Buffering device for the operating mechanism of a switchgear, and method of lubrication thereof

Abstract

A piston rod (15) and a first piston (13) are arranged in the interior of an external cylinder (11) and internal cylinder (12); a second piston for absorbing the change of volume of operating fluid (24) is also arranged therein. Also, a first return spring (18) for returning the piston rod (15) to the interruption position is provided and a second return spring (20) for returning the operating fluid 24 into the high-pressure chamber (25) by pressurizing the second piston (14) is provided. In addition, the air in the interior of the buffering device (10) is withdrawn by a vacuum pump (38), and operating fluid (24) is thus introduced in a degassed condition.

Claims

1. A method of lubrication of a buffering device of a movable electrical contact in an operating mechanism of a switchgear, the buffering device comprising an outer cylinder, and an internal cylinder provided in the outer cylinder and at least partially defining a pressure chamber for an operating fluid, the method comprising steps of: arranging a lubricating plug at an end of an internal cylinder of said buffering device, a tip of said lubricating plug having a packing to seal the pressure chamber of the internal cylinder of said buffering device; providing a flow path in an interior of said lubricating plug, said lubricating plug being connected with a conduit that bifurcates into two branches; connecting one of said conduit branches with a vacuum pump; connecting another of said conduit branches with a container of the operating fluid; arranging a first valve on said one of said conduit branches; arranging a second valve on said another of said conduit branches; closing said second valve while opening said first valve and operating said vacuum pump, to put the pressure chamber into a vacuum condition; thereafter closing said first valve and opening said second valve, to introduce the operating fluid in said container into the pressure chamber and thereby lubricate the buffering device; and thereafter replacing said lubricating plug sealing the pressure chamber with another plug that seals the pressure chamber, wherein the another plug is coupled for movement with the movable contact.

2. The method according to claim 1, wherein a piston is inserted in the outer cylinder and includes a piston head external to the outer cylinder and provided at an end of the outer cylinder opposite said lubricating plug; a tip of said lubricating plug is provided with cutaway sections, further comprising a step of inserting a plate between said piston head and said end of said outer cylinder in order to expand said pressure chamber, wherein said step of introducing the operating fluid into the pressure chamber is performed after the expansion of the pressure chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view showing the closure condition of a buffering device for the operating mechanism of a switchgear according to a first embodiment of the present invention;

(2) FIG. 2 is a cross-sectional view showing the interruption condition of the buffering device of FIG. 1;

(3) FIG. 3 is a view of the buffering device of FIG. 2 in the direction of the arrows A-A;

(4) FIG. 4 is a detail view to a larger scale showing a portion of the buffering device of FIG. 2;

(5) FIG. 5 is a cross-sectional view showing the closure condition of a buffering device for the operating mechanism of a switchgear according to a second embodiment of the present invention;

(6) FIG. 6 is a cross-sectional view showing the closure condition of a buffering device for the operating mechanism of a switchgear according to a third embodiment of the present invention;

(7) FIG. 7 is a cross-sectional view showing the interruption condition of the buffering device of FIG. 6;

(8) FIG. 8 is a cross-sectional view showing a method of lubrication of a buffering device for the operating mechanism of a switchgear according to a fourth embodiment of the present invention;

(9) FIG. 9 is a cross-sectional view showing a method of lubrication of a buffering device for the operating mechanism of the switchgear according to a fifth embodiment of the present invention.

EMBODIMENTS OF THE INVENTION

(10) Embodiments of a buffering device for the operating mechanism of the switchgear according to the present invention and a method of lubrication thereof are described below with reference to the drawings.

[1] First Embodiment

Construction

(11) First of all, a first embodiment of a buffering device for the operating mechanism of the switchgear according to the present invention will be described with reference to FIG. 1 to FIG. 4. FIG. 1 is a cross-sectional view showing the closure condition of a buffering device 10 for the operating mechanism of a switchgear; FIG. 2 is a cross-sectional view showing the interruption condition of the buffering device 10 shown in FIG. 1. FIG. 3 is a view of the buffering device of FIG. 2 in the direction of the arrows A-A. FIG. 4 is a detail view to a larger scale showing a portion of the buffering device of FIG. 2.

