ENERGY STORAGE APPARATUS FOR A LOAD TAP SELECTOR

Abstract: An energy storage apparatus for a load tap selector has a rotating input frame 13 which is concentrically disposed with respect to a rotating output frame 12 to which is connected an output shaft 13 which operates a load switching movable contact. The input frame and the output frame each have a pair of flanges 14-17 which extend in opposite radial directions and which overlap one another in the radial direction. An energy storage spring 4 which is disposed between the flanges has engaging members 18, 19 secured to opposite ends which are capable of releasably engaging with recesses formed in the flanges. When the input frame is rotated from a first position to a second position while the output frame is restrained in the first position. one end of the spring is restrained by engagement with the flanges on the output frame while the other end of the spring is moved together with the input frame by engagement with the flanges on the input frame. thereby stretching the spring and storing energy. When the restraint of the output frame is released, the energy which was stored in the spring is released and the output frame and the output shaft are rotated at a high speed to operate the load switching movable contact.

Description: This invention relates to an energy storage apparatus for a load tap selector, and particularly to a simple energy storage apparatus having improved drive performance. One example of a conventional energy storage apparatus for a load tap selector is illustrated in Figures 1 through 3. In this conventional apparatus, a rotating input frame 1 and a rotating output frame 2 are concentrically disposed about the center of an output shaft 3. The input frame 1 is able to rotate independently of the output frame 2 when a rotational drive force is applied to it by unillustrated drive means. The output frame 2 is secured to the output shaft 3 so that when the output frame 2 is rotated, the output shaft 3 will rotate therewith and transmit a drive force to an unillustrated load switching movable contact. At a number of locations between the input frame 1 and the output frame 2 are provided radially-extending energy storage springs 4. The outer end 5 of each spring 4 is rotatably secured to the input frame 1 in a manner such that the spring 4 can rotate in the plane of the input frame 1 without a bending moment being applied thereto, and the inner end 6 of each spring is rotatably secured to the outer periphery of the output frame 2 in a similar manner. In the state shown in Figure 1 in which the energy storage springs 4 are aligned along radii of the input frame 1, they are in a relaxed state, and no energy is stored therein. On-load tap changers of the above-described general type are manufactured by the Applicants and illustrated, for example, in JP-A-49-129825. The operation of this conventional energy storage apparatus is as follows. The output frame 2 is first restrained in the position shown in Figure 1 in which the springs 4 extend radially outwards. This will be referred to as a first position. The input frame 1 is then rotated by an angle A, as shown in Figure 2, and then restrained in this rotated position, which will be referred to as a second position. This rotation causes the energy storage springs 4 to stretch and store energy. An unillustrated drive angle control mechanism then releases the output frame 2 from the first position, and the torque exerted on it by the energy storage springs 4 causes it to rapidly rotate to the second position. as shown in Figure 3. The output shaft 3 is rotated together with the output frame 2, and the unillustrated load switching contact is operated. From the symmetry of the structure, it can be easily seen that the output shaft 3 can be rotated in the opposite direction from that shown in the figures if the input frame 1 is rotated clockwise instead of counterclockwise, and thus reversible operation is provided by this apparatus. The amount of energy which can be stored in each spring 4 is determined by the distance r of the inner end 6 of the spring 4 from the center of rotation of the input frame 1, the distance R of the outer end 5 of the spring 4 from this same center of rotation, the angle of rotation A of the input frame 1 with respect to the output frame 2, and the spring constant k of the spring 4. Given the values of these parameters. the extension of the spring 4 for a given angle of rotation A can be easily determined using the law of cosines. and once the extension is known the stored energy can be found. Taking a simple example, if R = 2r and A = 30 degrees. then the energy stored in the spring is given by the following equation: E=k/2 x 0.057r² = 0.029kr² (1) This conventional energy storage apparatus has the drawback that a large amount of energy, as expressed by Equation (1), can not be stored in the springs 4 with a typical angle of rotation A unless the dimensions of the apparatus (in particular, the magnitude of r) are increased or unless the number of energy storage springs 4 is increased, in which case the apparatus becomes undesirably large or complicated. US-A-3213214 discloses a drive mechanism for