GB2089572A - A Puffer-type Gas-blast Circuit Interrupter - Google Patents

Abstract

A puffer-type circuit-interrupter has an annular piston 142 slidable on a fixed contact 96 within a cylinder 146. A spring 154 biases piston 142 towards a fixed electrode 84 which has a movable contact 108, connected to an operating member 112, in sliding engagement therewith. A first abutment 152, on tube 150 secured to piston 142, engages a second abutment 136 on contact 108. Closure of the interrupter causes compression of spring 154 by piston 142. Upon opening of the interrupter, the abutments 152, 136 part and movement of the piston 142 by spring 154 is only minimal. The amount of piston movement at this stage is determined by the inertia of piston 142, spring 154 and tube 150, the force of spring 154 and the "impedance" of the gas circuit of the interrupter 12. Consequently, piston 142 is still moving when the contacts have attained their fully-open position and, therefore, a gas flow is at a maximum when it is most likely to contribute to extinguishment of the arc. <IMAGE>

Description

SPECIFICATION Gas-Blast Circuit-lnterrupters The invention relates to gas-blast circuitinterrupters.

Some forms of high voltage circuit interrupters are housed in enclosures filled with insulating medium, typically an insulating gas such as sulphur hexafluoride (SF8). An arc drawn between the interrupter contacts during operation of the interrupter is extinguished at a current zero. The gas-blast effect of the insulating medium heated by the arc assists in extinguishing the arc. That effect can be enhanced by mechanically induced or pneumatically induced gas-blasts.

Mechanically induced gas-blasts have been derived from interrupters having a puffer-type construction, i.e. having a cooperating piston and cylinder which operate to produce a gas-blast. In such constructions either the piston or the cylinder can be arranged to move. Movement is achieved by connecting the piston or cylinder to the movable contact(s) of the interrupter.

Consequently, the gas-blast produced by such an arrangement occurs over the whole of the opening movement of the contacts, apart from an initial compression of the insulating medium that is achieved in constructions that have a separate arcing contact as part of the movable contact arrangement.

However, an arc drawn between contacts can only be extinguished when the spacing of the contacts is such that current path cannot be reestablished in un-ionised in un-ionised insulating medium. Thus, at the start of the opening operation, the gas-blast is not having any real effect on the arc and, at the end of the opening operation when the gas-blast would be most effective, the gas-blast is substantially finished.

According to the invention, a puffer-type circuit-interrupter comprises a chamber which contains pressurised gas having arc-extinguishing properties, coaxial contacts, a spring and a cylinder member containing a piston member, one member being movable towards a position in which the spring is held in a stressed condition by engagement between a first abutment connected to said one member and a second abutment connected to an operating member, which operating member holds the abutments in engagement in the closed condition of the interrupter and, on opening of the interrupter, separates the abutments and the contacts to draw an arc across a gap between the contacts, the gap establishing communication between the chamber and an exit path provided by an axial passage through at least one of the contacts, consequent movement of said one member by the spring causing gas flow into the gap and along the path to assist in extinguishing an arc between the contacts, said movement being completed after the operating member has halted.

A circuit-breaker incorporating a circuitinterrupter will now be described to illustrate the invention by way of example only with reference to the accompanying drawings, in which: Figure 1 is a partial vertical section through the circuit-breaker; Figure 2 is a vertical section, on a larger scale, through the interrupter shown in Figure 1, the interrupter being in the open position; Figure 3 is a section on the line Ill-I II in Figure 2; Figures 4 to 9 are similar to Figure 2 but form a series showing the closing and opening sequences of the interrupter; Figure 10 is an enlarged section through a modified part of the interrupter; and Figure 11 is similar to Figure 2 but of a modified interrupter.

A circuit-breaker 10 has one or more circuitinterrupters 12 (only one shown), one for each phase of the current supply (see Figures 1 to 3).

The circuit-breaker 10 has operating mechanism 14 located in the lower casing 1 6 of aluminium or cast epoxy resin, for example. The mechanism 14 includes a shaft 18 rotatable by a charged-spring system (not shown), for example, a crank arm 20 and a pair of elongate members 22 of insulating material pivotted at one end to the crank arm 20 and at their other end to a movable contact assembly of the circuit interrupter 12, as is more fully described below.

