Patent Application
20060086694
The present invention relates to electrical circuit interrupters, as well as positioning and adjustment of parts in such circuit interrupters.
Electrical distribution and protection equipment is an important element in many applications, particularly those employing medium to high electrical voltages. For example, one such type of equipment is a circuit breaker. Circuit breakers provide protection for electrical systems from electrical fault conditions such as current overloads, short circuits, and low level voltage conditions. Typically, circuit breakers include at least one circuit interrupter, which contains a spring-powered operating mechanism that opens electrical contacts in response to abnormal conditions in order to interrupt the current passing through the conductors in an electrical system. Circuit interrupters are an integral part of not only circuit breakers, but other types of electrical distribution and protection equipment as well.
One particular type of circuit interrupter is a vacuum circuit interrupter, which includes separable main contacts disposed within an insulated and hermetically sealed housing. During the past several decades, vacuum circuit interrupters have gained world-wide acceptance over other technologies for use in circuit breakers, contactors, motor starters, tap changers, distribution reclosers, metal-clad switchgear, and other electrical distribution and protection equipment. Depending on vacuum circuit interrupter construction, vacuum circuit interrupters offer one or more of the following advantages as compared to other types of circuit interrupters: (1) relatively long life due to controlled contact erosion, (2) relatively maintenance-free operation provided by enclosure of the contacts within the hermetically sealed housing, (3) excellent sticking resistance due to the use of hard contact materials, (4) relatively little or no atmospheric contact contamination, which contamination can detrimentally form oxides and corrosion layers on the contacts, (5) relatively little or no noise during operation due to containment of arcing within the hermetically sealed housing, (6) relatively few environmental effects as compared to those interrupters where current interruption does not occur in a vacuum and hence, where greenhouse or toxic gases can be freely emitted into the operating environment, and (7) very low current chop, resulting in a minimal induced transient voltage spike during circuit interruption so that surge suppressors are not required.
Generally, one of the contacts in a vacuum circuit interrupter is fixed relative to both the housing and to an external electrical conductor that is interconnected with the circuit controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross-section having the contact at one end enclosed within the vacuum chamber, and a driving mechanism at the other end which is external to the vacuum chamber. In one type of vacuum interrupter, an operating rod assembly is provided which carries a rotatable contact bell crank that is slideable on the operating rod and rotates about a pivot pin upon motion of the operating rod. This operating rod assembly is connected to the stem of the moveable contacts. The stem is typically affixed to a bellows seal that maintains the vacuum environment within the chamber while enabling movement of the stem and thus the moveable contact. Motion of the operating rod assembly causes motion of the moveable contact into, or out of, engagement with the fixed contact.
The operating rod assembly is operatively connected to a latchable operating mechanism that is responsive to current. When an abnormal condition occurs, the latchable operating mechanism becomes unlatched, which causes the operating rod to move to the open position. The motion of the operating rod, in turn, causes the contact bell crank to rotate and, as described above, controls the motion of the moveable contact.
Contact springs are typically provided in the operating rod assembly in order to be able to separate the moveable contact from the fixed contact and to ensure the necessary force so that the contacts will not accidentally open under inappropriate conditions. In addition, when appropriate circumstances requiring interruption of the circuit do arise, an adequate force is needed to open the contacts with sufficient speed. If the contacts do not open quickly, there is a risk that the circuit interrupter will fail to interrupt the circuit.
In order to achieve the adequate interrupt speed and force, contact springs are mounted on the operating rod assembly. These contact springs are typically mounted towards one end of the operating rod between the moveable contact and the latchable operating mechanism to provide an over-travel gap (sometimes referred to as a “snatch” gap) or contact wipe portion within the operating rod assembly, a distance through which movement of the springs imparts the necessary speed and force for positioning of the moveable contact. The length of this over-travel gap, or contact wipe portion distance, is determined based on a measure of the force required to hold the vacuum interrupter contacts in a closed position (e.g., against counter forces caused by a peak momentary current). The length of the over-travel gap is also based upon the force required to open the contacts with sufficient speed for safe and clean interruption of an electrical circuit. Therefore, if such springs comprise compression springs, as is typically the case, it is important that the springs have sufficient compression during operation. On the other hand, if tension springs are utilized, adequate tension must exist.