an on-load tap changer, in which a pair of springs extend transversely between a main drive lever and respective secondary drive levers. To provide symmetrical rotation in both directions, a relatively complex and space-consuming structure comprising three levers and two springs is necessary. US-A-3153188 also requires the use of a pair of separate springs to provide symmetrical movement in both directions. SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-described drawbacks and to provide an energy storage apparatus for a load tap selector which has a much greater energy storage capacity than a conventional energy storage apparatus of the same size, has a very simple structure, and can provide symmetrical rotation employing a smaller number of energy storage springs than a conventional energy storage apparatus while storing a larger amount of energy. An energy storage apparatus for a load tap selector according to the present invention comprises a rotatable output member connected to a load switching movable contact for operating the said contact when the output member rotates, a rotatable input member rotatable relative to and coaxially with respect to the output member in a plane parallel to the plane of rotation of the output member, an energy storage spring disposed in a plane substantially parallel to the said planes of rotation and acting between the input and output members, which spring extends generally transversely to a radius extending from the axis of rotation to the spring, and means for restraining one end of said energy storage spring when said output member is restrained by a restraining mechanism and for moving the other end of said energy storage spring with said input member in the direction of rotation of said input member when said input member is rotated while maintaining the ends of said spring at a constant distance from the centre of rotation of said input member whereby energy is stored in said spring, characterised in that first restraining means are disposed symmetrically on the output member for selectively restraining a first or a second end of the spring, and second restraining means are disposed symmetrically on the input member for selectively restraining the second or first end of the spring, the ends of the spring being transferable between the first and second restraining means, whereby the spring and restraining means operate to urge the output member in the same direction as the input member in both directions of rotation. In a preferred embodiment, an input frame and an output frame each have a pair of flanges which extend in opposite radial directions and which overlap one another in the radial direction. An energy storage spring which is disposed between the flanges has engaging members secured to opposite ends which are capable of releasably engaging with recesses formed in the flanges. When the input frame is rotated from a first position to a second position while the output frame is restrained in the first position, one end of the spring is restrained by engagement with the flanges on the output frame while the other end of the spring is moved together with the input frame by engagement with the flanges on the input frame, thereby stretching the spring and storing energy. When the restraint of the output frame is released, the energy which was stored in the spring is released and the output frame is rotated at a high speed. Because the ends of the energy storage spring are maintained at the same distance from the center of rotation of the input frame, the energy which can be stored in the spring for a given angle of rotation is much larger than the amount which can be stored in a conventional apparatus of the same size in which each energy storage spring is radially disposed. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front view of a conventional energy storage apparatus for a load tap selector in an initial state prior to energy storage. Figure 2 is a front view of the energy storage apparatus of Figure 1 in the state in which energy is stored in the springs. Figure 3 is a front view of the energy storage apparatus of Figure 1 showing the state after the stored energy has been released. Figure 4 is a front view of an embodiment of an energy storage apparatus for a load tap selector according to the present invention in an initial state prior to storing energy in the spring 4. Figure 5 is a cross-sectional view taken along Line V-V of Figure 4. Figure 6 is a front view of the embodiment of Figure 4 showing the state in which energy is stored in the spring 4. Figure 7 is a front view of the embodiment of Figure 4 showing the state after the stored energy has been released. Figure 8 is a cross-sectional view taken along Line VIII-VIII of Figure 4. Figure 9 is a cross-sectional view taken along Line IX-IX of Figure 6. Figure 10 is a cross-sectional view taken along Line X-X of Figure 7. In the drawings, the same reference numerals indicate the same or corresponding parts. DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinbelow, an embodiment of the present invention will be described while referring to Figures 4 through 10 of the accompanying drawings. As shown in Figure 4, in