Electricity: circuit makers and breakers – Electric switch details – Contact
Reexamination Certificate
2002-05-21
2003-07-08
Enad, Elvin (Department: 2832)
Electricity: circuit makers and breakers
Electric switch details
Contact
C335S016000, C335S195000
Reexamination Certificate
active
06590173
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a molded case circuit breaker, and more specifically, to an assembled structure of a current-interrupting section having fixed contact shoes and a rotary bridge-type contact shoe.
First, a general configuration of a molded case circuit breaker is schematically shown in FIG.
5
. In this figure, reference numeral
1
denotes a main body case of a circuit breaker,
2
is an opening and closing handle or a switching handle,
3
is a toggle type opening and closing mechanism or a switching mechanism, and
4
is an over-current tripping device (based on a bimetal method or the like). Reference numeral
5
is a current-interrupting section containing fixed contact shoes, a movable contact shoe and arc extinguishing devices of a main circuit, and is linked to the opening and closing mechanism
3
. An opening and closing operation of such a circuit breaker is well known. Through an ON/OFF operation of the opening and closing handle
2
, the movable contact shoe in the current-interrupting section
5
opens or closes via the opening and closing mechanism
3
. Further, when an over-current flows to activate the over-current tripping device
4
while the main circuit is powered, the opening and closing mechanism
3
performs a trip operation to open the movable contact shoe in the current-interrupting section
5
, thereby interrupting the over-current flowing through the main circuit.
An interrupting method used for the current-interrupting section
5
includes a single-break method and a double-break method. An example of a double-break method using a movable contact shoe equipped with a bridging rotary contact shoe is disclosed in Japanese Patent Publications (KOKAI) No. 06-028964 and No. 06-52777. A configuration of this circuit breaker is shown in FIGS.
6
(
a
) and
6
(
b
). In this figure, reference numeral
6
denotes an insulated case of the current-interrupting section
5
;
7
shows power-supply-side and load-side fixed contact shoes disposed in the insulated case
6
and arranged diagonally opposite to each other;
7
a
is a fixed contact provided at a tip portion of each fixed contact shoe;
8
is a movable contact shoe that bridges the contacts of the fixed contact shoes
7
;
9
is a rotary drum-shaped contact shoe holder that holds the movable contact shoe
8
; and
10
is an arc extinguishing device or a grid positioned at each side of the movable contact shoe
8
and disposed in the insulated case
6
. The movable contact shoe
8
is loosely fitted in a through-hole
9
a
formed in the contact shoe holder
9
, and is urged and held in position in the contact shoe holder
9
by a pressure spring (a tension spring or a torsion coil spring)
11
.
In the illustrated structure, four tension springs are provided as the pressure spring
11
, and two of them are arranged at each of the right and left sides of the movable contact shoe
8
. Each tension spring is disposed vertically relative to the movable contact shoe
8
, and extends between a rod
12
supported between right and left side walls of the contact shoe holder
9
and a rod
13
disposed on a top or bottom surface of the movable contact shoe
8
. In this state, the movable contact shoe
8
is positioned and held in a floating sate and is pressed so that a force acts counterclockwise relative to the center of rotation ‘O’ thereof. Thus, at an activation position shown in the figure, a predetermined contact pressure is exerted between the movable contact shoe
8
and the contact
7
a
of each of the fixed contact shoes
7
.
Further, the tip portion of each of the fixed contact shoes
7
is folded in a U-shape. When an over-current such as short circuit current flows through the main circuit, the movable contact shoe
8
is substantially instantaneously opened before the over-current tripping device
4
(see
FIG. 5
) operates by an electromagnetic resilient force exerted between the tip portions of the fixed contact shoes
7
and the movable contact shoe
8
. Furthermore, the folded portion of each fixed contact shoe has a magnetic yoke
14
to enhance a magnetic field acting on an arc generated between the contacts of the fixed and movable contact shoes during current interruption, thereby increasing the electromagnetic arc driving force to the arc extinguishing devices
10
.
A configuration in which the pressure spring
11
is formed of torsion coil springs instead of tension springs has been disclosed and known in Japanese Patent Publication (KOKAI) No. 01-166429. This assembled structure is shown in FIGS.
7
(
a
) and
7
(
b
). In this configuration, the pressure spring
11
is formed of two torsion coil springs, each being disposed at the right or left side of the movable contact shoe
8
. One of the springs has its opposing ends interposed between a recess groove
8
a
formed on a top surface side of the movable contact shoe
8
and the contact shoe holder
9
, while the other spring has its opposing ends interposed between a recess groove formed on a bottom surface side of the movable contact shoe
8
and the contact shoe holder
9
. The springs thus urge the movable contact shoe
8
counterclockwise with a predetermined contact pressure between the movable contact shoe
8
and the contact
7
a
of each of the fixed contact shoes
7
like the case shown in FIG.
6
.
The current-interrupting section described above has the following problems. Namely, in the structure in FIG.
6
(
b
) in which the pressure spring
11
of the movable contact shoe
8
is formed of the tension springs, the rods
13
and the rods
12
are provided at the top and bottom surfaces of the movable contact shoe piece
8
between the right and left side walls of the contact shoe holder
9
, respectively. And, each tension spring is extended between the corresponding rods
13
and
12
. The resulting structure becomes complex, and the procedure for mounting the pressure springs
11
is cumbersome. Furthermore, due to the nature of the tension springs, when the movable contact shoe
8
is opened by the electromagnetic force resulting from over-current, the spring force in a return direction, which pushes back the movable contact shoe piece
8
to a closed position, increases. Accordingly, in order to prevent inadvertent return contact between the contacts due to this spring force, a special mechanism for latching the movable contact shoe
8
to its open position is required, further complicating the structure and assembly.
In the structure in FIGS.
7
(
a
) and
7
(
b
), the pressure spring
11
is formed of the two pairs of the torsion coil springs arranged at the right and left sides of the movable contact shoe
8
, and each spring is interposed in the space between the movable contact shoe
8
and the right or left side wall of the contact shoe holder
9
. However, the space available between the movable contact shoe piece
8
and the right or left side wall of the contact shoe holder
9
is limited so small that if the torsion coil spring interposed in the corresponding space has a small coil length, it needs to have a large spring constant in order to exert a predetermined contact pressure on the movable contact shoe
8
. Thus, even if the pressure spring
11
comprises the torsion coil springs as shown in FIGS.
7
(
a
) and
7
(
b
), when the movable contact shoe
8
is opened by the electromagnetic reaction force resulting from the over-current as described above, the spring forces of the torsion coil springs cause the delay of the opening. Moreover, when extension of an arc generated between the contacts suppresses the current and reduces the electromagnetic reaction force exerted on the movable contact shoe, the spring force pushes back the movable contact shoe
8
to its closed position where the contacts touch again.
The present invention has been made in view of these points, and an object of the invention is to provide a structure of a current-interrupting section of a molded case circuit breaker, in which pressure springs of a movable contact
Kawahara Fumiyoshi
Sugiyama Syuichi
Uchida Naoshi
Enad Elvin
Fishman M.
Fuji Electric & Co., Ltd.
Kanesaka & Takeuchi
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