Patent Description:
Actuating mechanisms for high-voltage (HV) circuit breakers are well-known. These often take the form of (purely) mechanical devices having numerous components, such as gears, levers, springs, cam, freewheels etc., which carry high loads and have complex movement, making them prone to failure. Attempts to make these components stronger has been met with limited success, as the cost of new or lighter materials is generally prohibitive, and so they often end up heavier and in turn require more energy to operate the circuit breaker. There is also the matter of the actuating mechanism being susceptible to corrosion being made largely of metal. Maintenance of such mechanical actuating mechanisms is therefore expensive.

Hydraulic actuating mechanisms are also known. These typically possess a piston for opening and closing the circuit breaker, the piston deriving its energy through hydraulic fluid passages from an accumulator. Hydraulic actuating mechanisms not only allow large loads to be developed and transmitted, they generally have fewer components and less complex movement compared to their mechanical counterparts. Unfortunately however, a leak in the hydraulic fluid passage may cause a loss of energy being transferred from the accumulator, meaning that the actuating mechanism is unable to open the circuit breaker or may open it too slowly, which could be dangerous.

The document <CIT> discloses an actuating mechanism for a circuit breaker according to the preamble of claim <NUM>.

As such, there is a need for an actuating mechanism for a circuit breaker which is reliable, has a lower part count and less complex movement, and is cheaper.

The present invention relates to an actuating mechanism for a circuit breaker comprising an opening accumulator comprising a first piston, a first cylinder and a first compressible member, the first piston being movable in the first cylinder, against the force of the first compressible member, from a discharged position to a charged position by admitting hydraulic fluid, and movable to return, under the force of the first compressible member, to the discharged position by releasing the hydraulic fluid, wherein the first piston is directly mechanically connected to the first compressible member, and wherein the first cylinder is connected to an outlet fluid passage which can be opened and closed, the actuating mechanism further comprising a closing accumulator comprising a second piston, a second cylinder and a second compressible member, the second piston being movable in the second cylinder, against the force of the second compressible member, from a discharged position to a charged position by admitting hydraulic fluid, and to return, under the force of the second compressible member, to the discharged position by releasing the hydraulic fluid, wherein the first cylinder and the second cylinder are connected by an interconnecting fluid passage which can be opened and closed, arranged such that when the outlet fluid passage is closed and the interconnecting fluid passage is opened, hydraulic fluid released from the second cylinder will be admitted into the first cylinder to move the first piston to the charged position.

The present invention also relates to a method of operating the abovementioned actuating mechanism.

Preferable features of the invention are defined in the appendant claims.

The invention will be better understood when reading the following detailed description and non-limiting examples, as well as studying the figures, wherein:.

In all of these figures, identical references can designate identical or similar elements. In addition, the various portions shown in the figures are not necessarily shown according to a uniform scale, in order to make the figures more legible.

<FIG> show an actuating mechanism <NUM> for a high-voltage (HV) circuit breaker <NUM> according to a preferred embodiment of the invention in various states of operation. It is connected, as shown in a rather simplified manner, to a circuit breaker <NUM> of a switchgear <NUM>. Referring initially to <FIG>, the actuating mechanism <NUM> comprises an opening accumulator <NUM> and a closing accumulator <NUM>. The opening accumulator <NUM> comprises a first piston <NUM>, a first cylinder <NUM> and a first spring <NUM>, with the first piston <NUM> slidably mounted in the first cylinder <NUM> and movable between a discharged position (shown in <FIG>) and a charged position (shown in <FIG>).

The first piston <NUM> further comprises a first piston rod <NUM>. When the first piston <NUM> is in the charged position, the first piston <NUM> and the first piston rod <NUM> are extended, and when the first piston <NUM> is in the discharged position, the first piston <NUM> and the first piston rod <NUM> are retracted. The first piston <NUM> also comprises a first flange <NUM> for receiving a spring.

The first spring <NUM> exerts an axial force on the first piston <NUM>, urging it towards the discharged position (shown in <FIG>). It acts through the first flange <NUM> on which the first spring <NUM> sits. The first piston <NUM> is directly mechanically connected to the first spring <NUM>. Movement of the first piston <NUM> towards the charged position causes the first spring <NUM> to be compressed, and the resulting force acting on the first piston <NUM> to increase.