this embodiment a rotating input frame 11 and a rotating output frame 12 are concentrically disposed with respect to a rotating output shaft 13. The input frame 11 is rotatably supported by the output shaft 13 so as to be able to freely rotate about the center of the output shaft 13, and the output frame 12 is secured to the output shaft 13 so that when the output frame 12 is rotated, the output shaft 13 will rotate with it. The output shaft 13 is connected to an unillustrated load switching movable contact which is operated by its rotation. As best shown in Figure 5, which is a cross-sectional view taken along Line V-V of Figure 4, the input frame 11 has two parallel plate-shaped flanges 14 and 15 formed thereon which extend radially inwards towards the output shaft 13. Similarly. the output frame 12 has two parallel plate-shaped flanges 16 and 17 formed thereon which extend radially outwards from the output shaft 13 and which overlap the flanges 14 and 15 of the input frame 11 in the radial direction. The widths of all four flanges (the distance from the left sides to the right sides of the flanges as seen in Figure 4) are identical. In this embodiment, the two flanges 16 and 17 of the output frame 12 are located on the outside of the flanges 14 and 15 of the input frame 11, but the opposite arrangement is possible with flanges 16 and 17 located between flanges 14 and 15. In the left end of each of the flanges 14, 15, 16, and 17 is formed an arcuate seat indicated by reference numerals 14, 15a, 16a, and 17a, respectively, which opens onto the end surface of the member. In the right ends of the flanges, identical arcuate seats 14b, 15b, 16b, and 17b, respectively, are formed which open onto the end surfaces at the opposite ends of the flanges. The distance between the two holes in a given flange is the same for each of the four flanges 14, 15, 16, and 17. The four seats 14a, 15a, 16a, and 17a at the left ends of the flanges are for the purpose of engaging with a first engaging member 18, and the other four seats 14b, 15b, 16b, and 17b at the right ends of the flanges are for the purpose of engaging with a second engaging member 19. The first engaging member 18 comprises two coaxial, cylindrical flange engaging portions 18b and 18f having a shape complementary to the shapes of the seats in the left ends of the flanges, with which they engage. On the outside ends of the flange engaging portions 18b and 18f are formed two outside collars 18a and 18g, respectively, and on the inside ends of the flange engaging portions 18b and 18f are formed two inner collars 18c and 18e, respectively. These collars are coaxial with respect to the flange engaging portions 18b and 18f but have a larger diameter than the flange engaging portions 18b and 18f so as to prevent the movement of engaging member 18 in its axial direction. Between the inner collars 18c and 18e is secured an eccentric cylindrical portion 18d having a diameter larger than that of the inner collars 18c and 18e. The eccentric cylindrical portion 18d is disposed so that at least one part of its outer periphery is closer to the axial center of the inner collars 18c and 18e than are the outer peripheries of the inner collars 18c and 18e. In this manner, a recess 18h is formed between the two inner collars 18c and 18e. The second engaging member 19 is identical in shape to the first engaging member 18, comprising outer collars 19a and 19g. cylindrical flange engaging portions 19b and 19f, inner collars 19c and 19e, and an eccentric cylindrical portion 19d which is displaced with respect to the axial centers of the inner collars 19c and 19e so that a recess 19h is formed therebetween. The above-described seats 14a - 17a and 14b - 17b in the flanges 14 - 17 which engage with the flange engaging portions of the engaging members 18 and 19 are disposed such that when the engaging members 18 and 19 engage with any of the seats, the axial centers of the engaging members 18 and 19 will be equally distant from the center of rotation of the output shaft 13 by a distance Ra. In addition, the seats are shaped such that they can easily disengage from the engaging portions when the engaging members 18 and 19 are rotated away from the seats about the center of the input frame 11. An energy storage spring 4 is disposed in a space between the flanges 14 and 15 of the input frame 11, the space being large enough so as not to obstruct the extension of the spring 4. The ends of the energy storage spring 4 are connected to the first engaging member 18 and the second engaging member 19 by connecting plates 20 and 21, respectively. Connecting plate 20 has an oval through hole 20a formed in its center, the through hole 20a being larger than eccentric cylindrical portion 18d but the end portions of the through hole 20a having a radius of curvature which is identical to the radius of the eccentric cylindrical portion 18d. The connecting plate 20 fits over the eccentrical cylindrical portion 18d inside recess 18h with the surface of its through hole 20a contacting eccentric cylindrical portion 18d. The radius of curvature of the end portions of through hole 20a is chosen to be the same as the radius of eccentric cylindrical