The shaft 1 8 is common to all the interrupters when more than one interrupter is used. The lower casing 1 6 has an inspection hatch 24 adjacent the crank arm 20 of the, or each, interrupter.

An upper casing 26, of the same meterial as the lower casing 16, is secured to the lower casing 1 6. The upper casing 26 is substantially cylindrical, is closed at its upper end and has two lateral, vertically separeted, hollow limbs 28, 30 in each of which is located a transition conductor 32, 34 of copper, for example.

The conductors 32, 34 each terminate in spring-finger connectors 36, 38 at one end and engage spring-finger connectors 40, 42 on the terminals of the circuit-interrupter 12. The conductors 32, 34 are encased in respective bushings 44, 46, which locate the conductors 32, 34 centrally within respective annular insulating members 48, 50. The members 48, 50 are secured by respective annular metal caps 52, 54 to the limbs 28, 30 of the upper metal casing 26.

The circuit-breaker 10 is filled with insulating medium, for example SF6 gas, which can flow between the upper and lower casings 1 6 and 26 internally and externally of the interrupter 12.

The circuit-interrupter 12 is mounted within the circuit-breaker 10 by a tubular support 56 of insulating material secured to the lower end of the interrupter 1 2'and to the lower casing 1 6.

The circuit-interrupter 12 has a lower terminal 58 and an upper terminal 60, to which are attached the spring-finger connectors 40, 42.

The lower terminal 58 is made of conducting material, for example brass. The terminal 58 is cylindrical and cup-shaped and has a boss 62, engaged by the connector 40, and an annular end wall 64.

The upper terminal 60 is also made of conducting material, for example brass. The terminal 60 is cylindrical and cup-shaped and has a boss 66, engaged by the connector 42, and an annular end wall 68. An annular boss 70 extends inwardly from the wall 68.

A cover 72 is fixed to the wall 68 of the terminal 60. The cover 72 has a plurality of openings 74 and contains a pressure-responsive valve 76. The operating member of the valve 76 is biased to close the central aperture 78 in the wall 68 of the terminal 60.

The terminals 58 and 60 are interconnected by a tube 80 of insulating material. The tube 80 is secured at its upper end to the terminal 60 and at its lower end to an annular member, for example made of brass, screwed into the terminal 58.

The terminals 58 and 60 together with the tube 80 define a contact and arc-interruption chamber 82.

A first fixed tubular contact 84 is secured to the lower terminal 58 by an outwardly-extending flange 86. The flange 86 has a plurality of oneway valves 88 formed by, for example, using an annular plate 90 to retain balis 92 within stepped openings 94, the plate 90 being secured with the flange 86 to the wall 64 of the terminal 58.

A second fixed main and arcing tubular contact 96 has an upper flange 98 secured by screws to the annular boss 70 of the upper terminal 60 such that it is coaxial with the first contact 84 on the axis 1 Oci of the interrupter 1 2. The second contact 96 has an arcing tip 102 of arc-resistant material, for example Elkonite (Trade Mark). The second contact 96 has apertures 104, which communicate with radially-directed recesses 106 in the annular boss 70 of the terminal 60.

Third and fourth contacts 108 and 110 are located within the chamber 82 and are coaxial with the axis 100 of the interrupter 12.

The third contact 108 is a main contact 108, and the fourth contact 110 is an arcing contact.

An operating member 11 2 is connected to the contact 108 to move it relative to the first and second contacts 84 and 96.

The member 112 is a tube, for example made of steel, which is pivotted at its lower end to the elongate members 22 of the operating mechanism 14 and is guided by bearings 114 supported within the first contact 84. The member 112 has a bush 116, also of for example steel, which reinforces the pivot and also provides an abutment for one end of a compression spring 118. The other end of spring 118 engages the lower end of the fourth contact 110, which siides in bearings 120 suppored within the tube 112.

The spring 11 8 is still under compression in the open position of the interrupter 12, thereby ensuring good electrical contact in the closed position of the interrupter.

The tube 11 2 has circumferentially-extending external abutments 122 interposed with larger external protuberances 124 at its upper end and an internal annular abutment 126 spaced from its upper end.