In a typical case, the contact spring is held on the operating rod between a disk-spacer member that is carried along by the operating rod and a shoulder portion of a set of plates that are mounted at one end of the operating rod and spaced apart from the spacer member. When the contacts are closed, the operating rod travels toward its closed position. The plates are slideably mounted on the operating rod in such a way that when the contacts seat, motion of the plates stop. However, motion of the operating rod continues a further distance until it travels to its full extended position. At this point, the contact spring is fully compressed between the spacer member and the shoulder portion of the plates. The further distance traveled by the operating rod is referred to as the over-travel gap (also known as snatch gap) when the operating rod motion is essentially linear or contact wipe portion when the operating rod motion deviates in a non-linear manner with respect to the direction of opening and closing of the contacts. Generally non-linear operating rod motion is associated with those vacuum circuit interrupters that are encased within an open-air system (e.g., fastened to a box in a cantilever arrangement). Linear operating rod motion is associated with those vacuum circuit interrupters that are encased within a closed-air system (e.g., supported by encasement in molded epoxy or another similar material).
In order to ensure that appropriate compression (or tension) is imparted to the contact spring during operation, and hence providing the necessary forces associated with opening and closing the contacts, the over-travel gap is integrated into the circuit breaker design and maintained at a fixed distance. In one typical scenario, when adjustment is needed in order to maintain the fixed distance, repositionable shims are inserted in, removed from, or adjusted within a space residing between the lower end of the vacuum housing (e.g., the plastic bushing surface on the exterior of a vacuum bottle) and the upper end of a support frame (e.g., that provided by a crosshead drive rod or a pole unit support casting). Such shims are identified, for example, in U.S. Pat. No. 4,064,383.
Moreover, due to their repositionability, shims are capable of realigning themselves and even popping out of their intended positions during operation—and often do just that. Circuit breaker users are often ill-equipped to handle needed adjustment and hence vacuum interrupter circuit breakers operated as such often did not work as intended, or required frequent replacement due to the imprecise manner in which they were operated. While adjustment during a circuit breaker's operating life can be needed, due to settling of parts after manufacture and before initial use (e.g., during shipping), adjustment can also be required prior to initial use. In that case, the circuit breaker is adjusted after it reaches, and is positioned within, its destination of intended use.
Thus, more efficient techniques for maintaining or adjusting over-travel gaps and contact wipe portions in operating rod assemblies of circuit interrupters are needed. Not only is reliability desired in that regard, but ease of adjustment is also desired.
The present invention provides improved and more efficient techniques for maintaining and/or adjusting over-travel gaps and contact wipe portions in operating rod assemblies of circuit interrupters. Such maintenance and adjustment is provided with relative ease as compared to conventional techniques and apparatus for the same.
According to one embodiment of the invention, a circuit interrupter comprises a fixed electrical contact; a moveable electrical contact; an operating rod assembly comprising at least one contact spring for imparting a corresponding opening or closing force to the contacts; a moveable contact stem operatively coupled between the moveable electrical contact and the operating rod assembly for positioning the moveable electrical contact into or out of engagement with the fixed electrical contact; and an adjustment member adjustably disposed on an opposite end of the circuit interrupter relative to the moveable electrical contact from the at least one contact spring; wherein motion of the operating rod assembly causes the moveable electrical contact to move into or out of engagement with the fixed electrical contact via motion of the moveable contact stem and wherein the moveable electrical contact moves into or out of engagement with the fixed electrical contact with application of force imparted by the contact spring, and wherein the adjustment member is capable of adjusting the force imparted by the contact spring when moving the moveable electrical contact into or out of engagement with the fixed electrical contact.