portion 18d so as to reduce the maxiumum compressive stress acting on the surface of through hole 20a when it is being pressed against eccentric cylindrical portion 18d. Similarly, connecting plate 21 has an oval through hole 21a formed in its center which is larger than eccentric cylindrical portion 19d and whose end portions have a radius of curvature which is the same as the radius of eccentric cylindrical portion 19d. The opposite ends of the spring 4 are connected to the ends of the connecting plates 20 and 21, respectively. The flanges 14 - 17 and the engaging members 18 and 19 together consitute means for restraining one end of the energy storage spring 4 on the output frame 12 and moving the other end of the spring 4 with the input frame 11 when the input frame is rotated, thereby stretching the spring 4 and storing energy in it. The operation of this embodiment is as follows. Figure 4 and Figure 8 illustrate the embodiment when the input frame 11 and the output frame 12 are in a first position in which no energy is stored in the energy storage spring 4. An unillustrated restraining mechanism restrains the output frame 12 in the illustrated first position, and an unillustrated drive mechanism rotates the input frame 11 in the counterclockwise direction by an angle A to a second position, as shown in Figure 6. When the input frame 11 is so rotated, the seats 14b and 15b which engage with the flange engaging portions 19b and 19f, respectively, of the second engaging member 19 force the second engaging member 19 to move together with the input frame 11, and the second engaging member 19 is rotated clockwise about the center of the output shaft 13 and away from the first engaging member 18. The seats 16b and 17b in the right ends of flanges 16 and 17, respectively are shaped such that when the engaging member 19 is rotated about the center of the output shaft 13, the flange engaging portions 19b and 19f can easily disengage from the seats 16b and 17b, respectively. Similarly. the seats 14a and 15a in the left ends of flanges 14 and 15, respectively, can easily disengage from the flange engaging portions 18b and 18f of the first engaging member 18. When the second engaging member 19 is rotated away from the first engaging member 18 by the rotation of the input member 11, a force is exerted on the first engaging member 18 through the energy storage spring 4 which tries to make it follow the movement of the second engaging member 19. However, as the flange engaging portions 18b and 18f are engaged with seats 16a and 17a of the flanges 16 and 17 of the output frame 12, and as the output frame 12 is restrained from rotating by the restraining mechanism, the first engaging member 18 remains stationary in the first position. As a result, the rotation of the second engaging member 19 stretches the energy storage spring 4 by an amount D as shown in Figure 9, and energy is stored in the spring 4. When the input frame 11 has reached the second position, an unillustrated rotational angle control mechanism causes the restraining mechanism to release the restraint of the output frame 12. When the restraint is released, the first engaging member 18 is drawn towards the second engaging member 19 by the tensile force of the energy storage spring 4, the engagement between the first engaging member 18 and the flanges 16 and 17 of the output frame 12 produces a torque on the output frame 12, and the output frame 12 is rapidly rotated clockwise towards the second position, as shown in Figures 7 and 10. The rapid rotation of the output frame 12 causes the output shaft 13 to which it is secured to rapidly rotate and operate the unillustrated load switching movable contact. When the output frame 12 reaches the second position, seats 14a and 15a once again engage with engaging portions 18b and 18f of the first engaging member 18, and seats 16b and 17b again engage with the engaging portions 19b and 19f of the second engaging member 19. Due to the symmetry of the structure, rotation of the output shaft 13 in the clockwise direction can be performed by the same series of operations described above except that the input frame 11 is rotated in the clockwise direction. The energy stored in the spring 4 by rotation of the input frame 11 can be found given the angle of rotation A, the initial separation L between the centers of the engaging members 18 and 19, the distance Ra of the centers of the engaging member 18 and 19 from the center of the output shaft 13, and the spring constant k of the energy storage spring 4. For example, if Ra = 1.3r (wherein r has the same value as in Figure 2), L = r x √2, and A = 30 degrees, then the stored energy E is expressed by the following equation: E = k/2 x 0.277r² = 0.139kr² (2) It can be seen that if k has the same value as for the conventional apparatus illustrated in Figure 1, the stored energy is about 5 times as large as the amount expressed by Equation (1) for the same angle of rotation A. Accordingly, an energy storage apparatus according to the present invention is able to store more energy than the conventional apparatus of Figure 1 with a decrease in size while employing only 1/4 as many energy storage springs 4.

