GB2126423A - Gas blast interrupters - Google Patents

Abstract

In a contacts closed position of the interrupter, one contact 20 engages a further contact 21 and passes substantially sealingly through an insulating orifice 25 in a tubular housing 24 which surrounds the contact 21 and through a further insulating orifice 27 in a tubular guide 26 which surrounds the housing 24. Upon initial contact separation formations 20a on the contact 20 disengage from contact formations 22 on the contact 21 and subsequently also disengage from a metal probe 23, thereby drawing an arc between the contact 20 and the probe. Pressurised gas is supplied to an annular chamber 28 defined between the housing 24 and the guide 26 so that, when upon further contact opening the contact 20 passes out of the orifice 25, the pressurised gas is able to flow out of the chamber 28 and through the orifice 25 to cool and de-ionise the arc. Upon still further contact opening, the contact 20 also passes out of the orifice 27, thereby permitting the pressurised gas to flow therethrough out of the chamber 28 in the opposite direction to the flow of gas through orifice 25. <IMAGE>

Description

SPECIFICATION Gas blast interrupters This invention relates to interrupters of the gas-blast type.

Such interrupters are required to carry the related currents in the closed position and interrupt the electrical power circuit by drawing an arc between a pair of axially cooperating electrodes where it can be extinquished by the scavenging and de-ionising action of a flow of gas directed essentially along the arc. It is preferred that these interrupters should also be able to isolate the circuit in the open position, close onto the rated currents and that their current carrying ability should not be impaired by arcing on interruption or by pre-arcing on closure of the circuit.

In order to achieve an efficient interruption and limit the duration of arcing or pre-arcing, relatively high operating speeds must be achieved on contact parting or approaching movements of the co-operating electrodes.

Measures must also be taken to protect the current carrying contacts against erosion by the arc so that their current carrying ability is not impaired by repetitive opening and closing operation of the interrupter.

Hitherto, attempts to overcome the above problems have been embodied in three basic constructions of gas blast interrupter, all of which permit the contacts initiating the arc to accelerate from rest and part at speed on interruption and to touch and flow through at speed on closing. One of these constructions permits the arc to be inititated on one set of contacts which is also required to carry the rated currents and thereby is not protected against erosion unless another set of contacts is provided externally to the interrupting zone and in parallel with the arcing contacts. These external contacts tend to reduce the inherent dielectric strength outside the interrupting zone, and require larger diameter enclosures to be used.The second of these basic constructions employs a movable auxiliary contact which, whilst affording protection, must be separately driven by spring or pressure forces with the attendant drawbacks in simplicity and reliability.

Furthermore, in the case of the so-called "duo-blast" type interrupters, in which the arc is subtended through a pair of nozzles, none of the three constructions readily permit both nozzles to be made of a suitable insulating material to enhance the interrupting and the isolating capabilities of the interrupter.

It is an object of the present invention to obviate or mitigate the above-described problems.

According to the present invention, there is provided a gas-blast type interrupter comprising: (a) first and second electrodes which are relatively movable between a closed position wherein they are in mutual electrical engagement and an open position wherein they are mutually separated, movement of the electrodes from their closed to their open position causing an arc to be drawn therebetween in use, the first electrode including a tubular portion having a first set of contact formations thereon and a probe surrounded by the tubular portion, the second electrode including a tubular portion having a second set of contact formations thereon, the first set of contact formations slidably engaging the second electrode and the second set of contact formations slidably engaging the probe when the electrodes are in their closed position, and the first set of contact formations disengaging from the second electrode before the second set of contact formations disengage from the probe during movement of the electrodes towards their open position; (b) a tubular housing enclosing the first electrode and being fixed against movement relative thereto; (c) a tubular guide co-axially surrounding the housing and also being fixed against movement relative to the first electrode; (d) an annular chamber defined between the housing and the guide, into which pressurised gas is supplied upon movement of the electrodes from their closed position towards their open position;; (e) a first insulating orifice provided in the tubular housing, through which the second electrode substantially sealingly passes when the electrodes are in their closed position, the second electrode passing out of the first insulating orifice during movement of the electrodes towards their open position thereby permitting the pressurised gas from said annular chamber to flow through the first insulating orifice into the interior of the tubular housing in a direction essentially along said arc; and (f) a second insulating orifice provided in the tubular guide, through which the second electrode also substantially sealingly passes when the electrodes are in their closed position, the second electrode passing out of the second insulating orifice during movement of the electrodes towards their open position thereby permitting the pressurised gas from said annular chamber also to flow through the second insulating orifice in a direction opposed to the direction of gas flow through the first insulating orifice, the first and second insulating orifices being co-axial and of essentially the same size.

