US2781435A

US2781435A - Arc-extinguishing mechanism for electric switches

Info

Publication number: US2781435A
Application number: US275832A
Authority: US
Inventors: Heilmann Philipp; Losch Herman; Marx Erwin; Schmitz Ludwig
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-03-18
Filing date: 1952-03-10
Publication date: 1957-02-12
Anticipated expiration: 1974-02-12

Description

.Feb. 12, 1957 P. HElLMANN ET AL 2,781,435 ARC-EXTINGUISHING MECHANISM FOR ELECTRIC SWITCHES Filed March 10, 1952 6 Sheets-Sheet 2 24 Fly. 2 W

' Inventor's; W Hu LM $1M Feb. 12, 1957 P. HEILMANN El AL 2,781,435

ARC-EXTINGUISHING MECHANISM FOR ELECTRIC SWITCHES Filed March 10, L952 6 Sheets-Sheet 3 Inventor's: MM LWL.

Feb. 12, 1957 P. HElLMANN ETAL 2,781,435

ARC-EXTINGUISHING MECHANISM FOR ELECTRIC SWITCHES Filed March 1o,' 1952 Q Sheets-Sheet 4 Invemars:

Hum... LWL.

6, Sheets-Sheet 6 P. HEILMANN ET AL Feb. 12, 1957 ARC-EXTINGUISHING MECHANISM FOR ELECTRIC SWITCHES Filed March 10, 1952 United States Patent ARC-EXTINGUISHING MECHANISM FOR ELECTRIC SWITCHES Philipp Heilmann, Hosel, near Dusseldorf, Herman Losch, Ratingen, near Dusseldorf, Erwin Marx, 'Braunschweig, and Ludwig Schmitz, Ratingen, near Dusseldorf, Germany Application March 10, 1952, Serial No. 275,832

17 Claims. (Cl. 200-150) This invention relates to certain improvements in means for switching electric currents with the aid of an extinguishing agent.

In electric switches operated with an extinguishing agent, besides various other quantities, the flow of the extinguishing agent, which may be for instance a liquid or a gas, and the pressure in the arc chamber, are of decisive importance.

It is an object of the present invention to provide means for directing the extinguishing fluid against the arc in a very intensive stream or jet both in the case of light and heavy currents.

A further object of the present invention consists in providing switches which are constructed in such a way that the various determining features can be varied independently of each other and that the construction 'of the switch can be easily adapted to a wide variety of different requirements.

With these and further objects in view, as will hereinafter appear, according to the present invention the extinguishing fluid is passed from a -first chamber to a second chamber by action of the circuit breaking motion, i. e. at least primarily independent of the current, in such a way that it flushes the are or spark, and then the extinguishing fluid is passed, through fluid passage resistances which are independent of the dynamic pressure, into a third chamber of a lower pressure. Hence according to the invention, as distinguished from the conventional method, not only the flow of the extinguishing fluid towards the are but also its flow away from the arc is directed and controlled in such a way that optimum switching capacities can be achieved. The extinguishing fluid may be supplied to the arc in such a manner, for instance, that the switch pin on separation of the contacts is quickly moved into the most favorable extinguishing position in relation to the blow-out nozzle associated'to it and in the further course of the circuit breaking process remains stationary in relation to the blow-out nozzle. Thus, the optimum extinguishing position is maintained during the whole circuit breaking process. A special advantage of the mode of operation according to the invention consists in that apart from the stream of the extinguishing fluid flushing the are also the pressure in the arc chamber can be adjusted in such a way by suitable adaptation, arrangement and dimensioning of the fluid passage resistances which are independent of the dynamic pressure that on the one hand a suflicient choking efiect is attained and on the other hand a predetermined maximum pressure is not exceeded, so that it is not necessary to dimension the arc chamber for unduly high pressures.

It is important for the extinguishing of the are that it is kept as short and straight as possible; this can be achieved in the simplest and most reliable way by supplying and leading away the extinguishing fluid axially symmetrically or nearly axially symmetrically.

In accordance with the present invention, a switch provided with a relatively small quantity of an extinguishing fluid is so constructed that this fluid is forced in the form of a high-speed jet into or against the are which occurs onmaking or breaking of contact.

