft assembly of the circuit breaker according to the present invention will be explained as follows.

Firstly, the connecting plate122is assembled to the moveable plate121. Then, the connecting pin123is insertion-fixed to the connecting plate122, and the latching plate131is inserted to two sides of the connecting pin123. Then, the connecting springs124and the washers125are inserted into the connecting pin123from two side surfaces of the latching plate131, respectively.

Then, the assembled moveable plate121is inserted into the shaft110, thereby forcibly inserting the latching plate131into a recess (not shown) of the shaft110. Under this state, the first latching pin132is inserted into the latching pin hole131aof the latching plate131, thereby assembling the two latching plates131. The second latching pin133is assembled to the sliding recess121bof the moveable plate121, and two ends of each latching spring134are assembled to the first latching pin132and the second latching pin133, respectively.

The shaft assembly according to the present invention has the following effects.

Firstly, when the circuit breaker is in a tripped status, the moveable plate121and the latching plate131are integrally coupled to the shaft t110by the connecting pin123as shown inFIG. 10. As a result, the moveable plate121is rotated along a rotation direction of the shaft110, thereby causing the moveable contact121ato be separated from the fixed contact5a. Here, the first latching pin132and the second latching pin133are assembled to the latching pin hole131aof the latching plate131and the sliding recess121bof the moveable plate121, respectively. And, a tensile force of the latching springs134is transmitted to the moveable plate121through the latching plate131. As a result, the moveable plate121maintains an ‘OFF’ status. The first latching pin132is locked by the first stop surface122dof the connecting plate122, thereby preventing excessive rotations of the latching plate131.

When the circuit breaker is in an ‘ON’ status, the moveable plate121is rotated, by the switching mechanism102, in a direction opposite to that of the tripped status along a rotation direction of the shaft121. As a result, the moveable contact121acomes in contact with the fixed contact5a. Here, the tensile force of the latching springs134is transmitted to the latching plate131, and thus a forward rotation force is transmitted to the moveable plate121. Accordingly, a constant contact pressure is generated between the fixed contact5aand the moveable contact121a.

In the occurrence of an accident current, a contact repulsive force is generated between the fixed contact5aof the fixed plate5and the moveable contact121aof the moveable plate121. As a result, the moveable plate121is lifted up. Here, the second latching pin133moves along the cam surface131bof the latching plate131. While moving, the second latching pin133is locked by the second stop surface131cbetween the cam surface131band the second stop surface131c, thereby restricting a rotation of the moveable plate121. A backward rotation force is transmitted to the latching plate131by the tensile force of the latching springs134, and the latching plate131transmits the backward rotation force to the moveable plate121. As a result, the moveable plate121maintains a lifted status.

When the circuit breaker is in a tripped status, a closed status and an accident current status consecutively, a contact pressure generated between the fixed contact5aof the fixed plate5and the moveable contact121aof the moveable plate121is shown inFIG. 13. The numerical values shown inFIG. 13are not absolute values, but relative values for comparison with the conventional values. The horizontal axis indicates time, and the vertical axis indicates a contact pressure.

It takes about 11 seconds for the moveable contact121ato be lifted up from a time point when the fixed contact5aand the moveable contact121acome in contact with each other. A contact pressure when the circuit breaker is in an ‘ON’ status is 3.0. This means that the time taken for the moveable contact121to be lifted up is shortened more than the conventional time (17 seconds) by 35%, approximately, and the contact pressure (3.0) is maintained more constantly than in the conventional art.

In the circuit breaker according to the present invention, time taken for the moveable contact to be lifted up from the time point when the fixed contact5aand the moveable contact121acome in contact with each other is shortened. This may reduce a time duration for which an accident current flows. Accordingly, the amount of energy applied to the circuit breaker may be reduced, and a breaking function of the circuit breaker may be enhanced.

Furthermore, the cam surface of the latching plate is almost linearly formed based on an inflection point. Accordingly, the contact pressure between the moveable contact and the fixed contact has a constant change after the inflection point. This may enhance a reliability on a conductive state of the moveable contact and the fixed contact.