Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Multiple contact type
Reexamination Certificate
2000-05-18
2001-10-30
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Multiple contact type
C335S202000
Reexamination Certificate
active
06310528
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a circuit breaker having an overcurrent-tripping device for detecting a short-circuit current to allow an opening-and-closing mechanism to perform a tripping operation, and opening a movable contact shoe before opening the same by the tripping operation of the opening-and-closing mechanism.
FIG. 7
is a vertical sectional view of a conventional circuit breaker of the above design in an ON state. In
FIG. 7
, a molded case
1
has conduction paths therein, each being formed of a pair of opposed fixed contact shoes
2
and
3
, and a movable contact shoe
4
bridging the fixed contact shoes
2
and
3
, with a power supply side terminal
5
integrally formed at an end of the fixed contact shoe
2
. The movable contact shoe
4
is held in a movable contact shoe holder
6
formed of an insulating material so that the movable contact shoe
4
can move linearly in a vertical direction of
FIG. 7
, and the movable contact shoe holder
6
is guided in the molded case
1
to enable linear movement. The movable contact shoe
4
is pressed against the fixed contact shoes
2
,
3
by a contact spring
7
formed of a compressed coil spring, and inserted between the movable contact shoe
4
and the bottom of the molded case. Thus, the movable contact shoe
4
is contacted with the fixed contact shoes
2
,
3
via movable and fixed contacts.
An opening-and-closing mechanism
8
is installed above the fixed contact shoe
2
in
FIG. 7
, and a tip of an opening-and-closing lever
10
that is rotated around a rotating shaft
9
is located to oppose an upper surface of the movable contact shoe holder
6
. When an opening-and-closing handle
11
of the opening-and-closing mechanism
8
is operated in an ON state, the opening-and-closing lever
10
is rotated clockwise in
FIG. 7
to depress the movable contact shoe holder
6
against the force of the contact spring
7
. The movable contact shoe
4
is then opened from the fixed contact shoes
2
,
3
to clear the conduction path.
A thermally operated electromagnetic overcurrent-tripping device
12
, which is formed of a bi-metallic element and an electromagnet (not shown), is disposed on the fixed contact shoe
3
. The overcurrent-tripping device
12
has one end connected to the fixed contact shoe
3
and the other end connected to a load-side terminal
13
so as to unlock the opening-and-closing mechanism
8
by means of the bi-metallic element, which is bent when an overloading current flows through the conduction path, or by instantaneously attracting the movable iron core of the electromagnet if a heavy current such as a short-circuit current flows through the conduction path, whereby a stored force of an opening-and-closing spring (not shown) rotates the opening-and-closing lever
10
to open the movable contact shoe
4
.
In this case, particularly in the presence of a heavy current, the movable iron core drives the movable contact shoe holder
6
downward to open the movable contact shoe
4
before the tripping operation of the opening-and-closing mechanism
8
. When the current is shut off to eliminate the attractive force on the movable iron core, the movable contact shoe
4
attempts to rise under the force of the contact spring
7
. However, since the rotation of the opening-and-closing lever
10
has been completed, the movable contact shoe
4
is held open. Furthermore, an arc occurs between the movable contact and the fixed contact when a heavy current is interrupted. This arc is guided into arc extinguishing chambers
14
and
15
installed below the fixed contact shoes
2
and
3
, where it is extinguished. In order to transfer the current from the movable contact shoe
4
, a commutation plate
16
is installed to extend across the arc extinguishing chambers
14
,
15
.
An example of the above overcurrent-tripping device
12
is described in Japanese Patent Application Laid-Open No. 6-52782.
FIG. 8
shows a modified version of this patent. In this figure, the overcurrent-tripping device
12
is formed of a bi-metallic element
17
and an electromagnet
18
. The bi-metallic element
17
has a heater
19
wound around it, and the electromagnet
18
comprises a movable iron core
21
inside an electromagnet coil
20
. The heater
19
has one end connected to a fixed contact shoe (not shown) and the other end connected to the upper end
17
a
of the bi-metallic element
17
. On the other hand, the bi-metallic element
17
is supported by a bi-metallic element support
22
at its lower end and is electrically connected to the bi-metallic element support
22
.
In addition, although not seen in
FIG. 8
, the bi-metallic element support
22
is connected to a lower end of the electromagnet coil
20
, which has an upper end
20
a
connected to a terminal
23
. The electromagnet coil
20
is supported by a coil support
24
. The coil support
24
has a lever
25
to enable rotation around a shaft
26
, and a tip portion
25
a
of the lever
25
extends in a direction crossing the bi-metallic element support
22
. The other end of the lever
25
, which is not shown in
FIG. 8
, is connected to a lower end of a movable iron core
21
. Although not shown, a fixed iron core is joined to a surface of the terminal
23
, which is opposed to an upper-end surface of the movable iron core
21
, and the movable iron core
21
is forced downward by means of a return spring interposed between the fixed iron core and the movable iron core
21
.
A conduction path in this overcurrent-tripping device
12
comprises the heater
19
, the bi-metallic element
17
, the bi-metallic element support
22
, the electromagnet coil
20
, and the terminal
23
, in that order. When a heavy current such as a short-circuit current flows through this conduction path, the movable iron core
21
is attracted upward toward the fixed iron core, while rotating the lever
25
in the direction of the arrow in the figure. In response to this operation, an opening-and-closing mechanism (not shown) will be tripped to open the movable contact shoe, but before this tripping action, the lever
25
pushes a movable contact shoe holder (not shown) downward to open the movable contact shoe. After the current has been shut off to eliminate any attractive force on the movable iron core, the movable contact shoe is maintained in the opened state by means of the opening-and-closing mechanism, which has performed the tripping operation.
The above conventional overcurrent-tripping device
12
has the following problems:
(1) The movable iron core
21
is attracted to the fixed iron core to rotate the lever
25
in order to push the movable contact shoe holder downward and open the movable contact shoe. Mechanical slack, however, inevitably occurs in a connection between the movable iron core
21
and the lever
25
, and in a rotation-support-point portion of the lever
25
, so that a time delay occurs between the linear movement of the movable iron core
21
and the rotational movement of the lever
25
, resulting in a corresponding increase in operating time.
(2) Since the tip portion
25
a
of the lever
25
is located adjacent to the bi-metallic element
17
, the increase in the thickness of the heater
19
for augmentation of its rating is limited.
(3) Although the lever
25
is used to push the movable contact shoe holder downward to open the movable contact shoe, the movable contact shoe holder's large mass makes it difficult to increase the opening speed of the movable contact shoe by an appropriate degree.
It is thus an object of the present invention to solve these problems in order to improve the shutting-off performance of the circuit breaker while facilitating rating augmentation.
SUMMARY OF THE INVENTION
In order to attain the above object, the present invention provides a circuit breaker, which comprises a pair of opposed fixed contact shoes, a holder formed of an insulating material and guided in a case to move linearly, a movable contact shoe held at the holder for linear movement and pr
Kuboyama Katsunori
Nagahiro Isamu
Uchida Naoshi
Donovan Lincoln
Fuji Electric & Co., Ltd.
Kaneska & Takeuchi
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