The third contact 108 has an outer cover 128 of brass, for example, secured to the protuberances 124 of the member 112 and a plurality of contact fingers 1 30. The contact fingers 1 30 are each internally recessed to engage one of the abutments 122 of the member 11 2 and are each externally recessed to provide a seating for a leaf spring 1 32 compressed between the cover 128 and the respective finger 130. The lower end of each contact finger 1 30 is in sliding engagement with the first contact 84 and the upper and of each contact finger 1 30 is in sliding contact with the fourth contact 110 in the open position of the circuit-interrupter 12.The outer cover 128 has spokes 134 at its lower end which form abutments 136.

The fourth contact 110 has an arcing tip 138 of arc-resistant material, for example Elkonite (Trade Mark) at its upper end and an external abutment 140 at its lower end for engaging the abutment 126 of the tube 112.

An annular piston 142 of, for example, aluminium is mounted by bearings 144 on the second contact 96 for reciprocation within the cylinder 146 in the terminal 60. The piston 142 is sealed with respect to the cylinder 146 by a seal 148. A tube 1 50 of insulating material is fixed at its upper end to the piston 142, and forming at its lower end an abutment 1 52 which abuts the abutments 136 of the spokes 1 34 of the third contact 108, a spring 154 biasing the tube 150 downwardly to engage the abutments 136 and 154.

The insulating material used in the interrupter can be, for example, polytetrafluoroethylene or cast epoxy resin, which may be glass fibre reinforced and suitably protected from the corrosive effect of SF8 gas decomposition.

The contacts 84, 96, 108 and 110 are made of copper, for example.

The operation of the circuit-breaker 10 will now be described with particular reference to Figures 4 to 9.

The interrupter 1 2 is shown in the fully-open position in Figure 4. The operation of the mechanism 14 moves the operating member 112 upwardly to move the third contact 108, and consequently, the fourth contact 110, towards the second contact 96. The movement of the contact 108 causes the piston 142 to stress the spring 154, gas flowing from the cylinder 146 through the apertures 104 and recesses 106 and through the second contact 96 into the chamber 82.

As the assembly 106 advances, the fourth contact 110 abuts the second contact 96 and further movement of the fourth contact 110 is prevented. The gas flowing from the cylinder 146 now has to flow through the fourth contact 110 and the first contact 84 to the exterior of the interrupter 12. Valves 88 permit gas to flow into the chamber 82 from the exterior of the interrupter 12. Further advance of the third contact 108 separates the abutments 126 and 140 and compresses the spring 118, so that the main contact 108 now moves relative to the fourth contact 110 to engage the second contact 96 (see Figure 5). The contact 108 ultimately reaches the fully-closed position (see Figure 6).

The mechanism 14 is operated in reverse and moves the operating member 112 downwardly to move the third and fourth contacts 108 and 110 away from the second contact 96 and so to open the interrupter 12. Initially, only the third contact 108 moves to disengage from the second contact 96 (see Figure 7) and to engage the fourth contact 110, which is maintained in engagement with the second contact 96 by the compressed spring 118. As part of the sleeve 112 leaves the chamber 82, the resultant slight change in volume causes an initial in-flow of gas as indicated by the arrows (see Figure 7).

During the initial stage of the opening operation, the abutments 136 and 1 52 part and movement of the piston 1 42 by the spring 1 54 is only minimal. The amount of movement of the piston 1 42 is determined by the interia of the piston 142, the spring 154 and the tube 150, the force of spring 1 54 and the impedance of the gas flow paths which are still closed at this stage.

Following disengagement of the second contact 96 and the third contact 108, the abutments 126 and 140 re-engage and the fourth contact 110 separates from the second contact 96 and draws an arc across the gap between the arcing tips 138 and 102 of the fourth and second contacts 110, 96. By this time, acceleration of the piston 142 by the spring 1 54 is increasing causing a pressure rise in the chamber 82. The pressure rise causes gas to flow into the gap and along an exit path formed by the axial passage through the tubular contacts 96 and 110 (as indicated by the arrows in Figure 8).

The third and fourth contacts 108 and 110 rapidly achieve the fully-open position (see Figure 8), the arc at this stage being of relatively low current. Gas flow from the chamber 82 causes gas ionised by the arc to be swept away in order to minimize the size of the arc.

