GB2089571A - A Gas-blast Circuit Interrupter - Google Patents

Abstract

A gas-blast circuit-interrupter has a fixed electrode 84 and a main fixed contact 96 coaxial with an axis 100, a main movable contact 108 is movable along the axis 100 in sliding engagement with electrode 84 and a arcing contact 110 is coaxial with the axis 100. An operating member 112 connected to contact 108 is guided for movement along the axis 100. Abutments 126, 140 on the member 112 and to contact 110, respectively are forced together by a spring 118. On closure, member 112 moves towards the fixed contact 96; contact 110 abuts contact 96, abutments 126, 140 separate and contact 108 disengages contact 110 and engages contact 96. On opening, member 112 moves away from contact 96 and causes contact 108 to disengage contact 96 and to engage contact 110. During this period, abutments 126, 140 approach one another while contact 110 is maintained stationary by spring 118. Abutments 126, 140 then engage so that further movement of member 112 disengages contact 110 from contact 96. The gas blast is achieved by arc heating effects and by piston 142 moving in cylinder 146, gases exhausting from chamber 82 through contacts 110, 96. <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 (SF6). 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 additional mechanically induced or pneumatically induced gas-blasts.

An interrupter has been proposed having two fixed contacts and a movable bridging contact. An arc is initially drawn between one of the fixed contacts and the movable contact and then transfers to the other fixed contact in order that the arc can be extinguished at an appropriate current zero, which delays the instant at which the arc is extinguished as compared to an arc drawn directly between only two arcing contacts.

Additionally, all of the contacts must have portions of arc-resistant material.

An interrupter has also been proposed comprising a simple switch which is operated simultaneously with an arcing arrangement connected, in parallel with the switch, to circuit terminals. The arcing arrangement consists of a fixed contact, and movable main and arcing contacts. The arcing contact remains engaged with the fixed contact whilst the main contact separates from the fixed contact and the switch is opened. The arcing contact then separates from the fixed contact, an arc being drawn therebetween which can be extinguished at an appropriate current zero. The movable contact assembly is connected to a terminal by a flexible conductor strip which could give rise to failure owing to repeated flexing of the strip.

An interrupter has also been proposed which comprises substantially the arcing arrangement described in the preceding paragraph but without any separate current path containing a further switch. In that arrangement, the movable contact assembly is connected to the terminal through a second fixed contact and through fixed springfingers so that there is a relatively large number of contact interfaces.

The aim of the invention is to minimise the number of contact interfaces in a circuit interrupter in which the arc is not transferred from one contact to another and in which flexible conductors are not required.

According to the invention, a gas-blast circuitinterrupter comprises a chamber which contains pressurised gas having arc-extinguishing properties and in which an increased gas pressure arises upon opening operation of the interrupter, the chamber also containing first and second coaxial fixed main contacts, a third main contact coaxially slidable in engagement with the first contact and a fourth coaxial, arcing, contact, an operating member connected to the third contact and guided for axial movement, first and second abutments connected, respectively, to the operating member and the fourth contact, and a spring forcing the abutments into engagement, the third and fourth contacts engaging the second contact and the abutments being separated in the closed condition of the interrupter and the operating member on moving away from the second contact disengages the third and second contacts and then engages the third and fourth contacts, the spring maintaining the fourth contact in engagement with the second contact until the abutments engage, further movement of the operating member disengaging the fourth and second contacts to draw an arc across a gap therebetween, the gap establishing communication between the chamber and an exit path provided by an axial passage through at least one of the second and fourth contacts and said increased gas pressure causes gas flow into the gap and along the path to assist arc extinction.

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-Ill in Figure 2; and Figures 4 to 9 are similar to Figure 2 but form a series showing the closing and opening sequences of the 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 a lower casing 1 6 of aluminium or cast epoxy resin, for example. The mechanism 14 includes a shaft 1 8 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 material 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 separated, 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 SF8 gas, which can flow between the upper and lower casings 1 6 and 25 internally and externally of the intterupter 12.

The circuitinterrupter 12 is mounted within the circuit-breaker 10 by a tubular support 56 of insulating material secured to the lower end of the interrupter 12 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 arcinterruption 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 100 of the interrupter 12. 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 radialiy-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, and the fourth contact 110 is an arcing contact. An operating member 112 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 member 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 11 8. The other end of spring 11 8 engages the lower end of the fourth contact 110, which slides in bearing 120 supported within the tube 112.