Depending on the application, such circuit interrupters can comprise an over-travel gap for imparting contact spring force. One exemplary over-travel gap is about 5.0 mm. In other applications, such circuit interrupters can comprise a contact wipe portion for imparting contact spring force. The contact spring can be a compression spring, a tension spring, or combinations thereof. In one exemplary embodiment, a circuit interrupter of the invention comprises two contact springs.
While variations are understood to be within the scope of the invention, in one embodiment of the invention the adjustment member comprises a conductive material. According to a further aspect of the invention, external threads on the adjustment member are received by a threaded adjustment member housing interposed between the adjustment member and the fixed electrical contact.
When the circuit interrupter is a vacuum circuit interrupter having a vacuum housing for enclosure of the fixed electrical contact and the moveable electrical contact, the adjustment member is coupled to the vacuum housing in a manner that facilitates longitudinal movement of the vacuum housing along a longitudinal axis shared with the adjustment member during adjustment according to an exemplary embodiment. The adjustment member can be coupled to the vacuum housing, for example, in a fixed manner using a cap screw. Further, the adjustment member can be secured (e.g., using a bearing locknut, such as one that threadably engages with the adjustment member housing) between adjustments.
Further to the vacuum circuit interrupter embodiment of the invention, such a circuit interrupter can comprise an over-travel gap for imparting contact spring force, wherein distance traveled by the vacuum housing during adjustment corresponds to adjustment of the over-travel gap by the same distance. While dimensions may vary depending on the application, an initial set dimension of about 30.5 mm can be provided between an upper surface of the adjustment member and an upper surface of the vacuum housing to facilitate adjustment latitude.
Circuit interrupters of the invention are useful in, among many larger assemblies and applications, electrical systems (e.g., a circuit breaker or larger systems employing circuit breakers). In one embodiment, a circuit breaker of the invention comprises a medium voltage vacuum circuit breaker.
Further assemblies comprising circuit interrupters of the invention include kits for maintaining desired force imparted by a contact spring when positioning a moveable electrical contact into or out of engagement with a fixed electrical contact in a circuit interrupter. In one embodiment, such a kit comprises, in addition to a circuit interrupter of the invention, a spanner wrench for locking and unlocking the bearing locknut and an adjustment spanner assembly for adjusting the adjustment member.
Methods of the invention include those for adjustment of force imparted by a contact spring when positioning a moveable electrical contact into or out of engagement with a fixed electrical contact in a circuit interrupter (e.g., a vacuum circuit interrupter). In this embodiment, the method comprises steps of providing an adjustment member adjustably disposed on an opposite end of the circuit interrupter relative to the moveable electrical contact from the at least one contact spring and adjusting the adjustment member (which is optionally secured between adjustments) in an amount necessary to obtain the desired force. The method can further comprise a step of unlocking the adjustment member prior to adjustment. Similarly, the method can further comprise a step of locking the adjustment member after adjusting the adjustment member in the amount necessary to obtain the desired force. For example, the adjustment member can be locked and unlocked using a spanner wrench. While many alternatives are within the scope of the invention, the adjustment member can be adjusted using an adjustment spanner assembly.
Referring to
The circuit breaker 1 has a front low voltage portion 13 adjacent to the front panel 7 and a rear high voltage portion including the vacuum circuit interrupter assembly 5. The high and low voltage portions are electrically insulated from one another by upper and lower isolators 15 and 17, respectively. Vacuum circuit interrupter assembly 5 encloses a pair of separable contacts, including stationary contact 21 and moveable contact 23 within a vacuum housing 25. The circuit breaker illustrated in
Details regarding the operating mechanism for moving the contacts 21 and 23 between an open and a closed circuit position are described in U.S. Pat. No. 4,743,876, which is herein incorporated by reference in its entirety. Briefly, as shown in
The operating linkage for opening the contacts 21 and 23, described in general terms, includes a trip latch having a series of links that are pivotally mounted with respect to the operating shaft 39 and the operating rod 37, such that when the trip latch falls from an initially upright position, the operating rod 37 recedes back toward the trip latch and the breaker 1 is then opened and moveable contact 23 is separated from fixed contact 21. A more thorough description is set forth in U.S. Pat. Nos. 5,095,293 and 4,743,876.