The switch includes a pressure-proof cylinder which encloses a stationary terminal or switching element and also a movable terminal in the form of an elongated member or pin, such pin being disposed in a hollow piston which provides a first chamber and is slidably guided in the pressure-proof cylinder which forms a second chamber. Means are provided for moving the piston at the beginning of its switch-closing movement in sole mechanical dependence on the switch pin movement; the piston being provided with an opening whose cross-section is larger than the cross-section of the switch pin, so that the switch pin can pass through such opening to move into contact with the stationary switching element. The means which move the hollow piston include a driver disposed on the switch pin and adapted to carry the hollow piston with it in the circuit breaking movement after a predetermined relative movement between the tip of the switch pin and theopening'of the hollow piston. The stationary switching element is located in the second chamber which forms the arc chamber. A casing surrounds the first chamber, i. e. the pressure-proof cylinder, and forms therewith a third chamber. There are also provided a number of passages between the second and third chambers'which form fluid pass-age resistances which are independent of the dynamic pressure. It will be understood that various means may be provided for imparting .a switch-closing and switch-opening motion to theswitchpin.

In the accompanying drawings several now preferred embodiments of the invention are shown by way of illustrationand not by way of limitation.

Fig. l is a vertical longitudinal section through a switch 'havinga valve-controlled hollow piston, in the most favorable extinguishing position,

Fig. 2 .is a similar view showing a switch with two switch pins,

Fig. 3 is a similar view showing a switch with four switch pins.

Figs. 4a and 4b are similar views showing a modification of Fig. l in the closed and open positions, respectively;

Figs. 5a and 5 b are similar views of a further modification in the closed and open positions, respectively,

Fig. 6 is a sectional view of a switch comprising means for producing a flow of extinguishing agent which is independent of the current, and additional means for causing a further flow of extinguishing agent which is dependent on the electric current,

Fig. 7 is a section showing the concentric arrangement of the parts, and

Fig. 8 i s an axial section of a switch comprising a slide valve-controlled hollow piston and control means of a simple shape to provide optimum extinguishing conditions.

Similar reference numerals denote similar parts in the diflerent views.

It follows from fundamental considerations and from the results of numerous experiments that the extinguishing :of electric arcs with the aid of a flow of the extinguishing agent passed through a nozzle will take place in the most favourable manner where the electrode belonging to the nozzle is located in a definite position in relation-to the nozzle in which at least the root points of the electric arc and the zone in the vicinity of these root points are flushed by the extinguishing agent and intensively cooled in the periods when the instantaneous values of the current are small. The described position of the switch pin and associated nozzle is the most favorable position and it will be so designated hereinafter. It is reached after a predetermined relative movement between pin and nozzle opening and is the position wherein the arc root points on the switch pin tip are flushed by extinguishing agent of maximum speed.

This is achieved by the switch arrangement shown in Fig. 1. It will be seen that the switch elements, consisting of a movable switch pin 1 and a stationary contact sleeve 2 are housed in a pressure-resistant chamber 3. Accommodated in the chamber 3 is a hollow piston 5 encompassing the first chamber 4, the recess or opening 6 of this hollow piston 5 in cooperation with the switch pin 1 forming the annular gap 7 and acting pump-fashion, as will be hereinafter described. According to the present invention these parts are combined with

restrictions

7 and 8 whose fluid passage resistance is independent of the dynamic pressure and which are arranged between the arc chamber constituted by the second chamber 9 located in the pressure-resistant chamber 3 and a third chamber 10 of a lower pressure for the extinguishing agent flowing first into chamber 9 at 11 and consisting, for instance, of oil, compressed air, nitrogen, or the like.

The switch pin 1 is rigidly connected with a spoke-ring 12 which in carrying out the circuit breaking motion engages the annular stop 13 of the carrier 5 of the annular gap or extinguishing nozzle, which carrier is in the shape of a hollow piston, so that from this moment the hollow piston 5 is carried with the switch pin in the cutting out direction and the nozzle cross-section at 7 remains constant. Disposed within the hollow piston 5 is moreover a piston ring 14 which is secured on a stationary guide body 16 with the aid of at least three threaded pins which are uniformly distributed over the circumference. Springs 17 permit the piston ring 14 to yield in an upward direction in case of a high internal pressure in the hollow piston 5. On movement of the hollow piston 5 in an upward direction, the extinguishing agent situated therein is extruded through the annular gap 7, producing a stream of the extinguishing agent. During high instantaneous values of the current of the electric arc a very high gas pressure prevails in the electric arc chamber, so that the discharge of the extinguishing agent is decelerated; in the vicinity of the zero value of the electric arc current the velocity of flow of the extinguishing agent is all the more intensive. Moreover, with very high instantaneous values of the current, the issuing extinguishing agent is evaporated very quickly, while in the neighborhood of zero current the extinguishing agent gets to the core of the electric are without being evaporated.