The spring 118 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 112 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 130. The contact fingers 130 are each internally recessed to engage one of the abutments 122 of the member 112 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 130 is in sliding engagement with the first contact 84 and the upper end of each contact finger 130 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 1 36.

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 134 of the third contact 108, a spring 1 54 biasing the tube 1 50 downwardly to engage the abutments 1 36 and 154.

The insulating material used in the interrupter can be, for example, polytetrafluorethylene or cast epoxy resin, which resin may be glass fibre reinforced and suitably protected from the corrosive effects 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 refernece to Figures 4 to 9.

The interrupter 12 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 11 0, 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 1 2. 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 11 8, 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 arrow (see Figure 7).

During the initial stage of the opening operation, the abutments 136 and 1 52 part and movement of the piston 142 by the spring 1 54 is only minimal. The amount of movement of the piston 1 42 is determined by the inertia of the piston 142, the spring 1 54 and the tube 1 50 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 11 0, 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 passages 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 minimise the size of the arc.

However, the arc rapidly enlarges (see Figure 9) to a maximum at which time the spring 1 54 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 136 completes its stroke, i.e. the abutments 136 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. The gas-blast mechanism is the subject of Applications No. 8137023 (Applicants' reference R-DS 1246) filed on even date herewith and modifications described therein can be applied to the interrupter construction described above.

However, the contact arrangement described above can be used with other forms of gas-blast mechanisms, i.e. other types of puffer mechanisms; or the gas blast may be derived entirely from the heating effects of the arc.

The contact arrangement described avoids introducing any delay in extinguishing the arc owing to transfer of the arc between contacts as suggested in one of the prior proposals. Also, since the third contact 1 08 engages both of the fixed contacts 84 and 96 to conduct current, the number of contact interfaces is reduced as compared to other prior proposals as discussed previously, the likelihood of hot spots at such interfaces also being reduced. Furthermore, the use of flexible conductors is avoided.

The contact arrangement described can be modified within the scope of the invention. For example, the contact assembly could be mounted wholly externally of the first contact or the main contact of the assembly could be mounted internally of the arcing contact of the assembly.

The second and fourth contacts could be sliding contacts instead of the preferred arrangement of plain butting contacts as described above. The exit path could be only through the second or the fourth contact instead of, as preferred, through both as described above. In other constructions, the casing can be of steel.

The interrupter 12 need not be positioned vertically although that is preferred.

The contact arrangement described is particularly suitable for circuit-interrupters having a fault current rating of up to 40kA with a normal current rating of up to 1.25kA and a voltage rating of 12kV to 36kV.

Claims (6)

Claims

1. A gas-blast circuit-interrupter comprising a chamber which contains pressurised gas having arc-extinguishing properties and in which an increased gas pressure arises upon opening operation of the interrupter, the chamber also containing first and second coaxial fixed main contacts, a third main contact coaxially slidable in engagement with the first contact and a fourth coaxial, arcing, contact, an operating member connected to the third contact and guided for axial movement, first and second abutments connected, respectively, to the operating member and the fourth contact, and a spring forcing the abutments into engagement, the third and fourth contacts engaging the second contact and the abutments being separated in the closed condition of the interrupter and the operating member on moving away from the second contact disengages the third and second contacts and then engages the third and fourth contacts, the spring maintaining the fourth contact in engagement with the second contact until the abutments engage, further movement of the operating member disengaging the fourth and second contacts to draw an arc across a gap therebetween, the gap establishing communication between the chamber and an exit path provided by an axial passage through at least one of the second and fourth contacts and said increased gas pressure causes gas flow into the gap and along the path to assist arc extinction.

2. A circuit-interrupter according to claim 1, in which the contacts are tubular.

3. A circuit-interrupter according to claim 1 or claim 2, in which the first, third and fourth contacts are in nested relationship, the third and fourth contacts being the outer and inner contacts, respectively, for the nested contacts.

4. A circuit-interrupter according to any preceding claim, in which the operating member is tubular and passes through and is guided by the first contact, the fourth contact being nested within and guided by the operating member, the spring being located between the fourth contact and a third abutment connected to the operating member.

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

6. A circuit-breaker having at least one circuitinterrupter as claimed in any preceding claim.