HYDRAULIC OPERATING APPARATUS

Abstract: A hydraulic operating apparatus in which a differential piston (126) is used as a drive unit, and in which the differential piston (126) is driven by applying a high pressure fluid on a large piston face side through a hydraulic pressure control device (129) for controlling the hydraulic pressure, and a high pressure fluid always being applied on the small piston face side. The hydraulic operating apparatus is constructed such that a high pressure fluid is applied concurrently on both piston faces (107a, 107b) when the differential piston (126) stops at its receeded position, and a thrust generated due to the difference between teh forces applied on the both piston faces is held in check by a holding device (131) acting on the differential piston or its extension. The differential piston (126) is moved forward upon the removal of the holding force of the holding device (131), and the piston is moved backward upon the removal of the high pressure fluid on the large piston face side.

Description: The invention relates to a hydraulic operating apparatus, in which a hydraulic switching valve with a differential piston having a large piston face side and an opposing small piston face side is used as a drive unit, wherein the differential piston is driven into a retracted position and an expanded position, respectively, by applying a high pressure fluid on one or both of the respective piston face sides. In units for driving a load at a high speed upon the receipt of an operating command, both pneumatic pressure such as air pressure and hydraulic pressure such as oil pressure have been utilized heretofore as driving sources for units having a high speed linear or rotary motion, and pneumatic operation apparatus are often used for relatively light loads. However, when a heavy load of for example several tons is to be operated, pneumatic operating apparatus must necessarily become large and generate a great deal of noise due to the supply and exhaust of air at the time of operation, and the costs of maintaining an air compressor for building up the pneumatic pressure are increased, so that hydraulic operating systems are most often used. Hydraulic operating apparatus can easily be made to have a high pressure as compared to pneumatic systems, because the used fluids are relatively incompressible, so that noise at the time of operation is low; also the apparatus can be made small and superior response at high speed operation can be obtained. In a hydraulic operating system, if air is mixed in the hydraulic fluid during the assembly of the apparatus or if air is dissolved in the fluid during the fluid compressing procedure, such air in the fluid delays the response speed of the apparatus and the operating time may not be constant. One typical example of a high speed apparatus of this kind is a switching apparatus used in electrical power transmission systems. As a power transmission system is increased in capacity and voltage, the switches, particularly the power interrupters, are increasingly required to have improved performance. Not only are gas insulated interrupters in which an SF₆ gas is used as an arc extinguishing medium utilized, but improvements in performance which contributes to the stability of the system such as increases in switching speed and reductions in switching time differences are also desired. Also, reduction of the problems during usage such as improvements in the maintenance of the apparatus and decrease in noise generation are also being increasingly demanded. While the present invention is described in terms of an operating apparatus for electrical power switches, the invention is also applicable to other similar high speed operating apparatus. Fig. 1 schematically illustrates a conventional hydraulic operating apparatus disclosed in JP-A-1972 - 111 915, in which 101 is a switching unit of a switchgear such as an interrupter. The switching unit 101 comprises a stationary contact 102 and a movable contact 103 and is driven by a drive apparatus 104 to open and close the contacts. The drive apparatus 104 comprises a differential piston 106 having a rod 105 connected to the movable contact 103, and a cylinder 107, the differential piston 106 being fluid-tight sealed in the cylinder by a packing 106a therebetween. A conduit 108 connected to a head side (large area side) 107a of the cylinder 107 is connected to a hydraulic pressure control unit 109, which is connected to a low pressure tank 110 through a low pressure conduit 111. An accumulator 113 is connected through a port 112 to a rod side (small area side) 107b of the cylinder 107, and a high pressure conduit 114 is provided to connect it to the hydraulic pressure control device 109. Further, a pump unit 115 for supplying a high pressure fluid is provided to recover the fluid exhausted within the low pressure tank 110 through a conduit 117. Another conduit 116 is provided for supplying a high pressure to the accumulator 113 through the conduit 116. The operation of the above-described conventional apparatus will now be described. A high pressure fluid from the accumulator 113 is always supplied through the port 112 on the rod side 107b of the differential piston 106. When an operating command for opening the switching unit 101 is supplied to the hydraulic control unit 109, the high pressure fluid supplied to the head side 107a of the differential piston 106 through the conduit 114 is exhausted to the low pressure tank 110 through the conduits 108 and 111. At this time, the passage for supplying the high pressure fluid to the conduit 108 is closed. Therefore, the high pressure fluid on the rod side 107b of the differential piston 106 pushes down the differential piston 106, opening the switching unit 101 as shown in Fig. 1. In this state, since the head side 107a of the differential piston 106 including the conduit 108 is filled with the low pressure fluid, the packing 106a of the piston 106 must have good sealing properties so that ideally no fluid leaks between the high and low pressure fluids. When an operating command for closing the switching unit 101 is supplied to the hydraulic control device 109, the communication passage from the conduit 108 to the low pressure conduit 111 is closed and, at the same time, the supply passage for the high pressure fluid to the conduit 108 is opened, so that the conduit 108 is communicated with the high pressure conduit 114. As a result, the high pressure fluid is supplied to both the head side 107a and the rod side 107b of the differential piston 106, and the thrust due to the difference in areas of the head side 107a and the rod side 107b causes the differential piston 106 to move upward, thereby closing the switching unit 101. When the switching unit 101 is closed, the conduit 108 is filled with high pressure fluid. Apart from this, an operating apparatus for an interrupter must have a so-called "anti-pumping function". For example, when an interrupting command for removing abnormalities from the power system is supplied while a closing command is being supplied manually to the interrupter, the concurrent excitation preventing function (usually constructed by an electrical circuit) functions to achieve the interrupting operation after the closing operation has been completed. At this time, if the closing command still exists after the completion of the interrupting operation, the interrupter recloses, so that there is a possibility that the abnormalities in the electrical power system will continue. This phenomenon is called a pumping operation, which should be prevented by electrical or mechanical measures. Figs. 2 and 3 illustrate a conventional hydraulic operating apparatus in sectional views which is known for example from JP-PS 55-9770 and the publication "Operating Technology for Siemens Puffer (BK) Breakers", published in Siemens Power Engineering VI (1984) No. 1. In these Figs. 2 and 3, a contact 1 of a switch is operationally connected to a driving unit 6 through a rod 2 for the closing and interrupting operations. The drive unit 6 comprises a differential piston 3 for driving the contact 1, a packing 3a, a cylinder 5 and dash pot rings 4a and 4b. The drive unit 6 is operated by a main valve 7, and a high pressure fluid is supplied thereto through an amplifying valve 8. The high pressure fluid is provided from an accumulator 9 which is always maintained at a predetermined high pressure by a pump (not shown). The high pressure fluid is supplied from the accumulator to a chamber 5a on a small piston face side inside the cylinder 5 through a conduit 10 and is also supplied to the main valve 7 through a conduit 11. The main valve 7 is composed of an exhaust valve 14 and a supply valve 13 which are disposed in opposing relationship, and a spring 13a. A pilot chamber 15 of the exhaust valve 14 provided with a spring 14a is subjected to the action of the high pressure fluid introduced from the amplifying valve 8 through a conduit 16. As a result, the supply valve 13 and the exhaust valve 14 operate together to switch the main valve 7. That is, when the high pressure fluid does not act on the pilot chamber 15 of the exhaust valve 14, it is communicated with a low pressure tank 18 through the chamber 5b on the large piston face side of the differential piston 3. On the other hand, when the high pressure fluid acts on the pilot chamber 15 of the exhaust valve 14, the chamber 5b of the large piston face side of the differential piston 3 is connected