GB2024332A - Hydraulically operated actuation device for a high voltage circuit-breaker - Google Patents

Abstract

The device is intended to operate the interrupter head (1) of a pole of a high voltage circuit breaker and comprises driving devices (5) corresponding one to each of the interrupter heads (1), each driving device (5) having a differential piston (3) and a cylinder (4) which are relatively movable between first and second positions corresponding to on and off positions of the associated interrupter head (1). The supply of pressure liquid to each driving device (5) is controlled by a corresponding main valve device (6) which has a differential piston (18) which is arranged to be movable in response to the supply of pressure liquid to the main valve device so as to vary the manner in which pressure liquid is supplied to the respective driving device (5). A common pre-control valve device (15) is connected hydraulically to all of the main valve devices (6) and is operable to control the movements of the differential pistons (18) of the main valve devices (6) substantially simultaneously. A coupling line (47) intercommunicates the cylinders (4) of the driving devices (5) on the larger-area sides of the differential piston (3) thereof to provide pressure equalisation therebetween. <IMAGE>

Description

SPECIFICATION Hydraulically operated actuation device for a high voltage circuit-breaker The invention relates to an hydraulically operated actuation device for operating at least two interrupter heads of a -- pole of a high voltage circuit breaker.

Hydraulic actuating devices for high voltage circuit-breakers are known from "Siemens Zeitschrift", No. 9, September 1975, pages 600 to 609. In this case, each switch pole is provided with two interrupter heads, each switching point having two breaker units. Via in each particular instance one control rod per interrupter head and also intermediate gearing, the two breaker units associated with an interrupter head are actuated. A single hydraulic drive, having a differential piston as drive piston, actuates the two switching rods via deflecting gearing and also a coupling linkage. Such high voltage circuit-breakers having two interrupter heads, and thus up to four breaker units per switch pole, are employed for voltages above 380 kV at nominal currents of above 2500 Ampere, if a single switching point is no longer adequate for switching a phase in entirely satisfactory manner.

In order to further increase the synchronism of operation of a plurality of interrupter heads, for example to provide a time difference of less than 2 ms in the reversal of two interrupter heads associated with one pole, in the case of the known actuating device (having the coupling linkage and deflecting gearing) it would be necessary to enlarge the masses of the mechanical elements thereof, in order to take up the surge loading when switching is carried out. The increase of the masses of the elements is achieved without any appreciable variation in the lengths of the elements so that the related time delay of the switching procedure also remains substantially unaltered. Accordingly, the power of the hydraulic drives for the elements would require to be amplified.

It is an object of the invention to provide an hydraulic actuation device for operating the interrupter heads of a ----- pole of a high voltage circuit breaker, in which improvided synchronism in the operation of the interrupter heads can be achieved in simple manner.

According to the invention, there is provided an hydraulically operated actuation device for operating interrupter heads of a pole of a high voltage circuit breaker and comprising: a plurality of driving devices corresponding one to each of said interrupter heads to operate the latter, each driving device comprising a differential piston and a cylinder which are relatively movable between first and second positions corresponding to on and off positions of the associated interrupter head;; a respective main valve device corresponding to each driving device and operable to control the supply of pressure liquid thereto so as to operate the driving device between its first and second positions, said main valve device having a differential piston arranged to be movable in response to the supply of pressure liquid to the main valve device so as to vary the manner in which pressure liquid is supplied to the respective driving device; a common pre-control valve device connected hydraulically to all of said main valve devices and operable to control the movements of the differential pistons of the main valve devices substantially simultaneously; and a coupling line intercommunicating the cylinders of the driving devices, on the larger-area sides of the differential pistons thereof, to provide pressure equalisation therebetween.

Thus, in an actuating device according to the invention, there is provided per interrupter head a driving device and also an hydraulic main valve device. All of the main valve devices are controlled by the common pre-control valve device, which is also hydraulically operated. Owing to the common pre-control valve device, the main valve devices are operated substantially simultaneously so that interrupter heads associated therewith are also operated substantially simultaneously. Thereby, good synchronism in the operation of the interrupter heads may be achieved. Owing to pressure equalisation via said line, synchronism is still further improved.

