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(11) | EP 2 884 513 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Circuit Breakers |
| (57) A circuit breaker that is particularly suitable for use in MVDC and HVDC networks
is described. The circuit breaker includes one or more arcing contact modules (1a,
1b). Each arcing contact module (1a, 1b) typically includes a first dielectric fluid
inlet (16), a first stationary contact (2), at least one second stationary contact
(4), and at least one moving contact (14). The first and second stationary contacts
(2, 4) are spaced apart by a gap that defines a dielectric fluid outlet (6). Each
moving contact (14) is movable using hydraulic actuation. Pressurised dielectric fluid
is introduced through the first inlet (16) to move each moving contact (14) from (a)
a closed position where the moving contact (14) is in electrical contact with the
first and second stationary contacts (2, 4) to provide an electrically conductive
pathway between the first and second stationary contacts (2, 4), to (b) an open position
where the moving contact (14) is not in electrical contact with the first stationary
contact (2), thereby establishing an arc across the gap between the first and second
stationary contacts (2, 4), and wherein the introduced pressurised dielectric fluid
flows through the outlet (6) to cool the arc.
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Field of the Invention
[0001] The present invention relates to circuit breakers, and in particular to circuit breakers for use in medium or high voltage direct current (MVDC or HVDC) circuits.
Background Art
[0002] Examples of high voltage alternating current (HVAC) circuit breakers that employ rapidly flowing dielectric fluids to de-ionise an arc include: oil explosion pot, minimum oil, air blast and SF6 puffer types with series connected contacts and non-linear or linear resistive voltage sharing. Although it is intended that the series-connected contacts of such circuit breakers generally operate in mechanical synchronism, as circuit breakers employ more contacts in series and as voltage ratings increase, the effect of the response of the actuating linkages and control systems is to cause contacts to be actuated at differing rates and at different times. All of the circuit breakers have a limited capability to develop arc voltage, relying instead on the inherent current zeros that occur in ac currents to initiate arc extinction. The described mechanical synchronisation limitations are not of great significance in present HVAC circuit breakers because electrical synchronisation dominates, i.e., all contacts experience the same current zero condition since they are connected in series. In these circuit breakers, contact actuation is by means of a mechanical linkage which may be driven by a range of electromagnetic, pneumatic, hydraulic and spring devices, such devices commonly being provided with energy storage means. These known circuit breakers have insignificant capability to interrupt current in HVDC circuits.
[0003] Series-connected and parallel-connected arrays of known HVAC circuit breakers have been proposed as a means of reducing the switching stress in any particular element within the array to tolerable levels when switching HVDC circuits, but all such proposals have been shown to be non-viable.
[0004] Known HVAC circuit breakers have been adapted for use in HVDC circuits by hybridisation with other technologies that forcibly cause current zeros and arc extinction to occur in the circuit breaker. These hybridisation arrangements fall within the following basic descriptions:
- (i) Where a series resonant circuit is connected in parallel with the circuit breaker contacts, arc instability is promoted by the low impedance of the parallel-connected resonant circuit, and where the amplitude of the associated resonant current increases until current zeros occur in the circuit breaker.
- (ii) Where a pre-charged capacitor is connected in parallel with the circuit breaker contacts by turning on a power electronic switching device, and where the polarity of the pre-charge is such as to cause a current zero to occur in the circuit breaker.
- (iii) Where a power electronic switching device assembly is connected in series with the circuit breaker and the power electronic switching device assembly is actively turned off, thereby causing a current zero to occur in the circuit breaker.
[0005] Since HVDC circuits contain significant series inductance, any attempt to interrupt current results in the generation of a transient voltage and a requirement to dissipate the inductively stored energy. It is therefore a mandatory requirement that the above hybridised arrangements are used in conjunction with a surge arrester. It is commonplace for hybridised HVDC circuit breakers to be used in conjunction with a metal oxide varistor (MOV) type surge arrester that is connected in parallel with the hybrid circuit breaker and/or between one terminal of the hybrid circuit breaker and ground. Moreover, hybrid arrangement (iii) requires that current is rapidly diverted into a switching aid network or additional power electronic circuit breaker that is connected in parallel with the series-connected power electronic switching device assembly and circuit breaker.
[0006] A further limitation of known HVAC circuit breakers is their low operating speed. It is commonplace for circuit breaker contacts to start to separate after a delay of at least 10 ms and often more than 20 ms (excluding delays in protection relays and controlling devices). Moreover, once circuit breaker contacts have started to separate it may take a further 10 ms or much more for full contact separation to be established. As more contacts are series connected in order to achieve a high working voltage capability, the physical size of the circuit breaker becomes a significant factor in limiting the operating speed because longer and more compliant contact actuation linkages are required.
[0007] Emerging HVDC circuit breaker requirements are extremely stringent because prospective fault energy, fault current and rate of increase of fault current are sufficiently high to require a circuit breaker total opening time, prior to diversion of current into the surge arrester, in the region of 2 ms. Although it is possible to add series inductance to limit the rate of increase of fault current, this simply increases the total fault energy per unit interrupted current. Whilst it is the case that the power electronic switching devices of hybrid arrangements (ii) and (iii) may be turned on and off, respectively, in less than 5 µs, there remains a requirement for an extremely fast acting (circa 2 ms) mechanical switching device to be employed if the ratings, size and complexity of hybridisation components, e.g., IGBTs and capacitors, are to be brought within commercially viable limits.
[0008] Further requirements are that continuous 'on' state power loss must be minimised in the interest of reduced 'loss capitalisation' and that HVDC circuit breakers must be extremely dependable in the interest of power network availability. Accordingly there is a desire to eliminate any requirement to have power semiconductor or other active devices in the continuous 'on' state path. The current in a modem HVDC network may flow in either direction in accordance with the direction of power flow and it is desirable that this bidirectional capability be provided without requiring additional power components.
[0009] A circuit breaker that requires no additional components beyond a surge arrester would be very desirable from the perspective of simplicity and in having low continuous 'on' state power losses.
Summary of the Invention
[0010] An objective of the present invention is to produce a circuit breaker whose arc voltage starts to increase after the minimum possible delay, and preferably less than 2 ms from receipt of a signal to open. Thereafter, arc voltage will increase rapidly and preferably attain its maximum prospective level within 4 ms from receipt of a signal to open. The circuit breaker includes a moving contact that is actuated by a pressurised dielectric fluid to initiate arcing and where the pressurised dielectric fluid is also used to extinguish the arc.
[0011] A further objective of the present invention is that the circuit breaker is modular and scalable.
[0012] The present invention provides a circuit breaker (e.g., an MVDC or HVDC circuit breaker that is suitable for use in an MVDC or HVDC circuit or network) comprising at least one arcing contact module, each arcing contact module including:
a first (or opening) dielectric fluid inlet;
a first stationary contact;
a second stationary contact, the first and second stationary contacts being spaced apart by a gap that defines a dielectric fluid outlet; and
a moving contact, the moving contact being movable (without any mechanical linkage) by the introduction of pressurised dielectric fluid through the first inlet from:
- (a) a closed position (e.g., where the moving contact is in electrical contact with the first and second stationary contacts to provide an electrically conductive pathway between the first and second stationary contacts), to
- (b) an open position where arcing is initiated (e.g., where the moving contact is not in electrical contact with the first stationary contact, thereby establishing an arc across the gap between the first and second stationary contacts, and wherein the introduced pressurised dielectric fluid flows through the outlet to cool the arc).