The pressure-resistant chamber 3 at first absorbs the high pressure forming in the arc chamber 9. In the walls of this chamber 3 which like the hollow piston 5 may consist partly of insulating substances and of metals or of metal parts coated with insulating substances, further recesses or

openings

18 and 19 are provided in addition to the recesses, openings or bores 8 already mentioned, at least three of these recesses being distributd over the circumference at distances which are as uniform as possible, so as to cause the extinguishing agent to flow substantially symmetrically to the axis. The

recesses

8, 18, 19, are arranged and dimensioned in such a Way that optimum interrupting capacities can be attained and that the pressure in the outer barrel-shaped body 20, which for instance may consist of porcelain, does not become unduly high. The vapor forming on breaking the circuit produces in the interior of the pressure-resistant chamber 3 a high pressure which can be communicated to the outside only very slowly, through the

apertures

8, 18, and 1.9. By reason of the high pressure in the vicinity of the arc, arcing back is rendered difiicult; primarily it is also used to drive the hollow piston 5. By the provision of the piston guide 21 a much higher pressure is produced in the lower pressure chamber 9 during the circuit breaking than in the upper chamber 22 which is connected to the outer chamber 10 through the

apertures

18, 19. The pressure in chamber 9 exerts a force upon the hollow piston 5 which is upwardly directed. On the ring or guide 21 there may be provided springy bufiers 21 by which the movement of the hollow piston 5 is braked in the last part of the switching-on operation.

The central bore 87 in the switch pin 1 is connected with the chamber 10 through apertures 23. The level in case of a liquid extinguishing agent is approximately at 24.

The switching-on operation takes place as follows:

In the open position the switch pin 1 is drawn upwards as far as possible; the hollow piston 5 is in its top position. When the locking pawl 25 is not present, the switch pin 1 with the spoke ring 12 is moved downwards for switching on, without taking along the hollow piston 5. Only when the ring 12 strikes against the stop face 26, the switch pin 1 carries the hollow piston 5 along in a downward direction. Thus the extinguishing agent is sucked into the chamber 27; the fluid passes through the valves 28 and through the gap between switch pin 1 and the walls of the hollow piston defining the recess 6. The switch pin 1 is decelerated by taking along the hollow electrode 5, so that the switching-on motion in its very last part, i. e. when the head of the switch pin 1 engages the contact 2, takes place with a small force. Where the switching-on action establishes a short circuit, difficulties may be caused thereby. The switching-on operation takes place in a more favourable way, however, if the switch pin carries the hollow piston 5 along on the first part of its motion and is relieved from the hollow piston only in the last part of the closing motion. To this end a locking pawl 25 may be used which permits a relative motion of the ring 12 in relation to the hollow piston only when the lever 29 strikes against the cam member 30. Thus the last part of the motion of the switch pin is no longer braked by the necessity of carrying the hollow piston with it; the switch pin 1 can contact sleeve 2 with a large dynamic energy which may be increased by additional weights, if necessary.

In dimensioning and arranging all parts of the switch it should be considered that certain periods of time and paths are always required to produce movements of the extinguishing agent and for starting and breaking switch members. Therefore, in the switched-on position the nozzle-shaped annular gap 7 should be located very close to the switch member 2 in order that the required flow of the extinguishing agent is set up even after a short path and the switch pin is braked by the hollow piston.

The liquid stream can be impeded during high instantaneous values of the current by an elastic member while it can be accelerated by such a member during small instantaneous values of the current. It is also possible to use as such an elastic member an amount of gas which is disposed above the liquid level in the hollow piston. In order to give such a body of gas a definite dimension, the same may be accommodated in a rubber container. Such a rubber container may be inserted under the ring 14 in Fig. 1 and may be of an annular shape. In order to ensure that this rubber container is intact, a pipe may be lead from said container to the outside, with a control apparatus being provided at the outer end of the pipe.

In the above explanations it has been assumed that the hollow piston 5 produces the motion of the extinguishing agent. It is also possible, however, to produce the flow of extinguishing agent by one or more special pistons which may be arranged in the interior or outside of the real switching chamber and may be operated shortly after the beginning of the circuit breaking motion, through a linkage or compressed gases and on termination of the circuit breaking action is or are returned to its or their initial positions. The provision of separate pistons is advisable especially Where several nozzles for the flow of the extinguishing agent are provided in a switch gear.