Already known are hydraulic actuating devices for reversing three poles with, in each particular instance, one interrupter head for the switching of three phases, wherein each ----- pole is provided with an hydraulic drive and an hydraulic main valve device controlled by a common pre-control valve device, but here, already due to the phase differences of the voltages to be switched with the switch poles, synchronism plays a smaller part (Siemens Prospectus "SF6 Circuit breaker 3AS 1" Order No.

El 2211564-220, September 1976).

In the event of malfunction of one of the valve devices, in an actuating device according to the invention, supplementary advantages are achieved by means of said coupling line.

If, for example, one of the main valve devices malfunctions, then in the event of an "on" command the pressure liquid flows away from the correctly functioning main valve via said line and through the malfunctioning main valve, i.e. at all large-area sides of the differential pistons there obtains a pressure which is so low that cutting-in of the interrupter heads is prevented. The malfunctioning switch pole therefore remains in its safe "off" position.

In the event of an "off" command, the high pressure on the large-area side of the differential piston associated with one interrupter head cannot be directly reduced with the main valve malfunctioning.

Here again, this pressure is reduced via said coupling line and the correctly functioning main valve of another interrupter head. The high pressure on the small-area side of the differential pistons drives the latter into their other preference position, i.e. the interrupter heads open. Also in this case, in the event of malfunction, the switching procedure serving for safety of the phase to be switched and the breaker units is carried-through in entirely satisfactory manner.

In a preferred embodiment of the actuation device according to the invention, there is provided between the common pre-control valve device and the main valve devices at least one further precontrol valve device. The said further pre-control valve device represents so to speak a control force amplifier; thus, the pre-control valve device common to all switching points of a switch pole can be designed to be weaker.

In the event of an "on" command, the pressure liquid may be guided directly from an accumulator (or reservoir} via a line and the small-area side of the differential piston of the main valve device to the large-area side of the piston of the driving device.

Additional advantages may be achieved if the supply of the driving device with pressure liquid, when cutting-in of the interrupter heads is to take place, is effected via a line leading from the further precontrol valve device, via which simultaneously the main valve device is triggered.

In the event of a malfunction of one ofthefurther pre-control valve devices, the same applies as in the case of the main valve devices. In this case also, via said coupling line pressure equalisation is achieved in such mannerthatthe interrupter heads still cut-in or out reliably.

In the case of an advantageous embodiment of the invention, a throttle is provided in the line which conveys the pressure liquid to the large-area side of the piston of the driving device. With the aid of the throttle, in the event of a malfunctioning valve device on an "off" command being issued the result is achieved that the high pressure on the small-area side of the piston of the driving device associated with the malfunctioning interrupter head can be reduced only gradually, so that at all events reliable cutting out of this interrupter head is guaranteed.

With this arrangement, the throttle must be so designed that an entirely satisfactory cutting-in function is maintained. Expressed otherwise, this means that the free flow cross-section of the throttle must always be so large that in the event of an "on" com- mand the liquid under high pressure is able to pass sufficiently rapidly and in adequate quantity onto the large-area side of the piston of the driving device, so as to make possible normal switching of this interrupter head.

In the case of a further advantageous embodiment of the invention, a flow-dependent valve may be so connected into the line conveying the pressure liquid to the large-area side of the piston of the driving device that in the event ob increasing liquid throughout the flow cross-section is diminished. The principle of such flow-dependent valves is known.

The liquid stream to be controlled flows through a diaphragm (or stop) on the end face of a hollow cyli nder acting as a displaceable slide. In the event of an increasing throughflow quantity, the hollow cylinder moves under the influence of the pressure difference against a spring. Thereby, transverse bores on the generated surface of the hollow cylinder, which represent the opening cross-section to the output of the flow-dependent valve, are constricted. With the aid of such a valve, in the event of a malfunction, both in the case of an "on" and also an "off" com mand, outflow of the entire liquid into a low pressure chamber is prevented.With this arrangement, the response threshold of this flow-dependent valve is so determined by the selection of the spring that the valve responds only in the event of a malfunction, i.e. only in the event of abnormally large liquid extraction. In the normal case of operation, the valve leaves its largest-possible flow cross-section open.