The first cylinder <NUM> comprises an inlet <NUM> and an outlet <NUM> for admitting and releasing hydraulic fluid respectively. When hydraulic fluid is admitted into the first cylinder <NUM>, hydraulic pressure is applied to the first piston <NUM> and it moves to the charged position, against the force of the first spring <NUM>. Equally, when the hydraulic fluid is released from the first cylinder <NUM>, hydraulic pressure is removed from the first piston <NUM> and it moves to return to the discharged position, under the force of the first spring <NUM>. The first piston <NUM> is arranged to be directly mechanically connected to the circuit breaker <NUM>.

The actuating mechanism <NUM> also comprises a closing accumulator <NUM>. In so far as the features above are concerned, it is near identical to the opening accumulator <NUM>, the main difference in this particular embodiment being that it comprises a stiffer spring <NUM>. For completeness, the closing accumulator <NUM> will also be described here.

The closing accumulator <NUM> comprises a second piston <NUM>, a second cylinder <NUM> and a second spring <NUM>, with the second piston <NUM> slidably mounted in the second cylinder <NUM> and movable between a discharged position (shown in <FIG>) and a charged position (shown in <FIG>).

The second piston <NUM> further comprises a second piston rod <NUM>. When the second piston <NUM> is in the charged position, the second piston <NUM> and the second piston rod <NUM> are extended, and when the second piston <NUM> is in the discharged position, the second piston <NUM> and the piston rod <NUM> are retracted. The second piston <NUM> also comprises a second flange <NUM> for receiving a spring.

The second spring <NUM> exerts an axial force on the second piston <NUM>, urging it towards the discharged position (shown in <FIG>). It acts through the second flange <NUM> on which the second spring <NUM> sits. As much as possible, the second piston <NUM> is also directly mechanically connected to the second spring <NUM> (which is shown in the figures). Movement of the second piston <NUM> towards the charged position causes the second spring <NUM> to be compressed, and the resulting force acting on the second piston <NUM> to increase.

The second cylinder <NUM> comprises an inlet <NUM> and an outlet <NUM> for admitting and releasing hydraulic fluid respectively. When hydraulic fluid is admitted into the second cylinder <NUM>, hydraulic pressure is applied to the second piston <NUM> and it moves to the charged position, against the force of the second spring <NUM>. Equally, when the hydraulic fluid is released from the second cylinder <NUM>, hydraulic pressure is removed from the second piston <NUM> and it moves to return to the discharged position, under the force of the second spring <NUM>.

A pump <NUM> is provided on an inlet fluid passage <NUM> connected to the inlet <NUM> of the second cylinder <NUM>. When the pump <NUM> is activated, hydraulic fluid is pumped into the second cylinder <NUM>. When it is deactivated, hydraulic fluid is not pumped into the second cylinder <NUM>.

A pump switch <NUM> is provided for operating the pump <NUM>. It is arranged to remain switched on unless acted on by a force. For example, the pump switch <NUM> may comprise a spring urging it closed. This pump switch <NUM> is provided at a location where the second piston rod <NUM> does not act on the pump switch <NUM> unless it is in the extended position where it pushes the pump switch <NUM> open to switch it off. In other words, hydraulic fluid is pumped into the second cylinder <NUM> whenever the second piston <NUM> is not in the charged position. A reservoir <NUM> with hydraulic fluid is provided from which the pump <NUM> can draw hydraulic fluid and to which hydraulic fluid can be returned.

An interconnecting fluid passage <NUM> connects the outlet <NUM> of the second cylinder <NUM> and the inlet <NUM> of the first cylinder <NUM>. It allows the hydraulic fluid released from the second cylinder <NUM> to be admitted into the first cylinder <NUM>. As alluded to before, the hydraulic pressure in the second cylinder <NUM> when the second piston <NUM> is in the charged position is higher than that of the first cylinder <NUM> when the first piston <NUM> is in the discharged position. When the interconnecting fluid passage <NUM> is opened, second piston <NUM> will move to the discharged position, pumping the hydraulic fluid into the first cylinder <NUM> and moving the first piston <NUM> to the charged position. This pressure differential is realised by the second spring <NUM> being stiffer than the first spring <NUM>.