[0013] A pair of moving contacts can be provided, the first inlet being positioned to cause the moving contacts to move in opposite directions as a result of the introduction of the pressurised dielectric fluid. In other words, a pair of moving contacts can have a common first inlet located between them. The circuit breaker is constructed from one or more arcing contact modules. In one arrangement, each arcing contact module can include a first inlet, a pair of moving contacts (a moving contact being disposed on each side of the first inlet so that they are forced to move in opposite directions by the introduced pressurised dielectric fluid), a first stationary contact, a pair of second stationary contacts, and a pair of outlets. The circuit breaker might include a plurality of such arcing contact modules arranged in series, each being activated in a synchronous manner on receipt of a signal to open the circuit breaker. The number of arcing contact modules will be selected with reference to a desired arc voltage or total arcing performance. The designer is free to employ a relatively large number of moving contacts, each having a relatively small stroke, in the interest of achieving maximum practical operating speed, i.e., defining that the actuation energy per moving contact is minimised with due regard for the compromise between speed and complexity, and also taking into account that arc voltage and transient recovery voltage withstand are less than proportional to contact separation. All arcing contact modules can be controlled by a suitable control unit that receives a signal to open the circuit breaker for protection purposes when a fault current is developed, or in response to an operator request.
[0014] The first and second stationary contacts can be substantially tubular defining a linear passageway in fluid communication with each first inlet and outlet. Each moving contact can be positioned within the linear passageway. Each moving contact can have a substantially cylindrical shape and preferably has a relatively low mass. In particular, the mass of each moving contact can be minimised by providing an internal cavity.
[0015] The interface between corresponding moving and stationary contacts can be defined as having three regions, namely a fluid sealing region, an electrical sliding contact region, and an arc erosion resistant region.
[0016] Each moving contact is preferably a close fit within the linear passageway. One or both of each moving contact and the surrounding stationary contacts can be constructed (e.g., shaped) to minimise leakage of dielectric fluid past the moving contact, but some leakage may be tolerated in practice. Generally it is preferred that moving and stationary contacts have dimensional tolerances that minimise leakage without recourse to the use of additional sealing means, but such sealing means (e.g., O-rings and gland seals) can optionally be employed where appropriate. In one arrangement, where the dielectric fluid is a liquid, the viscosity of the liquid can also restrict leakage to an acceptable level.
[0017] One or both of each moving contact and the surrounding stationary contacts can be constructed (e.g., shaped or formed of a suitable material) to minimise electrical contact resistance therebetween. Generally it is preferred that the bulk of the moving and stationary contacts are made of a metal or metal alloy with a high electrical conductivity and that the stationary contacts in particular have a region that benefits from a radially inwardly directed bias force in order to ensure reliable electrical sliding contact with the moving contact. The bias force may be facilitated by segmenting at least a part of each stationary contact (e.g., in an electrical sliding contact region) so that it provides a spring pre-load. The segmented stationary contact would be deflected radially outwardly against the spring pre-load by the moving contact so that a desired electrical sliding contact force is provided therebetween. Other ways of providing a bias force will be known to the skilled person. Typically, the electrical sliding contact resistance will be sufficiently low to ensure that there is substantially no passage of current through the fluid sealing region.
[0018] One or both of each moving contact and the surrounding stationary contacts can be constructed (e.g., shaped or formed of a suitable material) to minimise erosion as a result of arcing. It will be readily appreciated that when the moving contact is initially separated from the first stationary contact upon movement towards a fully open position, an arc will be established between the moving contact and the first stationary contact. With further separation between the moving contact and the first stationary contact, arcing will subsequently be established between the first and second stationary contacts. Generally it is preferred that the arc-facing regions of the stationary and moving contacts are resistant to the intense heat of the arc and that their arc-facing geometries do not tend to concentrate both current density and heat flux density whilst locally increasing thermal resistance. Copper chromium, copper tungsten and molybdenum alloys that are commonly used in other switch contact technologies might be deposited or otherwise used in the arc-facing regions. The arc-facing regions may be of sufficient thickness and have sufficient mass to provide a transient thermal resistance that is sufficiently low to minimise the degree of contact erosion. Arc-facing extremities of the moving and stationary contacts can be machined to give a radiused profile.
[0019] In one arrangement, each moving contact can be a lightweight aluminium alloy cylindrical body upon which a high electrical conductivity and wear-resistant layer is applied or deposited in order to facilitate the sliding contact mechanism, and have a suitably profiled arc erosion-resistant arcing face or contact tip.
[0020] The present invention relies on fluid actuation of each moving contact by the pressurised dielectric fluid that is introduced through each first inlet, and using actuating fluid flow to blast the dielectric fluid through each outlet, thereby rapidly removing heat and ionised material from each arc in order to cause its extinction. In other words, the pressurised dielectric fluid fulfils two important technical functions, namely fluid actuation of the moving contact(s) and arc cooling. A suitable number of moving contacts are actuated simultaneously, with minimal delay and with rapidly increasing contact separation. As such, the initiation of arcing is expected to be subject to the minimum practical delay and the total arc voltage is expected to increase rapidly to an unusually large magnitude. The desired total arc voltage and rate of change of arc voltage, and the equalisation of arc voltages, is substantially achieved by using a suitable number of series-connected arcing contact modules whose actuation means comprises a suitable number of parallel-connected fluid paths. Although the equalisation of arc voltage is substantially achieved as described, additional voltage equalisation means may be electrically parallel connected with each switch contact system within each arcing contact module - an arcing contact module with a single moving contact defines a single switch contact system whereas an arcing contact module with two moving contacts defines two switch contact systems that are inherently series connected.
[0021] The circuit breaker preferably further includes an opening fluid actuation system that it is fluidly connected to each first inlet. In an arrangement where the circuit breaker includes a plurality of first inlets (e.g., a plurality of series-connected arcing contact modules), each first inlet can be connected to its own fast-acting fluid actuation means that includes an opening accumulator for storing the pressurised dielectric fluid, a release valve and associated passageways. But fluid actuation means can also be shared by two or more first inlets. For example, the opening fluid actuation system can include a single opening accumulator that is connected to each first inlet, either by a single release valve or by a series of release valves (i.e., each first inlet has its own respective release valve). Each release valve is opened and closed under the control of a control unit. Each release valve can have any suitable construction but will preferably be extremely fast-acting, e.g., with opening times typically less than about 0.5 ms. In one arrangement, poppet-type release valves with repulsion-type actuation can be employed. On receipt of a signal to open the circuit breaker, each release valve is opened to allow the pressurised dielectric fluid in the associated opening accumulator to flow through each first inlet to provide the fluid actuation that forces the moving contact(s) towards the open position. Where the opening fluid actuation system includes two or more release valves they are preferably controlled to open substantially simultaneously to ensure proper synchronisation of the arcing contact modules. The action of the arc that forms as each moving contact separates from the surrounding first stationary contact causes thermal decomposition of the dielectric fluid, and in the case of the preferred dielectric liquids, the resultant generation of gaseous products causes additional actuating pressure to be applied to the moving contact(s). This allows some economy to be made in sizing the opening accumulator(s) but there must be sufficient capacity to accommodate the case where only a small current is interrupted by the circuit breaker and arc energy is insufficient to cause the development of gas pressure that would otherwise supplement the fluid moving contact actuation.