A device may be connected in the line conveying the pressure liquid to the large-area side of the piston of the driving device, controlled by the precontrol valve device, for varying the free line cross section, and conveniently take the form of a springloaded slide valve having two bores of varying size formed in the slide. With the aid of the pressure com- ing from the pre-control valve device, in the event of an "on" command the slide is so displaced against a spring that the large bore passes into registry with the line.In the event of an "off' command, the line from the pre-control valve device to the slide valve is pressureless; the spring displaces the slide in such manner that the small bore passes into registry with the line. Therewith, practically prior to movement of the pistons of the driving devices, the line carrying the pressure liquid is almost 5hut-o. Flow-off of the entire liquid quantity into the low pressure chamber is prevented in this manner.

In L'nown manner, the pressure liquid passes out of an hydraulic accumulator into the actuating device. If, in the event of a malfunction, the pressure medium flows away completely into a low pressure chamber, then the accumulator pressure in the said hydraulic accumulator decreases. With decreasing accumulator pressure, the pole first of all travels through a short-interruption barrier, then a cut-in barrier and finally a function barrier.

Simultaneously, there is provided an indication that the -- - pole is malfunctioning. Since, in the event of a spring-biassed slide valve, and an "off' command taking place, the pressure-conveying line is to a considerable extent shut-off and therewith emptying of the accumulator is prevented, the pole 8401e is not able to travel through this barrier.

According to a further preferred feature of the invention, therefore, a flow-dependent switch may be arranged in the coupling line. Since, in the event of malfunction, there is always pressure compensation via the coupling line the flow-dependent switch gives an indication of the malfunction.

Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a diagrammatic illustration, partly in section, of one embodiment of an hydraulic actuat ing device for two zoo interrupter heads of a switch pole of a high voltage drcuit-breaker, the --- pole being in the "switch-off" position; Figure 2 is similarto Figure 1, but shows the pole poly in the "switch-on" position; Figure 3 is a detail view of a modification to the device shown in Figures 1 and 2; Figure 4 is a detail view of a further modification to the device shown in Figures 1 and 2; and Figure 5 illustrates, in similar manner to Figure 1, a further embodiment of hydraulic actuating device according to the invention.

Referring now to the drawings, Figure 1 shows two interrupter heads of a ----- pole and which are connected in series in a phase (for example R) of a three-phase system. Each interrupter head 1 can actuate, for example, a blast-piston switch having sulphur hexafluoride as quenching agent and which, at a voltage of 110 kV or more, exhibits a switching capacity of 5 GVA and more. Each interrupter head 1 is actuated by a respective hydraulic actuating device 2, and each of the two (identical) hydraulic actuating devices 2 has a driving device in the form of a drive 5 comprising a differential piston 3 and a cylinder4 and which is adapted to be subjected to the action of pressure liquid by a main valve device 6 and a second pre-control valve device 7 which controls the main valve device 6.The differential piston 3 and cylinder 4 are relatively movable between first and second positions corresponding to on and off positions of the associated switching point 1. The pressure liquid is extracted from an hydraulic accumulator 8 in which, by means of a pump 46, a predetermined pressure is maintained.

The differential piston 3 of the drive 5 is coupled via a piston rod 9 with the movable switching member of the interrupter head 1.

The pressure liquid is fed out of the accumulator 8, via a line 10, to the cylinder4 of the drive 5 and feeds a line 11 leading to the main valve device 6. The line is directly connected with a line 12 for pressure liquid, leading to the second pre-control valve device 7. Via a further line 13, the pressure liquid is conveyed from the hydraulic accumulator8 on the one hand to the first pre-control valve device 15 (common to both hydraulic actuating devices 2) and on the other hand to a spring-biased valve 16 (cut-in valve).

