Patent Publication Number: US-6335497-B1

Title: De-energized tap changer

Description:
FIELD OF THE INVENTION 
     This invention generally relates to de-energized tap changers used in power transformers. More particularly, the invention relates to a de-energized tap changer incorporating a self-aligning transmission system. 
     BACKGROUND OF THE INVENTION 
     Power transformers will typically utilize a de-energized tap changer, sometimes called a no-load tap changer, to make adjustments to the primary windings ratio. Such adjustments are necessary to compensate for long-term line voltage variations that depend on the physical distance of the transformer from the power source. This adjustment is initially made upon installation and further adjustments are usually only necessary a few more times over the life of the transformer based upon changes in the power system to which the transformer is connected. 
     Basically, a de-energized tap changer works by either increasing or decreasing the number of transformer windings utilized. Typically, the device will affect the number of windings on the primary side of the transformer, that is, the side of the transformer receiving power from the power source. Most de-energized tap changers are designed to operate around a five step switch. It is common practice to place the nominal system voltage as the middle step and split the remaining four steps into two groups of taps that will step up or step down the voltage usually by two and one-half percent for each step. This is the typical set-up as the American National Standards Institute recommends the utility supply a voltage that will not vary by more than five percent from the nominal system voltage. 
     A de-energized tap changer will typically include a series of fixed contacts, connected to the taps of the primary winding of the transformer, which are within the transformer tank and immersed in the transformer oil. A movable contact is driven between the contacts through a drive mechanism connected to a manually operated handle outside the tank of the transformer. Switching of tap positions is effected when there is no power being supplied to the transformer. 
     As mentioned, these changes are usually effected by a drive mechanism connected to a manually operated handle outside the tank of the transformer. The various positionings for each step, either up or down, will be marked on the outside of the tank such that the handle, and the contacts attached to it, can be properly aligned. As should be apparent, when the de-energized tap changer is installed it should be properly aligned such that with each position change of the handle on the outside of the tank, the proper corresponding positioning of the contacts is achieved on the interior of the tank. Thus, installation of a de-energized tap changer becomes a difficult task to undertake in light of having to align the contacts, as well as having to create a hole on the exterior of the tank whereby the handle of the de-energized tap changer may protrude. Currently, some de-energized tap changers utilize a universal joint to compensate for misalignment of the handle and the rest of the assembly. Such joints typically have a cross-shaped piece having pivots on its arms so arranged that each pair of pivots engage with the eyes of a yoke on the end of one shaft. While a universal joint may remedy some of the problems set forth above, they have a major drawback in that they can be very expensive. Therefore, a less complicated and less-expensive device is needed such that the degree of precision presently required upon installation may be lessened. 
     SUMMARY OF THE INVENTION 
     The tap changer of the present invention is designed to remedy the need for exact precision upon installing a de-energized tap changer and thus simplify the arduous task of installing the device. One presently preferred embodiment of the present invention achieves this goal by providing a de-energized tap changer which includes a contact rail assembly, a gear assembly, a handle assembly, and a transmission system which compensates for angular misalignment of the gear assembly and handle assembly. The transmission systems includes two elongated members which extend from the handle assembly and the gear assembly and are connected via an elongated hollow tube. 
     Other aspects of the present invention are described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of the invention will be apparent to those of ordinary skill in the art from the following detailed description of which: 
     FIG. 1 depicts a presently preferred embodiment of a de-energized tap changer in accordance with the present invention. The elongated tube of the transmission system is illustrated as transparent to give an improved perspective of the other aspects of the transmission system. 
     FIG. 2 depicts a cut-away view of a transformer tank with a de-energized tap changer installed on the top of a tank. Again, the elongated tube of the transmission system is illustrated as transparent. 
     FIG. 3 depicts a cut away view of a transformer tank with a de-energized tap changer installed on the side of a tank. Again, the elongated tube of the transmission system is illustrated as transparent. 
     FIG. 4 illustrates the coupling system of the transmission system of the present invention whereby the handle assembly is attached to the elongated tube via the elongated member with the attached block. Again, the elongated tube of the transmission system is illustrated as transparent. 
     FIG. 5 illustrates the coupling system of the transmission system of the present invention whereby the gear assembly is attached to the elongated tube via the elongated member with the attached block. Again, the elongated tube of the transmission system is illustrated as transparent. 
     FIG. 6 illustrates the transmission system of the de-energized tap changer of the present invention. Again, the elongated tube of the transmission system is illustrated as transparent. 