to the accumulator 9 through the conduit 11. A conduit 45 is branched from a conduit 12 for supplying the high pressure fluid to the side of a auxiliary supply valve 20 of the amplifying valve 8. Also, a conduit 46 introduces the high pressure fluid from the accumulator 9 to a pilot chamber 21. One end of an interrupting valve 28 is connected to the pilot chamber 21 through a conduit 40 and a conduit 25, and the other end is connected to the low pressure tank 18 through a conduit 27. The amplifying valve 8 is composed of an auxiliary exhaust valve 19 having a spring 19a, an auxiliary supply valve 20 and a spring 20a and is subjected to the action of the high pressure fluid through the pilot chamber 21 of the auxiliary exhaust valve 19. Thus, the auxiliary exhaust valve 19 and the auxiliary supply valve 20 operate together to switch the amplifying valve 8. That is, when the high pressure fluid acts on the pilot chamber 21, the conduit 16 is connected to the accumulator 9 through the conduit 45. On the other hand, when the high pressure fluid does not act on the pilot chamber 21, the conduit 16 is connected to the low pressure tank 18 through a conduit 22. The interrupting valve 28 is composed of a ball valve 30 and a return spring 32 and is operated by an interrupting electromagnetic device 36 which moves linearly in response to a command through an operating rod 34. The pilot chamber 21 of the auxiliary exhaust valve 19 is connected to the amplifying valve 8 at about its center through the contraction 24 and a conduit 23 and is also connected to the conduit 25. The conduit 25 is connected to one end of a closing valve 38 through a check valve 26 and a conduit 37, and is connected to one end of the interrupting valve 28 through the conduit 40. the interrupting valve 28 is connected to the low pressure tank 18 through the conduit 27. The closing valve 38 and the interrupting valve 28 are composed of ball valves 29 and 30 and return springs 31 and 32, respectively, and are operated by electromagnet devices 35 and 36 which linearly move in response to commands through the operating rods 33 and 34. The electromagnetic devices 35 and 36 are composed of movable iron cores 35a and 36a and stationary coils 35b and 36b. In the interrupted state of the hydraulic operating apparatus of the above-described construction shown in Fig. 2, when a closing command is provided to the electromagnetic device 35, the movable core 35a is driven and the closing valve 38 is actuated through the operating rod 33 to open the ball valve 29. This allows the high pressure fluid to reach from the conduit 37 to the pilot chamber 21 of the auxiliary exhaust valve 19 through the check valve 26 and the conduit 25. The action of this high pressure fluid moves the auxiliary exhaust valve 19 of the amplifying valve 8 downward to close the conduit 22 connected to the low pressure tank 18 and to open the auxiliary supply valve 20 disposed in opposition to the conduit 22. This allows the high pressure fluid to reach the pilot chamber 15 of the exhaust valve 14 through the conduit 12, the conduit 45 and the conduit 16 to switch the main valve 7. In this condition, since the high pressure fluid is applied via the conduits 45 and 23 as well as the contraction 24, the above new position sustains itself even when the closing valve 38 is reset. When the action of the high pressure fluid is applied to the pilot chamber 15, the exhaust valve 14 closes the conduit 17 connected to the low pressure tank 18 and the opposing supply valve 13 is opened. As a result, the high pressure fluid reaches the chamber 5b on the large area side of the differential piston 3 through the supply valve 13 and the conduit 11, and the differential piston 3 is thrust upwards in the figure by a force generated by the difference in the pressure receiving area of the differential piston 3, to close the contact 1 as shown in Fig. 3. When an interrupting command is supplied to the electromagnetic device 36, the movable iron core 36a is driven to act on the interrupting valve 28 through the operating rod 34 to open the ball valve 30. As a result, the pilot chamber 21 of the auxiliary exhaust valve 19 of the amplifying valve 8 is connected to the low pressure tank 18 through the conduits 25 and 27, so that the high pressure fluid is exhausted. Thus, the auxiliary exhaust valve 19 of the amplifying valve 8 opens and the auxiliary supply valve 20 closes. Therefore, the pilot chamber 15 of the exhaust valve 14 of the main valve 7 is communicated to the low pressure tank 18 through the conduits 16 and 22 and the high pressure fluid in the pilot chamber 15 is exhausted. When the high pressure fluid in the pilot chamber 15 is exhausted, the exhaust valve 14 of the main valve 7 opens the conduit 17 connected to the low pressure tank 18 and closes the oppositely positioned supply valve 13. Then, the high pressure fluid in the chamber 5b on the large piston face side of the differential piston 3 is exhausted through the conduit 17. As a result, the differential piston 3 is thrust in the downward direction in the figure, causing the contact 1 to break to return to the state shown in Fig. 2. While poppet valves may replace the ball valves used in the above construction, their structure and function are similar to ball valves, so that a description thereof will be omitted. If the conventional hydraulic operating apparatus is constructed as described above, the conduit is a so-called high-low fluctuating circuit in which high pressure states and low pressure states appear alternately. therefore, when a gas such as air is mixed or dissolved into the fluid, gas bubbles, which are not present when the conduit is held at a high pressure condition, appear within the fluid while the conduit is held at a low pressure condition for a long period of time, resulting in a clogging of the high-low pressure fluctuating conduit. When a high pressure fluid is again supplied into the high-low pressure fluctuating conduit under these conditions, the propagation of pressure is delayed due to the compression and collapse of the gas bubbles. Therefore, the transmission of the operational signal is delayed making switching times inconsistent. Therefore, in such a conventional hydraulic operating apparatus, a number of time consuming preparatory operations are necessary for removing the gas within the apparatus after the assembly of the apparatus. Since these preparatory operations require a prolonged period of time, when such operations are made after the apparatus has been installed in the sub-station or the like, the recovery time needed for the sub-station to come on line could be overly long, posing power sub-station management problems. Also, in the closed state, the high pressure fluid and the low pressure fluid are fluid tightly sealed by the packing 3a. If this packing 3a is damaged due to a rapid sliding, a large amount of the high pressure fluid is discharged into the low pressure tank 18 so that the pressure within the accumulator 9 rapidly decreases. From US-A-4,166,937 a hydraulically activated operating system for an electric circuit breaker is known. In this publication, the differential piston of a fluid motor is connected to an accumulator, namely with its smaller surface through a large opening and with its larger surface through a small opening. Also, the space at the large piston face side of the differential piston can be connected to a sump for discharging fluid through a control valve. In the apparatus according to US-A-4,166,937, the control valve is normally closed by a spring and can be opened by an electromagnetic device capable of withdrawing a valve member. In addition, separate electromagnetic means are provided for operating a latch formed as a pin in order to hold the circuit breaker element in its open position. Accordingly, three different units are provided for the operation of this prior art operating apparatus, namely a hydraulic circuit for the differential piston, a first electromagnetic circuit for operating an auxiliary valve so that the differential piston may be moved downwards, and a second electromagnetic circuit of a holding device so that the differential piston may be moved upwards. The prior art document DE-A-2 905 100 describes a locking apparatus of a specific type wherein the cooperation of a protrusion and a recess is used. In the one embodiment thereof, a locking piston may engage an annular groove, in the other embodiment thereof a spring-biassed element may cooperate with a flange in order to hold a drive piston in a predetermined position. According to the intention of this publication, the construction of a hydraulic operating apparatus as a whole and the respective connections and elements thereof are not of interest. The publication US-A-3,334,202 discloses a manually controlled circuit breaker tripping arrangement, wherein quite a number of mechanical components are used. A circuit breaker element is connected to a piston which is operated by mechanical spring, a mechanical control member and a hydraulic reset motor through corresponding circuits. So, the switching operation is carried out using a mechanical linkage provided with a latch member which is manually controlled by means of a trip rod. Also, a hold-open latch is provided formed as a reciprocating pin which is operated by a spring and an electromagnet, respectively. The object underlying the present invention is to provide a hydraulic operating apparatus of the type as specified