Fig. 2 shows a further embodiment exemplifying a double or twin arrangement in which the switch pins 31 and 32 are moved from each other in opposite directions for circuit breaking. In the switched-on condition these switch pins engage the

counter contacts

33 and 34 which are electrically connected with each other. During the circuit breaking motion the piston 35 acts to produce a flow of extinguishing agent through the

nozzles

89 and 90 which flow of extinguishing agent flushes the are additionally to the streams of extinguishing agent through the

nozzles

36 and 37 known from the arrangement according to Fig. 1. The operation of the nozzles 36 to 37 is the same as in Fig. l. The

switch electrodes

31, 32 have to be located in the correct position in relation to the

nozzles

36, 37 during the whole extinguishing process. The movements of the

hollow pistons

38, 39 are subject to the conditions already discussed with reference to Fig. 1.

The arrangement according to Fig. 3 has four extinguishing nozzles. Therefore, since these nozzles during the circuit breaking phase are connected in series, the switch is able to control approximately the fourfold of the voltage which can be controlled by the arrangement according to Fig. 1 in which only one nozzle is provided. In case of switche for extremely high working voltages a series connection of a plurality of units as shown in Fig. 2 may be used. Therefore, in Fig. 2 the ends of further

similar switch units

40 and 41 have been indicated. The switch pins or contact pins in this case have to be operated through rods which are con-- nected with the connecting

fittings

42 and 43.

The connection of two maximum output switches with four extinguishing nozzles each as shown in Fig. 3 permits a construction of such series connections which is shorter in length compared to arrangements according to Fig. 2. Moreover, the switch gear of Fig. 3 has been provided for horizontal mounting. Its operation will be described only in as much as it differs from that of the arrangements already described. The switch pins 44, 45 etc. which are visible in the drawing are moved towards each other through diagrammatically indicated rods 46 for circuit breaking. To this end, piston 47 i moved downwards, thereby extruding the extinguishing agent through the

pipes

48 and 49 into the hollow piston chambers 56 and 51. The

hollow pistons

52 and 53 are slidably mounted on the guide members 54 and 55 which are fixedly connected to the switch frame. The parts of these guide members extending towards the switch points are constructed in the form of spokes, so that the constructional elements 56 and 57 fixedly mounted on the switch pin are able to move the

hollow pistons

52 and 53 in the manner as described above during the Y switching on and circuit breaking operations. To this end the elements 56 and 57 are also constructed in the form of spokes.

During the switching on and circuit breaking operations the switch pins 44 and 45 etc. slide on cylindrical guide bolts which are fixed on the central disc 5? which is held in the pressure-proof chamber 69. Moreover, in the vicinity of the central plane of the switchgear is arranged an air container or tank 61 communieating with the outer atmosphere through small openings 62. A hood 63 covers these openings where a switch is mounted in the open air.

The remaining constructional elements of the switch have been described already in connection with Figs. l and 2.

Figs. 4a and 412 show a further embodiment of the invention which has been modified compared to Fig. 1 in regard to details only and exemplifies a switch intended for switching large powers, using small quantities of oil. To facilitate comprehension Fig. 4a shows the device in closed position while Fig. 4b shows it in open position, in the movement of most effective flushing by the extinguishiug agent. The difference compared to the embodiment of Fig. 1 consists in the construction of the hollow piston which in this case consists of an insulating body 64 secured to a metallic sleeve '65 which in turn is sliding in the piston guide '66. The pressure-proof chamber also consists of an insulating body 67 and a metallic sleeve 68. The metallic sleeve body slides in the

closure member

66, 69 of the pressure-

proof chamber

67, 68 which closure member is closed at 69 against the issue of oil.

In the switching-on motion, the switch pin 1 is moved downwards from the position shown in Fig. 4b. The spokes 12 in this case engage with the edge 26 of the

hollow piston

64, 65, taking the same along in a downward direction. When the switch pin has reached its closed position, the

parts

64 and 65 continue to move downwards at a low speed, until the member 64 engages the contact sleeve 2. Care should be taken in order that during the switching-on motion oil is permitted to enter into the hollow cylindrical chamber 10 without too high fluid passage resistances. The ring 14, which otherwise is drawn upwards by the spring 17 and bolt 15, during the downward motion of the switch pin 1 uncovers passages or ports 70 for the oil. Moreover, the switch pin 1 is formed with a restricted cross section at 71 so that oil also during the switching-on motion is permitted to pass from below in an upward direction between the insulating member 65 and the switch pin 1.