     FIG. 7 illustrates the de-energized tap changer of the present invention. The elongated tube of the transmission systems is illustrated as solid in this figure, as it would be with the preferred embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The de-energized tap changer  10  illustrated in FIG. 1 includes a contact rail assembly  15 , gear assembly  20 , transmission system  25 , handle assembly  30  and cantilever support  35 . The contact rail assembly  15  includes a series of fixed contacts  40  as well as movable contacts  45  which can be driven between the fixed contacts  40  by the gear assembly  20 . The gear assembly  20  is connected to the transmission system  25 , which in turn is connected to the handle assembly  30 . 
     The contact rail assembly  15  contains the fixed contacts. The rail can have any number of fixed contacts  40 . The rail as shown, and the preferred embodiment, has twenty four contacts and some embodiments of the present invention may have more and some may have less. 
     The driving gear  105  is part of the gear assembly  20  and drives the rack which contains the movable contacts  45  that bridge across any of six of the fixed contacts  45  at any designated position. The gear bracket  50  secures the contact rail  15  and the driving gear  105  and is attached to the suspension bracket  55 . 
     The transmission system  25  as shown in FIG. 1 is made up of a hollow tube  60  (shown transparent) and a first  65  and second  70  block attached to a first  75  and second  80  elongated member respectively. The first elongated member  75  is attached to the handle assembly  30  and the second elongated member  80  is attached to the gear assembly  20 . The two blocks  65  and  70  engage the tube  60  and deliver torque to the gear  105  to move the movable contacts  45 , while simultaneously allowing for angular misalignment of the first and second elongated members  75  and  80  extending from the handle assembly  30  and the gear assembly  20 . 
     The handle assembly  30  includes a mounting boss  85  which is attached on the interior portion of the transformer tank (not shown). The mounting boss  85  is used to secure the entire switch to the transformer tank wall via a nut  90  which attaches to the bottom of the mounting boss  85 . The entire tap changer  10 , except for the hand assembly  30 , can be pre-assembled before placement in the transformer tank, and the nut  90  can then secure the entire tap changer  10  to the tank. On the exterior of the tank, the handle  95  and indication plate  100  are then attached. 
     A cantilever support  35  is shown in FIG.  1 . The cantilever support  35  is a diagonally positioned strip running from the mounting boss  85  to the end of the contact rail assembly  15  furthest away from the gear assembly  20 . The preferred embodiment has a cantilever support  35  which is used to support the weight of the contact rail assembly  15 . 
     FIG. 2 illustrates a cut-away view of a transformer tank  110  with a de-energized tap changer  10  installed on the top of the tank  110 . It is also possible with the present invention, as illustrated in FIG. 3, to install the de-energized tap changer  10  on the side of the transformer tank  110 . FIGS. 2 and 3 illustrate the contact rail assembly  15  in connection with the taps of the primary winding  115  of the transformer inside the transformer tank  110 . The contact rail assembly  15  will typically be immersed in transformer oil (not shown). The preferred embodiments of the present invention include the de-energized tap changer  10  set forth in this application incorporated into a transformer tank  110 , as depicted in FIGS. 2 and 3. 
     FIG. 4 illustrates the coupling system of the transmission system  25  whereby the handle assembly  30  is attached to the elongated tube  60  via the first elongated member  75  with the attached first block  65 . The preferred embodiment of the first block  65  used in the present invention is a truncated square pyramid, that is, a pyramid with a square base and the upper portion of the pyramid removed such that a square face is formed that is parallel to the square base. Various blocks of other shapes may be used which, when attached to the elongated member, have either a proximal or distal face that is larger in area than the other. Other possible shapes include a pyramid and a pyramidal frustum where the base of such pyramid or frustum can be any polygon such as a rectangle, pentagon or hexagon. A frustum is the portion of a solid which lies between two parallel planes cutting the solid. Further embodiments of the present invention also include shapes similar to the frustum described but where the resulting planes are not parallel. The distal face described herein is the face of any of the blocks  65  and  70  which is furthest into the tube  60 , i.e., the face of the block that is on the opposite end of the elongated member to which the block is attached. With reference to the preferred shapes mentioned, the base can either be the proximal face or the distal face, with the opposite face, or the tip in the case of the pyramid, being the other. The first block  65  described herein may be positioned with either the larger face as the distal face or the smaller face as the distal face, but the preferred embodiment of the present invention has the larger face further into the tube  60  and is thus the distal face. Thus, an important characteristic of the blocks  65  and  70  is that they have a shape that permits some misalignment of the tube  60  and either elongated member  75  or  80 , while still transmitting torque from the handle  95  to the gear  105 . 