above and having an improved reliability over a long period of use in operation. In a first specific embodiment, the solution according to the invention is characterized in that the differential piston is held in one end position by means of a releasable holding device eliminating any thrust generated by different forces acting on the respective sides of the differential piston; in that the holding device is a mechanical holding device supported by hydraulic pressure; in that the amplification of an operating signal for the holding device as well as the amplification of an input signal for operating the hydraulic switching valve are both achieved by a hydraulic pressure supplied by the same hydraulic control device which permanently maintains a high pressure condition; in that for moving the expanded differential piston to its retracted position in the switching valve the high pressure fluid is supplied through a contraction from a pressure accumulator to an amplifying valve device shifting the exhaust and supply valves thereof so that the high pressure at the large piston face side is temporarily lowered; and in that for moving the retracted differential piston to its expanded position in the switching valve, the high pressure fluid to the holding device is temporarily by-passed so that the engagement thereof is released. In a second specific embodiment the solution according to the invention is characterized in that the differential piston is held in one end position by means of a releasable holding device eliminating any thrust generated by different forces acting on the respective sides of the differential piston; in that the holding device is a mechanical holding device supported by hydraulic pressure; in that the amplification of an operating signal for the holding device as well as the amplification of an input signal for operating the hydraulic switching valve are both achieved by a hydraulic pressure supplied by the same hydraulic control device which permanently maintains a high pressure condition; in that for moving the expanded differential piston to its retracted position in the switching valve, the high pressure fluid is applied from a pressure accumulator through a pressure releasing function portion to an amplifying valve device shifting the exhaust and supply valves thereof so that the high pressure at the large piston face side is temporarily lowered, wherein the pressure releasing function portion opens and closes with respect to the large piston face side in response to the movement of the differential piston; and in that for moving the retracted differential piston to its expanded position in the switching valve the high fluid to the holding device is temporarily by-passed so that the engagement thereof is released. In a third specific embodiment the solution according to the invention is characterized in that the differential piston is held in one end position by means of a releasable holding device eliminating any thrust generated by different forces acting on the respective sides of the differential piston; in that the holding device is a mechanical holding device operated by an electromagnetic closing device wherein the closing device comprises a latch cooperating with a pivotable trigger which is biassed into its holding position and operable into its releasing position by a lever; in that the amplification of an input signal for operating the hydraulic switching valve is achieved by hydraulic pressure supplied by the hydraulic control device which permanently maintains a high pressure condition; in that for moving the expanded differential piston to its retracted position in the switching valve, the high pressure fluid is supplied through a contraction from a pressure accumulator to an amplifying valve device shifting the exhaust and supply valves thereof so that the high pressure at the large piston face side is temporarily lowered; and in that for moving the retracted differential piston to its expanded position in the switching valve, the high pressure fluid is temporarily by-passed so that the engagement thereof is released. In a fourth specific embodiment the solution according to the invention is characterized in that the differential piston is held in one end position by means of a releasable holding device eliminating any thrust generated by different forces acting on the respective sides of the differential piston; in that the holding device is a mechanical holding device operated by an electromagnetic closing device wherein the closing device comprises a latch cooperating with a pivotable trigger which is biassed into its holding position and operable into its releasing position by a lever; in that the amplification of an input signal for operating the hydraulic switching valve is achieved by a hydraulic pressure supplied by the hydraulic control device which permanently maintains a high pressure condition; in that for moving the expanded differential piston to its retracted position in the switching valve, the high pressure fluid is applied from a pressure accumulator through a pressure releasing function portion to an amplifying valve device shifting the exhaust and supply valves thereof so that the high pressure and the large piston face side is temporarily lowered, wherein the pressure releasing function portion opens and closes with respect to the large piston face side in response to the movement of the differential piston; and in that for moving the retracted differential piston to its expanded position in the switching valve, the high pressure fluid to the amplifying valve device is temporarily by-passed so that the engagement thereof is released. According to a further development of the third and fourth embodiments, the holding device comprises a rotatable latch pivotable around a pin, which latch has a hook-shaped configuration for engaging a projection pin of the differential piston and is actuated on by means of the lever through a movable part of the electromagnetic closing device. According to a further development of the third and fourth embodiment of the invention, the holding device comprises a spring biassed rotatable latch, a spring biassed rotatable trigger for actuating the latch, and a sliding and pivotable lever connected to the electromagnetic closing device and mounted for cooperating with the trigger in order to engage or disengage the latch by means of the trigger. A further development of such specific constructions is characterized in that an anti-pumping pin is mounted opposite to the lever which holds the lever in its extended position and prevents a return movement thereof. According to a further development of the second and fourth embodiment according to the invention, the pressure releasing function portion comprises an annular member which engages the differential piston in its retracted position and in a concentric relationship and which is axially slidable along the inner surface of the switching valve, wherein the annular member is provided with a by-pass connecting the pressure accumulator with the amplifying valve device. A further development of these specific constructions according to the invention is characterized in that the annular member is formed as a dash pot ring and provided with an annular groove formed around its periphery and communicating with a fluid supply conduit. A further development of such specific constructions of the second and fourth embodiments is characterized in that the annular member is formed as a dash pot ring and provided with a packing for fluid tight sealing a sliding clearance between the differential piston and the annular member. According to a further development of the specific constructions of the second and fourth embodiments the annular member is a separate space in the switching valve connected to the fluid supply conduit through a branch conduit. A still further development of the constructions according to the second and fourth embodiments is characterized in that a contraction element is disposed between the pressure releasing function portion and the pressure accumulator. The invention will be explained in further detail hereinafter with reference to the drawings, wherein Fig. 1 is a schematic diagram showing a conventional hydraulic operating apparatus; Fig. 2 is a sectional view showing in detail another conventional hydraulic operating apparatus in an interruption state; Fig. 3 is a sectional view showing the closed state of the hydraulic operating apparatus according to Fig. 2; Fig. 4 is a schematic diagram showing a first construction according to the present invention in the closed state; Fig. 5 is a view similar to Fig. 4 but illustrating the interruption state; Fig. 6 is a time chart for explaining the operation of the construction according to Figs. 4 and 5; Fig. 7 is a sectional view of a first embodiment of the hydraulic operating apparatus of the present invention in its open state; Fig. 8 is a sectional view similar to Fig. 7 but illustrating its closed state; Fig. 9 is a time chart explaining the operation of the apparatus according to Figs. 7 and 8; Fig. 10 is a sectional of a second embodiment of the hydraulic operating apparatus of the present invention in its closed state; Fig. 11 is a sectional view similar to Fig. 7 but illustrating the open state of the second embodiment; Fig. 12 is a time chart explaining the operation of the apparatus according to Figs. 10 and 11; Fig. 13 is a sectional view of an embodiment of the main portion of the hydraulic