Claims: An energy storage apparatus for a load tap selector comprising a rotatable output member (12) connected to a load switching movable contact for operating the said contact when the output member (12) rotates, a rotatable input member (11) rotatable relative to and coaxially with respect to the output member (12) in a plane parallel to the plane of rotation of the output member (12), an energy storage spring (4) disposed in a plane substantially parallel to the said planes of rotation and acting between the input and output members (11, 12), which spring (4) extends generally transversely to a radius extending from the axis (13) of rotation to the spring (4), and means (14 - 17) for restraining one end of said energy storage spring (4) when said output member (12) is restrained by a restraining mechanism and for moving the other end of said energy storage spring (4) with said input member (11) (11) in the direction of rotation of said input member (11) when said input member (11) is rotated while maintaining the ends of said spring (4) at a constant distance from the centre (13) of rotation of said input member (11) whereby energy is stored in said spring (4), characterised in that first restraining means (16, 17) are disposed symmetrically on the output member (12) for selectively restraining a first or a second end of the spring (4), and second restraining means (14, 15) are disposed symmetrically on the input member (11) for selectively restraining the second or first end of the spring (4), the ends of the spring (4) being transferable between the first and second restraining means (14-17), whereby the spring (4) and restraining means (14-17) operate to urge the output member (12) in the same direction as the input member (11) in both directions of rotation. An energy storage apparatus as claimed in Claim 1, wherein said means for restraining comprises; a first pair of flanges (16, 17) which extend radially outwards from the axis (13) of rotation and a second pair of flanges (14, 15) which extend radially inwards towards the rotational axis (13), one of said pairs of flanges being secured to said input member (11) so as to rotate therewith and the other pair being secured to said output member (12) so as to rotate therewith, said first and second pair of flanges overlapping in the radial direction with both flanges of one of said pairs of flanges (14, 15) being disposed between the flanges of said other pair of flanges (16, 17) with a space between said first and second pairs, there being a gap between the inner pair of said pairs which accommodates said energy storage spring, each of said flanges having end surfaces formed on its opposite ends which face in the directions of rotation of said input member (11) and in each of which is formed a seat (14a - 17a, 14b - 17b) which opens onto said end surface, each of said seats being equidistant from the rotational centre of said input member, the distance between the seats in opposite ends of each flange being the same for all of said flanges; and a first engaging member (18) and a second engaging member (19) are connected to opposite ends of said energy storage spring and are disposed at opposite ends of said flanges and extend perpendicular to the plane of rotation of said input member, each of said engaging members having engaging portions which can releasably engage with said seats in said flanges. An energy storage apparatus as claimed in Claim 2, wherein said first (18) and second (19) engaging members are generally cylindrical members each comprising; two of said engaging portions (18b, 18f; 19b, 19f); and two outer collars (18a, g; 19a, g) formed on its ends outside the said engaging portions and two inner collars (18c, 18e; 19c, 19e) formed inside said engaging portions with respect to the lengthwise centres of said engaging members, each of said collars having a larger diameter than said engaging portions, said outer collars being disposed outside the outer pair of said flanges and said inner collars being disposed inside the inner pair of said flanges with respect to the lengthwise centres of said engaging members when said engaging portions engage with any of said seats in said flanges. An energy storage apparatus as claimed in Claim 3 further comprising; an eccentric cylindrical portion (18d, 19d) which is formed in each of said engaging members between said inner collars and which is eccentric with respect to said inner collars so that a recess (18h, 19h) is formed between said inner collars of each of said engaging members; and a first and a second connecting plate (20, 21) secured to opposite ends of said energy storage spring, each of said connecting plates having a through hole formed therein which is larger than said eccentric cylindrical portions but whose radius of curvature for a portion of its circumference is the same as the radius of each of said eccentric cylindrical portions, said first and second connecting plates being disposed in the recesses of said first and second engaging members, respectively, with said through holes surrounding said eccentric cylindrical portions and with the portions of the surfaces of said through holes having the same radius of curvature as said eccentric cylindrical portions contacting said eccentric cylindrical portions of said first and second engaging members, respectively.

Inventors: IMAI, MICHIO ITAMI WORKS MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: H01H19
IPC codes: H01F29, H01H9, H01H19