(12) The buffering device 10 serves to reduce the speed of the movable contact 1 constituting the moving body in the operating mechanism of the switchgear. Operating fluid 24 is sealed in the interior of the buffering device 10: braking force is generated by compression of the operating fluid 24 immediately before arrival at the terminal position of movement of the movable contact 1.

(13) As shown in FIG. 1 and FIG. 2, a support structural body 6 is provided in the operating mechanism of the switchgear. An interruption spring 2 is accommodated in the interior of the support structural body 6 and a restraining plate 7 is fixed at the end thereof. An interruption spring seat 4 is mounted at the movable end 3 of the interruption spring 2, facing the aforementioned restraining plate 7. Also, a spring rod 5 is coupled with the movable contact 1 through a linkage section 8: the buffering device 10 is provided so as to be clamped by this spring rod 5 and interruption spring seat 4.

(14) The buffering device 10 comprises: double-layer cylinders 11, 12 and double-layer pistons 13, 14 having the same central axis; a unitary piston rod 15, two packings 16, 22, two return springs 18, 20, the spring seats 17, 19 of these return springs, and a plug 23.

(15) The construction of the buffering device 10 referred to above will now be described in detail. One end of the external cylinder 11 is fixed to the interruption spring seat 4 and this external cylinder 11 extends towards the spring rod 5. The internal cylinder 12 is telescopically fitted in the interior of this external cylinder 11.

(16) The first piston 13 is arranged on the inside of the internal cylinder 12 and the second piston 14 is freely slidably arranged on the inside of the external cylinder 11, respectively. In the closure condition shown in FIG. 1, the second piston 14 is stationary in a condition making contact with the end of the internal cylinder 12, and the first piston 13 is stationary in a condition contacting the second piston 14.

(17) Also, the first piston 13 and second piston 14 are adjacent to each other in the closure condition as shown in FIG. 1, but, in the interruption condition, are slid in the direction such as to separate these, as shown in FIG. 2. Specifically, when the movable contact 1 moves from the closure condition to the interruption condition (from the condition of FIG. 1 to the condition of FIG. 2), the first piston 13 moves to the right-hand side in the Figure and the second piston 14 moves to the left-hand side in the Figure.

(18) The piston rod 15 is arranged so as to be freely slidable with respect to the first piston 13 and the second piston 14. The packings 16 are provided in the second piston 14 at the sliding portion of the external cylinder 11 and the piston rod 15. Also, a piston head 15b is provided at the end (left-hand side end in FIG. 1 and FIG. 2), nearest to the restraining plate 7, on the piston rod 15. This piston head 15b comprises a circular convex surface section 15c having a gently convex surface facing the restraining plate 7, and a flat surface 15d facing the side of the interruption spring seat 4.

(19) The circular convex surface section 15c of the piston head 15b is capable of being moved into contact with or away from the restraining plate 7 and its diameter is set to be less than the diameter of the piston rod 15. Also, in the piston head 15b, the flat surface 15d that is positioned on the opposite side to the circular convex surface section 15c is engaged with the end of the external cylinder 11 that is fixed to the interruption spring seat 4 in such a way that it can be freely separated therefrom.

(20) In the closed condition shown in FIG. 1, the circular convex surface section 15c of the piston head 15b is separated from the restraining plate 7 and the flat surface 15d on the opposite side is separated from the end of the external cylinder 11. From this closed condition, in the interruption condition shown in FIG. 2, the circular convex surface section 15c of the piston head 15b contacts the restraining plate 7 and, furthermore, the flat surface 15d of the piston head 15b and the end of the external cylinder 11 are in contact and stationary.

(21) In addition, a first return spring seat 17 that restricts the range of movement of the first piston 13 is fitted at the end (right-hand side end in FIG. 1 and FIG. 2) on the opposite side of the piston head 15b, on the piston rod 15. Also, between the piston rod 15 and the first return spring seat 17, this one end is formed with an oil return path 15a that is opened and closed by sliding action of the first piston 13. Furthermore, a first return spring 18 is arranged between the first return spring seat 17 and the end of the internal cylinder 12. The first return spring 18 has the function of returning the piston rod 15 to the interruption position.

(22) A second return spring seat 19 with the same central axis is fitted on the inside of the external cylinder 11. A second return spring 20 is arranged between the second return spring seat 19 and the second piston 14. Due to the combination of this second return spring 20 and the second piston 14 referred to above, change in volume of the operating fluid 24 in the high-pressure chamber 25 can be absorbed.