Such an arrangement enables the axial spacing of the first and second insulating orifices to be set to provide the optimum aerodynamic conditions for the flow of gas through the interrupter, and also allows the electrostatic conditions to be set readily in the fully open position of the electrodes.

Preferably, an annular space is defined between the first electrode and the tubular housing and communicates with a gas exhaust passage, and the tubular portion of the first electrode has venting spaces therein through which gas flowing through the first insulating orifice can pass.

Desirably, the first electrode, the tubular housing and the tubular guide are all moved in unison relative to the second electrode, which is fixed.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a generalised, part-sectional view of a gas-blast interrupter according to the present invention, showing the interrupter in a closed position; Figure 2 is a sectional view of a portion of a first embodiment of the gas-blast type interrupter, the interrupter being shown in a closed position; Figure 3 is a longitudinal section through an alternative form of downstream electrode for the interrupter of Fig. 2; Figure 4 is a sectional view of an upstream electrode assembly which forms part of a second embodiment of the gas-blast type interrupter; and Figure 5 is a sectional view of an upstream electrode assembly which forms part of a third embodiment of the gas-blast type interrupter.

Referring first to Figs. 1 and 2, the interrupter shown therein is of the open terminal, porcelain enclosed form and is part of a threephase circuit breaker. The interrupter comprises an insulating enclosure 1 having a flange 2 at each end thereof and housing a pair of relatively movable co-operating electrodes 3 and 5. The electrode 3 (which is fixed) is formed by a hollow tubular conductor 20 terminating at one end thereof in a set of resiliently biassed contacts 20a. The internal bore of of the conductor 20 forms a gas vent passage which communicates with a space remote from the contacts 20a.

The electrode 5 (which is movable) comprises a tubular portion 21 having a set of resiliently biassed contacts 22 at its end, and a metal probe 23 disposed within the tubular portion 21 and projecting beyond the contacts 22. When the electrodes are in a closed position, the contacts 20a on the electrode 3 slidably engage the probe 23, while the contacts 22 on the electrode 5 slidably engage the conductor 20 in spaced relation to the contacts 20a.

The metal probe 23 and the tubular portion 21 are immovably coupled to and enclosed by a tubular housing 24 which overlaps both contact sets 20a and 22 and which has an insulating orifice 25 in one end thereof through which the conductor 20 passes. An annular space defined between the portion 21 and the housing 24 communicates with an exhaust passage at an end of the housing 24 remote from the orifice 25. The housing 24 may be made wholly of metal or of an electrically insulating material, or only one end may be made of insulating material.

The housing 24, the tubular portion 21 and the probe 23 are immovably coupled to and enclosed by a tubular gas flow guide 26 which has an insulating orifice 27 at one end thereof through which the conductor 20 passes. The orifice 27 is co-axial with and the same size as the orifice 25. An annular passage 28 defined between the housing 24 and the gas flow guide 26 communicates with a supply of compressed gas produced or stored at a higher pressure than present in the remainder of the enclosure 1. The gas is highly insulating, and is preferably sulphur hexafluoride.