operating apparatus according according to Figs. 10 and 11; Fig. 14 is a sectional view similar to Fig. 13 but illustrating another embodiment thereof; Fig. 15 is a circuit diagram of an anti-pumping device of a coventional design; Fig. 16 is a sectional view of a third embodiment of the hydraulic operating apparatus of the present invention in its closed state; Fig. 17 is a view showing the relationship between a trigger and an anti-pumping lever in a contact closed state; Fig. 18 is a sectional view of the apparatus according to Fig. 16 in a contact open state; Fig. 19 is a view similar to Fig. 17 but illustrating a contact open state; Figs. 20 and 21 are partial sectional views showing the relationship between the trigger and the anti-pumping lever; Fig. 22 is a sectional view of a fourth embodiment of the hydraulic operating apparatus of the present invention in its open state; and Fig. 23 is a sectional view similar to Fig. 22 but illustrating its contact closed state. A first construction according to the present invention is described below with reference to the drawing in Fig. 4 showing a switchgear in a closed state, wherein a driving unit 124 comprises a differential piston 126 and cylinder 107. A conduit 128 connected to the head side 107a of the cylinder 107 is connected to the hydraulic pressure control device 129 which is also connected to a low pressure tank 110 through a low pressure conduit 111. An engagement device 131 for holding the upward thrust of the differential piston 126 in check comprises a slidable engagement pin 132 and is connected to the hydraulic pressure control device 129 through a conduit 130. The engagement pin 132 is moved in the right and left directions in Fig. 4 according to the supply and exhaust of the hydraulic fluid with respect to the engagement device 131. The operation of the hydraulic operating apparatus of the present invention constructed as above described will now be described with reference to the time charts shown in Fig. 6. In this figure, (a) represents the ON and OFF phases of the operating command signal, (b) represents the pressure changes in the conduit 128 and the head side of the differential piston 126, (c) represents the movement of the differential piston 126, and (d) represents the movement of the engagement pin 132. In Fig. 4 illustrating the closed state, when an operating command is given to the hydraulic control unit 129 at the point of time a₁ of Fig. 6(a) in order to open the switching unit 101, the high pressure fluid supplied to the head side 107a of the differential piston 126 through the conduit 114 is exhausted to the low pressure tank 110 through the conduit 128 and the conduit 111. Since the hydraulic control unit 129 is arranged so that the supply of the high pressure fluid to the conduit 128 is instantaneously stopped at this time, the chamber at the head side 107a and the conduit 128 are instantaneously reduced to low pressure as shown at the point b₁ in Fig. 6(b). Then the differential piston 126 initiates its contact opening movement as shown by the connection from point c₁ to c₂ in Fig. 6(c). At this time, since the high pressure fluid is supplied to the engagement device 131 from the hydraulic control unit 129 through the conduit 130, the engagement pin 132 initiates its leftward movement as shown by the connection from point d₁ to d₂ of Fig. 6(d) when the differential piston 126 has completed its movement in the contact opening direction (see Fig. 6(c), point c₂). The engagement between the differential piston 126 and the engagement pin 132 is completed within a short period of time (see Fig. 6(d), point d₂), and thereafter, by the operation of the hydraulic pressure control unit 129, the high pressure fluid supply path to the conduit 128 is opened, and the conduit 111 communicating with the low pressure tank 110 is closed, so that the head side 107a of the differential piston 126 and the conduit 128 are in communication with the high pressure conduit 114, with its interior filled with a high pressure fluid as shown in Fig. 6(b), the point b₂, presenting the interruption state shown in Fig. 5. When an operating command for contact closing is supplied to the hydraulic pressure control unit 129, the pressure within the conduit 130 drops instantaneously, whereby the force urging upon the engagement pin 132 is removed and the engagement pin 132 is returned to the right in Fig. 5 by the action of an unillustrated spring or the like disposed within the engagement device 131. At this time, since the high pressure fluid is filled within the interior of the conduit 128 and the head side 107a of the differential piston 126 and in communication with the conduit 114, the differential piston 126 is driven in the contact closing direction toward the state shown in Fig. 4 as soon as the engagement between the engagement pin 132 and the differential piston 126 is released. When the driving of the differential piston 126 is started, the high pressure fluid is supplied to the conduit 130 by the operation of the hydraulic pressure control unit 129 in preparation for the subsequent operation. A first embodiment of the present invention will now be described in more detail in conjunction with Fig .7 in which a conduit 51 supplies high pressure fluid from the accumulator 9 to the side of the auxiliary supply valve 20 of the amplifying valve 8. A conduit 52 conducts high pressure fluid from the accumulator 9 to one end of the closing valve 38 through a contraction 54 and a conduit 56 as well as to the pilot chamber 21 through a contraction 53 and a conduit 55. One end of the interrupting valve 28 is connected to the pilot chamber 21 through a conduit 57 and the conduit 55, and the other end is connected to the low pressure tank 18 through a conduit 58. The conduit 56 connected to one end of the closing valve 38 is connected to a holding device 61 through a conduit 59, and the other end of the closing valve 38 is connected to the low pressure tank 18 through a conduit 60. The holding device 61 comprises a small piston 62 driven by the action of the high pressure fluid, and this small piston 62 pushes a latch 63 rotatably mounted around a shaft 64 secured to the cylinder 5 to maintain the engaged state between a projection pin 50 secured to the differential piston 3 and the latch 63. It is to be noted that the configuration of the latch 63 is such that when the compression force on the small piston 62 is removed while the axial (upward) thrust force is being applied to the differential piston 3, the thrust on the differential piston 3 automatically disengages the latch 63 from the projection pin 50. Next, the interrupting operation will now be described in connection with the time chart shown in Fig. 9. In Fig. 9, (a) represents the ON and OFF sequence of the excitation signal of the interrupting electromagnetic device 36, (b) represents the changes in hydraulic pressure in the pilot chamber 21 of the auxiliary exhaust valve 19, (c) represents the movement in the positions of the auxiliary exhaust valve 19 and the auxiliary supply valve 20 which move together, (d) represents the changes in hydraulic pressure in the pilot chamber 15 of the exhaust valve 14, (e) represents movement in the positions of the exhaust valve 14 and the supply valve 13 which move together, (f) represents the changes in hydraulic pressure in the chamber 5b on the large face side of the differential piston 3, (g) represents the movement of the differential piston 3, and (h) represents the movement of the latch 63. In Fig. 8 showing the closed state, when an opening command is supplied to the electromagnetic device 36 for opening the contact 1 at the time point a₁ of Fig. 9(a), the movable iron core 36a is driven to act on the interrupting valve 28 through the operating rod 34 to open the ball valve 30. As a result, the pilot chamber 21 of the auxiliary exhaust valve 19 of the amplifying valve 8 is connected to the low pressure tank 18 through the conduits 57 and 58, so that the high pressure fluid is exhausted at the time point b₁ of Fig. 9(b). Thus, the auxiliary exhaust valve 19 of the amplifying valve 8 opens and the auxiliary supply valve 20 closes at the time point c₁ of Fig. 9(c). Therefore, the pilot chamber 15 of the exhaust valve 14 of the main valve 7 is communicated to the low pressure tank 18 through the conduit 22, and the high pressure fluid in the pilot chamber 15 is exhausted at the time point d₁ of Fig. 9(d). When the high pressure fluid in the pilot chamber 15 is exhausted, the exhaust valve 14 of the main valve 7 opens the conduit 17 connected to the low pressure tank 18 and closes the oppositely positioned supply valve 13 at the time point e₁ of Fig. 9(e). Then, the high pressure fluid in the chamber 5b on the large piston face side of the differential piston 3 is exhausted through the conduit 17 at the time point f₁ of Fig. 9(f). As a result, a downward thrust in Fig. 8 is generated, causing the differential piston 3 to initiate the movement in the interrupting direction at the time point f₁ of Fig. 9(f). When the differential piston 3 completes its movement in the interrupting direction and the projection pin 50 traverses the position of the latch 63 (Fig. 9(g), time point g₁), the latch 63 pushed by the piston 62 initiates its rotation about the shaft 64 at the time point h₁ of Fig. 9(h) and engages with the projection pin 50 at the time point h₂. At this time, since the high pressure fluid is supplied to the holding device 61 from the