(23) A plurality of through-holes 21 are formed in the internal cylinder 12. In addition, a plug 23 is arranged at the end of the internal cylinder 12, a packing 22 being fixed to this plug 23. Also, the plug 23 is fitted onto a threaded section 5a that is formed at the end of the spring rod 5. The space defined by the external cylinder 11, the internal cylinder 12, the plug 23, the second piston 14 and piston rod 15 constitutes a high-pressure chamber 25: the operating fluid 24 is sealed therein.

(24) Also, between the second piston 14 and a second return spring seat 19, a collar 26 having the same central axis as the piston rod 15 is freely slidably arranged with respect to the piston rod 15. This collar 26 is a member for restricting the height of compression of the second return spring 20.

(25) When the operating fluid 24 in the high-pressure chamber 25 is compressed by the action of the first piston 13, the space into which the operating fluid 24 is injected from the through-hole 21 constitutes a low-pressure chamber 27. Also, as shown in FIG. 2, in the interruption condition, the first piston 13 and the second piston 14 are separated and a liquid chamber 28 is formed constituting the space defined by these pistons 13, 14 and the piston rod 15.

(26) The operating fluid 24 that has flowed out from the through-holes 21 into the low-pressure chamber 27 flows in from the low-pressure chamber 27 to the liquid chamber 28. Cutaway sections 12a and projections 12b to obstruct the flow of the operating fluid 24 are then arranged at the end of the internal cylinder 12; the projections 12b are arranged in substantially the same plane as the through-holes 21 (see FIG. 3).

(27) Incidentally, while, as shown in FIG. 4, the packings 16 are provided at the sliding portion of the external cylinder 11 and the piston rod 15 in the second piston 14, in more detail, these packings are fixed at two respective locations at the outer circumference and inner circumference of the second piston 14. An outer circumferential groove 14a is formed between the two packings 16 on the outer circumferential side and an inner circumferential groove 14b is formed between the two packings 16 on the inner circumferential side. Also, a plurality of through-holes 14c that link these two are arranged between the outer circumferential groove 14a and the inner circumferential groove 14b. A space for accumulation of operating fluid 24 is formed by means of the outer circumferential groove 14a, inner circumferential groove 14b and through-holes 14c.

(28) (Interruption Action)

(29) The interruption action, from the closed condition shown in FIG. 1 to the interrupted condition shown in FIG. 2 in the first embodiment constructed in this way will now be described. When an interruption instruction is delivered to the operating mechanism of the switchgear, not shown, from a control device, not shown, the interruption spring 2 starts the interruption action. When the interruption spring 2 has extended by a certain fixed distance, the circular convex surface section 15c of the piston head 15b abuts the restraining plate 7.

(30) From this instant, the piston head 15b and the piston rod 15 start movement towards the side of the spring rod 5. The first piston 13 blocks one end of the oil return path 15a of the piston rod 15 and starts compression of the operating fluid 24 in the high-pressure chamber 25. The first piston 13 blocks a plurality of through-holes 21 but forces the operating fluid 24 in the high-pressure chamber 25 out towards the low-pressure chamber 27 through the open through-holes 21. In this process, the pressure generated in the high-pressure chamber 25 provides braking force, which is transmitted between the piston rod 15 and the spring rod 5, providing a force which halts the action of the interruption spring 2.

(31) The flow of operating fluid 24 flowing into the low-pressure chamber 27 is temporarily held up by the projections 12b that are arranged in substantially the same plane as the through-holes 21, but the operating fluid flows out into the liquid chamber 28 from the portions where the projections 12b are absent i.e. the cutaway portions 12a. The first return spring 18 is compressed with movement of the piston rod 15 and the first return spring seat 17.

(32) The volume of the operating fluid 24 that has flowed into the liquid chamber 28 increases with movement of the second piston 14 towards the piston head 15b. The second piston 14 is subjected to pressure by the spring force of the second return spring 20 as it moves towards the second return spring seat 19, until it is arrested, having undergone a fixed displacement, by the collar 26. FIG. 2 shows the condition in which this interruption action has been completed.

