Patent Application
20180254162
The present application relates to electric circuit breakers, and more specifically to systems, apparatus, and methods for tripping of circuit breakers.
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by an electrical overload or short circuit. A circuit breaker automatically opens its contacts if an overcurrent condition is sensed. To do this, a circuit breaker comprises a trip unit, which determines when the contacts are to open.
Some circuit breakers include trip units including a thermomagnetic tripping mechanism. Such breakers are well known in commercial and industrial applications. These breakers include multi-metallic strips (e.g., a strips of two or more metals with different thermal expansion rates bonded together) for triggering a thermal trip resulting from overload currents and a magnetic element for instantaneous trip resulting from short-circuit current surges. Some breakers use bimetallic, while others use tri-metallic strips that are fixed on one end (these are collectively referred to as “bimetal levers” herein). In other words, the thermomagnetic tripping mechanisms include elements designed to both sense the heat resulting from an overload condition and the high current resulting from a short circuit. In addition, some circuit breakers incorporate a “push to trip” button.
It is possible that a temperature profile for a thermomagnetic trip mechanism of a standard circuit breaker does not meet the requirements for different circuit breakers under different operating conditions. For example, increasing the temperature inside the thermomagnetic trip mechanism of a circuit breaker can generate higher temperatures on the lugs and current path that do not comply with temperature range ratings (e.g., temperatures out of the acceptable range) of the circuit breaker. While using an arrangement with a low temperature profile can reduce the heat applied to the current path of the circuit breaker, low temperatures in the bimetal lever of a thermomagnetic trip unit can result in an inadequate amount of bimetal deflection and an insufficient amount of pushing power to actuate the trip bar, latch, or latching mechanism. Although a limited amount of deflection of the bimetal lever can be compensated for when using a low temperature profile by using a calibration mechanism (e.g., an adjustment screw) to locate the end of the bimetal lever closer to the trip bar of the breaker, the deflection strength may still not be sufficient for the bimetal lever to produce enough force to rotate the trip bar and release the energy storage spring of the thermomagnetic tripping mechanism.
If sufficient overcurrent flows through the circuit breaker's current path, heat build-up causes the bimetal lever 108 of the thermomagnetic tripping mechanism 100 to deflect. As the bimetal lever 108 is heated, it bends from its high thermal expansion side toward its low thermal expansion side. After bending a predetermined distance, the bimetal lever 108 contacts and pushes on the trip bar 110 activating the energy storage spring 112 and thus the trip mechanism of the circuit breaker. Typically, if approximately 20% current over the nominal current rating of the breaker flows through the current path, the bimetal lever 108 generates pushing force based on the heat generated which rotates the trip bar 110 and releases the energy storage spring 112. Therefore, to insure reliable operation of thermomagnetic circuit breakers, systems, apparatus, and methods for improved tripping of circuit breakers are desirable.
In some embodiments, an improved circuit breaker is provided. Embodiments of the improved circuit breaker include a current path including contacts openable to interrupt a circuit; a thermoelectric tripping mechanism adjacent the current path, the thermoelectric tripping mechanism including a thermoelectric plate disposed between the current path and a bimetal lever; and a trip bar disposed to be pressed by the bimetal lever, the trip bar coupled to a stored energy mechanism releasable to open the contacts. A power supply is included to apply DC current to the thermoelectric plate in response to a current overload condition.
In some other embodiments, a thermoelectric tripping mechanism is provided. Embodiments of the thermoelectric tripping mechanism include a current path; a bimetal lever; and a thermoelectric plate disposed between the current path and the bimetal lever. In some embodiments, the thermoelectric tripping mechanism can further include a DC power supply coupled to the thermoelectric plate. In some embodiments, the thermoelectric plate is operative to heat the bimetal lever and use the current path as a heat sink.
In yet other embodiments, a method of tripping a circuit breaker is provided. The method includes providing a circuit breaker with a thermoelectric tripping mechanism, the thermoelectric tripping mechanism including a thermoelectric plate disposed between a current path and a bimetal lever of the circuit breaker; applying a DC current to the thermoelectric plate to heat the bimetal lever; and deflecting the bimetal lever to press upon a trip bar in response to a current overload occurring on the current path.