accumulator 9 through the conduit 59 and the contraction 54 and the latch 63 is always pushed from the behind by the small piston 62, the differential piston 3 completes its movement in the interrupting direction (Fig. 9(g), time point g₁). When the projection pin 50 traverses the position of the latch 63, the latch 63 pushed by the small piston 62 initiates its rotation about the shaft 64 at the time point h₁ of Fig. 9(h) and engages with the projection pin 50 at the time point h₂ of Fig. 9(h). On the other hand, when the command to the electromagnetic device 36 is removed at the time point a₁ of Fig. 9(a), the ball valve 30 is moved upward by the hydraulic pressure to reset, thereby closing the interrupting valve 28. As a result, the high pressure fluid is gradually supplied at the time point b₂ of Fig. 9(b) to the pilot chamber 21 through the contraction 53 and the conduit 55 and, when the pressure in the pilot chamber 21 reaches a predetermined value, the back pressure applied to the auxiliary supply valve 20 in the closed state is overcome by the back pressure applied to the auxiliary exhaust valve 19, so that the auxiliary exhaust valve 19 and the auxiliary supply valve 20 move together (Fig. 9(c), time point c₂). The auxiliary exhaust valve 19 of the amplifying valve 8 closes the conduit 22 connected to the low pressure tank 18 and opens the opposing auxiliary supply valve 20. Then, the high pressure fluid is supplied to the pilot chamber 15 of the exhaust valve 14 through the conduit 51 and the conduit 16 (Fig. 9(d), the time point d2) to switch the main valve 7 again. When the high pressure fluid acts on the pilot chamber 15 of the exhaust valve 14, the conduit 17 connected to the low pressure tank 15 is closed and causes the opposingly positioned supply valve 13 to open at the time point e₂ of Fig. 9(e). As a result, the high pressure fluid reaches the chamber 5b on the large area side of the differential piston 3 through the supply valve 13 and the conduit 11 and an upward thrust is generated at the time point f₂ of Fig. 9(f) due to the difference in the pressure receiving areas. However, since the latch 63 has already completed its engagement with the projection pin 50 the above upward thrust applied to the differential piston 3 is held by the latch 63, thereby completing the interruption to maintain the condition as shown in Fig. 7. The closing operation will now be described. In Fig. 7, when a closing command is supplied to the electromagnetic device 35 to close the contact 1, the movable iron core 35a is driven to act on the closing valve 38 through the operating rod 33 to open the ball valve 29. This causes the conduits 56 and 59 to be connected to the low pressure tank 18 to exhaust the high pressure fluid. As a result, the force pushing the small piston 62 of the holding device 61 from behind is removed, but since the latch 63 is configured such that the engagement between the latch 63 and the projection pin 50 is automatically released by the thrust force of the differential piston 3 when the force of the small piston 62 is removed, the differential piston 3 starts to move upward and ultimately complete the closing operation. On the other hand, the high pressure fluid in the accumulator 9 is slowly supplied to the conduit 59 through the conduit 52 and the contraction 54, providing the state shown in Fig. 8 in which the conduit 59 is filled with the high pressure fluid to be ready for the subsequent interruption when the operation of the differential piston 3 has been completed. Since the apparatus of the present invention is arranged such that the conduit and the head side of the differential piston are almost always kept at a high pressure except for the instance at which the operation is made, any air mixed or dissolved into the fluid will not form bubbles, resulting in a constant switching time. Therefore, after the assembly of the apparatus, there is no need for repeated operations to expel air mixed in the fluid, providing advantages in the operation of the substation. Also, since the high pressure fluid is almost always supplied to the head side 5b and the rod side 5a of the differential piston 3,the provision of a fluid tight packing between the differential piston 3 and the cylinder 5 is not necessary, and no abrupt decrease in pressure due to leakage of the high pressure fluid to the low pressure tank 18 occurs. In the description of embodiments of the present invention, similar advantageous effects can be obtained when the terms "interruption" and "closing" are replaced by "closing" and "interruption", respectively. While the description has been made in terms of the case where the main valve 7 and the amplifying valve 8 are used together for supplying and exhausting the high pressure fluid with respect to the large area side of the differential piston 3, it is also possible to directly supply and exhaust the high pressure fluid with respect to the large area side 5b of the differential piston 3 by the above amplifying valve 8, and similar advantageous effects can be obtained in this case, too. As has been described, since the hydraulic operating apparatus of the present invention is constructed such that a hydraulic pressure applied on a large piston face side on the head side is always kept high except for the instance at which an operating command is supplied, and when the piston stops at its receeded position, the thrust generated due to the difference between the forces applied on said both piston faces is held by a holding device, any gas dissolved into the fluid will not form gas bubbles which would make the switching time inconsistent and so there is no need after the assembly of the apparatus for repeated operations to expel air mixed in the fluid. The hydraulic operating apparatus of the present invention is constructed such that a hydraulic pressure applied on a large piston face side on the head side and the hydraulic pressure within the conduits forming the control circuit for the main valve for the selective change is always kept high except for the instance at which an operating command is supplied, and when the piston stops at its receeded position, the piston thrust generated due to the difference between the areas of said both piston rod side and the head side faces is held in check by a holding device. Therefore, the gas dissolved and mixed within the fluid dose not form bubbles which would change the switching time. If the conventional hydraulic operating apparatus is constructed as described earlier, when only a short pulse operating command is supplied to the interrupting electromagnetic device 36, the ball valve 30 opens for an instance to lower the pressure in the pilot chamber 21 for an instance, causing the amplifying valve 8 to reverse its state. However, since the operating command lasts only for a very short time, the ball valve 30 immediately returns and the high pressure fluid is again supplied from the contraction 53 to the pilot chamber 21, whereby the amplifying valve 8 returns to the same state as immediately before the operating command is given. Thus, since the main valve 7 is also reset to its first state (after the reversal of the state in response to the operating command), the differential piston 3, which ultimately initiates its movement toward the interrupting direction, disadvantageously returns again to move in the closing direction (upward) before the movement is completed. The hydraulic operating apparatus of the present invention is constructed so that the high pressure fluid for returning the hydraulic switch valve upon the completion of the interrupting operation is supplied through regions which open and close in response to the differential piston. As a result, the hydraulic switch valve is supplied with the high pressure fluid after the completion of the operation of the differential piston 3 is detected, and even when an operating command in the form of a short pulse is given to the interrupting electromagnetic device 36, the hydraulic operating apparatus operates properly. A second embodiment of the present invention will now be described in conjunction with Fig. 10 and 11. In Fig. 10, 74 is a dash pot ring, which is arranged to be slightly vertically slidable along the inner surface of the cylinder 5. In the state in which the piston 3 is pushed against the dash pot ring 74, an annular groove 73 formed around the dash pot ring 74 communicates a conduit 76 to a conduit 77 provided in the cylinder 5 and is isolated in a fluid-tight manner from the chamber 5b on the large piston face side. Also, when the dash pot ring 74 is not pressed by the piston 3 and the fluid pressure is higher in the interior of the conduits 76 and 77 than in the chamber 5b on the large piston face side, the dash pot ring 74 is pushed upward to communicate the chamber 5b on the large piston face side to the conduits 76 and 77. The conduit 76 is connected to the conduit 11 which is always at a high pressure through a contraction 75 for regulating the discharge of the high pressure fluid to the low pressure tank 18 from the accumulator 9, and the conduit 77 is connected to the pilot chamber 21 through a contraction 72 and the conduit 71. Next, the interrupting operation of this apparatus of the present invention will now be described in connection with the time chart shown in Fig. 12. In Fig. 12, (a) represents the ON and OFF state of the excitation signal of the interrupting electromagnetic device 36, (b) represents the changes in hydraulic