The circuit breaking process takes place substantially as follows:

The upward motion of the switch pin 1 takes place at first under action of a circuit breaking spring. On separation of the

contacts

1 and 2 from each other an electric are i produced by which the surrounding oil is evaporated. Shortly thereafter the spokes 12 engage the edge 13 and the fiow of extinguishing agent through the

nozzle

6, 7 is started. The tension which the switch is able to stand on extinguishing of an are without arcing over, is defined by the electrode distance between the

members

1 and 2 by the pressure and temperature of the gas bubble. In the arrangement of Figs. 4a and 4b the flow of oil is produced a very short time after the separation of the contacts; hence a very short time after the separation of the contacts a favourable extinguishing distance has been set up. As soon as the switch pin 1 engages and carries with it the

members

64 and 65, its motion will be decelerated accordingly, which has a very favourable effect.

Since the moment of separation of the contacts is not defined as to its position in relation to the phase of the alternating current to be interrupted, it cannot be anticipated in which position of the switch pin the current will pass through its zero value. This moment may vary by one half period, that is to say, in the ease of 50 cycles per second it may vary by second. During this time the switch pin should move only slowly. The velocity of the extinguishing agent is determined by the surface of the pressure piston, i. e. substantially by the maximum diameter of the

members

64, 65 if the properties of the circuit breaking spring are regarded as constant. The pressure of the gas bubble forming in the real are chamber imparts to the switch pin 1 an additional acceleration, since the upper part of this switch pin extend into the atmospheric air. In case of maximum currents to be interrupted the force exerted thereby on the contact pin is of the same magnitude as the force of the circuit breaking spring. On the other hand, in case of switchgears or switching operation with smaller current intensities occurring much more frequently, the switching speed is determined almost exclusively by the circuit breaking spring.

The amount of oil passing between the contact pin 1 and member 64 is determined by the narrowest point of 1 the nozzle cross section. Finally the pressure in the arc chamber with given values of current and voltage is determined by the position and cross section of the

openings

18 and 19 in the pressure-

proof chamber

67, 68. This discovery, i. e. that these apertures and their position are of a particular importance for the circuit breaking operation and the extinguishing of the arc represents a particularly important part of the present invention. It has been found by very thorough experiments that too large apertures result in too low pressures in space 9 and thu cause arcing back or persisting arcs. This is true especially with low current intensities which have to be switched frequently. Too small apertures between the

chambers

22 and 10 on the other hand cause a too intensive increase of the pressure within the chamber 67, so that destruction of thi chamber may occur especially with very high current interrupting intensities. It is a decisive and fundamental feature of the present invention that the course of the flow of the extinguishing agent has to be considered not only up to the arc chamber, but in the same way from the are chamber 9, since as already mentioned, in examining the safety of a switch against arcing back and persisting arcs, the pressure prevailing in the arc chamber 9 immediately after the zero values of the current is of particular importance. The development of gas by the are of course is particularly intensive in case of high instantaneous values of the current, while with a view to the reliability or safety of the extinguishing it is important to obtain a high pressure in the are chamber 9 a short time after the zero value of the current. The temporal course or characteristic of the pressure which is closely connected to the flowing otf of the extinguishing agent from the are chamber, is determined by the size and also by the position of the

apertures

18 and 19 as well as 87.

This requires large insulating lengths of chamber 67 and of member 64. Moreover it is advisable that the

apertures

18, 19, by which the fluid passage resistances are determined, are arranged in such a way that their distance from the stationary contact 2 is greater than the distance between the stationary contact and the movable contact 1 in the case of open position of the switch. Since the direction of the flowing oil or discharge of the extinguishing agent in the arc chamber is determined mainly by the direction of the motion of the contact pin, a large insulating length can be arranged in a favourable manner. A rectangular deflection of the flow of the extinguishing agent, i. e. a deflection from the radial into an axial direction is moreover favorable for controlling the pressure conditions in the are chamber 9. A Zone of stagnation of the flow which will favour depositions, can be arranged in such. a way that a zone which is free from flow is formed under the same as a sump. The chamber 72 in Fig. 4 is such a sump chamber which simultaneously is relieved electrically.

Figs. a and 51) show some modifications or supplements to Figs. 4a and 4b, the reference numerals for the rest corresponding to those of the latter figures.

In Figs. 5a and 5b the switch is shown approximately in it optimum extinguishing condition for an average amount of rated voltage. By the provision of :a member 73 which for instance may be a spring ring, the

hollow piston body

64, 65 is prevented from sinking down into engagement with the contact sleeve 2 when the switch is in its closed position. The contact pin 1 in this case is free to move into the position shown in Fig. 5b, under the action of the circuit breaking spring and only from this position will take along the extinguishing nozzle, 6, 7.