Referring to the electrode 5 and its immovably coupled components 24 and 26 as the upstream electrode assembly and the electrode 3 as the downstream electrode, the operation of the interrupter is as follows:- When the interrupter is in its closed position, the conductor 20 is at the position indicated by A in Fig. 2 and current flows between the upstream electrode assembly and the downstream electrode through contacts 22 and 20a. An intitial movement between the electrodes to bring the conductor 20 to the position indicated at B in Fig. 2 causes the current flowing through the contacts 22 to be readily commuted to the probe 23 by virture of the negligible or very small electromagnetic energy stored in the commutating loop formed by the two contact sets 20a and 22.This initial movement permits the electrodes to accelerate to the required velocity without a loss of contact while compressed gas is allowed to fill the annular passage 28 whose exit is restricted at this stage by the conductor 20 in co-operation with the orifices 25 and 27.

Further movement to the position indicated at C in Fig. 2 causes the contact set 20a to disengage from the probe 23, thereby initiating an arc between the erosion resistant end 23a of the probe 23 and the erosion resistant contacts 20a of the downstream electrode, whilst a further increase in gas pressure takes place within the annular passage 28.

Upon further movement to the position indicated at D in Fig. 2, the conductor 20 passes through the orifice 25 and thereby allows the gas which has accumulated at pressure in the annular space 28 to be accelerated and flow at high velocity through the orifice 25. The gas flow thus acts axially on the arc subtended between the probe end 23a and the contacts 20a to cool and de-ionise the arc column. The exhaust gases are free to flow down the annular space between the tubular portion 21 and the housing 24.

Movement to the position indicated at E in Fig. 2 causes the orifice 27 also to be opened to the high pressure gas stored in the annular passage 28 giving a full duo-blast action, that is, accelerating the gas and causing it to flow in two directions axially along the length of the arc to cool and de-ionise, resulting in the arc extinction at a natural current zero. The construction of the interrupter enables the axial spacing between the two orifices 25 and 27 to be set for optimum areodynamic conditions for the gas flow.

F in Fig. 2 indicates the position of the conductor 20 relative to the upstream electrode assembly in the fully open position and the movable electrode assembly at rest. In this position the high pressure gas that has accumulated in the annular passage 28 is exhausted and the ambient pressure surrounding the interrupter is maintained to ensure an adequate voltage withstand level exists in the gap between the downstream electrode and the upstream electrode assembly. The constuction of the interrupter enables the electrostatic conditions to be readily set when the electrodes are in their fully open position.

To maximise the performace of the interrupter shown in Fig. 2 the downstream electrode can be replaced by a construction as shown in Fig. 3. In this construction the electrode comprises a hollow tubular conductor 29 which is similar to the conductor 20, except that for the major portion of its length it is recessed to accept a relatively thin tube 30 of thermoplastic material, such as heat shrinkable P.T.F.E. sleeving. The effect of this tube 30 is to restrict premature gas loss from the annular space 28 via the spaces between the plurality of resiliently biased contacts at the co-operating end of the conductor 29 during initial movement of the interrupter as shown at B, c and D in Fig. 2.

A downstream assembly forming part of another embodiment of the invention is shown in Fig. 4, and comprises an electrode 40 which is engageable with a fixed electrode similar to the downstream electrode shown in Fig. 2. The electrode 40 is enclosed by a tubular housing 41 having an insulating orifice 42 therein, the interior of the tubular member 41 communicating with a gas exhaust passage 43. The tubular member 41 is in turn surrounded by a guide 44 having a further insulating orifice 45 therein, the guide and the tubular member defining therebetween an annular passage 46 to which pressurised gas is supplied in use. The orifices 42 and 45 are co-axial and of the same size, and the aforementioned fixed electrode passes substantially sealingly through both of the orifices when the interrupter is in a closed position.

The electrode 40 is composed of an inner tubular member 47 having a plurality of fingers arranged in an annulus and carrying a set of contacts 48 at their ends, and an outer tubular member 49 co-axial with the inner tubular member 47 and having a plurality of fingers which extend axially beyond the contact set 48 and which carry at their end a further set of contacts 50. When the interrupter is in its closed position, the contact sets 48 and 50 engage the external surface of the fixed electrode (which is tubular) at points axially spaced along the latter, so that during opening of the interrupter the fixed electrode disengages from the contact set 50. A metal probe 51, which is electrically connected to both of the inner and outer tubular members 47 and 49, extends axially of the electrode 40 and terminates at a point intermediate the contact sets 48 and 50.This probe is engaged by contacts on the fixed electrode in an analagous manner to that described previously, with reference to Fig. 2.