Although the first spring <NUM> and the second spring <NUM> are of the coil spring type, it will be appreciated that other types of springs may be employed, such as bellow springs. It will equally be appreciated that while first compressible member is ideally a spring, this may not always be the case. The same applies to the second compressible member. It should also be noted that 'compressible members' are mechanical in nature and do not include 'compressible fluid' devices such as nitrogen accumulators.

A valve <NUM> is provided, located on the interconnecting fluid passage <NUM>. It is also located on an outlet fluid passage <NUM>, which connects the outlet <NUM> of the first cylinder <NUM> to the hydraulic fluid reservoir <NUM>. It is arranged to open and close the interconnecting fluid passage <NUM> and the outlet fluid passage <NUM> in opposite fashion. This valve <NUM> can be selectively operated to open and close the circuit breaker <NUM>. In <FIG>, the valve <NUM> is in the open position, i.e. corresponding to the circuit breaker <NUM> being open, while in <FIG>, it is in the closed position, i.e. corresponding to the circuit breaker <NUM> being closed. In the open position, hydraulic fluid can flow through the outlet fluid passage <NUM> but not through the interconnecting fluid passage <NUM>, and in the closed position, hydraulic fluid can flow through the interconnecting fluid passage <NUM> but not the outlet fluid passage <NUM>. It will be understood that other valve arrangements are possible, for example, a separate valve on each of the interconnecting fluid passage <NUM> and the outlet fluid passage <NUM>.

The first piston <NUM> will now be discussed in further detail. As mentioned above, first spring <NUM> exerts a force on the first piston <NUM> via the first flange <NUM>. There is therefore a direct mechanical connection between the first spring <NUM>, i.e. the energy storage device of the opening accumulator <NUM>, and the first piston <NUM>, and not a fluidic connection/hydraulic passage between the two. In use, the first piston <NUM> will be directly mechanically connected to the circuit breaker <NUM>, typically through its piston rod <NUM>. This represents a direct mechanical connection between the first spring/compressible member <NUM> and the circuit breaker <NUM>. It is further intended that the first piston <NUM> in use be connected to the circuit breaker <NUM> such that when the first piston <NUM> is in the charged position, the circuit breaker <NUM> is closed, and when it is in the discharged position, the circuit breaker <NUM> is open.

Therefore, when the first piston <NUM> is in the charged position, the compressed first spring <NUM> stands ready to directly mechanically transfer its energy to the first piston <NUM> to open the circuit breaker <NUM>. Crucially, the energy for opening the circuit breaker <NUM> is not transferred through a fluidic connection/hydraulic passage as in the prior art, which as mentioned earlier may be prone to leak.

The actuating mechanism <NUM> has a housing <NUM> within which are located the opening accumulator <NUM> and the closing accumulator <NUM>, in parallel orientation. The first cylinder <NUM> and second cylinder <NUM> are provided near one axial end of the housing <NUM>. The first piston <NUM> and second piston <NUM> are located in their respective cylinders, although the first piston rod <NUM> and second piston rod <NUM> protrude from the housing <NUM> at an opposing axial end, in particular from an end wall <NUM> of the housing <NUM>. The interconnecting fluid passage <NUM> is also located in the housing <NUM>. The first spring <NUM> and second spring <NUM> are respectively mounted around the first piston rod <NUM> and second piston rod <NUM>, between the end wall <NUM> of the housing <NUM> and the respective first flange <NUM> and second flange <NUM>. At least the first piston rod <NUM> is provided with a stop <NUM>, located within the housing <NUM>, for engaging the end wall <NUM> and preventing it moving beyond the charged position. The housing <NUM> may further house the pump <NUM> and the outlet fluid passage <NUM>.

In this preferred embodiment, the pressure differential across the interconnecting fluid passage <NUM> is realised by the second spring <NUM> being stiffer than the first spring <NUM>. However, it will be appreciated that other arrangements may allow the same effect. For example, the first and second cylinders <NUM>, <NUM> may be of different sizes or cross-sectional area, or the first and second compressible members <NUM>, <NUM> may be preloaded differently, etc. The important thing is that hydraulic fluid released from the second cylinder <NUM> is able to move the first piston <NUM> to the charged position.