(33) (Closure Action)

(34) Next, the closure action from the interruption condition shown in FIG. 2 to the closure condition shown in FIG. 1 will be described. When an interruption instruction is delivered to the operating mechanism of the switchgear, not shown, from a control device, not shown, the interruption spring 2 starts the interruption action, by means of a closure spring, not shown. In the case of the closure action, the interruption spring 2 starts movement in the opposite direction (closure direction) to the interruption direction, and movement of the spring rod 5, which is linked with the interruption spring 2, the external cylinder 11 and the internal cylinder 12 in the closure direction is commenced.

(35) At this point, since the piston rod 15 is slidable with respect to the external cylinder 11 and internal cylinder 12, it tries to stay in the interruption position. Since the second piston 14 starts movement together with the external cylinder 11, the operating fluid 24 in the liquid chamber 28 is compressed, the first piston 13 moves in the direction of the first return spring seat 17, the oil return path 15a is opened, and a flow path to the liquid chamber 28 and high-pressure chamber 25 is formed.

(36) With further progress of the closure action, the piston rod 15 is forced out towards the restraining plate 7 by the spring force of the first return spring 18 and the operating fluid 24 that is pressurized by the second piston 14 and the second return spring 20 flows into the high-pressure chamber 25 through the oil return path 15a, low-pressure chamber 27 and the plurality of through-holes 21. When the closure action terminates, the second piston 14 is arrested in a position contacting the end of the internal cylinder 12, and the first piston 13 is arrested in a position contacting the second piston 14. The completion condition of the closure condition as described above is shown in FIG. 1.

(37) (Beneficial Effects)

(38) The beneficial effects of the first embodiment described above are as follows. Specifically, in the first embodiment, the piston rod 15 that projects to the atmosphere side is in a single location. Consequently, the cross-sectional area of the first piston 13 can be made large.

(39) Also, there is no need to provide packing for sealing while sliding in the high-pressure chamber 25 that is compressed by the first piston 13. Consequently, the operating fluid 24 that is sealed into the high-pressure chamber 25 can be kept in a high-pressure condition. In this way, a large braking force can be generated with a small-diameter first piston 13 and internal cylinder 12, making it possible to reduce the size and weight of the device.

(40) Furthermore, during braking by the buffering device 10, the operating fluid 24 is reduced in pressure by passing through the through-holes 21 from the internal cylinder 12 and flows out through the cutaway sections 12a constituted by the gaps of the projections 12b from the low-pressure chamber 27 to the liquid chamber 28, and the pressure of the operating fluid 24 is thereby further lowered.

(41) As a result, there is no possibility of the packings 16 that are provided in the sliding portion of the external cylinder 11 and the piston rod 15 being subjected to the action of operating fluid 24 in high-pressure condition. In this way, inconveniences such as leakage of oil can be reduced, and use of expensive sealing members made unnecessary, thereby achieving cost reduction.

(42) Also, in the first embodiment, the second piston 14 and the second return spring 20 perform the function of adjusting for the change of volume of the operating fluid 24 within the buffering device 10. Consequently, it is unnecessary to provide an air layer on the operating fluid 24 within the buffering device 10. In this way, admixture of air with the operating fluid 24 is minimized and considerable stabilization of the braking force of the buffering device 10 can be achieved.

(43) Furthermore, thermal expansion of the operating fluid 24 due to temperature change can be absorbed by the second piston 14 and the second return spring 20. Consequently, leakage of oil from the interior of the buffering device 10 and/or penetration of the air from the outside can be prevented, considerably increasing the reliability in regard to leakage of the operating fluid 24.

(44) Also, as shown in FIG. 4, an external circumferential groove 14a and internal circumferential groove 14b are formed and through-holes 14c are arranged between the two packings 16 in the second piston 14, while a storage space for the operating fluid 24 is formed from the space between these. Consequently, even if traces of operating fluid 24 are scraped out by the piston rod 15, this operating fluid 24 can be accumulated in the aforementioned accumulation space between the two packings 16. It is thereby possible to prevent the operating fluid 24 from being put into a high-pressure condition and leaking to the outside, and entrainment of air from outside the buffering device 10 can be minimized.