[0022] It will be readily appreciated that the term 'accumulator' is intended to refer to any suitable pressure storage reservoir or device for the dielectric fluid. The ability of such an accumulator to rapidly release its stored energy when discharged into the fluid actuation system is an essential aspect of the present invention and therefore the preferred form of accumulator is one where the energy is stored in a compressible gas and where this energy acts upon an actuating fluid that is in the liquid phase. As such, the actuating fluid will be substantially incompressible and will exhibit a beneficially high speed of sound. However, it is within the scope of the present invention that the energy storage medium and the actuating fluid may be of the same medium, also that the energy is stored in other ways, e.g., by a mechanical spring device.
[0023] In one arrangement, the opening of a release valve will cause a pressure wave to propagate from the release valve to the moving contact(s) at substantially the speed of sound, which is typically greater than about 1.3 km/s in the preferred dielectric liquids. The tensile compliance of the fluid connection between opening accumulator and the release valve will typically have little impact upon the speed of the pressure wave but that of the fluid connection between the release valve and the moving contact(s) causes a small reduction in the speed of the pressure wave. In practice it is expected that opening accumulator pressure can be applied to the moving contact(s) within about 200 µs of a release valve being opened. The present invention therefore overcomes the mechanical operating speed limitations of known multiple contact actuation linkages. Contact actuation speed is not compromised as the number of moving contacts is increased. Moving contacts are all actuated with substantially identical performance.
[0024] It is often necessary to be able to move each moving contact back towards the closed position when the circuit breaker needs to be closed. Although any suitable means (including mechanical means) can be provided for moving contact closing, fluid actuation is preferably used for both opening and closing of the circuit breaker and the circuit breaker also includes a closing fluid actuation system. Each arcing contact module preferably further includes a second (or closing) dielectric fluid inlet. If each arcing contact module includes a pair of moving contacts then a pair of second inlets are typically also provided with the first inlet and the outlets being positioned between them. Each moving contact has a first end which faces towards an associated first inlet and a second end which faces towards an associated second inlet. A pair of moving contacts (e.g., from physically adjacent arcing contact modules) can share a common second inlet.
[0025] The closing fluid actuation system may have a similar overall construction to the opening fluid actuation system but a lower-performance closing accumulator and release valve arrangement may be specified. The opening and closing fluid actuation systems are typically separate, but may be integrated with suitable means (e.g., control valves) being provided to direct the pressurised dielectric fluid to each first inlet or second inlet as required for opening and closing, respectively. In general terms, it will be readily appreciated that the circuit breaker is opened by introducing pressurised dielectric fluid from the opening fluid actuation system through each first inlet to force each moving contact towards the open position and initiate arcing between the first and second stationary contacts. The circuit breaker is closed (or reset) by introducing pressurised dielectric fluid from the closing fluid actuation system through each second inlet to force each moving contact back towards the closed position where the electrically conductive pathway between the first and second stationary contacts is reestablished.
[0026] The closing fluid actuation system is fluidly connected to each second inlet. The requirements for closing each moving contact are far less stringent than those for opening and thus the fluid containment may be far more compliant. But the closing fluid actuation system is preferably designed to minimise back-pressure which might hinder opening performance. The closing accumulators at each end of series-connected arcing contact modules may optionally have smaller capacity than the intermediate closing accumulator(s). In an arrangement where the circuit breaker includes a plurality of second inlets, each second inlet can include its own fluid actuation means that includes a closing accumulator for storing the pressurised dielectric fluid, a release valve, and associated passageways. But fluid actuation means can also be shared by two or more second inlets. For example, the closing fluid actuation system can include a single closing accumulator that is connected to each second inlet, either by a single release valve or by a series of release valves (i.e., each second inlet has its own respective release valve). Each release valve is opened and closed under the control of a control unit, and can have any suitable construction. On receipt of a signal to close the circuit breaker, each release valve is opened to allow the pressurised dielectric fluid in the associated closing accumulator to flow through each second inlet and provide the fluid actuation that forces the moving contact(s) back to the closed position. Where the closing fluid actuation system includes two or more release valves they can be controlled to open simultaneously to ensure synchronisation of the arcing contact modules, but absolute timing precision is not essential for circuit breaker closing.
[0027] It will be readily appreciated that any dielectric fluid on the second inlet-side of each moving contact must be displaced through the second inlet during opening of the circuit breaker (i.e., the dielectric fluid is displaced as each moving contact moves from the closed position towards the open position). The closing fluid actuation system therefore preferably includes at least one drain valve that allows the dielectric fluid to be displaced through the associated fluid actuation means fluidly connected to each second inlet. Pressurised dielectric fluid will flow from each closing accumulator into the linear passageway through the associated second inlet(s) during circuit breaker closing and displaced dielectric fluid will flow out of the linear passageway through the second inlet(s) during circuit breaker opening.
[0028] The displaced dielectric fluid during circuit breaker opening will typically flow through each drain valve into a drain system. But at least a portion of the displaced dielectric fluid can be allowed to flow through each suitably adapted release valve to pressurise the closing accumulator(s). When the circuit breaker is opened, each drain valve in the closing fluid actuation system is typically opened substantially simultaneously with each release valve in the opening fluid actuation system to allow for the displacement of the dielectric fluid on the second inlet-side of each moving contact to flow into an un-pressurised receiver of the drain system as a result of moving contact opening.
[0029] It will also be readily appreciated that any dielectric fluid on the first inlet-side of each moving contact must be displaced during closing of the circuit breaker (i.e., the dielectric fluid is displaced as each moving contact moves from the open position back towards the closed position). The opening fluid actuation system therefore preferably includes at least one drain valve that allows the dielectric fluid to be displaced through the associated fluid actuation means. Pressurised dielectric fluid will flow from each opening accumulator into the linear passageway through the associated first inlet(s) during circuit breaker opening and displaced dielectric fluid will flow out of the linear passageway through the first inlet(s) during circuit breaker closing.
[0030] The displaced dielectric fluid during circuit breaker closing will typically flow through each drain valve into a drain system. A common drain system for both the opening and closing fluid actuation systems can be used. But at least a portion of the displaced dielectric fluid can be allowed to flow through each suitably adapted release valve to pressurise the opening accumulator(s). When the circuit breaker is closed, each drain valve in the opening fluid actuation system is therefore opened substantially simultaneously with each release valve in the closing fluid actuation system to allow for the displacement of the dielectric fluid on the first inlet-side of each moving contact to flow into the drain system as a result of moving contact closing. The displaced dielectric fluid flowing through the various drain valves can be collected by a common un-pressurised receiver that can be the main holding tank for the dielectric fluid. Dielectric fluid in the un-pressurised receiver can be pumped into a pressurised receiver that forms part of a vent system (see below).