The actuating mechanism <NUM> may of course comprise other features known in the field. For example, O-rings <NUM> are provided at the mouth of the cylinders <NUM>, <NUM> so that they seal against their pistons <NUM>, <NUM> and prevent hydraulic fluid leaking out. Damping valves <NUM> may be provided to slow the pistons <NUM>, <NUM> as they approach the discharged position. Flow adjustment valves <NUM> may be provided in the various fluid passages <NUM>, <NUM> to adjust the opening and closing operation speed of the circuit breaker.

The terms 'charged position' and 'discharged position' of the pistons used in the foregoing correspond to whether energy has been respectively stored or released from their springs. Meanwhile, the terms 'opening accumulator' and 'closing accumulator' correspond to the actuating operation they conduct on the circuit breaker when their stored energy is released.

To facilitate understanding of the invention, the operation of the actuating mechanism in the context of a circuit breaker <NUM> in a switchgear <NUM> will be briefly discussed, with reference to <FIG>. The first piston <NUM> is directly mechanically connected to the circuit breaker <NUM> and such that in the charged position the circuit breaker <NUM> is closed and in the discharged position the circuit breaker <NUM> is open.

In <FIG>, the actuating mechanism <NUM> is in the initial position. The first piston <NUM> and the second piston <NUM> are in the discharged position, while the circuit breaker <NUM> is in the open position. We note that the pump switch <NUM> is in the closed position. The pump <NUM> is therefore activated and pumps hydraulic fluid through inlet fluid passage <NUM> from the reservoir <NUM> into the second cylinder <NUM>. We note that the valve <NUM> is in the open position, and so the interconnecting fluid passage <NUM> is closed, meaning that hydraulic fluid being admitted into the second cylinder <NUM> is prevented from being released, and thus begins filling (or 'charging') the second cylinder <NUM>. As a result, the second piston <NUM> moves from its discharged position towards the charged position and compresses the second spring <NUM>. At the same time, the piston rod <NUM> of the second piston <NUM> extends towards the pump switch <NUM>.

<FIG> shows the state where the second piston <NUM> is in the charged position. The second piston rod <NUM> has pushed the pump switch <NUM> to switch it off, thereby deactivating the pump <NUM>. The second spring <NUM> maintains the hydraulic pressure in the second cylinder <NUM>. The circuit breaker <NUM> is presently still in the open position.

When the circuit breaker <NUM> is to be closed, the valve <NUM> is moved to the closed position. This opens the interconnecting fluid passage <NUM>, allowing hydraulic fluid to be released from the second cylinder <NUM> under the force of the second spring <NUM>. The hydraulic fluid flows through the interconnecting fluid passage <NUM>, and is admitted into the first cylinder <NUM>. Concurrently, the valve <NUM> has closed the outlet fluid passage <NUM>, meaning that the hydraulic fluid admitted into the first cylinder <NUM> is prevented from being released, and thus begins filling the first cylinder <NUM>.

As the second spring <NUM> is stiffer than the first spring <NUM> and is compressed, the hydraulic pressure in the second cylinder <NUM> is higher than that of the first cylinder <NUM>. The second piston <NUM> thus moves rapidly to the discharged position, causing in turn the first piston <NUM> to move rapidly to the charged position and the first piston rod <NUM> to extend to move the circuit breaker <NUM> from the open position to the closed position, thereby allowing current to flow from the switchgear <NUM> to the grid.

<FIG> shows the actuating mechanism <NUM> (just) after the circuit breaker <NUM> has been closed. With the second piston <NUM> now in the discharged position, the pump switch <NUM> is switched on, meaning the pump <NUM> is activated and begins pumping hydraulic fluid into the second cylinder <NUM> again until the second piston <NUM> reaches the charged position. We note that the stop <NUM> on the first piston <NUM> is engaged with the end wall <NUM> of the housing, which prevents the first piston <NUM> moving beyond its charged position. Limiting the stroke of the first piston <NUM> in this way not only allows the second cylinder <NUM> to be filled without moving the first piston <NUM>, it also defines the stroke of the first piston <NUM> allowing precise control of the of the circuit breaker <NUM>. A stop may optionally be provided on the second piston rod <NUM> too.