It has been found by experiences that with switchgears according to Figs. 4a, 4b, 5a, 5b,

pressure chambers

67, 68 which are tested with static pressures of several hundred atmospheres are sometimes destroyed. However, by normal measuring equipments with such arrangements only pressures far below these values are recorded. Such de structions can result only where on separation of the contact approximately in the crest value of very heavy currents, pressure waves are formed by the very sudden development of gas, which pressure waves cause very short timed, but extremely high pressures. For protection against such pressure waves it is advisable to provide the inner surface of the pressure chamber with gas buffers at those points where such pressures can occur. Since these pressure waves occur only for extremely short times and since the quantities of gas produced up to the moment where they can be carried off through the

apertures

37, 18 and 19 in the case of very high pressure are also only very small, it is sufficient that such a gas buffer has only a very small volumetric content of a few percent of the real are chamber 9 within the pressuure chamber 67. Such a small dimensioning of the gas buffer or cushion is favourable because in this way it is prevented that the pressure in the arc chamber 9 will be reduced with small currents to be interrupted. The gas cushions proposed in this connection, which are intended exclusively to absorb the first pressure wave, accordingly differ by their small volume from the gas chamber already known for switches. Instead of a gas cushion accommodated in an air hose it is also possible to provide a rubber cushion 74 with inclusions of air (aerated or expanded or crepe rubber). The rubber surface may be coated with heat resistant substances, if necessary, to prevent its being damaged by radiated heat.

Finally in Figs. 5a and 5b springs 75 and 76 are shown by which the ring which in this case is slidable, with its spokes 12 is resiliently connected to the contact pin 1. The shock upon the parts 64 and occurring during interruption or connection is thus damped.

The arrangements shown in Figs. 4a, 4b, 5a and 5b of course may be used also in a horizontal position or in a reversed position, so that the lower contact pin is moved. The teachings given by the present invention in this case have to be modified accordingly. Moreover, it is possible to connect a plurality of the arrangements hereinbefore described in per se known manner.

The special advantage of the

hollow switch pin

1, 87 used according to Figs. 1 to 5b consists in the fact that the extinguishing agent flows off in an outward direction through the hollow switch pin about the front end tip of the switch pin. By the deflection of the flow of the extinguishing agent thus constrained immediately before the tip of the switch pin the same is surrounded by a fresh insulating jacket of extinguishing agent from all sides and thus the path of .the arc is effectively cut through or pierced. The are in this case is attacked on a relatively small part of its length only, so that the voltage of the arc and so also the switch work remain small.

It is of no importance for the efliciency of this extinguishing arrangement whether a liquid or a gaseous extinguishing fluid is used. The blow-out fluid may be fed to the switch from outside, from a pressure accumulator or tank, or it may be pressured by the circuit breaking force of the switch pin and forced through the annular nozzle about the tip of the switch pin.

Figs. 6 and 7 show flow type switches in which the ho]- low switch pin is retained; in this case a mechanically moved pumping device of the kind already described and a second pumping device influenced in dependence upon the current i. e., of the arc effect upon the extinguishing agent cooperate to supply extinguishing fluid to an annular nozzle arranged concentrically about the switch pin, forcing the extinguishing agent in a sharp jet onto the root point of the are at the tip of the switch pin which is exposed to maximum specific load.

The embodiments shown in Figs. 6 and 7 are two different exemplifications of this kind. According to Fig. 6 the pumping device which is moved in dependence upon the current is connected through pipes with the switch chamber and with a nozzle, while according to Fig. 7 this pumping device is arranged concentrically about the annular nozzle.

Again, 2 is the stationary switch member, 1 is the movable switch pin with the

stop flange

12, and 5 is the hollow piston with annular nozzle 6. Moreover, 77, 73 designate a two step piston, 3 the pressure-proof chamber and 79 an excess pressure valve.

The hollow piston 5 in the connected position of the switch rests on the stationary switch member 2. In the moment of the separation of the contacts it is taken along in upward direction by the stop flange 12 .of switch pin 1. The oil displaced by it from the upper part of chamber 3 flows through the annular nozzle 6 concentrically in a sharp stream onto the root point of the are at the tip of the switch pin. The gases which are produced escape through the hollow switch pin into the chamber 10 of minimum pressure of the switch.

The volume displaced by the hollow piston is rated in such a way that the injected amount of oil is suflicient for extinguishing small currents with short duration of the are, without the driving power becoming too large. Where heavy currents are to be interrupted, the piston 7 8, 77 is raised by the pressure resulting in the switch chamher in this case and a correspondingly larger quantity of oil is injected through the annular nozzle. Excess pressure will escape through valve 7%.