pressure in the pilot chamber 21 of the auxiliary exhaust valve 19, (c) represents the positions of the auxiliary exhaust valve 19 and the auxiliary supply valve 20 which move together, (d) represents changes in the hydraulic pressure in the pilot chamber 15 of the exhaust valve 14, (e) represents the positions of the exhaust valve 14 and the supply valve 13 which move together, (f) represents the changes in hydraulic pressure in the chamber 5b on the large piston side of the differential piston, (g) represent the movement of the differential piston 3, (h) represents the movement of the latch 63, and (i) represents the changes in hydraulic pressure within the annular groove 73. In Fig. 10 showing the closed state, when an opening command is supplied to the electromagnetic device 36 for opening the contact 1 at the time point a₁ of Fig. 12(a), the movable iron core 36a is driven to act on the interrupting valve 28 through the operating rod 34 to open the ball valve 30. As a result, the pilot chamber 21 of the auxiliary exhaust valve 19 of the amplifying valve 8 is connected to the low pressure tank 18 through the conduits 57 and 58, so that the high pressure fluid is exhausted at the time point b₁ of Fig. 12(b). Thus, the auxiliary exhaust valve 19 of the amplifying valve 8 opens and the auxiliary supply valve 20 closes at the time point c₁ of Fig. 12(c). Therefore, the pilot chamber IS of the exhaust valve 14 of the main valve 7 is communicated to the low pressure tank 18 through the conduit l6 and the conduit 22 and the high pressure fluid in the pilot chamber 15 is exhausted at the time point d₁ of Fig. 12(d). When the high pressure fluid in the pilot chamber 15 is exhausted, the exhaust value 14 of the main valve 7 opens the conduit 17 connected to the low pressure tank 18 and closes the oppositely positioned supply valve 13 at the time point e₁ of Fig. 12(e). Then, the high pressure fluid in the chamber 5b on the large piston face side of the differential piston 3 is exhausted through the conduit 17 at the time point f₁ of Fig. 12(f). As a result, a thrust in the downward direction in Fig. 10 is generated, causing the differential piston 3 to initiate the movement in the interrupting direction at the time point f₁ of Fig. 12(f). When the differential piston 3 completes its movement in the interrupting direction and the projection pin 50 traverses the position of the latch 63 (Fig. 12(g), the time point g₂), the latch 63 pushed by the piston 62 initiates its rotation about the shaft 64 at the time point h₁ of Fig. 12(h) and engages with the projection pin 50 at the time point h₂. On the other hand, when the command to the electromagnetic device 36 is removed at the time point a₂ of Fig. 12(a), the ball valve 30 moves upward due to the hydraulic pressure to close the interrupting valve 28. When the pressure in the chamber 5b on the large area side of the differential piston 3 is decreased, the high pressure fluid in the conduit 76 and 77 is exhausted while pushing up the dash pot ring 74, and the high pressure fluid slowly supplied from the contraction 75 is also concurrently exhausted (Fig.12(i), time point i₂). Therefore, even when an operating command in the form of a pulse is supplied, once the amplifying valve 8 and the main valve 7 reverse their states, the high pressure fluid within the conduit 77 is exhausted as above described, so that even when the interrupting valve 28 is closed after the removal of the operating command, the amplifying valve 8 and the main valve 7 do not reverse and reset their state until the differential piston 3 completes its operation. In this state in which the interruption has been completed, the lower surface of the dash pot ring 74 intimately contacts with the cylinder 5. Therefore, the high pressure fluid from the accumulator 9 is supplied to the annular groove 73 through the contraction 75 at the time point i₂ of Fig. 12 (i) and further is slowly supplied to the pilot chamber 21 through the contraction 72 and the conduit 71 at the time point b2 of Fig. 12(b). When the pressure within the pilot chamber 21 reaches a predetermined value which is previously determined, the back pressure applied on the auxiliary supply valve 20 is overcome by the operating pressure applied on the auxiliary exhaust valve 19 to move the auxiliary exhaust valve 9 and the auxiliary supply valve 20 together (Fig. 12(c), time point c₂). The auxiliary exhaust valve 19 of the amplifying valve 8 closes the conduit 22 connected to the low pressure tank 18 and opens the auxiliary supply valve 20 to the oppositely disposed conduit 22. This causes the high pressure fluid to reach the pilot chamber 15 of the exhaust valve 14 as shown at the point d₂ of Fig. 12(d) through the conduits 12, 51 and 16 to switch the main valve 17 again. The exhaust valve 14 closes the conduit 17 which is connected to the low pressure tank 18 and opens the supply valve 13 disposed in opposition to the conduit 17 at the time point e₂ of Fig. 12(e) when the high pressure fluid acts on the pilot chamber 15. As a result, the high pressure fluid is supplied to the large area side chamber 5b of the differential piston 3 through the supply valve 13 and the conduit 11 as shown at time point f₂ of Fig. 12(f), and an upward thrust force is generated due to the difference in the pressure receiving areas of the differential piston 3. However, since the engagement between the latch 63 and the projection pin 50 has already been completed (Fig. 12(h), time point h₂), and since a back pressure due to the high pressure fluid supplied through the contraction 54 and the conduit 59 is applied to the small piston 62, the upward thrust is held in check by the latch 63, thus completing the interruption and the condition shown in Fig. 10 is maintained. Since the closing operation is similar to the apparatus previously described in conjunction with Figs. 7 to 9, the description thereof will be omitted. Next, a modified embodiment of the present invention will be described. Fig. 13 is a sectional view showing the main portion of this embodiment of the present invention. In Fig. 13, 152 is a packing for fluid tight sealing the sliding clearance 151 between the cylinder 5 and the dash pot ring 74. At the final state of the interrupting operation, when the differential piston 3 initiates its engagement with the dash pot ring 74, the pressure within the space defined by the differential piston 3 and the dash pot ring 74 increases, and this fluid pressure generates a controlling force. At this time, the high pressure fluid would work its way into the conduit 77 through the clearance 151 if the packing 152 were not provided. Thus, when the braking force generated by the dash pot ring 74 is very large, the high pressure fluid intrudes into the conduit 77 through the clearance 151 since the space 153 is at a very high pressure and the fluid pressure within the conduit 77 varies, resulting in the variation in pressure in the pilot chamber 21 through the the contraction 72. Therefore, an erroneous operation may occur in which the auxiliary exhaust valve 19 is actuated at a time point earlier than initially set. In such a case, the packing 152 can be provided between the cylinder 5 and the dash pot ring 74 as shown in Fig. 13 to prevent the high pressure fluid from working past the dash pot ring 74, eliminating the danger of erroneous operation. Still another modified embodiment which has an object similar to the one described in conjunction with fig. 13 will now be described with reference to Fig. 14. In Fig. 14, 77a is a conduit for connecting the contraction 75 and the contraction 72 and is always provided with a high pressure fluid from the accumulator 9 through the contraction 75. The middle portion of the conduit 77a is branched into a conduit 160. The end of the conduit 160 which is opposite from the conduit 77a forms an opening 160a, and when the dash pot ring 74b is pushed by the differential piston 3 downward into the bottom position, the opening 160a is closed. If the pressure within the conduit 77a and 160 becomes high when the dash pot ring 74b is not completely pushed downward by the differential piston 3, the dash pot ring 74b is pushed upward by the fluid pressure, whereby the opening 160a of the conduit 160 is opened. Therefore, during the initial states of the interrupting operation, the high pressure fluid within the conduit 77a is discharged from the opening 160a, preventing the high pressure fluid from being supplied into the conduit 71 and the pilot chamber 21. On the other hand, at the final stage of the interrupting operation, the opening 160a is closed by the dash pot ring 74b, so that the high pressure fluid within the conduit 77a supplied from the contraction 75 is maintained and the high pressure fluid is supplied into the conduit 71 and the pilot chamber 21. At this time, the high pressure fluid within the space 153 between the differential piston 3 and the dash pot ring 74b works into the clearance 151 but it does not work into the interior of the conduit 77a because the opening 160a is blocked by the dash pot ring 74b. As has been described, since the circuit is arranged such that the high pressure fluid is supplied to the hydraulic switching valve after the interrupting operation has been completed according to the present invention, even when a pulse-like operating command is supplied to the interrupting electromagnetic device, the hydraulic operating apparatus operates properly. Apart from this, the operating