(45) Also, when the switchgear is a circuit breaker and high-speed re-closure and interruption action is performed in which a second interruption action is implemented in a short time (within 0.3 sec), the first piston 13 and the piston rod 15 must be returned to their prescribed positions. In the first embodiment, the first piston 13 and the piston rod 15 are moved by the action of the first return spring 18. Also, the pressurized operating fluid 24 in the liquid chamber 28 can be returned from the oil return path 15a of the piston rod 15 and the through-holes 21 into the high-pressure chamber 25 by the second return spring 20 and the second piston 14. In this way, the first piston 13 and the piston rod 15 can be rapidly returned to their original positions.

(46) Also, the second piston 14 is forced onto the second return spring 19 by the pressure of the operating fluid 24 flowing into the liquid chamber 28 from the low-pressure chamber 27, with the result that the second return spring 20 is compressed. If the pressure at this point is larger than the force of the second return spring 20, there is a possibility that the second return spring 20 may get stuck. If the second return spring 20 gets stuck, damage occurs between the bare wires, with the risk that the durability of the spring itself may be lowered. Accordingly, in the first embodiment, generation of this inconvenience is prevented by providing a collar 26 that restricts the height of the compression of the second return spring 20.

(47) Furthermore, as shown also in FIG. 7, by making the diameter of the circular convex surface section 15c (i.e. the diameter of the circular section that makes planar contact with the spring rod 5 on the side of the opposite face) of the piston head 15b less than the diameter of the piston rod 15, it is possible to keep the bending force acting on the piston rod 15 small while employing a large contact area, when the piston head 15b collides with the restraining plate 7. In this way, mechanical strength and reliability of the piston rod 15 can be improved.

(48) Incidentally the reason for referring to FIG. 7, which is described later, is that it might not be altogether easy to identify what is meant by the diameter of the circular convex surface section 15c in FIG. 1.

[2] Second Embodiment

Construction

(49) Next, a second embodiment of a buffering device for the operating mechanism of a switchgear according to the present invention will be described with reference to FIG. 5. FIG. 5 is a cross-sectional view showing the closed condition of the second embodiment of a buffering device for the operating mechanism of a switchgear. It should be noted that parts that are identical with or similar to corresponding parts in the first embodiment are given the same reference numerals, to avoid duplication of description.

(50) In the second embodiment, the mounting position of the buffering device 10 shown in FIG. 1 and the construction of the plug 23 and second return spring seat 19 are altered. Specifically, a construction is adopted in which the external cylinder 11 is fixed to the restraining plates 7, the spring rod 5 is fixed to the interruption spring seat 4, and the end of the spring rod 5 and the end of the piston rod 15 are engaged in such a way that they can be freely brought into contact or separated.

(51) Also one end of the plug 23 projects into the interior of the internal cylinder 12 and is engaged with a step 12a of the internal cylinder 12 in such a way that it can be freely separated therefrom, so that an air chamber 29 is formed from the internal cylinder 12 and plug 23. Furthermore, a plug hole 23a is formed in the plug 23 so as to link the high-pressure chamber 25 and the air chamber 29. A throttle valve 30 having an extremely small flow path is arranged on the side of the high-pressure chamber 25 in the plug hole 23a, so that the air in the operating fluid 24 is shut into the high-pressure chamber 29. Also, projections 19a are arranged at the outer circumference of the second return valve seat 19 and the collar 26 that is employed in the first embodiment is dispensed with.

(52) (Interruption Action)

(53) In the second embodiment constructed as above, during interruption action, the same action as in the case of the first embodiment is performed; however, a difference is that the circular convex surface section 15c of the piston head 15b abuts the end of the spring rod 5 rather than the restraining plate 7. A further difference is that the second piston 14 abuts the projections 19a of the second return spring seat 19 rather than the collar 26.

(54) (Closure Action)

(55) It should be noted that, in the second embodiment, in closure action, the same action as in the case of the first embodiment is performed: the closure action in the second embodiment can thus be easily deduced from the description of the interruption action given above, so a detailed description thereof is dispensed with.

(56) (Beneficial Effect)

(57) In addition to the same beneficial effects as in the case of the first embodiment described above, in the second embodiment constructed as described above, owing to the formation of the air chamber 29 defined by the internal cylinder 12 and plug 23, the air in the high-pressure chamber 25 can pass through the plug hole 23a into the air chamber 29, where it is trapped.

