Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Automatic circuit-interrupting devices
Reexamination Certificate
1998-12-14
2001-11-06
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Automatic circuit-interrupting devices
C335S007000, C335S013000, C335S043000, C361S103000, C361S106000, C361S115000
Reexamination Certificate
active
06313723
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the use of remote controllable circuit breakers with positive temperature coefficient resistivity (PTC) elements and reduced size and weight thermoplastic cases.
2. Background of the Art
Remote controllable circuit breakers are widely used for the interruption of electrical current in power lines upon conditions of severe overcurrent caused by short circuits or by ground faults. The remote signal is, for example, transmitted from a personal computer hundreds of miles away. The prior art circuit breakers include disadvantages such as, a very large size and high costs.
FIG. 1
(prior art) is a longitudinal sectional view of a typically remote controllable circuit breaker
10
for interrupting the flow of electrical current in a line. The circuit breaker
10
is, for example, the QOAS™ circuit breaker, manufactured by Square D Company, which is large in size and weight and very costly to manufacture. The circuit breaker
10
can be turned on or off by a remote signal while the breaker in the “ON” position. The remote control function of the circuit breaker
10
is of
FIG. 1
is accomplished using a small motor
12
, which is a very expensive part in such circuit breakers. When the circuit breaker
10
in the “ON” position, current is received at the line terminal
14
and passes through the two closed contacts
16
and
18
, respectively. The contact
16
is welded onto blade
20
. The current passes through the blade
20
to a bimetal
22
, and leaves the circuit breaker
10
through terminal
24
and lug
26
. The circuit breaker
10
includes an operating handle
11
and a spring
21
connected to the blade
20
.
When a remote signal to turn the circuit breaker
10
off is received by printed circuit board
28
, the motor
12
rotates driver
30
counter-clockwise. A sector gear
32
translates the rotation into a displacement of a lever
34
. The lever
34
pulls the blade
20
and separates the contacts
16
and
18
, respectively. The current is then interrupted or “turned off”, and the circuit breaker
10
remains in the “OFF” position until another remote control signal is received to turn the circuit breaker
10
on. When a remote control signal to turn the circuit breaker
10
on is received by the printed circuit board
28
, the motor
12
rotates clockwise. The sector gear
32
forces the lever
34
to push the blade
20
and close the contacts
16
and
18
, respectively, wherein the flow of current may be resumed.
The circuit breaker
10
includes conventional technology, such as the bimetal
22
used for overload protection. When the circuit breaker
10
is in an overload situation, such as 135% of the rated current, the high current brings additional heat to the bimetal
22
. The bimetal
22
is deflected by the heat and causes a trip lever
36
to detach. Circuit breakers using bimetal for overload protection must be calibrated. The calibration is performed using screw
38
. Calibration of the bimetal circuit breakers typically causes problems, and the manufacture of these types of circuit breakers including the bimetal is costly. The bimetal used in the circuit breakers does not behave consistently, even after calibration, and therefore, some circuit breakers will not trip at the rated 135% overload situation. In addition to many of the other problems associated with the use of bimetal in circuit breakers is terminal cracking, particularly in miniature circuit breakers. The calibration of the miniature circuit breakers also results in high stress of the load terminal.
For short circuit interruptions, the prior art circuit breaker
10
uses arc stacks
40
and a large arc chamber, large contacts
16
and
18
, and a large separation between the two contacts after the circuit breaker
10
trips. One of the problems associated with the process of interruption of the current during severe overcurrent conditions is arcing. Arcing occurs between the contacts of circuit breakers used to interrupt the current, which is highly undesirable for several reasons. Arcing causes deterioration of the contacts or blades of the breaker and causes gas pressure to build up. Arcing also necessitates circuit breakers with larger separation between the contacts in the open position to ensure that the arc does not persist with the contacts in the fully open position. In the circuit breaker
10
of
FIG. 1
, the large components and designs are used because almost 100% of the interruption energy becomes arcing, which generates high interruption pressure during a short circuit interruption. At least six rivets
42
are typically used in the prior art circuit breaker
10
design to hold the circuit breaker cover and base together because of interruption pressure. The interruption pressure also causes damage to end use equipment.
Another disadvantage in the prior art circuit breaker
10
design involves the mag-trip function. If the current through the circuit breaker
10
reaches a value higher than a predetermined value such as, for example, approximately 500% of the ampere rating, the circuit breaker
10
trips before the bimetal
22
has a chance to deflect. The predetermined current value is the mag-level of the circuit breaker
10
. An armature
44
and yoke
46
provide the tripping function. Under normal conditions, there is an air gap between the armature
44
and the yoke
46
. When the current reaches the predetermined mag-level, the armature
44
is pulled to the yoke
46
to close the air gap. The trip lever
36
is then delatched and the flow of electrical current in the line is cut off instantaneously by the circuit breaker
10
. However, the prior art designs of the armature
44
and yoke
46
cannot ensure consistent mag-levels among a batch of the same circuit breakers. The standard deviation of the mag-level of the prior art circuit breakers is too large to consistently protect circuits.
The prior art circuit breakers include disadvantages such as, a very large size and high costs. In order to hold the existing circuit breaker
10
mechanisms, such as the motor
12
and tripping mechanisms, the circuit breaker
10
base and enclosure (not shown) is designed with a very large size. The motor
12
, the large contacts
16
and
18
, the arc stacks
40
and the calibration of the bimetal
22
all contributes to the costly manufacturing of the existing circuit breaker
10
design. The thermosetting material used in manufacturing the base (not shown) and cover
48
of the circuit breaker
10
is also costly, especially compared to the manufacturing and use of thermoplastic cases. Other disadvantages in the prior art circuit breaker design include mechanical variations, and wear and contamination of parts.
Chen (U.S. Pat. No. 5,629,658) discloses a number of devices in which PTC elements are used in conjunction with two or more switches to limit the current under short circuit conditions and thereby reduce the associated arcing. U.S. patent application Ser. No. 08/918,768, filed Aug. 25, 1997 (Chen et al.) also discloses a number of devices in which PTC elements are used in conjunction with two or more switches to limit the current under short circuit conditions.
There is a need, therefore, for a circuit breaker design which is less costly to manufacture, is more reliable across a batch of circuit breakers manufactured and is of a much smaller size overall.
SUMMARY OF THE INVENTION
The present invention provides a circuit breaker and method for interrupting the flow of electric current in a line having a load and a source including a first switch, having an open and a closed position, connected in series with the line. A first actuating device is coupled to the first switch and is adapted to be actuated by at least one activating signal, to move the first switch from the closed position to the open position. A resistor having a positive temperature coefficient of resistivity is connected in series with the first switch and a voltage limiting device is connected in parallel with the resistor. A seco
Chen William W.
Lindholm Bruce F.
Barrera Ramon M.
Golden Larry I.
Irfan Kareem M.
Square D Company
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