[0031] During the opening process, each moving contact attains a high velocity and this may be moderated to some extent by defining that the energy that is stored in the opening accumulator(s) is significantly dissipated during the initial acceleration of each moving contact thereby avoiding the attainment of a needlessly high velocity at end of stroke. As has already been mentioned, the opening accumulator(s) are not always the sole source of actuating pressure once arcing has been initiated between moving and stationary contacts. Each moving contact is preferably brought to rest at the end of its opening stroke and suitable stopping means, e.g., a rebound damper, can be provided. Similarly, each moving contact is preferably brought to rest at the end of its closing stroke and suitable stopping means, e.g., a rebound damper, can be provided.
[0032] Each outlet can optionally be configured as an annular vent. When each moving contact separates from the surrounding first stationary contact, an arc is rapidly established across the outlet between the adjacent first and second stationary contacts. The movement of each moving contact towards the open position places each outlet in direct fluid communication with the associated first inlet (i.e., the moving contact is no longer interposed between them in the linear passageway) and the pressurised dielectric fluid from the opening accumulator(s) flows into the linear passageway through each first inlet and out of the linear passageway through the associated outlet(s). In one arrangement where the pressurised dielectric fluid is a liquid, a liquid/gas mixture is blasted through each outlet and displaces the established arc into the surrounding annular vent whose outer extremity can be in the form of an annular space between two opposing flanges. The annular space can have a vent opening that communicates with a vent chamber. The dielectric fluid can flow radially outwardly through the annular vent and then linearly through the vent chamber.
[0033] The fast-flowing and pressurised dielectric fluid serves to extinguish the arc by removing the heat that would otherwise sustain the ionisation process within the arc and maintain its electrically conductive state. In one arrangement, where the dielectric fluid is a liquid, some of the dielectric decomposes as a result of receiving heat from the arc and the preferred liquids decompose to form a highly pressurised dielectric gas bubble with a high heat diffusion rate that surrounds the arc. Heat is removed from the arc by a combination of conduction, forced convection and radiation processes that are effective from arc initiation between the moving and first stationary contacts until the arc is displaced by the pressurised dielectric fluid into the annular vent. An undesirably but inevitable effect of arcing is that small particles of carbon and metal will be sparsely dispersed within the fluid that flows through the annular vents. The volumetric flow rate of fluid and the relatively low concentration of entrained gas and particles is such that these pollutants have a tolerable small effect on the current breaking and transient voltage withstand capability of the circuit breaker. Nevertheless, these pollutants must not be permitted to accumulate in an uncontrolled manner and their removal from the fluid circuit is described below. It is also inevitable that any gaseous products of decomposition must be dissolved in the dielectric fluid and these have minimal effect on circuit breaker performance providing they are not allowed to accumulate in an uncontrolled manner. In accordance with best practice, the condition of the dielectric fluid must be analysed periodically and replaced if necessary. The arc-facing surfaces of each annular vent and vent chamber can be constructed using any convenient insulation material and preferably benefit from ablation protection as used in HVAC circuit breakers. Each vent chamber is preferably fluidly connected to a pressurised vent system that is maintained at a pressure that is preferably above atmospheric pressure and is typically less than 10% of the opening accumulator pressure. In one arrangement, pressure is preferably applied to the vent system in order to increase the dielectric strength of any entrained gas within the liquid/gas mixture that is blasted through each outlet in order to eliminate the risk of voltage breakdown and re-strike after current interruption. Pressure is also preferably applied to the vent system so that a defined retaining force is applied to each moving contact to retain it in the open position. Mechanical retainers can also be used but the use of fluid pressure is normally preferable.
[0034] The present invention further provides a method of operating a circuit breaker comprising at least one arcing contact module, each arcing contact module including:
a first dielectric fluid inlet;
a first stationary contact;
a second stationary contact, the first and second stationary contacts being spaced apart by a gap that defines a dielectric fluid outlet; and
a moving contact;
the method comprising the steps of:
on receipt of a signal to open the circuit breaker, introducing pressurised dielectric fluid through the first inlet to move the moving contact from:
- (a) a closed position (e.g., where the moving contact is in electrical contact with the first and second stationary contacts to provide an electrically conductive pathway between the first and second stationary contacts), to
- (b) an open position where arcing is initiated (e.g., where the moving contact is not in electrical contact with the first stationary contact, thereby establishing an arc across the gap between the first and second stationary contacts, and wherein the introduced pressurised dielectric fluid flows through the outlet to cool the arc).
[0035] In one arrangement, dielectric fluid can be circulated through the circuit breaker (e.g., through the linear passageway) for a pre-determined period after circuit breaker opening, and optionally on a continuous basis until it is required that the circuit breaker is closed. This ensures that entrained gas and particulate pollutants are purged from the arcing and vent chambers to the vent system.
[0036] The vent system can be pressurised by a pump with any convenient form of pressure regulation. The vent system can include a pressurised receiver that receives the dielectric fluid from each outlet. The pump inlet can be connected to the un-pressurised receiver of the drain system. In other words, dielectric fluid in the un-pressurised receiver of the drain system can be pumped into the pressurised receiver of the vent system. The vent system is preferably out-gassed by any convenient means and this out-gassing may be facilitated by a pumped system. Particulate pollutants are preferably filtered out of the dielectric fluid. The out-gassed dielectric fluid from the pressurised receiver can be pumped by at least one positive displacement pump in order to achieve accumulator pressurisation. In other words, the vent system preferably forms part of a closed-loop system where out-gassed dielectric fluid is returned to each accumulator or circulated through the linear passageway. The at least one pump can run continuously until accumulators attain their desired working pressure and also for a defined period as previously described when the circuit breaker is opened, and optionally may run continuously. Any convenient form of pressure regulation may be employed. Separate pumps may be employed to pressurise respective opening and closing accumulators when these have different operating pressures.
[0037] Non-return valves can be employed in any or all of the connections between the accumulator pressurisation feed or feeds and respective accumulators.
[0038] The circuit breaker has three modes of operation, namely an opening mode, a holding mode, and a closing (or reset) mode.
[0039] Opening mode:
Before receipt of a signal to open, each moving contact is in the closed position where it is in electrical contact with the surrounding first and second stationary contacts of the associated arcing contact module. On receipt of a signal to open, each release valve in the opening fluid actuation system and each drain valve in the closing fluid actuation system is opened as described above. Pressurised dielectric fluid flows rapidly from each opening accumulator, through associated fluid actuation means, and into the linear passageway where it provides fluid actuation to force each moving contact towards the open position.
[0040] As each moving contact is forced towards the open position, dielectric fluid on the second-inlet side is forced out of the linear passageway through each second inlet and through the associated fluid actuation means of the closing fluid actuation system to the un-pressurised receiver of the drain system. Each closing accumulator can also be pressurised if flow is allowed through the release valve(s) of the closing fluid actuation system. The displacement of dielectric fluid into the un-pressurised receiver substantially stops once each moving contact reaches the open position. But in practice it is possible for there to be a small amount of leakage of pressurised dielectric fluid past each moving contact when in the open position.