(58) In this way, admixture of air with the operating fluid 24 on the side of the high-pressure chamber 25 can be reliably eliminated, making it possible to promote stabilization of the braking performance. At the same time, restrictions on the attitude of mounting of the buffering device 10 can be eliminated, so the degrees of freedom regarding installation of the buffering device 10 can be increased.

(59) Also, the buffering device 10 in the second embodiment is fixed at the side of the restraining plate 7 of the support structure 6 of the operating mechanism of the switchgear rather than installed on the interruption spring 2. Consequently, there is no possibility of the buffering device 10 being driven with movement of the interruption spring 2. As a result, no loss in drive energy of the operating mechanism can occur in this way, so the efficiency of utilization of the drive energy is further increased. It should be noted that, in the second embodiment, the beneficial effect produced by the collar 26 can be achieved by the provision of projections 19a on the second return spring seat 19, so the number of members can be cut by eliminating the collar 26.

[3] Third Embodiment

Construction

(60) Next, a third embodiment of the buffering device for the operating mechanism of a switchgear according to the present invention will be described with reference to FIG. 6 and FIG. 7. FIG. 6 is a cross-sectional view showing the closure condition of the third embodiment and FIG. 7 is a view showing the interruption condition of the device of FIG. 6. It should be noted that parts that are identical with or similar to corresponding parts in the first embodiment and a second embodiment are given the same reference numerals, to avoid duplication of description.

(61) The third embodiment is an improvement on the second embodiment and is characterized in that the construction is modified by dispensing with the first return spring 18 of the buffering device 10 shown in FIG. 5. Specifically, a stud 32 extending on the opposite side to that of the movable contact 1 is provided on the restraining plate 7 and a cylinder fixing plate 31 is mounted on the stud 32.

(62) An external cylinder 11 is fixed between this cylinder fixing plate 31 and the restraining plate 7. An internal cylinder 12a having the same central axis is freely slidably arranged on the inside of the external cylinder 11 and a first piston 13 having the same central axis is freely slidably arranged on the inside of the internal cylinder 12.

(63) Also, a first piston 13 is fixed to the end of the piston rod 15, a piston head 15b is fixed at the other end of the piston rod 15, and a second piston 14 having the same central axis is freely slidably arranged within the external cylinder 11. In addition, a packing 16 is fixed to the second piston 14 in the sliding portion of the external cylinder 11 and the piston rod 15.

(64) Also, a return spring 33 is arranged between the end of the second piston 14 and the piston head 15b. Furthermore, a plurality of through-holes 21 are arranged in the internal cylinder 12 and operating fluid 24 is sealed in a high-pressure chamber 25 constituting the space defined by the external cylinder 11, internal cylinder 12, second piston 14 and piston rod 15.

(65) When the end of the spring rod 5 that is fixed to the interruption spring seat 4 comes into contact with the circular convex surface section 15c of the piston head 15b and presses thereon, the operating fluid 24 in the high-pressure space 25 that is defined by the first piston 13 and the internal cylinder 12 is compressed, raising its pressure. Braking force of the buffering device 10 is thereby generated. Also, a ring 34 having the function of restraining the height of compression of the return spring 33 referred to above and the function of positional location is arranged between the external cylinder 11 and the restraining plate 7.

(66) (Interruption Action)

(67) In the third embodiment constructed as above, in interruption action, the same action is performed as in the case of the first embodiment and second embodiment, but the planar surface section 15d (opposite face to the circular convex surface section 15c) of the piston head 15b abuts (see FIG. 7) the restraining plate 7. Also this embodiment differs in that the second piston 14 abuts the ring 34.

(68) (Closure Action)

(69) Also, the same closure action is performed in the third embodiment as in the case of the second embodiment: however, the following points are different. Specifically, with extension of the return spring 33, the spring force of the return spring 33 is applied to the second piston 14, with the result that the operating fluid 24 in the liquid chamber 28 is rapidly returned to the high-pressure chamber 25 through the through-holes 21, so that return to the closed condition of the piston rod 15 can be rapidly effected. The details of the action can easily be inferred from the first embodiment and second embodiment, so a detailed description thereof may be dispensed with.