Still other features, aspects, and advantages of embodiments will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings by illustrating a number of exemplary embodiments and implementations, including the best mode contemplated for carrying out the embodiments. Embodiments may also be capable of other and different applications, and several details may be modified in various respects, all without departing from the spirit and scope of the disclosed embodiments. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. The drawings are not necessarily drawn to scale. The description is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the claims.
Embodiments disclosed herein describe a thermoelectric tripping mechanism for use in a thermomagnetic circuit breaker. As discussed above, thermomagnetic circuit breakers use a bi-metallic or tri-metallic element to sense temperature on the current path and use the deflection of the bimetal lever to activate the tripping mechanism in case of an overload. To achieve sufficient deflection with adequate pushing force, the bimetal lever is conventional coupled to a heater element for indirect heating or is connected as part of the current path for direct heating. However, the heat generated from heating the bimetal is transferred to the rest of the current path, mainly by conduction and convection. As a result, the temperature of the entire circuit breaker is increased. The increased temperature can damage the lugs and cables connected to the circuit breaker, or may cause a generalized overheating condition of the surroundings of the circuit breaker.
Conventionally, in order to limit the maximum temperature of the circuit breaker during normal operation, the size of the elements in the current path, where the heater of the bimetal is located, are increased to provide more heat dissipation. In addition, more expensive materials with very good thermal or electrical conductivity are used to further help dissipate the heat. Thus, conventional thermomagnetic circuit breakers are forced to balance competing aspects: on one hand, increasing heat to achieve sufficient deflection with adequate pushing force with the bimetal lever and, on the other hand, limiting heat to prevent damage to the circuit breaker and surrounding elements. Achieving this balance has conventionally been accomplished at the expense of using larger components and more expensive materials.
The thermomagnetic circuit breakers of embodiments disclosed herein avoid the competing aspects of conventional circuit breakers. Instead, embodiments use a thermoelectric plate to heat the bimetal lever without providing extra heat to the current path. A thermoelectric plate works based on the principal of the “Peltier effect”. Due to the Peltier effect, a thermoelectric plate creates voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side. This effect can be used to generate electricity, measure temperature or, in the case of embodiments disclosed herein, change the temperature of objects such as the bimetal lever. Because the direction of heating and cooling is determined by the polarity of the applied voltage, thermoelectric plates can be used as temperature controllers. The cold side of the thermoelectric plate is attached to the current path to use the current path as a heat sink. The bimetal lever is attached to the hot side to aid in deflection.
In some embodiments, a DC current is applied to the thermoelectric plate to induce the temperature gradient between the two sides. The DC current can be generated from the current path using a current transformer and a rectifier diode. The heat produced by the thermoelectric plate, is only applied to the bimetal lever without heating the entire current path. Therefore, the material cost of the current path can be reduced and the entire size of the circuit breaker can also be reduced. Circuit breakers that operate at lower temperatures than conventional breakers allow optimization the panel board design upon which they are mounted. For example, with reduced size breakers, more breakers can be included within a smaller panel. Further, by controlling the DC current applied to the thermoelectric plate so that it only flows above a predefined value, the thermal calibration process of the circuit breaker can be eliminated or greatly simplified.
Turning now to
Referring to
Notably, support 304 is used as a heat sink by the thermoelectric plate 306 and thus, a narrowed section which creates the conventional “heater” is not needed. Therefore, the overall width of support 304 can be significantly smaller than the widest portion of the structure conventionally used for supporting the bimetal lever. For example, whereas a conventional structure for a 600A breaker may be formed from approximately 0.091″ inch thick material with a reduced cross section from approximately 1.5″ in its widest area to approximately 0.96″ in the narrowest area (“for heating effects”) and a length of approximately 5 inches, the support 304 of present embodiments can be reduced to being only approximately 4 inches long and approximately 1.2″ wide for an overall reduction of material of approximately 20%.
Turning now to
In some embodiments, the DC current applied to the thermoelectric plate 1218 can be controlled so that current only flows to it above a predefined value as illustrated in
If the voltage of the DC current from the rectifier 1212 is less than the reference voltage, the voltage comparator 1230 does not output any current on line 1232 as indicated in the “OFF” portion of graph 1234. If however, the voltage of the DC current from the rectifier 1212 is greater than the reference voltage, the voltage comparator 1230 does output a current on line 1232 as indicated in the “ON” portion of graph 1234.
