Circuit breaker

Electricity: circuit makers and breakers – Electric switch details – Indicators

Reexamination Certificate

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Details

C200S323000, C200S324000, C200S330000, C200S331000

Reexamination Certificate

active

06566618

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a circuit breaker, such as an autobreaker applied to a control of an electric motor, in particular, to an interlock mechanism for indicating errors that allow an operator to identify an abnormal state of main circuit contacts caused by welding thereof, on the basis of a position of a rotary-operating handle.
The basic structure of the autobreaker in which the present invention is implemented will be described with reference to FIGS.
4
(
a
) to
4
(
d
). In FIG.
4
(
a
), reference numeral
1
denotes a breaker case, numeral
2
denotes a breaking section for main circuit contacts, numeral
3
is an opening and closing mechanism section, numeral
4
is an overcurrent tripping device, numeral
5
is a rotary-operating handle installed on a top surface of the case
1
, numeral
6
is a gear mechanism for coupling the rotary-operating handle
5
to the opening and closing mechanism section
3
for transmission, and numeral
7
is an accessory, i.e. auxiliary switch, alarm switch, or the like.
In this case, as shown in FIGS.
4
(
b
) and
4
(
c
), the opening and closing mechanism section
3
comprises an upper toggle gear
3
a
, an opening and closing lever
3
b
disposed in a lower part of the breaker, a toggle link mechanism
3
c
for linking the toggle gear
3
a
and the opening and closing lever
3
b
, and a latch mechanism
3
d
, with all of these components being assembled to the opening and closing mechanism. The toggle gear
3
a
is coupled to the rotary-operating handle
5
via a driving gear
8
for transmission. Further, the opening and closing lever
3
b
is journaled so as to rotationally move in a vertical direction via a support shaft
3
b
-
1
. An urge spring, i.e. torsion coil spring
3
b
-
2
provided on the shaft impels the lever in a direction to open the main circuit contact. The tip of the lever
3
b
projects to the side through a frame slot portion in the opening and closing mechanism section
3
. The driving gear
8
is directly coupled to a shaft of the operating handle
5
. The operating handle
5
is impelled and biased by a relatively weak return spring (spiral spring) in a direction such that it returns to the OFF position.
On the other hand, the breaking section
2
for the main circuit contacts is formed of an assembly of a fixed contact shoe
2
a
, a bridge-type movable contact shoe
2
b
, a movable contact shoe holder
2
c
, a contact spring (compression spring)
2
d
for the movable contact shoe
2
b
, and arc-extinguishing plates
2
e
. An upper end of the movable contact holder
2
c
is located opposite to a tip of the opening and closing lever
3
b
. The figure shows an ON state in which the main circuit contacts are closed. In this state, the tip of the opening and closing lever
3
b
is held in a position in which it retreats upward, and the movable contact shoe
2
b
is in contact with the fixed contact shoe
2
a
under the force of the contact spring
2
d.
With this construction, while the main circuit contacts are closed, the operating handle
5
is held in the ON position so as to indicate that position. Then, when the operating handle
5
is manually rotated from the ON position to the OFF position so as to open the main circuit contact, the toggle link mechanism
3
c
of the opening and closing mechanism section
3
releases the opening and closing lever
3
b
via the driving gear
8
and the toggle gear
3
a
. Thus, the opening and closing lever
3
b
rotationally moves clockwise under the accumulated force of the urge spring
3
b
-
2
to strike the movable contact shoe holder
2
c
, thereby opening the movable contact shoe
2
b.
Further, in contrast, when the operating handle
5
is rotated from the OFF position to the ON position, the link mechanism
3
c
of the opening and closing mechanism section
3
pushes a rear end of the opening and closing lever
3
b
downward against the urge spring
3
b
-
2
. Thus, the opening and closing lever
3
b
rotationally moves counterclockwise to release the movable contact shoe holder
2
c
from the pressure, so that the movable contact shoe
2
b
moves upward under the force of the contact spring
2
d
, subsequently comes to contact with the fixed contact shoe
2
a
, and is then closed. Simultaneously, the operating handle
5
is held in the ON position to indicate that the main circuit contacts are closed.
On the other hand, if the overcurrent tripping device
4
is activated when the main circuit contacts are closed to conduct electricity through the breaker, the latch mechanism
3
d
of the opening and closing mechanism section
3
is released to activate the toggle link mechanism
3
c
. Then, as in the above-described OFF operation, the opening and closing lever
3
b
rotates clockwise to perform a trip operation, to thereby open the movable contact shoe
2
b
. In this case, the operating handle
5
is stopped at a TRIP position between the ON and OFF positions to indicate that the main circuit contacts are opened due to the trip operation. To activate the main circuit contacts after the trip operation, the operating handle
5
is rotated from the TRIP position to the OFF position to reset a latch receiver of the latch mechanism
3
d
, and is then rotated to the ON position to close the main circuit contact.
In the circuit breaker constructed as described above, if an excess current flows during the conduction, the contacts of the fixed contact shoe
2
a
and movable contact shoe
2
b
of the main circuit contacts may be welded together. If such contact welding occurs and is severe, the movable contact shoe
2
b
does not separate from the fixed contact shoe
2
a
, despite the fact that the overcurrent tripping device
4
of the circuit breaker is activated to cause the opening and closing mechanism section
3
to perform the trip operation. Further, the opening and closing lever
3
b
of the opening and closing mechanism section
3
is restrained by the movable contact shoe holder
2
c
and can not be rotated to the contact open position. Thus, it remains stopped at a position between the ON and TRIP positions, while pressing the movable contact shoe holder
2
c
. On the other hand, the operating handle
5
moves from the ON position to the TRIP position, following the operation of the opening and closing mechanism section
3
despite the contact welding. In this position, the operating handle indicates the trip operation of the circuit breaker.
Accordingly, if a maintenance worker touches the load-side circuit while performing an inspection following the trip operation based on the wrong assumption that the main circuit contacts are opened, on the basis that the operating handle
5
indicates the TRIP position, without noticing the abnormal state of contact welding, an electric shock may occur, due to the fact that the main circuit contacts of the circuit breaker are not actually open.
Thus, as measures for preventing such an accident, there is known a circuit breaker comprising interlock means that restrains the operating handle
5
to be located to a position closer to the ON position than to the TRIP position, so that the handle will not indicate the TRIP position when the contact welding occurs during the trip operation of the circuit breaker. A conventional construction of such a circuit breaker is shown in FIGS.
5
(
a
)-
5
(
d
). That is, as shown in this figure, the opening and closing mechanism section
3
has a metallic handle lock lever
9
incorporated therein and linked therewith so as to move in the vertical direction and follow the rotational movement of the opening and closing lever
3
b
. An upper end of the lever
9
is located at a side opposite to a circular recess groove
5
a
formed in a rear surface of the rotary-operating handle
5
. FIG.
5
(
a
) is a top view showing ON and OFF positions of the rotary-operating handle
5
and a position indicating the occurrence of contact welding. FIGS.
5
(
b
) to
5
(
d
) show the operational states of the main circuit contact, the openin

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