     FIG. 5 illustrates the coupling system of the transmission system  25  whereby the gear assembly  20  is attached to the elongated tube  60  via the second elongated member  80  with the attached second block  70 . As with the system described in FIG. 4, the preferred embodiment of the second block  70  used in the present invention is a truncated square pyramid, that is, a pyramid with a square base and the upper portion of the pyramid removed such that a square face is formed that is parallel to the square base. Various other shapes are possible for the blocks  65  and  70 , including the examples set forth above. The second block  70  described herein may be positioned with either the larger face as the distal face or the smaller face as the distal face, but the preferred embodiment of the present invention has the larger face further into the tube  60  and is thus the distal face. 
     FIG. 6 illustrates a complete view of the transmission system  25  of the present invention. The preferred embodiment of the present invention includes a hollow elongated tube  60 . It is further preferred that the hollow portion of the interior of the tube  60  have a shape similar to that of the larger of the proximal or distal faces of the first and second blocks  65  and  70  that are to be inserted into it. Preferably the larger of the proximal and distal faces of the first and second block  70  results in a snug fit when inserted into the hollow portion of the elongated tube  60 . A snug fit-will result in a contact plane that includes the cross-section of the tube  60  and the plane of the larger of the proximal and distal faces of the blocks  65  and  70 . A proper fit will result in proper operation of the de-energized tap changer  10  as discussed more fully below. 
     Transformer tanks can be constructed in a number of ways. Typically in a pad mounted transformer, the tank is mounted on a pad first and then the various other elements needed on the interior of the transformer are installed, including the de-energized tap changer. As previously mentioned, when installing the de-energized tap changer it is necessary to drill a hole either in the top or the side of the tank for the transmission system on the interior of the tank to connect to the handle on the exterior of the tank. In the prior art, the handle assembly then must be in proper alignment with the transmission system, which in turn must be in proper alignment with the gear assembly which has to drive the movable contacts which also have to be properly positioned. As should be evident in the prior art, installation becomes a difficult task. 
     A preferred embodiment of the present invention includes the de-energized tap changer  10  set forth above where the first and second elongated members  75  and  80 , attached to the first block  65  and second block  70  respectively, can be of various lengths. An elongated member which has an extended length obviates the need for exact precision on the length of the de-energized tap changer  10  from the handle assembly  30  to the gear assembly  20 . In other words, the de-energized tap changer  10  can be installed as one unit, and the contact rail and handle assemblies  15  and  30  can be properly positioned because the elongated member which will have room to move vertically (assuming the tap changer is top-mounted) inside the elongated tube  60 . The preferred embodiment of the present invention will have approximately five inches of vertical adjustment. Thus, the same de-energized tap changer  10  gives the installer a transmission system  25  of variable length and therefore eases the installation process. 
     The vertical movement in the hollow tube  60  remedies the problem of distance from the handle assembly  30  to the gear assembly  20 , but the problem of angular misalignment between those two assemblies also exists. The preferred embodiments of the present invention also allow for such angular misalignment between the handle assembly  30  and the gear assembly  20  upon installation. In other words, the handle assembly  30  and the gear assembly  20 , as well as the distal faces of the first and second blocks  65  and  70 , do not have to run on parallel planes with respect to each other. Instead, the angled sides of the blocks  65  and  70 , which result from unequal proximal and distal faces, allow the tube  60  to pivot in various directions and upon installation, can allow for the tube  60  to connect the first and second blocks  65  and  70  which may be somewhat misaligned. With the transmission system  25  then connecting the handle assembly  30  and the gear assembly  20  and installed in the de-energized tap changer  10 , rotational synchronization can be maintained among the entire transmission system  25 , as well as the handle assembly  30  and gear assembly  20  to which it is attached. Thus, the preferred embodiment of the de-energized tap changer  10  of the present invention will function by rotating the handle assembly  30  which transmits torque through the transmission system  25  to the gear assembly  20 , which in turn drives the gear wheel  105  which changes the position of the movable contacts  45  on the rail assembly  15 . With rotational synchronization maintained throughout the transmission system  25 , any misalignment of the handle assembly  30  or the gear assembly  20  will not present a serious difficulty as the elongated tube  60  can pivot along the first and second block  65  and  70  and render the whole apparatus functional. 
     A preferred embodiment of the present invention also includes a transformer tank  110  as illustrated in FIGS. 2 and 3. The preferred embodiments will contain a core, a primary winding, a secondary winding, a circuit power interrupter, and a de-energized tap changer  10 . Further preferred is a transformer tank  110  utilizing the de-energized tap changer  10 , and the preferred embodiments, as set out above. 
     The scope of protection of the following claims is not intended to be limited to the presently preferred embodiments disclosed herein. Those skilled in the art will readily appreciate that many modifications can be made to the preferred embodiments described herein.