Both the main valve device 6 and also the precontrol valve devices 7 and 15 are reversing valves (three-way valves).

The main valve device 6 has a differential piston 18 arranged to be subjected to the action of pressure liquid from a line 17 and which, via the second precontrol valve device 7, is adapted to be transferred into either of two preference positions which are a function of the pressure of the pressure liquid. In one of the preference positions, the large-area side of the differential piston 3 of the drive 5 is connected via a line 19 with a low pressure chamber 20, whereas in the other position, shown in Figure 2, it is connected with a high-pressure-conveying chamber 21 fed from the line 11. For reversing the differential piston 3, the differential piston 18 of the main valve device 6 is connected to a valve rod 24 which couples together the inlet valve 22 and the outlet valve 23 of the drive 5.

The pressure of the pressure liquid in the line 17 is controlled by the second pre-control valve device 7.

The pre-control valve device 7 has a differential piston 25 secured to a valve rod 28 which couples together an inlet valve 26 and an outlet valve 27. The differential piston 25 of the second pre-control valve device 7 is adapted to be subjected to the action of pressure liquid via a line 29. Via the two switching positions of the common first precontrol valve device 15, the differential piston 25, as also is the differential piston 18, is adapted to be transferred into either of two preference positions which are a function of the pressure of the pressure fluid.

Also, the common, first pre-control valve device 15 has a differential piston 30 and which is associated a by-pass 31 which includes a throttle point 32. The differential piston 30 is adapted to be subjected to the action of pressure via a control line 33 conveying selectable pressure liquid. In the line 33, the springbiassed valve 16 is connected via a recall valve 34 to a spring-biassed valve 35 ("off' valve) the output of which extends to a line 37 which interconnects both of the low pressure chambers 20 (each associated with a respective drive 5). From the first pre-control valve device 15 there leads a line 40 to the output 36 of the valve 35 and from the second pre-control valve device 7 there leads a line 41 to the low pressure chamber 20.The spring-biassed valves 16 and 35 are actuated by a electromagnetic correcting elements 42 and 43 respectively, whenever a signal leads to excitation of the associated armatures 44 or 45. Via the line 37 and the pump 46, pressure liquid from the low pressure chamber 20 is once again returned to the hydraulic accumulator 8.

A coupling line 47 interconnects the chambers 48 (each defined between the inlet valve 22 and the outlet valve 23 of the respective main valve device 6).

Arranged in the line 11 is a supplementary throttle 49.

The mode of operation of the hydraulic actuating device described above is as follows: On occurrence of an "on" signal at the electromagnetic correcting element 42, the armature 44 is displaced and the spring-biassed valve 16 is opened. Thereby, pressure liquid from the accumulator 8 passes out of the line 13, via the recall valve 34 into the line 33, so that the pressure liquid displaces the differential piston 30 from the position shown in Figure 1 to the position shown in Figure 2.

Unthrottled pressure liquid derived from the line 13 is then able to pass into the line 29 via the end of the valve 15 remote from line 33, whereby the differential pistons 25 of both of the second pre-control valve devices 7 are also displaced. Therewith, via the valve rod 28, the inlet valve 16 of each device 7 is opened.

Due to opening of the inlet valve 26, pressure liquid flows out of the line 12 into the line 17. When the differential piston 25 has adopted the position shown in Figure 2, there is able to build-up in the line 17 the full pressure necessary for reversing the differential piston 18 so that the lattertakes up the position shown in Figure 2. Thereby, the inlet valve 22 is lifted-off from its seat and is pushed into the chamber 21,so that the pressure liquid derived from line 11 is able to act on the large-area side of the differential piston 3. In the event of full opening of the inlet valve 22, via the rigid coupling of the valve rod 24 the outlet valve 23 is closed. The differential piston 3 travels, under the building-up pressure of the pressure liquid, into the position shown in Figure 2 in which the interrupter head 1 is closed.In the event of a short-period or interrupted "on" signal the by-pass 31 ensures that the first pre-control valve device 15 remains in its switch-on position. Evidently, in that the pre-control valve device 15 con trols simultaneously both of the pre-control valve devices 7 of the drives 5, both interrupter heads 1 will be operated substantially simultaneously.