Finally, <FIG> shows the main operational state of the actuating mechanism, wherein the first piston <NUM> and the second piston <NUM> are both in the charged position. As can be seen, the circuit breaker <NUM> is closed, although the first piston <NUM> is ready to open the circuit breaker <NUM> if necessary. Meanwhile, the second piston <NUM> is ready to close the circuit breaker <NUM> again (should it be opened).

When a fault is detected and the circuit breaker <NUM> needs to be opened, the valve <NUM> is moved to the open position. This opens the outlet fluid passage <NUM> while concurrently closing the interconnecting fluid passage <NUM>, allowing hydraulic fluid to be released from the first cylinder <NUM> to the reservoir <NUM>. The first piston <NUM> will rapidly return from the charged position to the discharged position, the energy released from the first spring <NUM> being directly mechanically transferred to the circuit breaker <NUM> to open it, with the first piston rod <NUM> retracting in the process to move the circuit breaker <NUM> from the closed position to the open position, thereby preventing current from flowing from the switchgear <NUM> to the grid.

At this point, the actuating mechanism <NUM> is effectively in the state as shown in <FIG>, and will typically need to cycle through the states shown in <FIG> and <FIG> to revert to the main operational state (with the circuit breaker <NUM> closed).

The present invention provides a unique actuating mechanism which cleverly combines aspects of mechanical actuating mechanisms and hydraulic actuating mechanisms, retaining their advantages while doing away with their disadvantageous.

Like known mechanical actuating mechanisms, the actuation mechanism of the present invention comprises a direct mechanical connection from the compressible member for opening the circuit breaker to the component for operating the circuit breaker. It is however of simpler construction, having far fewer components and less complex movement when compared to known mechanical actuating mechanisms, and as such is less likely to fail and has reduced maintenance cost. By employing hydraulics, large forces can be developed easily, and thus the energy for operating the circuit breaker can readily be provided. Furthermore, it will be appreciated that many of its moving component, in use, are in contact with hydraulic fluid, maintaining them lubricated and mitigating corrosion.

At the same time, the actuating mechanism of the present invention has increased reliability when compared to known hydraulic actuating mechanisms, as there is a greatly reduced risk of the circuit breaker not opening or opening too slowly. Importantly, this actuating mechanism provides a direct mechanical connection from the compressible member to the piston for opening the circuit breaker. All the energy stored in the compressible member can therefore be utilised to open the circuit breaker, ensuring that the circuit breaker can always be opened. This is unlike known hydraulic actuating mechanisms where a leak in the hydraulic passage may cause a loss of energy being transferred to the piston for opening the circuit breaker. This actuating mechanism of the present invention thus has improved reliability and safety.

Claim 1:
An actuating mechanism (<NUM>) for a circuit breaker (<NUM>) comprising an opening accumulator (<NUM>) comprising a first piston (<NUM>), a first cylinder (<NUM>) and a first compressible member (<NUM>), the first piston (<NUM>) being movable in the first cylinder (<NUM>), against the force of the first compressible member (<NUM>), from a discharged position to a charged position by admitting hydraulic fluid, and movable to return, under the force of the first compressible member (<NUM>), to the discharged position by releasing the hydraulic fluid, wherein the first piston (<NUM>) is directly mechanically connected to the first compressible member (<NUM>), and wherein the first cylinder (<NUM>) is connected to an outlet fluid passage (<NUM>) which can be opened and closed, the actuating mechanism (<NUM>) further comprising a closing accumulator (<NUM>) comprising a second piston (<NUM>), a second cylinder (<NUM>) and a second compressible member (<NUM>), the second piston (<NUM>) being movable in the second cylinder (<NUM>), against the force of the second compressible member (<NUM>), from a discharged position to a charged position by admitting hydraulic fluid, and to return, under the force of the second compressible member (<NUM>), to the discharged position by releasing the hydraulic fluid, characterised in that the first cylinder (<NUM>) and the second cylinder (<NUM>) are connected by an interconnecting fluid passage (<NUM>) which can be opened and closed, arranged such that when the outlet fluid passage (<NUM>) is closed and the interconnecting fluid passage (<NUM>) is opened, hydraulic fluid released from the second cylinder (<NUM>) will be admitted into the first cylinder (<NUM>) to move the first piston (<NUM>) to the charged position.