apparatus for an interrupter must have a so-called "anti-pumping function". For example, when an interrupting command for removing abnormalities from the power system is supplied while a closing command is being manually supplied to the interrupter, the concurrent excitation preventing function (usually performed by an electrical circuit) functions to achieve the interrupting operation after the closing operation has been completed. At this time, if the closing command still exists after the completion of the interrupting operation, the interrupter recloses, providing the possibility of continuing the abnormalities in the electrical power system. This phenomenon is referred to as a pumping operation, which should be prevented by electrical or mechanical measures. The pumping operation will be described with reference to Fig. 15, in which an interrupting command and a closing command are supplied to terminals T and C, respectively, and the interrupter is operated by energizing the interrupting coil TT or the closing coil CC. Contacts Aa and Ab are auxiliary contacts operating in cooperation with the interrupter, the contact Aa being opened and the contact Ab being closed in the interrupted state of the interrupter. In the closed state, the contact Aa is closed and the contact Ab is opened. A coil Y is an anti-pumping electromagnetic relay. When the coil Y is energized, the contact Ya closes and the contact Yb opens. In the interruption state, for example, when a closing command is supplied to the terminal C, the closing coil CC is energized through the contacts Yb and Ab, thereby causing the interrupter to be closed. When the contact closing has been completed, the contact Aa closes and the contact Ab opens to discontinue the energization of the closing coil. At this time if the closing command continues an electric current flows through the coil Y through the closed contact Ya to be self-held and the contact Yb opens. When an interrupting command is supplied to the terminal T under such circumstances, the interrupting coil TT is energized through the contacts Aa to interrupt the interrupter, whereby the contact Aa opens again to close the contact Ab. If the closing command still continues even in this state, the interrupter is re-closed an the pumping operation occurs unless the contact Yb is not inserted in series with the closing coil CC, but since the contact Yb of the self-held coil Y is inserted, no pumping operation occurs in the circuit shown in Fig. 15. If the conventional hydraulic operating apparatus is arranged as above described, the anti-pumping function is usually provided by an electromagnetic relay which requires a complicated control circuit. Therefore an erroneous operation may occur due to vibrations arising from the interruption itself and the apparatus becomes overly large and expensive because of the increased number of electromagnetic relays. The hydraulic operating apparatus of the present invention can also utilize a mechanical amplifying mechanism for amplifying operating signals for the holding device for holding a thrust acting on the differential piston in check, whereby the anti-pumping device of the hydraulic operating apparatus can be constructed as a mechanical means. Therefore, the anti-pumping mechanism can be made very simple and inexpensive. The electromagnetic closing device 135 shown in Figs. 16-21 comprises a stationary coil 135b mounted on a mount bed 80 and a movable iron core 135a. One end of the movable iron core 135a has mounted thereon an anti-pumping lever 81 pivotally mounted by a pin 82. On the side of the anti-pumping lever 81 biased by a spring 83, a notch 81a is formed and one end 84c of a trigger 84 is pivotable about the pin 85 for engaging therewith. The trigger 84 is biased by a spring 86. A stopper 87 is provided for determining the stop position of the trigger 84 and forms a holding device. The trigger 84 is provided with a projection 84b. An anti-pumping pin 89 is disposed at a position opposing to the anti-pumping lever 81 and is urged from the rear by a spring 90. One end 84a of the trigger 84 which is in opposition to the anti-pumping lever 81 supports a latch 63 from its back in the interrupting state of the interrupter, to mechanically hold the engagement of the projection pin 50 and the latch 63. The latch 63 is urged from its rear by a spring 88 having a spring force selected such that when the engagement between the trigger 84 and the latch 63 is released, the engagement between the latch 63 and the projection pin 50 is automatically released. Next, the description will now be made as to the closing operation of the above apparatus according to a third embodiment of the present invention as shown in Fig. 16 to 19. In Fig. 18 in which the interrupting state is illustrated, when a closing command is supplied to the electromagnetic device 135 for closing the contact 1, the movable iron core 135a is driven to move the anti-pumping lever 81 downward. Therefore, the one end 84c of the trigger 84 initiates a clockwise rotation of the trigger 84 and the engagement between the end portion 84a of the trigger 84 and the latch 63 is released. At this time, the high pressure fluid is supplied to both the piston faces 5a and 5b of the differential piston 3, and the thrust of the differential piston 3 produced by the difference in area of the piston faces causes the engagement between the latch 63 and the projection pin 50 to be released, thereby moving the differential piston 3 upwards to close the interrupter. At this time, as the trigger 84 rotates, the projection 84b causes the anti-pumping lever 81 to rotate and, at the instant that the closing command is removed, the trigger 84 and the anti-pumping lever 81 take the position as shown in Figs. 16 and 17 to complete the closing operation. The interrupting operation will now be described. In Figs. 16 and 17 showing the closed state, when an opening command is supplied to the electromagnetic device 36 for opening the contact 1, the movable iron core 36a is driven to act on the interrupting valve 28 through the operating rod 34 to open the ball valve 30. In the same manner as in a conventional device, the amplifying valve 8 and the main valve 7 are switched, the high pressure fluid in the chamber 5b on the large piston face side of the differential piston 3 is exhausted to move the differential piston 3 downward, and when the projection pin 50 traverses the latch 63 biased by the spring 88, the latch 63 and the projection pin 50 engage, and the end portion 84a of the trigger 84 biased by the spring 86 and the latch 63 engage. Thereafter, the amplifying valve 8 and the main valve 7 return similar to a conventional device, whereby the high pressure fluid is supplied to the chamber 5b on the large piston area side and the interruption is completed in the state shown in Figs. 18 and 19 in more detail. The anti-pumping function will now be described. When a closing command continues to be supplied even after the completion of the contact closure in the closed state shown in Figs. 16 and 17, the anti-pumping lever 81 becomes engaged with the anti-pumping pin 89 as shown in Fig. 20, preventing the return of the anti-pumping lever 81. In this state, when an interruption command is supplied and the differential piston 3 moves downward to engage the projection pin 50 and the latch 63, the trigger 84 is reset to hold the engagement of the projection pin 50 and the latch 63. However, since the anti-pumping lever 81 is prevented from being reset by the anti-pumping pin 89, the interrupter is not closed again unless the closing command is released and the notch 81a of the anti-pumping lever 81 and the end portion 84c of the trigger 84 are brought into engagement as shown in Figs. 18 and 19, so that the anti-pumping function is achieved. Fig. 21 shows a state wherein the trigger 84 holds the latch 63 in its engaged position, and the lever 81 is in its pivoted position and held by the anti-pumping pin 89. As has been described, the hydraulic operating apparatus of the present invention is constructed such that the amplification of the operating signal of the holding device for holding the thrust acting on the differential piston in check is achieved by a mechanical amplification means with a trigger rather than a hydraulic switch valve, so that an anti-pumping function can be obtained with a very simple mechanism as compared to a conventional device utilizing electromagnetic relays. therefore, a hydraulic operating apparatus which has a high reliability and an inexpensive anti-pumping function can be obtained. While the present invention has been described in terms of particular embodiments of the present invention, it is also possible to combine the embodiments with each other, e.g. the second embodiment shown in Figs. 10-14 with the third embodiment shown in Fig.s 16-21 to obtain a fourth embodiment as illustrated in detail in Figs. 22 and 23. Fig. 22 shows the closed state, and Fig. 23 illustrates the open state of the hydraulic operating apparatus of this embodiment. The conduit 71 provided with the contraction 72 provides a connection between the annular groove 73 of the cylinder 5 and the pilot chamber 21 of the amplifying valve 8. The holding device 61 according to Fig. 10 is replaced by the electromagnetic closing device 135 as described in detail with reference to Figs. 16 to 21. The operation of this embodiment is mainly the same as described above in connection with the diagrams shown in Fig. 12.