As is apparent from Fig. 4, the inner and outer tubular members 47 and 49 are radially spaced so that an annular gas flow passage 52 is formed therebetween which communicates with the exhaust passage 43 and which also communicates with an annular venting space between the contact sets 48 and 50.

When the fixed electrode passes through the insulating orifice 42 during opening of the interrupter, gas from the passage 46 flows through the orifice 42 and into the exhaust passage 43 via the venting space and the passage 52.

Fig. 5 shows another form of downstream electrode assembly which is generally similar to that described above with reference to Fig.

4, similar parts being accorded the same reference numerals. In this embodiment, however, the electrode 40 is engageable with a fixed electrode similar to the downstream electrode in Fig. 2, and comprises a single set of contacts 53 which are carried on the ends of a plurality of fingers 54 arranged in a ring.

Gaps between the fingers 54 provide venting spaces which communicate with the exhaust passage 43.

Claims (5)

1. A gas-blast type interrupter comprising: (a) first and second electrodes which are relatively movable between a closed position wherein they are in mutual electrical engagement and an open position wherein they are mutually separated, movement of the electrodes from their closed to their open position causing an arc to be drawn therebetween in use, the first electrode including a tubular portion having a first set of contact formations thereon and a probe surrounded by the tubular portion, the second electrode including a tubular portion having a second set of contact formations thereon, the first set of contact formations slidably engaging the second electrode and the second set of contact formations slidably engaging the probe when the elec trodes are in their closed position, and the first set of contact formations disengaging from the second electrode before the second set of contact formations disengage from the probe during movement of the electrodes towards their open position; (b) a tubular housing enclosing the first electrode and being fixed against movement relative thereto; (c) a tubular guide co-axially surrounding the housing and also being fixed against movement relative to the first electrode; (d) an annular chamber defined between the housing and the guide, into which pressurised gas is supplied upon movement of the electrodes from their closed position towards their open position;; (e) a first insulating orifice provided in the tubular housing, through which the second electrode substantially sealingly passes when the electrodes are in their closed position, the second electrode passing out of the first insulating orifice during movement of the electrodes towards their open position thereby permitting the pressurised gas from said annular chamber to flow through the first insulating orifice into the interior of the tubular housing in a direction essentially along said arc; and (f) a second insulating orifice provided in the tubular guide, through which the second electrode also substantially sealingly passes when the electrodes are in their closed position the second electrode passing out of the second insulating orifice during movement of the electrodes towards their open position thereby permitting the pressurised gas from said annular chamber also to flow through the second insulating orifice in a direction opposed to the direction of gas flow through the first insulating orifice, the first and second insulating orifices being co-axial and of essentially the same size.

2. A gas-blast type interrupter as claimed in claim 1, wherein an annular space is defined between the first electrode and the tubular housing and communicates with a gas exhaust passage, and the tubular portion of the first electrode has venting spaces therein through which gas flowing through the first insulating orifice can pass.

3. A gas-blast type interrupter as claimed in claim 1 or 2, wherein the axial spacing of the first and second insulating orifices is set to provide the optimum aerodynamic conditions for the flow of gas through the interrupter, and wherein the electrostatic conditions are set in the fully open position of the electrodes.

4. A gas-blast type interrupter as claimed in claim 1, 2 or 3, wherein the first electrode, the tubular housing anf the tubular guide are all moved in unison relative to the second electrode, which is fixed.

5. A gas-blast type interrupter substantially as hereinbefore described with reference to Figs. 1 and 7, or Figs. 1 and 7 as modified by Fig. 8, or Figs. 1 and 9, or Figs. 1 and 10 of the accompanying drawings.