In order to transfer the two interrupter heads 1 of the switch pole out of the switch-on position shown in Figure 2 into the switch-off position shown in Fig ure 1, there is required at the electromagnetic correcting element 43 a signal actuating its armature 45 in the sense of opening of the spring-biassed valve 35.

Thereby, the line 33 carrying the pressure liquid is opened and is connected to the low pressure chamber 20. The throttle point 32 in the by-pass 31 is so dimensioned that in the line 33, on opening of the valve 35, there takes place a pressure drop which, together with the pressure building-up out of the line 13 at the differential piston 30, results in reversal of the differential piston 30 until the latter is transferred back to its other position shown in Figure 1. To correspond to the reversal of the first pre-control valve device 15, also both the second pre-control valve devices 7 and the main valve devices 6 are reversed. Thus, each valve device 7 no longer receives pressure liquid along line 29, and the differential piston 25 returns to the position of Figure 1, whereupon the main valve device 6 also returns to the position of Figure 1.This results in a pressure drop at the large-area side of the differential piston 3, whereby also this piston travels back into its position shown in Figure 1, so that the switching point 1 is opened.

In normal operation, it is guaranteed via the common, first pre-control valve device 15, that the two hydraulic actuating devices 2 are simultaneously actuated. This, again, is the same as simultaneous actuation of the two interrupter heads 1 of a switch pole. The coupling line 47 which interconnects the chambers 48 has no function when the device is operating normally. The supplementary throttle 49 in the line 11 must be so dimensioned that the switch-on function of the hydraulic actuating device 2 is maintained in entirely satisfactory fashion.

The significance of the coupling line 47 becomes clear in an assumed case of disturbance. In this case, it is of no significance whether one of the two main valve devices 6 or one of the two pre-control devices 7 fails. Two cases are to be distinguished from each other. In the first case, the two interrupter heads 1 are to be conveyed from the switch-off position (such as is shown in Figure) into the switch-on position (as shown in Figure 2). First of all, all valve devices 6 and 7 are in the position as shown in Figure 1. it will now be assumed, by way of example, that the right-hand main valve device 6 cannot be moved out of this position, i.e. that this main valve device 6 cannot be reversed, but the other valve devices are to function in satisfactory manner.On occurrence of the "on" signal, therefore, the spring-biassed valve 16 is opened and subsequently the common, first pre-control valve device 15, the second pre-control valve devices 7 and the left-hand main valve device 6 are reversed. Thus, in the lefthand main valve device 6 the inlet valve 22 is opened, so that the chamber 21 with the pressure liquid is connected to the chamber 48 on the largearea side of the differential piston 3. On the other hand, in the right-hand main valve device 6 the out let valve 23 remains opened, so that its chamber 48 is connected via the line 19 to the low pressure chamber 20. Via the coupling line 47, the high pre ssure liquid flows from the opened (correctly func tioning) left-hand main valve device 6 through the malfunctioning and therewith closed right-hand main valve device 6 into the low pressure chamber 20.Cutting-in alone of the (entirely satisfactorily functioning) left-hand interrupter head 1 is thereby prevented. The accumulator pressure in the hydraulic accumulator 8 drops gradually down to zero, whereby the switch pole travels initially through its short-interruption barrier, subsequently through its cut-in barrier and finally even through its function barrier. Simultaneously, an indication is provided that the switch pole is malfunctioning.