Claims: A hydraulic operating apparatus, in which a hydraulic switching valve (6) with a differential piston (3) having a large piston face side (5b) and an opposing small piston face side (5a) is used as a drive unit, wherein the differential piston (3) is driven into a retracted position and an expanded position, respectively, by applying a high pressure fluid on one or both of the respective piston face sides (5a, 5b), characterized in that the differential piston (3) is held in one end position by means of a releasable holding device (61, 63) eliminating any thrust generated by different forces acting on the respective sides of the differential piston (3), in that the holding device (61, 63) is a mechanical holding device (61, 63) supported by hydraulic pressure, in that the amplification of an operating signal for the holding device (61, 63) as well as the amplification of an input signal for operating the hydraulic switching valve (6) are both achieved by a hydraulic pressure supplied by the same hydraulic control device (9) which permanently maintains a high pressure condition, in that for moving the expanded differential piston (3) to its retracted position in the switching valve (6) the high pressure fluid is supplied through a contraction (53) from a pressure accumulator (9) to an amplifying valve device (8) shifting the exhaust and supply valves (19, 20) thereof so that the high pressure at the large piston face side (5b) is temporarily lowered, and in that for moving the retracted differential piston (3) to its expanded position in the switching valve (6), the high pressure fluid to the holding device (61,63) is temporarily by-passed (56, 60) so that the engagement thereof is released. A hydraulic operating apparatus, in which a hydraulic switching valve (6) with a differential piston (3) having a large piston face side (5b) and an opposing small piston face side (5a) is used as a drive unit, wherein the differential piston (3) is driven into a retracted position and an expanded position, respectively, by applying a high pressure fluid on one or both of the respective piston face sides (5a, 5b), characterized in that the differential piston (3) is held in one end position by means of a releasable holding device (61, 63) eliminating any thrust generated by different forces acting on the respective sides of the differential piston (3), in that the holding device (61, 63) is a mechanical holding device (61, 63) supported by hydraulic pressure, in that the amplification of an operating signal for the holding device (61, 63) as well as the amplification of an input signal for operating the hydraulic switching valve (6) are both achieved by a hydraulic pressure supplied by the same hydraulic control device (9) which permanently maintains a high pressure condition, in that for moving the expanded differential piston (3) to its retracted position in the switching valve (6) the high pressure fluid is applied from a pressure accumulator (9) through a pressure releasing function portion (75, 73, 74, 72) to an amplifying valve device (8) shifting the exhaust and supply valves (19, 20) thereof so that the high pressure at the large piston face side (5b) is temporarily lowered, wherein the pressure releasing function portion (75, 73, 74, 72) opens and closes with respect to the large piston face side (5b) in response to the movement of the differential piston (3), and in that for moving the retracted differential piston (3) to its expanded position in the switching valve (6) the high pressure fluid to the holding device (61, 63) is temporarily by-passed (56, 60) so that the engagement thereof is released. The apparatus according to claim 2, characterized in that the pressure releasing funtion portion (75, 73, 74, 72) comprises an annular member (74,74b) which engages the differential piston (3) in its retracted position in a concentric relationship and which is axially slidable along the inner surface of the switching valve (6), wherein the annular member (74, 74b) is provided with a by-pass (73, 77; 77a, 160) connecting the pressure accumulator (9) with the amplifying valve device (8). The apparatus according to claim 3, characterized in that the annular member (74) is formed as a dash pot ring and provided with an annular groove (73) formed around its periphery and communicating with a fluid supply conduit (11). The apparatus according to claim 3 or 4, characterized in that the annular member (74b) is formed as a dash pot ring and provided with a packing (152) for fluid tight sealing a sliding clearance (151) between the differential piston (3) and the annular member (74b). The apparatus according to claim 3 or 4, characterized in that the annular member (74b) is provided in a separate space (153) in the switching valve (6) connected to the fluid supply conduit (11) through a branch conduit (160). The apparatus according to any one of claims 2 to 6, characterized in that a contraction element (75) is disposed between the pressure releasing function portion (74, 73, 72) and the pressure accumulator (9). A hydraulic operating apparatus, in which a hydraulic switching valve (6) with a differential piston (3) having a large piston face side (5b) and an opposing small piston face side (5a) is used as a drive unit, wherein the differential piston (3) is driven into a retracted position and an expanded position, respectively, by applying a high pressure fluid on one or both of the respective piston face sides (5a, 5b), characterized in that the differential piston (3) is held in one end position by means of a releasable holding device (63, 135) eliminating any thrust generated by different forces acting on the respective sides of the differential piston (3), in that the holding device (63, 135) is a mechanical holding device operated by an electromagnetic closing device (135) wherein the closing device (135) comprises a latch (63) cooperating with a pivotable trigger (84) which is biassed (86) into its holding position and operable into its releasing position by a lever (81), in that the amplification of an input signal for operating the hydraulic switching valve (6) is achieved by a hydraulic pressure supplied by the hydraulic control device (9) which permanently maintains a high pressure condition, in that for moving the expanded differential piston (3) to its retracted position in the switching valve (6) the high pressure fluid is supplied through a contraction (53) from a pressure accumulator (9) to an amplifying valve device (8) shifting the exhaust and supply valves (19, 20) thereof so that the high pressure at the large piston face side (5b) is temporarily lowered, and in that for moving the retracted differential piston (3) to its expanded position in the switching valve (6), the high pressure fluid to the holding device (61, 63) is temporarily by-passed (57, 58) so that the engagement thereof is released. A hydraulic operating apparatus, in which a hydraulic switching valve (6) with a differential piston (3) having a large piston face side (5b) and an opposing small piston face side (5a) is used as a drive unit, wherein the differential piston (3) is driven into a retracted position and an expanded position, respectively, by applying a high pressure fluid on one or both of the respective piston face sides (5a, 5b), characterized in that the differential piston (3) is held in one end position by means of a releasable holding device (63, 135) eliminating any thrust generated by different forces acting on the respective sides of the differential piston (3), in that the holding device (63, 135) is a mechanical holding device operated by an electromagnetic closing device (135) wherein the closing device (135) comprises a latch (63) cooperating with a pivotable trigger (84) which is biassed (86) into its holding position and operable into its releasing position by a lever (81), in that the amplification of an input signal for operating the hydraulic switching valve (6) is achieved by a hydraulic pressure supplied by the hydraulic control device (9) which permanently maintains a high pressure condition, in that for moving the expanded differential piston (3) to its retracted position in the switching valve (6) the high pressure fluid is applied from a pressure accumulator (9) through a pressure releasing function portion (75, 73, 74, 72) to an amplifying valve device (8) shifting the exhaust and supply valves (19, 20) therof so that the high pressure at the large piston face side (5b) is temporarily lowered, wherein the pressure releasing function portion (75, 73, 74, 72) opens and closes with respect to the large piston face side (5b) in response to the movement of the differential piston (3), and in that for moving the retracted differential piston (3) to its expanded position in the switching valve (6) the high pressure fluid to the amplifying valve device (8) is temporarily by-passed (57, 58) so that the engagement thereof is released. The apparatus according to claim 8 or 9, characterized in that the holding device (63, 135) comprises a rotatable latch (63) pivotable around a pin (64), which latch (63) has a hook-shaped configuration for engaging a projection pin (50) of the differential piston (3) and is actuated on by means of the lever (81) through a movable part (135a) of the electromagnetic closing device (135). The apparatus according to any one of claims 8 to 10, characterized in that the holding device (63, 135) comprises a spring (88) biassed rotatable latch (63), a spring (86) biassed rotatable trigger (84) for actuating the latch (63), and a sliding and pivotable lever (81) connected to the electromagnetic closing device (135) and mounted for cooperating with the trigger (84) in order to engage or disengage the latch (63) by means of the trigger (84). The apparatus according to claim 11, characterized in that an anti-pumping pin (89) is mounted opposite to the lever (81) which holds the lever (81) in its extended position and prevents a return movement thereof. The apparatus according to any one of claims 9 to 12, characterized in that the pressure releasing function portion (75, 73, 74, 72) comprises an annular member (74, 74b) which engages the differential piston in its retracted position and in a concentric relationship and which is axially slidable along the inner surface of the switching valve (6), wherein the annular member (74, 74b) is provided with a by-pass (73, 77; 77a, 160) connecting the pressure accumulator (9) with the amplifying valve device (8). The apparatus according to claim 13, characterized in that the annular member (74) is formed as a dash pot ring and provided with an annular groove (73) formed around its periphery and communicating with a fluid supply conduit (11). The apparatus according to claim 13 or 14, characterized in that the annular member (74b) is formed as a dash pot ring and provided with a packing (152) for fluid tight sealing a sliding clearance (151) between the differential piston (3) and the annular member (74b). The apparatus according to claim 13 or 14, characterized in that the annular member (74b) is provided in a separate space (153) in the switching valve (6) connected to the fluid supply conduit (11) through a branch conduit (160). The apparatus according to any one of claims 9 and 13 to 16, characterized in that a contraction element (75) is disposed between the pressure releasing function portion (74, 73, 72) and the pressure accumulator (9).

Inventors: SUGIYAMA, TSUTOMU ITAMI WORKS MITSUBISHI DENKI, YOSHIZUMI, TOSHIAKI ITAMI WORKS MITSUBISHI DENKI
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: H01H33
IPC codes: H02H7, H01H33, H01H9