The cool side of the thermoelectric plate 1218 is coupled to the bimetal lever 1222. The hot side of the thermoelectric plate 1218 is coupled to the current path 1220. When a current overload occurs on the current path 1220, the voltage of the DC current from the rectifier 1212 exceeds the reference voltage, a current is applied to line 1232, and the thermoelectric plate 1218 is energized to heat the bimetal lever 1222 and to use the current path 1220 as a heat sink. The heated bimetal lever 1222 deflects due to the heat from the thermoelectric plate 1218 and the deflected bimetal lever 1222 presses upon the trip bar 1224 to release the stored energy spring 1226 which opens contacts 1228 to interrupt the circuit.
Therefore, a benefit of the embodiment of
In normal operation, voltage comparator 1330 applies a current on line 1332 that flows to the thermoelectric plate 1318 as shown in the “ON” portion of graph 1334. The thermoelectric plate 1318 is disposed with the cool side against the bimetal lever 1322 and the hot side against the current path 1320. Thus, in normal operation, the bimetal lever 1322 is held in a deflected position without pressing on the trip bar 1324. In a current overload condition, the voltage comparator 1330 cuts off the current on line 1332 and flow to the thermoelectric plate 1318 is stopped as shown in the “OFF” portion of graph 1334. The bimetal lever 1322 is no longer cooled and thus, returns to a non-deflected position which presses on the trip bar 1324 to release the stored energy spring 1326 which opens contacts 1328 to interrupt the circuit.
Therefore, in addition to the reduced configuration benefit of binary operation due to the use of a voltage comparator 1330, a safety and reliability benefit of the embodiment of
Note that throughout the present specification, the term “bimetal lever” is used to refer to the temperature responsive structure that deflects due to different coefficients of thermal expansion of the materials used to form the lever. In some embodiments, three, four, or more materials can be used to form a temperature responsive lever. Thus, the term “bimetal” is only used for clarity and convenience and one of ordinary skill will understand that multiple materials (including non-metal) can be used together to form a temperature responsive lever.
Further, in some embodiments, the current path is used as a heat sink for the bimetal lever. However, a heat sink is not required in some embodiments and alternatively, a separate heat sink can be used. In some embodiments, a transceiver (e.g., a wired or wireless transceiver) can be coupled to the voltage comparator to adjust the reference voltage. Thus, a remote signal can be transmitted to the voltage comparator to cause the circuit breaker to trip. Likewise, in some embodiments, the transceiver can be connected to the output of the voltage comparator to send a signal when the thermoelectric plate is being energized or not, or if there is a change in the signal to the thermoelectric plate, indicating the occurrence of an overload condition and/or a current status of the circuit breaker.
Turning now to
Numerous embodiments are described in this disclosure, and are presented for illustrative purposes only. The described embodiments are not, and are not intended to be, limiting in any sense. The presently disclosed embodiments are widely applicable to numerous other embodiments, as is readily apparent from the disclosure. One of ordinary skill in the art will recognize that the disclosed embodiments may be practiced with various modifications and alterations, such as structural, logical, software, and electrical modifications. Although particular features of the disclosed embodiments may be described with reference to one or more particular embodiments and/or drawings, it should be understood that such features are not limited to usage in the one or more particular embodiments or drawings with reference to which they are described, unless expressly specified otherwise.
The present disclosure is neither a literal description of all embodiments nor a listing of features of the embodiments that must be present in all embodiments. The present disclosure provides, to one of ordinary skill in the art, an enabling description of several embodiments. Some of these embodiments may not be claimed in the present application, but may nevertheless be claimed in one or more continuing applications that claim the benefit of priority of the present application.
The foregoing description discloses only example embodiments. Modifications of the above-disclosed apparatus, systems. and methods which fall within the scope of the claims will be readily apparent to those of ordinary skill in the art. Accordingly, while the embodiments have been disclosed in connection with example embodiments thereof, it should be understood that other embodiments may fall within the intended scope, as defined by the following claims.