The foregoing description provides a general understanding of one embodiment of operation of the vacuum circuit interrupter and the operating mechanism that interfaces with the method and apparatus of the present invention. It is to be understood that variations in this embodiment do not depart from the spirit and scope of the invention as described more fully herein.
Note that components in the design illustrated in
Within the more detailed vacuum interrupter assembly of
In accordance with the present teachings, an over-travel gap portion 73 of one embodiment of an improved circuit breaker 1′ is illustrated in
Optimally, adjustment of the over-travel gap occurs when the contacts 21′ and 23′ are in the closed position. To facilitate such adjustment, an adjustment member 77 is moveably engaged within adjustment member housing 79 adjacent conductive terminal 9′. In one embodiment, adjustment member housing 79 comprises an internally threaded housing 214 adapted for receiving an externally threaded portion of the adjustment member 77. In this embodiment, threads on the adjustment member 77 and adjustment member housing 79 have a similar size and pitch with respect to one another. In one embodiment, the threads are of nominal size (e.g., M65), and have a pitch of about 2 mm. When threads of this size are used, one-quarter rotation of the adjustment member 77 provides longitudinal movement of the adjustment member 77 along a longitudinal axis 81 in an amount of approximately 0.5 mm. It should be noted that threads of different sizes and pitch can be utilized in order to obtain an adjustment having a desired resolution.
In the embodiment illustrated in
As long as the adjustment member housing 79 and the vacuum housing 25′ are coupled in a manner that promotes precisely calculated movement of vacuum housing 25′ in response to movement of adjustment member housing 79, any suitable mechanism and/or fixture for engagement of the two parts can be utilized. For example, mechanical or chemical fastening mechanisms can be used to fixedly couple the vacuum housing 25′ with the adjustment member housing 79. In an exemplary embodiment, the adjustment member housing 79 is coupled to the vacuum housing 25′ in a fixed manner using a cap screw 83. For example, the cap screw 83 can comprise a standard M16×75 mm cap screw.
Still referring to
Each of the parts described with respect to the present inventive improved circuit interrupter can be formed using any suitable material or combinations thereof. In one embodiment, the adjustment member housing 79 comprises a conductive material such as, for example, copper. While the entire adjustment member housing 79 need not comprise a conductive material, generally parts of the circuit breaker 1′ are fabricated and selected so as to provide a continuous conductive path between the conductive terminals 9′ and 11′, and through the contacts 21′ and 23′ when the improved circuit breaker 1′ is closed. Similarly, in one embodiment, the adjustment member 77 comprises a conductive material such as, for example, copper. However, as with the adjustment member housing 79, any suitable material or combinations thereof can be used as long as a continuous conductive path resides between the conductive terminals 9′and 11′ and through the contacts 21′ and 23′ in the circuit breaker 1′ when operated in the closed circuit position. In order to promote continuity, the presence of joints at the intersection of adjoining parts are minimized in such conductive paths according to exemplary embodiments of the invention. When the presence of joints is necessary, conductive lamination can be used to help facilitate uninterrupted conduction through the joint.
Depending on the materials used in implementing the various parts within the over-travel gap adjustment portion 75, safety precautions may be necessary by one performing the over-travel gap adjustment. For example, electrical power should be turned off to circuit breaker 1′ prior to performing an adjustment. As an added precaution, insulated gloves or other safety apparatus can be worn by one performing the adjustment.
With reference to
As further illustrated in
Medium voltage vacuum circuit interrupters are generally those operating in conjunction with rated currents of between 1,000 Volts and 38,000 Volts (and even up to 40,000 Volts in certain parts of the world). High voltage vacuum circuit interrupters are generally those operating in conjunction with rated currents of about 40,000 Volts and greater.