However, the arc rapidly enlarges (see Figure 9) to a maximum at which time the spring 154 has accelerated the piston 142 to a maximum and movement of the piston 142 within the cylinder 146 causes rapid compression of the gas in the chamber 82 to create a relatively strong gas-blast. The amount of travel of the piston 142 after the third and fourth contacts 108 and 110 have reached the fully-open position is a substantial proportion of the total travel of the piston 142. In addition to that mechanically induced gas-blast, the high arc current causes rapid expansion of the gas which contributes to the gas-blast effect. The flow of gas is now such that the pressure-responsive valve 76 opens and allows gas to escape through the openings 74 to the exterior of the interrupter 12.

The contacts now being at a maximum spacing and the gas-blast effect now being at a maximum, the arc extinguishes at a current zero and the interrupter reverts to the status shown in Figure 4 when the piston 1 36 completes its stroke, i.e. the abutments 1 36 and 1 52 re-engage.

The minimal movement of the piston 142 during the initial opening stage of the interrupter, which results in a substantial proportion of the piston's movement occurring when the separation of the second contact 96 and the fourth contact 110 is at a maximum, causes the gas-blast to be at a maximum when it is most likely to extinguish the arc.

In the interrupter 12, the total movement of the piston 142 is 70mm and the movement of the piston 142 after the contacts 96 and 110 are at their maximum spacing is of the order of 35mm.

The interrupter described is particularly suitable for fault current ratings of up to 40kA, normal current ratings of up to 1.25kA and voltage ratings of 12kV to 36kV.

The particular contact arrangement described above is the subject of Application No. 8136877 (Applicants' reference R-DS 1245) filed on even date herewith and modifications to the contact arrangement described therein can be applied to the interrupter construction described.

It will also be appreciated that other contact arrangements can be used with the invention.

Other modifications within the scope of the invention are also possible.

For example, the impedance of the gas circuit can be increased by providing a pressureresponsive valve 1 56 as part of the bush 11 6 in the operating member 112 (See Figure 10).

Alternatively, the bush 11 6 can be closed as indicated at 1 58 in Figure 11, the operating member 112 being provided with apertures 160 which are closed by the first contact 84 for most of the closing and opening operation of the interrupter.

Movement of the piston can be further restrained by restricting the gas flow into the cylinder 146 behind the piston 142a. That can be achieved by providing a valve 1 62 as shown in Figure 11; in which reference numerals have been made the same as in Figures 1 to 9 where possible and have been given a suffix "a" where the part is modified from that shown in Figures 1 to 9.

The valve 1 62 consists of a sleeve 1 64 positioned within the second contact 96 and biased by spring 1 66 towards the flange 68 of the terminal 60. In the open position of the interrupter 12a, the sleeve 1 64 does not seat on the flange 68 owing to the engagement of a plate 168, fixed in the sleeve 1 64 and extending through slots 1 70 in the contact 96, by laminated semi-eliptical springs 1 72. The springs 1 72 are retained relative to a ring 174 by brackets 1 76. The ring 1 74 is secured to tube 1 50a which, in this embodiment, is secured to cranked members 1 78 (instead of being secured to the piston 142 as shown in Figures 1 to 9), an abutment 1 52a being formed by its upper end for engaging an abutment surface, on the piston 142a, indicated at 1 80.

The members 178 are secured to the protuberances 124 of the operating member 112.

The cover 1 28a of the contact 1 08a is also secured to the cranked members 178 by lugs 1 82 (instead of to the protuberances 120 as shown in Figures 1 to 9).

The piston 1 42a has one-way valves 184 to allow gas to flow from the cylinder 146 during closing of the interrupter 12a. The valves 184 are similar to valves 88 but use a cruciform plate instead of a bail 92. In Figure 11, the valves 88 are also shown in that form at 88a.

The arrangement of the end wall 68 of the terminal 60, relative to the fixed contact 96 (including the apertures 104) as shown in Figure 11, is modified compared to the arrangement shown in Figures 1 to 9.

Operation of the interrupter 1 2a is similar to that of the interrupter 12.

However, as the interrupter 1 2a starts to close, movement of the ring 1 74, together with the piston 142a, relieves the load on the plate 168 and allows the valve 162 to close, gas venting from the cylinder 146 through valves 184.