Fig. 8 shows a switch in which the switch pin is formed with different cross sections. By this simple measure a number of decisive advantages are attained. First, the switch pin in the moment of carrying with it the hollow piston uncovers an annular gap for passage of the extinguishing agent at the passage opening into the closed switch chamber and in the circuit breaking motion it closes this annular gap only on reaching the extinguishing distance in the moment where the hollow piston is carried with the switch pin, reopening the same shortly before the open position is reached. By this construction on the one hand the switching-on action is substantially facilitated, on the other hand in the circuit breaking action, the force exerted on the switch pin with its enlarged cross section by the pressure produced in the switch chamber by the arc is so high that the hollow piston driven by the switch pin forces the extinguishing agent through the annular nozzle about the tip of the switch pin at an increased velocity.

Referring to Fig. 8 in detail, showing a high output switch, it will be seen that the pressure-proof switch chamber 3 of insulating material with a stationary switch member 2 and a movable switch pin 1 is accommodated in a casing 20, the tip tit? being screwed into the lower end of the switch pin 1, which is fitted with a driver 12 having passages 81 for the extinguishing agent and taking along the hollow piston 5 of insulating material, whose lower recess 6 forms an annular gap '7 together with the tip 8% of the switch pin.

Above the driver 12 the switch pin 1 is formed with a thickened portion 82 which in the position as shown, i. e. shortly after the taking along of the hollow piston 5 by the switch pin 1, closes the

passage33of switch pin

1, 82 in the closed switch chamber 3. As the switch pin 1 is moving in the circuit breaking direction, the extinguishing agent situated above the hollow piston is forced towards the annular gap 7. Since the are burning between the stationary switch member 2 and the tip 80 of the switch pin by evaporation of the extinguishing agent produces a pressure in the closed chamber 3, the extinguishing agent is prevented from issuing towards the lower part of the switch chamber 3, so that it is only permitted to flow off around the tip 80, through the hollow switch pin, towards the free switch chamber 10. With growing pressure in the lower part of the switch chamber 3 the switch pin is additionally accelerated and by means of the hollow piston 5 it will force or extrude the extinguishing agent at an increased intensity from the upper part of the chamber 3 through the annular gap 7 about the tip Si) of the switch pin. The thickened portion 82 of switch pin 1 is of such a length that shortly before reaching the open position-the

switch pin

1, 82 at its passage opening 33 leading into the switch chamber 3 will uncover an annular gap for the passage of the extinguishing agent which is larger than 83. Thus the switch chamber 3 will refill immediately as the cincuit breaking process is completed. The hollow piston 5 in the interrupted position uncovers the

bores

84, 85 of stepped'cross section, located in the switch chamber 3.

In the switching-on operation, the switch pin 1 at first closes the switch chamber 3 by its thickened portion 82. The extinguishing agent thus displaced by the switch pin is permitted to escape freely through the bores 84, in the switch chamber. As soon as the switch pin 1 with its driving member 12 has overtaken the hollow piston 5 and carries the same with it, the thickened portion d2 of switch pin 1 again uncovers an annular gap at the passage opening of switch pin 1 leading into the switch chamber 3, which second annular gap is larger in cross section than the first annular gap, so that the extinguishing agent displaced by the switch pin 1 in the switch chamber 3 is now permitted to issue freely from the switch chamber 3 through the

bores

84, 85 uncovered by the driver 12 and through the annular gap at the passage opening of the switch pin. By the thickened portion 82 on the switch pin 1 in connection with the bores 86 in the hollow piston 5 controlled by the driver 12, as well as with the aid of the

bores

84, 85 controlled by the hollow piston 5 in the closed switch chamber 3, the switching-on and circuit breaking actions are favourably assisted. The driver 12 in this case acts in regard to the recesses 86 as a slide valve control which is independent of the dynamic pressure.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and form-ing a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

2. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening Whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means com prising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, at least one additional pump piston having two portions of different diameter, the smaller action surface being exposed to the pressure of the hollow chamber in the hollow piston and the larger action surface being exposed to the pressure in the are chamber, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

3, A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in solo mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, at least one additional pump piston having two portions of different diameter, the smaller action surface being exposed to the pressure of the hollow chamber in the hollow piston and the larger action surface being exposed to the pressure in the arc chamber, said additional piston and said hollow piston being concentrically arranged in said chamber.

4. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switch ing element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, said passage means being formed by a central recess of the movable switch pin, means for imparting switching-on and circuit breaking 12 motions to the switch pin, and a supply of extinguishing fluid in said casing.

5. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, said passage means being formed by openings in the wall of said pressure-proof chamber, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

6. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, said passage means being formed by a central recess of the movable switch pin, and said passage means being formed by openings in the wall of said pressure-proof chamber, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

7, A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in solo mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, said passage means being formed by openings in the wall of said pressure-proof chamber, at least three of said openings being axially symmetrically arnanged in relation to the switch pin, means for imparting switchingon and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

8. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, valves between the hollow space of the hollow piston and the third chamber for admitting extinguishing fluid into the hollow piston space and preventing the discharge of extinguishing fluid from the hollow piston space, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

9. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and openings arranged in said hollow piston in such a way in relation to the driver that the driver is adapted 1-4 to uncover the openings by switching-on motions and to close them by circuit-breaking motions, and a supply of extinguishing fluid in said casing.

10. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which. owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, said switchpin having ditferent cross-sections, said cross sectional difierences being adapted to control the extinguishing fluid, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-0n and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

11. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in'the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, said switch pin having different cross-sections, a thickening of said switch pin being arranged in such a way that said thickening in the circuit-breaking motion enters into a passage opening of said pressure-proof chamber, whereby the circuitbreaking force is increased, passage means being pro vided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

12. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, said switch pin having different cross-sections, a thickening of said switch pin being arranged in such a way that the switch pin in the switching-on motion at the moment of taking the hollow piston along opens an annular gap at the point of its passage through the hollow piston, said annular gap being adapted to facilitate the switching-on motion, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

13. A switch operating wit-h small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching elements, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, said switch pin having different cross sections, a thickening of said switch pin arranged in such a way that the switch pin in the circuit-breaking motion in the moment of taking the hollow piston along closes an annular gap at the point of its passage through the hollow piston and reopens the same shortly before reaching the end of the circuit-breaking motion, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit break-ing motions to the switch pin, and a supply of extinguishing fluid in said casing.

14. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, pressure-proof chambers enclosing the switching elements, at least two switch pins, the switch pins being arranged in pairs in such a way that the two pins of each pair are movable in opposite directions, hollow pistons slidably guided in said chambers, their hollow spaces forming first chambers, means adapted to move the hollow pistons at the beginning of their movement in sole mechanical dependence on the switch pin movements, said hollow pistons having openings whose cross sections are larger than the cross sections of switch pins adapted to be passed through said openings owing to their slidability and contacting the stationary switching elements in the switching-on motion, said means comprising drivers provided on said switch pin and adapted to carry the hollow pistons along in the circuit-breaking motion after a predetermined relative movement between the tips of the switch pins and the openings in the hollow pistons, the spaces between said stationary switching elements and the first chambers constituting at least one second chamber, each of said second chambers forming an arc chamher, a casing enclosing the chambers and forming at least one third chamber, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to said switch pins, and a supply of extinguishing fluid in said casing.

15. A switch operating with small quantities of extinguishing fluid comp-rising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said hollow piston. forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuitbreaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, elastic means between the switch pin and the hollow piston, passage means being provided between said second and third chambers so as to form fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said casing.

16. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston s-lidably guided in said chamber, the hollow space of said hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on mot-ion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuit-breaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, passage means being provided between said first, second and third chambers, the passage means between said second and third chambers forming fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit breaking motions to the switch pin, and a supply of extinguishing fluid in said chambers.

17. A switch operating with small quantities of extinguishing fluid comprising stationary and movable switching elements, a pressure-proof chamber enclosing the switching elements, at least one of the elements being constructed as a movable switch pin, a hollow piston slidably guided in said chamber, the hollow space of said 17 hollow piston forming a first chamber, means adapted to move the hollow piston at the beginning of its movement in sole mechanical dependence on the switch pin movement, said hollow piston being formed with an opening whose cross section is larger than the cross section of the switch pin which owing to its slidability can be passed through said opening and in the switching-on motion contacts the stationary switching element, said means comprising a driver provided on said switch pin and adapted to carry the hollow piston with it in the circuitbreaking motion after a predetermined relative movement between the tip of the switch pin and the opening of the hollow piston, the space between said stationary switching element and said first chamber forming a second chamber constituting an arc chamber, a casing surrounding the first chamber and forming a third chamber, elastic means between the switch pin and the hollow piston, passage means being provided between said first,

second and third chambers, the passage means between said second and third chambers forming fluid passage resistances which are independent of the dynamic pressure, means for imparting switching-on and circuit-breaking motions to the switch pin, and a supply of extinguishing fluid in said chambers.

References Cited in the file of this patent UNITED STATES PATENTS