[0041] With initial separation, an arc is established between each moving contact. Further movement of each moving contact towards the open position causes an arc to be established across each outlet between the associated first and second stationary contacts. The pressurised dielectric fluid flows out of the linear passageway through each outlet where it cools the associated arc and promotes current interruption. The pressurised dielectric fluid flows out of the vent chamber to the pressurised receiver of the vent system.
[0042] Holding mode:
After current interruption has taken place, dielectric fluid can be circulated through the linear passageway, the outlets, and then to the pressurised receiver of the vent system to ensure out-gassing and to temporarily retain each moving contact in the open position. During this temporary phase of the holding mode it is the pressure within the pressurised receiver that defines the retaining force on the moving contact(s); it being the case that the pressure within the pressurised receiver is typically greater than that in the un-pressurised receiver. Also during this temporary phase of the holding mode the opening accumulator pressure continues to reduce until it becomes asymptotic with the pressure that is maintained in the pressurised receiver. A small amount of dielectric fluid may leak past the moving contact(s) and into the un-pressurised receiver through the second inlets. Dielectric fluid in the un-pressurised receiver of the drain system can be pumped into the pressurised receiver so that the fluid flow in the temporary phase of the holding mode can be sustained for as long as desired. At the end of the temporary phase, the opening accumulator pressure would be insufficient to allow the circuit breaker to be opened again should it be closed for any reason.
[0043] Closing accumulator pressure should be within normal operating limits and the circuit breaker should be capable of re-opening before the moving contact is returned to the closed position. The closing release valves must therefore be closed for a period of time that is sufficient to allow re-pressurisation of each opening accumulator prior to initiating a closing mode. In this final phase of the holding mode, it is the pressure within the pressurised receiver of the vent system that continues to define the retaining force on each moving contact. A small amount of dielectric fluid may continue to leak past the moving contact(s) and into the unpressurised receiver and thus the fluid flow in each outlet may reverse. Since the dielectric fluid in the pressurised receiver is out-gassed and flow through each outlet is minimal, gas entrainment in the reversed flow is insignificant, i.e., an insignificant amount of gas in introduced within the outlet(s). Dielectric fluid in the un-pressurised receiver of the drain system can be pumped back into the pressurised receiver such that the fluid flow in the final phase of the holding mode can be sustained for as long as desired. At the end of this final phase, the opening accumulator pressure is once again sufficient to allow the circuit breaker to be opened again.
[0044] Closing mode:
On receipt of a signal to close, each release valve in the closing fluid actuation system and each drain valve in the opening fluid actuation system is opened as described above.
Pressurised dielectric fluid flows from each closing accumulator, through associated fluid actuation means and into the linear passageway where it provides fluid actuation to force each moving contact towards the closed position.
[0045] As each moving contact is forced towards the closed position, dielectric fluid on the first-inlet side is initially forced out of the each outlet and also out of the linear passageway through each first inlet and through the associated fluid actuation means of the opening fluid actuation system to the un-pressurised receiver of the drain system. As each moving contact approaches the respective first stationary contact, the initial component of fluid flow through each outlet becomes restricted by the reducing opening cross section and eventually stops. The fluid flow is then entirely forced to flow out of the linear passageway through each first inlet and through the associated fluid actuation means of the opening fluid actuation system to the un-pressurised receiver of the drain system.
[0046] Each opening accumulator can also be pressurised. The displacement of dielectric fluid into the un-pressurised receiver substantially ceases once each moving contact reaches the closed position.
[0047] The circuit breaker can use any suitable dielectric fluid, e.g., a proprietary liquid dielectric oil such as MIDEL, or a gas. Preferred dielectric liquids are preferably incompressible, and have a high heat capacity and gaseous products of decomposition that predominantly comprise hydrogen. The dielectric liquid preferably has sufficient viscosity to provide beneficial lubrication to sliding interfaces and to resist leakage past the same. Many proprietary synthetic esters and refined natural esters have been developed for use as transformer oil for use in tap changers and other switch applications and would be suitable.
[0048] It will be readily understood that the dynamic behaviour of the moving contacts and the established arcs will preferably be substantially equal, and that the total arc voltage and rate of heat transfer and total heat capacity will preferably be substantially pro-rasta with the number of moving contacts that are connected in series. The total 'off state voltage, transient recovery voltage and rate of rise of transient recovery voltage capability of the moving contacts should ideally be substantially pro-rata with the number of moving contacts that are connected in series and it is preferable that conventional voltage balancing means are employed. These voltage balancing means may be connected in parallel with respective first and second stationary contacts, i.e., in parallel with each switch contact system in a string of series connected switch contact systems.
[0049] The circuit breaker is preferably used in conjunction with at least one surge arrester whose functions are to define the maximum voltage that is experienced by the series-connected moving contacts, and to dissipate the majority inductively stored energy in the dc circuit. It will be understood that the above-defined rapid development of total arc voltage is beneficial in speeding up the commutation of current from circuit breaker into surge arrester and consequently reducing the proportion of inductively stored energy that is dissipated within the circuit breaker. It will also be understood that the greater the initial rate of heat transfer between arcs and their surrounding medium, the lower the total heat transfer between arcs and their surrounding medium. The circuit breaker may be hybridised with any convenient form of switching aid network (or 'snubber') in order to further reduce the total heat transfer between arcs and their surrounding dielectric fluid.
Drawings
[0050]
Figure 1 is a cross sectional view of an arcing contact module that forms part of a circuit breaker according to the present invention;
Figure 2A is a cross sectional view of a circuit breaker according to the present invention in a closed position;
Figure 2B is a cross sectional view of the circuit breaker of Figure 2A in an opening position, i.e., during circuit breaker opening;
Figure 2C is a cross sectional view of the circuit breaker of Figure 2A in a fully open position;
Figure 3A is a schematic view of a circuit breaker according to the present invention showing external hydraulic components;
Figures 3B to 3E are schematic views of the circuit breaker of Figure 3A showing flow pathways of dielectric liquid through the circuit breaker during opening, holding and closing modes.
[0051] With reference to Figure 1, an arcing contact module 1 that forms part of a circuit breaker according to the present invention includes a first stationary contact 2 in the form of an electrically conductive tubular member with a radially outer support. A pair of second stationary contacts 4 in the form of electrically conductive tubular members with radially outer supports are coaxially aligned with the first stationary contact 2 and are spaced apart from first and second ends 2', 2" of the first stationary contact by respective annular gaps or vents 6 that define dielectric liquid (or gas/liquid) outlets. The radially outer part of each gap includes an annular vent opening 8 that communicates with an annular vent chamber 10. The arc-facing surfaces of the vents 6 and the vent chambers 10 can be constructed using any convenient insulation material and preferably benefit from ablation protection as used in HVAC circuit breakers.