When the interrupter 1 2a is opened, the tube 150a, and thus the ring 174, moves the contact 108a (as distinct from the arrangement described with reference to Figures 1 to 9), parting the abutments 1 52a and 180 and leaving the piston 1 42a behind. Movement of the piston 1 42a is dependent on the inertia of components and the impedence of the gas circuit.

In this instance, the gas circuit is maintained substantially closed by the valves 76 and 162 and the closed apertures 1 60 until the interrupter 1 2a is almost completely open.

As the interrupter 1 2a approaches the open position, the springs 170 engage the plate 168 and accelerate the valve 1 62 from rest and to open it to allow gas to flow into the cylinder 146 behind the piston 142a. The apertures 160 also open. When movement of the piston 142aby the spring 1 54 and the effect of the arc on the pressure are sufficiently great, valve 76 also opens.

In the interrupter 12a, the total movement of the piston 1 42a is 70mm and the movement of the piston 1 42a after the contacts 96 and 110 are at their maximum spacing is of the order of 60mm.

Other modifications (not shown) are also possible. For example, in the interrupter 12 (see Figures 1 to 9), the tube 1 50 could be fixed to the contact assembly 106 instead of to the piston 142 if the inertia of the remaining components and the strength of the spring 1 54 are such that the piston 142 is sufficiently slow during the initial stage of opening of the interrupter.

Additionally, in other constructions the cylinder could move relative to a fixed piston. In other constructions, the casing can be of steel.

Claims (11)

Claims

1. A puffer-type circuit-interrupter comprising a chamber which contains a pressured gas.having arc-extinguishing properties, coaxial contacts, a spring and a cylinder member containing a piston member, one member being movable towards a position in which the spring is held in a stressed condition by engagement between a first abutment connected to said one member and a second abutment connected to an operating member, which operating member holds the abutments in engagement in the closed condition of the interrupter and, on opening of the interrupter, separates the abutments and the contacts to draw an arc across a gap between the contacts, the gap establishing communication between the chamber and an exit path provided by an axial passage through at least one of the contacts, consequent movement of said one member by the spring causing gas flow into the gap and along the path to assist in extinguishing an arc between the contacts, said movement being completed after the operating member has halted.

2. A circuit-interrupter according to claim 1 , in which the piston member is movable within the cylinder member.

3. A circuit-interrupter according to claim 1 or claim 2, in which the contacts include first and second fixed contacts coaxial with a common axia and a third movable contact connected to the operating member and being in sliding engagement with the first contact and in which the piston member is annular and is in sealed sliding engagement with the second contact, the spring engaging the side of the piston member remote from the first and third contacts.

4. A circuit-interrupter according to claim 3, in which a tubular member is secured at one end to the outer periphery of the piston member, and in which the first abutment is the free end of said tubular member and in which the second abutment comprises part of the third contact.

5. A circuit-interrupter according to claim 3, in which a tubular member is secured at one end to the third contact, and in which the first abutment is the free end of said tubular member and in which the second abutment comprises part of the piston member.

6. A circuit-interrupter according to any preceding claim, in which at least one pressureresponsive valve is located in the exit path to increase resistance to flow along said path.

7. A circuit-interrupter according to any preceding claim, in which at least one valve operable by movement of the operating member is located in the exit path to prevent flow along said path during part of the movement of the operating member.

8. A circuit-interrupter according to claim 7 as dependent on claim 3, in which the exit path passes through the first contact and in which the valve is comprised by the operating member and the first contact, the operating member being tubular and slidable within the first contact and closed at an end remote from the first and third contacts, the operating member having at least one aperture intermediate its ends which is obturated by the first contact in the closed position of the interrupter and during part of the closing and opening operations of the interrupter.

9. A circuit-interrupter according to claim 7 as dependent on claims 3 and 5, in which at least part of the exit path leads to the cylinder member at the same side of the piston member as the spring and in which the valve comprises a sleeve slidable in the second contact and biased to close said at least part of the exit path, the sleeve having an abutment member, extending through apertures in the second contact, which is engaged, during opening of the interrupter, by an abutment means secured to the tubular member to move the sleeve against the bias to open said at least part of the exit path, the piston member having non-return valve means to permit exhaustion of the cylinder member during closing of the interrupter.

1 0. A circuit-interrupter according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

11. A circuit-breaker having at least one circuit-interrupter as claimed in any preceding claim.