Patent Application
20160181039
The inventive subject matter relates to circuit breakers and methods of operating the same and, more particularly, to circuit breakers with shunt trip mechanisms.
A circuit breaker typically includes at least one set of contacts and a contact actuator mechanism configured to open and close the contacts. Some circuit breakers include shunt trip mechanisms, which may be used to activate the contact actuator responsive to an externally supplied control voltage. An example of a circuit breaker incorporating such a shunt trip mechanism is the Eaton Type VCP-W medium voltage circuit breaker described in Cutler-Hammer I. B. 32-255-1F Instructions for Installation, Operation and Maintenance of Type VCP-W Vacuum Circuit Breakers (Eaton Corp., January 2000).
In some electrical distribution applications, it may be desirable to lock out a circuit breaker to prevent accidental closure of its contacts. For example, it may be desirable to prevent closure of a circuit breaker when performing maintenance or other operations in which personnel may be near circuitry fed by the circuit breaker.
Some embodiments of the inventive subject matter provide a circuit breaker including at least one set of breaker contacts and a contact actuating mechanism configured to open and close the at least one set of contacts. The circuit breaker further includes a polarity sensitive shunt trip mechanism mechanically coupled to the contact actuating mechanism and configured to lock the contact actuating mechanism responsive to a shunt trip voltage of a first polarity to prevent closing of the at least one set of contacts and to unlock the contact actuating mechanism responsive to a shunt trip voltage of a second polarity to enable closing of the at least one set of breaker contacts.
In some embodiments, the shunt trip mechanism may include an actuator member configured to engage the contact actuating mechanism, an electromagnet configured to receive the shunt trip voltages and to move the actuator member responsive thereto, and a locking device configured to impede movement of the actuator member. The locking device may be configured to be magnetically actuated by the electromagnet.
In further embodiments, the actuator member may include an arm having an end that engages a moveable member of the contact actuating mechanism. The electromagnet may be configured to attract the arm to pivot the arm about a pivot point to move the moveable member from a first position to a second position. The locking device may be configured to constrain the arm to maintain the moveable member in the second position.
In still further embodiments, the shunt trip mechanism may include a shaft, and the electromagnet may include a coil disposed proximate a first end of the shaft. The arm may include a plate having a first portion on a first side of a pivot point configured to engage the moveable member and a second portion on a second side of the pivot point and having an opening therein through which the shaft passes such that the opening moves along the shaft as the plate pivots. The locking device may be configured to impede movement of the second portion of the plate with respect to the shaft. The locking device may include a flexible member disposed along the shaft and having a toothed portion extending therefrom in a direction perpendicular to an axis of the shaft and a magnetic slide disposed on the shaft and configured to be drawn along the shaft towards the coil responsive to the shunt trip voltage of the first polarity to thereby displace the toothed portion of the flexible member away from the shaft and thereby engage the second portion of the plate with the toothed portion and to be forced away from the coil along the shaft responsive to the shunt trip voltage of the second polarity to release the flexible member and disengage the toothed portion from the second portion of the plate.
Still further embodiments provide a shunt trip mechanism including an actuator member configured to engage a contact actuating mechanism, an electromagnet configured to move the actuator member from a first position to a second position responsive to a shunt trip voltage of a first polarity, and a locking device configured to lock the actuator member in the second position. The locking device may be configured to be actuated by the electromagnet.
Some embodiments provide methods of operating a circuit breaker. The methods include applying a shunt trip voltage of a first polarity to a shunt trip mechanism to actuate a contact actuating mechanism, locking the contact actuating mechanism using the shunt trip mechanism to prevent closing of at least one set of contacts controlled by the contact actuating mechanism, and releasing the contact actuating mechanism by applying a shunt trip voltage of a second polarity to the shunt trip mechanism.
Specific exemplary embodiments of the inventive subject matter now will be described with reference to the accompanying drawings. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. In the drawings, like numbers refer to like elements. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Some embodiments of the inventive subject matter arise from a realization that lockout of a circuit breaker may be achieved by using a polarity-sensitive shunt trip mechanism that can be used to lock out the breaker contacts until a shunt trip voltage of a certain polarity is applied to the shunt trip mechanism. In some embodiments, the shunt trip mechanism may include a locking device that is actuated by an electromagnet used to actuate the mechanism. For example, the locking device may include a magnetic latch or similar feature that restrains movement of an actuator plate of the shunt trip mechanism that engages a contact actuator mechanism of the breaker, thus preventing movement of the contact actuator and closure of the breaker contacts until the magnetic latch is released.
Embodiments of the inventive subject matter are described below with reference to medium voltage vacuum circuit breakers. It will be appreciated, however, that the inventive subject matter is not limited to such applications, and is widely applicable to a wide variety of different types of circuit breakers and other switching devices that employ shunt trip mechanisms.
The shunt trip mechanism 60 further includes a shunt trip plate 120 (or “clapper”) that is actuated by the electromagnet 170. In particular, the shunt trip plate 120 is configured to pivot around a pivot point 130 supported by the frame 110. An upper portion 120a of the shunt trip plate 120 is configured to engage a protruding member 52 of the contact actuator mechanism 50. A lower portion 1201) of the shunt trip plate 120 has an opening 122 therein through which the shaft 140 passes. When the coil 172 of the electromagnet 170 is energized using a shunt trip voltage of a first polarity, the lower portion 120b of the shunt trip plate 120 is drawn towards the coil 172 (opposing a force generated by a spring 180), causing the shunt trip plate 120 to pivot about the pivot point 130. This causes the upper portion 120a of the shunt trip plate 120 to move the protruding arm 52 of the contact actuator mechanism 50 laterally, which, in turn, causes the contact actuator mechanism 50 to trip and open the contacts of the vacuum circuit interrupters 20.
The shunt trip mechanism 60 further includes a magnetic locking device. As shown, magnetic locking device includes a magnetic slide 150 that operates a catch in the form of one or more toothed flexible members 160 disposed along the shaft 140. The magnetic slide 150 may include one or more beveled faces 152 that, when the slide 150 is drawn toward the coil 172, deflect the members 160 away from the shaft 140 such that toothed portions 162 of the flexible members 160 engage a surface of the lower portion 120b of the shunt trip plate 120 adjacent the opening 122. This locks the shunt trip plate 120 against the coil 172, preventing movement of the protruding arm 52 of the contact actuator mechanism 50 back to a position that allows closure of the vacuum circuit interrupter contacts. Upon tripping of the breaker, auxiliary contacts that operate in coordination with the main breaker contacts may disconnect the shunt trip voltage source from the coil 172, thus deactivating the electromagnet 170.
The slide 50 may be configured to be frictionally held in the locked position until a shunt trip voltage of a second polarity opposite to the first polarity is applied to the coil 172, generating a repelling magnetic force sufficient to overcome friction and move the slide 150 away from the coil 172. As the slide 150 moves away from the coil 172, the flexible members 160 are released, disengaging the toothed portions 162 from the lower portion 120b of the shunt trip plate 120. This allows the shunt trip plate 120 to pivot back to a position that releases the contact actuator mechanism 50, thus enabling the breaker contacts to be closed.
It will be appreciated that the embodiments described are provided for purposes of illustration, and that the inventive subject may be implemented in any of a variety of other ways. For example, the inventive subject matter may be implemented in other types of circuit breakers and/or may use polarity-sensitive shunt trip mechanism locking devices with different configurations. Such locking device may be, for example, spring or gravity actuated, in contrast to the magnetically activated mechanism described above.
In the drawings and specification, there have been disclosed exemplary embodiments of the inventive subject matter. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being defined by the following claims.