In the other case, the two interrupter heads 1 are to be transferred from the cut-in position as shown in Figure 2 into the cut-out position as shown in Figure 1. In this case, initially all the valve devices are in the position shown in Figure 2. Again it will be assumed by way of example that the right-hand main valve device 6 cannot be displaced out of its position. Due to the "off' signal, initially the spring-biassed valve 35 is opened. Thereby, the common, first pre-control valve device 15, the second pre-control valve devices 7 and the left-hand main valve device 6 are reversed into the position such as is shown in Figure 1. The right-hand main valve device 6 is malfunctioning and remains in its original position. In this case, in the absence of the coupling line 47 the left-hand interrupter head 1 would open, but the right-hand interrupter head 1 would remain closed.This would result in overloading of the open switching point and destruction thereof.

However, via the coupling line 47, there may again be a pressure equalisation between the two chambers 48, i.e. the pressure liquid building up under high pressure in the right-hand chamber 48 is able to flow away via the coupling line 47 and the undisturbed main valve device into the low pressure chamber 20. Thus, on the large-area sides of the differential pistons 3, the pressure drops to zero, whereas on the small-area sides of the said differential pistons there is high pressure. Due to this pressure difference, the two differential pistons 3 are displaced into their other preference positions, i.e.

via the piston rods 9 the interrupter heads 1 are transferred into the cut-out position.

Once again, the accummulator pressure in the hydraulic accumulator 8 decreases and the switch pole travels through the switch barriers. The supplementarythrottle49 cut into the pressureconveying line 11 ensures in both disturbance cases that the accumulator pressure in the hydraulic accumulator 8 does not suddenly drop to zero. Precisely in the second, just discussed disturbance case, it might under some circumstances occur, without this throttle 49, that excessively rapid decrease of accumulator pressure affords no adequate pressure difference for entirely satisfactory cutting out of the disturbed interrupter head.

Figure 3 shows - partially sectioned - one of two interrupter heads 1 associated with a ----- pole, with the actuating device 2 associated therewith.

Instead of the throttle 49, as employed in the embod iment according to Figures 1 and 2, a flow dependent valve 50 is cut-in into the pressure liquid conveying line 11. The pressure liquid flows through a diaphragm or stop 51 on the end face of a hollow cylinder 52 (serving as a displaceable slide), into the hollow cylinder 52 and through transverse bores 53 in the surface of the hollow cylinder 52 once again out of the latter. With increasing throughflow quant ity, the hollow cylinder 52 travels under the influence of the pressure difference against a spring 54.

Thereby, the bores 53 are more and more sealed by an outer wall 55 of the flow-dependent valve 50: outflow of the pressure liquid in the event of distur bance is at least partially prevented. In principle, what is concerned in the case of such a flowdependent valve 50 is a series circuit of a fixed and a variable throttle location.

Figure 4 is a detail view similar to Figure 3, of another modification. Into the line 11 conveying the pressure liquid there is inserted a spring-biassed slide valve 60. The slide valve 60 comprises a guiding housing 61 in which a slide 62 is formed with two bores 64 or 65 of differing diameter. The slide 62 is controlled via a line 66 from the first pre-control valve device 15. In the event of an "on" command, the line 66 carries pressure liquid under high pressure; the slide 62 is pressed against the spring 63 and the bore 65 of large diameter passes into registry with the line 11. In the event of an "off' command, the pressure on the line 66 is almost zero, so that the spring 63 presses-back the slide 62, whereby the bore 64 of small diameter passes into registry with the line 11. Therewith, the liquid stream through the line 11 is very strongly throttled.This constriction of the line cross-section in the line 11 takes place prior to movement of the differential piston 3 in the direction of its position corresponding to the cut-out position of the interrupter head 1.

Here again - at least in the case of an "off' command, in the event of disturbance emptying of the hydraulic accumulator 8 is to a considerable extent prevented. Thereby, however, the ----- pole also does not, in the event of disturbance, travel through its barriers. In order nevertheless to be able to indicate the disturbance, a current-dependent switch 70 is also cut into the coupling line 47.

Figure 5 shows, again, two interrupter heads 1 of a pole, each actuated by an hydraulic actuating device 2. The two identical hydraulic actuating devices 2 each have a drive 5 which has already been described with reference to Figures 1 and 2. Again, due to a main valve device 6, the drive 5 is adapted to be subjected to the action of pressure liquid. In contradistinction to embodiments according to Figures 1 to 4, the embodiment according to Figure 5 has only a single common second pre-control valve device 71 (in place of the two valve devices 7) which is triggered by the first pre-control valve device 15.