[0052] The stationary contacts 2, 4 together define a linear passageway 12 in which a pair of moving contacts 14 are positioned. As explained herein, the interface between each moving contact 14 and the stationary contacts 2, 4 can include a hydraulic sealing region, an electrical sliding contact region and an arc erosion resistant region. Each moving contact 14 has a substantially cylindrical shape and preferably has a relatively low mass, the mass being minimised by providing an internal cavity. In one arrangement, each moving contact 14 has a lightweight aluminium alloy cylindrical body upon which a high electrical conductivity and wear-resistant layer is applied or deposited in order to facilitate a sliding contact mechanism, and has suitably profiled arc erosion-resistant arcing faces or contact tips. The moving contacts 14 are a close tolerance fit within the linear passageway 12 (i.e., within the radially inner cylindrical surfaces of the stationary contacts) so that leakage of dielectric liquid past the moving contacts is minimised.
[0053] An opening dielectric liquid inlet or port 16 is provided at the first stationary contact 2 and includes an opening 16' in fluid communication with the linear passageway 12. Closing dielectric liquid inlets or ports 18 are provided at the second stationary contacts 4 and each closing inlet includes an opening 18' in fluid communication with the linear passageway 12.
[0054] A hydraulic rebound damper arrangement 20 is provided at the first stationary contact 2, adjacent to the opening 16' of the opening inlet 16. A hydraulic rebound damper arrangement 22 is provided at each second stationary contact 4 adjacent the opening 18' of each closing inlet 18. The hydraulic rebound damper arrangements 20, 22 are designed to bring the moving contacts 14 to rest at the end of their opening and closing strokes as described in more detail below. Each hydraulic damper arrangement 20, 22 can include a pair of damper members arranged to contact a respective moving contact. Although the forces acting upon each damper member within a pair of damper members may be substantially equal and opposite, practical dimensional and performance tolerances may be such that pairs of damper members experience an axial force imbalance and hence each hydraulic rebound damper arrangement 20, 22 is preferably appropriately secured within the linear passageway 12, e.g., using securing webs.
[0055] Each moving contact 14 can move axially within the linear passageway 12 between a pair of hydraulic rebound damper arrangements.
[0056] Figure 2A shows a circuit breaker 100 constructed from a plurality of arcing contact modules arranged in series, each being activated in a synchronous manner on receipt of a signal to open the circuit breaker. For clarity, only part of two axially adjacent arcing contact modules 1a, 1b is shown. The arcing contact modules 1a, 1b share a second stationary contact 4', a closing inlet 18b and a hydraulic damper arrangement 22 as shown. The number of arcing contact modules will be selected with reference to a desired arc voltage or total arcing performance. The circuit breaker 100 can employ shedded insulators around the stationary contacts 2, 4 and any structural supports for the various liquid conduits etc. Box-type corona shields with nominal curved edges can house other components such as the accumulators, valves and associated controls.
[0057] Figure 3A is a schematic representation of the circuit breaker 100 shown in Figure 2A but includes the various external hydraulic circuits. The circuit breaker 100 includes dc terminals 102, 104 and is connected to a dc network (not shown). A switching aid network or 'snubber' 106 is connected in parallel with the circuit breaker 100. The circuit breaker 100 includes three arcing contact modules 1a-1c with three opening inlets 16a-16c, four closing inlets 18a-18d, six vent chambers 10a-10f and six moving contacts. But it will be readily appreciated that the circuit breaker can include any suitable number of arcing contact modules. A first intermediate closing inlet 18b is shared between the first and second arcing contact modules 1a, 1b and a second intermediate closing inlet 18c is shared between the second and third arcing contact modules 1b, 1c.
[0058] An opening hydraulic actuation system includes a plurality of fast-acting hydraulic actuation means 24a-24c. Each hydraulic actuation means 24a-24c is fluidly connected to a respective opening inlet 16a-16c and includes an opening accumulator 26a-26c, an opening release valve 28a-28c, and a closing drain valve 30a-30c. In particular, each opening inlet 16a-16c is fluidly connected to its respective opening accumulator 26a-26c through the respective opening release valve 28a-28c and suitable liquid conduits (e.g., piping or tubing), and is fluidly connected to an un-pressurised receiver 40 of a drain system through the respective closing drain valve 30a-30c and suitable liquid conduits.
[0059] A closing hydraulic actuation system includes a plurality of hydraulic actuation means 32a-32d. Each hydraulic actuation means is fluidly connected to a respective closing inlet 18a-18d and includes a closing accumulator 34a-34d, a closing release valve 36a-36d, and an opening drain valve 38a-38d. In particular, each closing inlet 18a-18d is fluidly connected to its respective closing accumulator 34a-34d through the respective closing release valve 36a-36d and suitable liquid conduits, and is fluidly connected to the un-pressurised receiver 40 through the respective opening drain valve 38a-38d and suitable liquid conduits. The end closing accumulators 34a, 34d can optionally have smaller capacity than the intermediate closing accumulators 34b, 34c that are fluidly connected to the intermediate closing inlets 18b, 18c.
[0060] The liquid conduits, valves, accumulators and all associated interconnections within a particular opening or closing hydraulic actuation system, and the interconnection between the system and the first stationary contact of the respective arcing contact module, can be electrically conductive and can conveniently be electrically connected to, and be housed within, an equi-potential shield. Associated control apparatus (not shown) can also be electrically connected to the equi-potential shield if desired. The equi-potential shield can act as a corona shield.
[0061] The un-pressurised receiver 40 is the main holding tank for the dielectric liquid (e.g., MIDEL).
[0062] The various release valves and drain valves are opened and closed under the control of a control unit (not shown).
[0063] The vent chambers 10a-10f are fluidly connected to a pressurised receiver 42 of a vent system by suitable liquid conduits that must be made of an electrically insulating material. The vent system is maintained at a pressure that is preferably above atmospheric pressure and is typically less than 10% of the opening accumulator pressure. The vent system is pressurised by a pump 44 with any convenient form of pressure regulation. The inlet of pump 44 is connected to the un-pressurised receiver 40 so that dielectric liquid in the un-pressurised receiver is pumped into the pressurised receiver 42.
[0064] The vent system is out-gassed by an out-gassing, drying and filtration means 46 that includes a pump 48. The dielectric liquid in the pressurised receiver 42 is generally maintained in a substantially gas- and particulate-free state but dielectric liquid that is recovered from vent chambers 10a-10f immediately following circuit breaker opening will contain finely entrained gas bubbles and particulates. These gas bubbles are preferably removed by the out-gassing means before the dielectric liquid is used by the opening and closing hydraulic actuation systems but a small gas content may be carried over into the opening hydraulic actuation systems and be re-circulated without adverse effect in practice. Several cycles of re-circulation may be needed before entrained gas bubbles are substantially removed. A desiccant or equivalent drying system can be used to remove moisture from the dielectric liquid and the entry of moisture is preferably minimised by sealing the fluid systems. Conventional replaceable paper cartridge or equivalent type filters can be connected in line with pump inlets.