(70) (Beneficial Effect)

(71) In addition to the beneficial effects possessed by the first and second embodiments described above, the third embodiment constructed as above has the following independent beneficial effect. Specifically, by arranging the return spring 33 between the piston rod 15 and the second piston 14, the two actions of return of the piston rod 15 and return of the operating fluid 24 of the liquid chamber 28 to the high-pressure chamber 25 can be achieved by a single member.

(72) In this way, the requirement to form an oil return path 15a in the piston rod 15 is eliminated and the layout of the members can be simplified. Furthermore, the overall length of the buffering device 10 can be reduced and the number of components also reduced: this contributes to increased compactness and lower costs.

[4] Fourth Embodiment

Construction

(73) In addition, a method of lubricating a buffering device for the operating mechanism of a switchgear according to a fourth embodiment of the present invention is described with reference to FIG. 8. FIG. 8 is a cross-sectional view showing the construction of a fourth embodiment of the present invention.

(74) As shown in FIG. 8, a lubricating plug 35 is inserted in place of the plug 23 and this lubricating plug 35 is connected with a conduit 36. A packing 37 is fixed in the vicinity of the tip of the lubricating plug 35. At some point, the conduit 36 is branched in two directions, one of these branches being connected with a vacuum pump 38 while the other is connected with the container 39 that accumulates operating fluid 24. In the conduit 36, a first valve 40 is arranged on the side of the vacuum pump 38 and a second valve 41 is arranged on the side of the container 39.

(75) (Method of Lubrication)

(76) In a buffering device 10 constructed as above, when the operating fluid 24 is introduced into the interior, the first valve 40 is opened and the second valve 41 is put into a closed condition; the interior of the buffering device 10 is then evacuated to a vacuum condition using the vacuum pump 38; next, by closing the first valve 40 and opening the second valve, the operating fluid 24 in the container 29 is introduced into the interior of the buffering device 10. Thus, as the operating fluid that is here employed, operating fluid is used that has been degassed beforehand in the vacuum container to remove air etc in the oil.

(77) (Beneficial Effect)

(78) With the fourth embodiment, operating fluid 24 that has been degassed by putting the interior of the buffering device 10 into a vacuum condition using the vacuum pump 38 is employed for lubrication, so gas such as air is substantially absent in the interior of the buffering device 10. Fluctuation of the braking force resulting from admixture of air with the operating fluid 24 can therefore be prevented. Furthermore, the operating fluid 24 can be made to enter all the narrow spaces between the components, without needing to introduce the operating fluid 24 into the interior of the buffering device 10 under pressure. In this way, the task of removing internal bubbles is eliminated, making it possible to greatly reduce the time for the lubrication task.

[5] Fifth Embodiment

Construction

(79) A second method of lubrication of a buffering device for the operating mechanism of the switchgear according to a fifth embodiment of the present invention is described with reference to FIG. 9. FIG. 9 is a cross-sectional view showing the construction of a fifth embodiment of the present invention. Parts that are identical with or similar to those of the fourth embodiment are given the same reference symbols, to avoid repetition of description.

(80) A construction is adopted in which partial cutaway sections 35a are formed at the tip of the lubricating plug 35 of FIG. 9, and the plug 23 is pushed into the interior of the internal cylinder 12. Consequently, when cancelling the amount of the change in volume produced by the insertion of the target 35 into the interior of the internal cylinder 12, the space into which the operating fluid 24 in the buffering device 10 enters is expanded by fitting of a plate 42 between the piston head 15b and the end of the external cylinder 11. Other details of the construction are substantially the same as in the case of the fourth embodiment.

(81) (Method of Lubrication)

(82) The procedure for introduction of the operating fluid 24 into the interior of the buffering device 10 is substantially the same as in the case of the fourth embodiment; however, the plate 42 may be removed after removing the lubricating plug 35.

(83) (Beneficial Effect)

(84) The same beneficial effects as in the case of the fourth embodiment described above may also be obtained with the construction as above.

[6] Other Embodiments

(85) The embodiments described above are purely by way of example and the present invention is not restricted to these embodiments. For example, although, in the above embodiments, compression coil springs were employed for the first return spring 18 and second return spring 20 and return spring 33, other resilient elements such as for example a dish spring or plate spring could be employed.

POSSIBILITIES OF INDUSTRIAL APPLICATION

(86) The present invention can be applied to switchgears for power interruption.