An exemplary embodiment of the invention comprises a medium voltage vacuum circuit interrupter. While not dispositive, generally medium voltage vacuum circuit interrupters are designed to work well with an over-travel gap of approximately 0.5 mm (0.02 inches) and higher. In one embodiment of a medium voltage vacuum circuit interrupter of the invention, the over-travel gap distance 91 is approximately 5.0 mm (0.20 inches). This distance is typically deemed sufficient to impart the necessary forces associated with the opening and closing of the contacts in an 80 kA 4,000 Ampere vacuum circuit interrupter. During typical operation, such a vacuum circuit interrupter has a distance between contacts, when in the fully open position, of approximately 11.0 mm (0.43 inches) in one embodiment. This distance is known as the “stroke” of a vacuum circuit interrupter. The combined length of the over-travel gap 91 and the stroke is the total distance that the operating rod travels when moving the contacts between fully closed and fully opened positions.
Based on the “stroke” length, and voltage characteristics of a vacuum circuit interrupter, the over-travel gap 91 is adjusted accordingly as known to those of skill in the circuit breaker art. Thus, the over-travel gap can have a length from just above 0 mm to as great as necessary to assist in breaking apart the contacts during interruption and minimize potential weldment of the contacts.
As further illustrated in the embodiment shown in
When the contacts of the circuit breaker 1′ are opened from a closed circuit position, the moveable contact stem 27′ travels the over-travel gap distance 91 upon opening before the fixed and moveable contacts 21′ and 23′ begin to move apart from one another. During this initial travel, stored energy in the contact spring 55′ is transferred to the moveable contact stem 27′, giving the moveable contact stem 27′ kinetic energy sufficient to provide the force necessary to break apart the contacts. Thus, with continuing movement, the moveable contact 23′ engages and joins with the moveable contact stem 27′ in descending from the fixed contact 21′ to its full open circuit position. The over-travel gap 85′ facilitates an effective opening of the contacts by providing for release of equivalent stored energy in the contact spring 55′ to break apart any welds formed between the closed contacts 21′ and 23′.
According to an exemplary embodiment, an initial set dimension of approximately 30.5 mm (1.2 inches), shown as a distance 95 in
To unlock and rotate the bearing locknut 87 when performing an adjustment, any suitable tools may be used. In one embodiment, as illustrated in
Once the bearing locknut 87′ is unlocked, the adjustment member 77′ is rotated the appropriate number of revolutions to obtain the over-travel gap adjustment needed or desired. In the embodiment illustrated in
As noted above, in order to determine when over-travel gap adjustment is needed or beneficial, indicators such as those described in U.S. Pat. Nos. 5,095,293 and 6,002,560, for example, can be used to test spring compression (or tension) and determine whether it is adequate. Adequate spring compression is, in one respect, an indication of the contacts being in acceptable condition. This is because worn contacts that require a greater degree of travel by the moving stem in the embodiments described above, which means that the compression of the contact spring is diminished. With less compression, less energy is stored in the contact spring and hence, adequate force may not be obtained for opening and closing the contacts as desired.
Various modifications and alterations of the invention will become apparent to those skilled in the circuit breaker art without departing from the spirit and scope of the present invention, which is defined by the accompanying claims. For example, while reference is made throughout to over-travel gap adjustment in circuit breakers, the present invention is similarly applicable to adjustment of contact wipe portions of circuit breakers employing such mechanisms in the alternative, or in addition to over-travel gap mechanisms for similar purposes. Further, the invention is applicable not only to circuit breakers, but also to any other apparatus employing a circuit interrupter. As noted in the background, a wide variety of electrical distribution and protection equipment utilizes electrical circuit interrupters. Vacuum circuit interrupters are useful in, for example, contactors, motor starters, tap changers, distribution reclosers, metal-clad switchgear, and other equipment. The appended claims are to be construed accordingly. It should also be noted that steps recited in any method claims below do not necessarily need to be performed in the order that they are recited. Those of ordinary skill in the art will recognize variations in performing the steps from the order in which they are recited.