Each hydraulic actuating device 2 has a line 11 which conveys the pressure liquid exclusively to the small-area side of the differential piston of the main valve devices 6. The large-area side of each drive piston 3, i.e. the chamber 48, is directly supplied with pressure liquid from a line 68 coming from the common, second pre-control valve device 71. From this line 68 there branch-off two lines 69 supplying the large-area sides of the differential piston of the main valve devices 6 with pressure liquid. Also in the case of this embodiment, the coupling line 47 supplies pressure equalisation in the event of malfunction of one of the main valve devices 6. If, for example, an "on" signal s effected via the electromagnetic correcting element 42, and if for example one of the main valve devices 6 is inoperative, again the high pressure on the large-area side of the drive piston having the operative main valve device is diminished via the coupling line 47 and the inoperative main valve device 6. Both interrupter heads 1 remain open. Via a flow switch 70, a disturbance or mal-function report is issued. If both interrupter heads are closed and if an "off' signal takes place via the electromagnetic control element 43, then the pressure decrease takes place, again with assumption of an inoperative main valve device 6, once again via the coupling line 47 and simultaneously also via the line 68 and the common second pre-control valve device 71.

Claims (10)

1. An hydraulically operated actuation device for operating interrupter heads of a pole of a high voltage circuit breaker and comprising: a plurality of driving devices corresponding one to each of said interrupter heads to operate the latter, each driving device comprising a differential piston and a cylinder which are relatively movable between first and second positions corresponding to on and off positions of the associated switching point; a respective main valve device corresponding to each driving device and operable to control the supply of pressure liquid thereto so as to operate the driving device between its first and second positions, said main valve device having a differential piston arranged to be movable in response to the supply of pressure liquid to the main valve device so as to vary the manner in which pressure liquid is supplied to the respective driving device;; a common pre-control valve device connected hydraulically to all of said main valve devices and operable to control the movements of the differential pistons of the main valve devices substantially simultaneously; and a coupling line intercommunicating the cylinders of the driving devices, on the larger-area sides of the differential pistons thereof, to provide pressure equalisation therebetween.

2. An hydraulically operated actuation device according to claim 1, in which at least one further pre-control valve device is arranged between said common pre-control device and said main valve devices.

3. An hydraulically operated actuation device according to claim 2 and having only one said further pre-control device, in which each driving device is arranged to receive a supply of pressure liquid via a line which intercommunicates the driving devices and said further pre-control device and which also serves simultaneously to control the operation of said main valve devices.

4. An hydraulically operated actuation device according to claim 1 or 2, including a respective line for conveying pressure liquid to the larger-area side of the differential piston of each driving device, in which a respective throttle is provided in each said line.

5. An hydraulically operated actuation device according to claim 1 or 2, including a respective line for conveying pressure liquid to the larger-area side of the differential piston of each driving device, in which a respective flow-dependent valve is provided in each said line and arranged so that, with increasing liquid throughput, the flow cross-section of the valve is diminished.

6. An hydraulically operated actuation device according to claim 1 or 2, including a respective line for conveying pressure liquid to the larger-area side of the differential piston of each driving device, in which there is provided in each said line a device controllable by said pre-control valve device for varying the free cross-section of the line.

7. An hydraulically operated actuation device according to claim 6, in which said device controllable by said pre-control valve device comprises a spring-loaded slide valve having a slide provided with different sizes of transverse bores.

8. An hydraulically operated actuation device according to any one of the preceding claims, in which a flow-dependent switch is provided in said coupling line.

9. An hydraulically operated actuation device according to claim 1 and substantially as hereinbefore described with reference to any one of the embodiments illustrated in the accompanying drawings.

10. A high voltage circuit breaker having coupled therewith an hydraulically operated actuation device according to any one of the preceding claims.