[0065] Positive displacement pumps 50, 52 pump the out-gassed, dried and filtered dielectric liquid to the closing accumulators 34a-34d and the opening accumulators 26a-26c, respectively. Non-return valves (not shown) are employed in any or all of the liquid connections between the accumulator pressurisation feed or feeds and respective accumulators.
[0066] Figure 2A shows the circuit breaker 100 in a closed position. In particular, the moving contacts 14 of the arcing contact modules 1a-1c are in a closed position where each moving contact is in electrical contact with respective first and second stationary contacts 2, 4 to provide a continuous electrically conductive pathway between the dc terminals 102, 104 of the circuit breaker 100.
[0067] All arcing contact modules are controlled by a suitable control unit (not shown) that receives a signal to open the circuit breaker 100 for protection purposes when a fault current is developed, or in response to an operator request. On receipt of a signal to open the circuit breaker 100, the opening release valves 28a-28c in the opening hydraulic actuation system and the opening drain valves 38a-38d in the closing hydraulic actuation system are opened by the control unit (not shown). Pressurised dielectric liquid in the opening accumulators 26a-26c flows through the opening release valves 28a-28c and into the linear passageway 12 through the opening inlets 16a-16c to provide hydraulic actuation that forces the moving contacts 14 towards an open position. The moving contacts 14 are actuated simultaneously, with minimal delay and with rapidly increasing contact separation. Figure 2B shows an intermediate stage of circuit breaker opening 100 where pressurised dielectric liquid flows through the opening inlets 16a-16c and where the moving contacts 14 are being forced by the pressurised dielectric liquid axially through the linear passageway 12 towards the opposing hydraulic damper arrangement 22. (In Figures 2B and 2C the flowpath of pressurised dielectric liquid is represented by faint solid arrows and in Figure 2B the movement direction of each moving contact 14 is represented by bold solid arrows.)
[0068] As the moving contacts 14 move towards the open position, they will come out of electrical contact with the surrounding first stationary contacts 2. The electrically conductive pathway between the dc terminals 102, 104 of the circuit breaker 100 is broken at multiple locations (i.e., six in the illustrated arrangement where each arcing contact module 1a-1c has two moving contacts) and initial arcing is established between the moving contacts 14 and the first stationary contacts 2 as shown in Figure 2B. The action of the arcs that form as the moving contacts 14 separate from the first stationary contacts 2 causes thermal decomposition of the dielectric liquid and the resultant generation of gaseous products causes additional actuating pressure to be applied to the moving contacts. The moving contacts 14 are all actuated with substantially identical performance.
[0069] The dielectric liquid on the closing inlet-side of the moving contacts 14 must be displaced through the closing inlets 18a-18d during opening of the circuit breaker 100. Displaced dielectric liquid flows out of the linear passageway 12 through the closing inlets 18a-18d and suitable liquid conduits to the un-pressurised receiver 40. (In Figure 2B the flowpath of displaced dielectric liquid is represented by faint dashed arrows.)
[0070] As the moving contacts 14 continue to move towards the open position, arcing is rapidly established across the vents 6 between the adjacent first and second stationary contacts 2, 4. The pressurised dielectric liquid from the opening accumulators 26a-26c flows out of the linear passageway 12 through the vents 6. A liquid/gas mixture is therefore blasted through each annular vent 6 and displaces the established arcs into the surrounding vent chambers 10, rapidly removing heat and ionised material from the arcs in order to cause their extinction. As shown in Figures 2B and 2C, the dielectric liquid can flow radially outwardly through the vent openings 8 and then linearly through the vent chambers 10. From the vent chambers 10, the dielectric liquid flows through suitable liquid conduits to the pressurised receiver 42.
[0071] The moving contacts 14 are brought to rest at the end of their opening stroke (i.e., in an open position) by the opposing hydraulic damper arrangements 22. Figure 2C shows the moving contacts 14 in the open position.
[0073] Dielectric liquid can be circulated through the circuit breaker (e.g., through the linear passageway 12) for a pre-determined period after circuit breaker opening, and optionally on a continuous basis until the circuit breaker is ready to be closed. This ensures that entrained gas and other pollutants are purged from the arcing and vent chambers to the vent system. The circulating dielectric liquid benefits from out-gassing, drying and filtration. The rate of pollutant removal, in combination with the desired liquid purity, defines the pre-determined period during which the dielectric liquid is circulated through the circuit breaker. The circulating dielectric liquid can be used to apply a force to the moving contacts 14 to temporarily retain them in the open position until the circuit breaker 100 needs to be closed (or reset). In this holding mode, the dielectric liquid flows from the pressurised receiver 42 of the vent system through the hydraulic actuation means 24a-24c of the opening hydraulic actuation system; out of the linear passageway 12 through the vents 6; and back to the pressurised receiver. This is because the pressure in the pressured receiver 42 is greater than that in the unpressurised receiver 40. Dielectric liquid in the un-pressurised receiver 40 of the drain system can be pumped into the pressurised vent receiver 42.
[0074] The opening accumulators 26a-26b are pressurised using the dielectric liquid in the pressurised receiver 42 with the pump 52 being operated to pump out-gassed, dried and filtered dielectric liquid to the hydraulic actuation means.
[0075] The flowpaths of dielectric liquid during the temporary phase of the holding mode are shown in Figure 3C. During the temporary phase, any flow of dielectric liquid into the un-pressurised receiver 40 is minimal and is defined by leakage past the moving contacts 14.
[0076] During the final phase of the holding mode, the closing release valves 36a-36d must be closed for a period of time that is sufficient to allow re-pressurisation of each opening accumulator 26a-26c prior to circuit breaker closing. During this time, any circulation of dielectric liquid from the vent system is minimal and is defined by leakage past the moving contacts 14 as shown in Figure 3D.
[0077] On receipt of a signal to close the circuit breaker 100, an action that must be inhibited until the pressure in the opening accumulators 26a-26c and in the closing accumulators 34a-34d are within respective operation limits, this inhibition being performed by the control system (not shown), the closing release valves 36a-36d in the closing hydraulic actuation system and the closing drain valves 30a-30c in the opening hydraulic actuation system are opened by the control unit (not shown). Pressurised dielectric liquid in the closing accumulators 34a-34d flows through the closing release valves 36a-36d and into the linear passageway 12 through the closing inlets 18a-18d to provide hydraulic actuation that forces the moving contacts 14 back towards the closed position. The dielectric liquid on the opening inlet-side of the moving contacts 14 must be displaced through the opening inlets 16a-16c during closing of the circuit breaker 100. The displaced dielectric liquid initially flows out of the linear passageway 12 through the vents chambers 10a-10f and to the pressurised receiver 42 and also through the opening inlets 16a-16c to the un-pressurised receiver 40. As the moving contacts 14 approach the first stationary contacts 2, the effective port area that is open to the vents reduces until it is closed. At this time, displaced dielectric liquid flows only out of the linear passageway 12 through the opening inlets 16a-16c and suitable liquid conduits to the un-pressurised receiver 40.
[0078] The moving contacts 14 are brought to rest at the end of their closing stroke (i.e., in the closed position shown in Figure 2A) by the opposing hydraulic damper arrangements 20.
[0079] It will be readily appreciated that other, non-hydraulic means (e.g., mechanical means) can also be used for circuit breaker closing.
1. A circuit breaker (100) comprising at least one arcing contact module (1a, 1b, 1c),
each arcing contact module (1a, 1b, 1c) including:
a first dielectric fluid inlet (16);
a first stationary contact (2);
a second stationary contact (4), the first and second stationary contacts (2, 4) being spaced apart by a gap that defines a dielectric fluid outlet (6); and
a moving contact (14), the moving contact (14) being movable by the introduction of pressurised dielectric fluid through the first inlet (16) from:
(a) a closed position, to
(b) an open position where arcing is initiated.
2. A circuit breaker (100) according to claim 1, wherein in the closed position, the
moving contact (14) is in electrical contact with the first and second stationary
contacts (2, 4) to provide an electrically conductive pathway between the first and
second stationary contacts (2, 4), and wherein in the open position, the moving contact
(14) is not in electrical contact with the first stationary contact (2).
3. A circuit breaker (100) according to claim 1 or claim 2, wherein each arcing contact
module (1a, 1b, 1c) further includes a second dielectric fluid inlet (18), the moving
contact (14) being movable by the introduction of pressurised dielectric fluid through
the second inlet (18) from:
(a) the open position, towards
(b) the closed position.
4. A circuit breaker (100) according to any preceding claim, wherein each arcing contact
module (1a, 1b, 1c) further includes:
a pair of second stationary contacts (4), one of the second stationary contacts (4) being spaced apart from the first stationary contact (2) by a gap that defines a first dielectric fluid outlet (6) and the other one of the second stationary contacts (4) being spaced apart from the first stationary contact (2) by a gap that defines a second dielectric fluid outlet (6);
a pair of moving contacts (14), one of the moving contacts (14) being disposed on one side of the first inlet (16) and being movable by the introduction of pressurised dielectric fluid through the first inlet (16) from:
(a) a closed position where the moving contact (14) is in electrical contact with the first stationary contact (2) and said one of the second stationary contacts (4) to provide an electrically conductive pathway between the first stationary contact (2) and said one of the second stationary contacts (4), to
(b) an open position where the moving contact (14) is not in electrical contact with the first stationary contact (2), thereby establishing an arc across the gap between the first stationary contact (2) and said one of the second stationary contacts (4), and wherein the introduced pressurised dielectric fluid flows through the first outlet (6) to cool the arc;
the other one of the moving contacts (14) being disposed on an opposite side of the first inlet (16) and being movable by the introduction of pressurised dielectric fluid through the first inlet (16) from:
(a) a closed position where the moving contact (14) is in electrical contact with the first stationary contact (2) and said other one of the second stationary contacts (4) to provide an electrically conductive pathway between the first stationary contact (2) and said other one of the second stationary contacts (4), to
(b) an open position where the moving contact (14) is not in electrical contact with the first stationary contact (2), thereby establishing an arc across the gap between the first stationary contact (2) and said other one of the second stationary contacts (4), and wherein the introduced pressurised dielectric fluid flows through the second outlet (6) to cool the arc; and
a pair of second dielectric fluid inlets (18a, 18b).
5. A circuit breaker (100) according to any preceding claim, wherein the first and second
stationary contacts (2, 4) are substantially tubular and define a linear passageway
(12) in fluid communication with each first inlet (16) and outlet (6), wherein each
moving contact (14) is positioned within the linear passageway (12).
6. A circuit breaker (100) according to any preceding claim, further comprising an opening
hydraulic actuation system that it is connected to each first inlet (16a-16c), the
opening hydraulic actuation system optionally including at least one opening accumulator
(26a-26c) and at least one release valve (28a-28c) and further optionally including
at least one drain valve (30a-30c) connected to an un-pressurised receiver (40) of
a drain system.
7. A circuit breaker (100) according to claim 3 or claim 4, further comprising a closing
hydraulic actuation system that is connected to each second inlet (18a-18d), the closing
hydraulic actuation system optionally including at least one closing accumulator (34a-34d)
and at least one release valve (36a-36d) and further optionally including at least
one drain valve (38a-38d) connected to an un-pressurised receiver (40) of a drain
system.
8. A circuit breaker (100) according to claim 3 or claim 4, further comprising:
an opening hydraulic actuation system that it is connected to each first inlet (16a-16c) and includes at least one opening accumulator (26a-26c), at least one release valve (28a-28c), and at least one drain valve (30a-30c); and
a closing hydraulic actuation system that it is connected to each second inlet (18a-18f) and includes at least one closing accumulator (34a-34d), at least one release valve (36a-36d), and at least one drain valve (38a-38d);
wherein the drain valves (30a-30c, 38a-38d) are connected to an un-pressurised receiver (40) of a drain system.
9. A circuit breaker (100) according to claim 8, wherein each outlet (6) is connected
to a pressurised receiver (42) of a vent system, the drain system further comprising
a pump (44) for pumping dielectric fluid in the un-pressurised receiver (40) into
the pressurised receiver (42).
10. A circuit breaker (100) according to claim 9, wherein the vent system is out-gassed
by out-gassing means (46) and includes at least one pump (50, 52) for pumping the
out-gassed dielectric fluid to pressurise the opening and closing accumulators (26a-26c,
34a-34d).
11. A circuit breaker (100) according to any preceding claim, comprising a plurality of
arcing contact modules (1a, 1b, 1c) arranged in series, and being adapted to be activated
in a synchronous manner.
12. A method of operating a circuit breaker (100) comprising at least one arcing contact
module (1a, 1b, 1c), each arcing contact module (1a, 1b, 1c) including:
a first dielectric fluid inlet (16);
a first stationary contact (2);
a second stationary contact (4), the first and second stationary contacts (2, 4) being spaced apart by a gap that defines a dielectric fluid outlet (6); and
a moving contact (14);
the method comprising the steps of:
on receipt of a signal to open the circuit breaker (100), introducing pressurised dielectric fluid through the first inlet (16) to move the moving contact (14) from:
(a) a closed position, to
(b) an open position where arcing is initiated.
13. A method according to claim 12, wherein in the closed position, the moving contact
(14) is in electrical contact with the first and second stationary contacts (2, 4)
to provide an electrically conductive pathway between the first and second stationary
contacts (2, 4), wherein in the closed position, the moving contact (14) is not in
electrical contact with the first stationary contact (2), and wherein on acing initiation,
an arc is established across the gap between the first and second stationary contacts
(2, 4) and the introduced pressurised dielectric fluid flows through the outlet (6)
to cool the arc.
14. A method according to claim 12 or claim 13, wherein each arcing contact module (1a,
1b, 1c) further comprises a second dielectric fluid inlet (18);
the method comprising the steps of:
the method comprising the steps of:
on receipt of a signal to close the circuit breaker (100), introducing pressurised dielectric fluid through the second inlet (18) to move the moving contact (18) from:
(a) the open position, towards
(b) the closed position.
15. A method according to any of claims 12 to 14, wherein dielectric fluid is circulated
through the circuit breaker (100) after circuit breaker opening for a pre-determined
period or until the circuit breaker (100) is closed.