GB2565304A

GB2565304A - A bistable electrical switching device

Info

Publication number: GB2565304A
Application number: GB1712708.5A
Authority: GB
Inventors: Ward Patrick
Original assignee: Tripco Ltd
Current assignee: Tripco Ltd
Priority date: 2017-08-08
Filing date: 2017-08-08
Publication date: 2019-02-13
Anticipated expiration: 2037-08-08
Also published as: GB201712708D0; GB2565304B

Abstract

A bistable electrical switching device 1 comprises a support element 4 housing a first electrical contact 3, a movable contact 2, and a latching mechanism. The latching mechanism comprises a carrier 11 for the movable contact that moves relative to the support, a closing actuator 20 coupled to the carrier and causing it to move between a first (open) position to a second (closed) position, and a latch 14 which is connected to the carrier and engages the support to maintain the carrier in the second position (see figure 2). The carrier is biased to the open state by being resiliently connected to the supporting element. A release mechanism 40 is actuated to disengage the latch from the supporting element so that it returns to the first position (see figure 3). An auxiliary contact (50, figures 4-6) may be provided, which is moved by an auxiliary actuator 60 to a closed state in which it provides a parallel conductive path between the first contact and moving contact. The auxiliary contact may be connected to the movable contact via a flexible conducting element 53 and may be arranged to couple with the first contact. The latching mechanism can thus be tested without interrupting current to a load.

Description

“A bistable electrical switching device”

Field

The present invention relates to a bistable electrical switching device comprising an electrically activated bistable latching mechanism.

Background

Known electrically latching mechanisms are used to latch the movable contacts of electrical switching devices in their closed state with respect to corresponding fixed contacts.

One problem with these mechanisms is that they consume energy whilst being in the latched state. Another problem is that on removal of the power supply, which may occur accidentally, e.g. due to a fault, the electrically latching mechanisms automatically revert to an unlatched state, which may be disadvantageous in some applications. A further problem related to switching devices is that the movable and fixed contacts may weld due to overheating, with the result that the movable contacts will be unable to open when an opening action is initiated. This can be dangerous, leading to potential shock or fire risk.

Thus, a test functionality for verifying that the movable contacts have correctly opened or are able to open can be implemented. This test functionality can be achieved in several ways, such as by monitoring the load circuit current, or by using the position of the movable contact carrier to verify the opening action. However, there may be cases where such simple verifications prove unacceptable due to a need to maintain electrical continuity between the circuit supply and load.

Summary

According to the present invention, there are provided a bistable electrical switching device according to claim 1 and a fault monitoring system according to claim 7. Embodiments of the bistable electrical switching device comprise an electrically latching mechanism which can remain in two stable states (latched and unlatched) without consuming electrical power.

Furthermore, the latching mechanism can remain in its current stable state independently of a removal or restoration of power supply, and it only reverts to the other stable state on application of an electrical pulse or signal. As such, no energy is consumed other than the energy of the electrical pulses for changing between the stable states.

Embodiments of the present invention can further provide a test functionality for verifying a correct opening of the switching device whilst maintaining an electrical continuity between the circuit supply and load.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates a bistable electrical switching device according to an embodiment of the present invention in a stable unlatched state;

Figure 2 illustrates the device of Figure 1 in a stable latched state;

Figure 3 illustrates a releasing actuator under activation to release the device of Figure 1 from the latched state and cause a return to the unlatched state;

Figure 4 illustrates a bistable electrical switching device according to a second embodiment of the present invention including an auxiliary contact in an open state; Figure 5 illustrates the auxiliary contact of Figure 4 in a closed state and the movable contact in the closed state;

Figure 6 illustrates the auxiliary contact of Figure 4 in the open state and the movable contact in the open state; and

Figure 7 illustrates schematically a fault monitoring system including a bistable electrical switching device according to an embodiment of the present invention.

Description of the Embodiments

Figures 1-3 illustrate a bistable electrical switching device 10 according to an embodiment of the present invention. The device 10 comprises a supporting element 4 housing a contact 3 in a first cavity 5. The supporting element 4 can be a structural element which is directly or indirectly connected with a case (not shown) of the switching device 10.

The device 10 comprises a contact carrier 11 onto which a movable contact 2 is mounted. The carrier 11 is movable inside a second cavity 6 defined in the supporting element 4 adjacent the cavity 5 housing the contact 3. An arm of the carrier extends out of the second cavity 6 and the movable contact 2 is mounted on the arm juxtaposed the contact 3 in the first cavity 5. The carrier 11 is movable between a first position where the movable contact 2 is in an open state with respect to the contact 3 (as illustrated in Figure 1) and a second position where the movable contact 2 is in a closed state with respect to the contact 3 (as illustrated in Figures 2 and 3). A compression spring 12 is located in the second cavity 6 between the carrier 11 and an end wall 7 of the supporting element 4, so that the spring 12 biases the carrier 11 to move the contact 2 away from contact 3.

The device 10 further comprises a closing solenoid actuator 20 mounted to the supporting element 4 on a surface opposite the spring 12 (note that the solenoid winding for delivering the energizing current is not shown in the drawings). The actuator 20 includes a plunger 21 which is actuable to urge the carrier 11 against the bias of the spring 12 to move the contact 2 towards the contact 3.

The closing actuator 20 further includes a compression spring 22 which biases the plunger 21 into a retracted state when the actuator 20 is deactivated. Thus, once the carrier 11 is latched with the contacts in a closed state, the plunger retracts away from contact with the carrier 11 back into its retracted state.

The carrier 11 comprises a hollow centre 13 defined between two end walls, one of which the plunger 21 bears against when the plunger is actuated and the other of which the spring 12 bears against. A latch member 14 is located within the centre of the carrier 11. In the embodiment, the latch member 14 is constrained to slide in a direction transverse to the movement of the carrier 11 between the first and second positions. The latch member 14 is connected to the carrier 11 through a leaf spring 15 which biases the latch member 14 towards a side wall 8 of the supporting element 4. A slot 16 is formed in the side wall 8 so that, when the carrier 11 moves into its second position (Figures 2 and 3) and with the contacts 2, 3 having made contact, the latch member 14 lies in register with the slot 16 and is urged through the slot 16 by the leaf spring 15. Thus, even when the actuator 20 is deactivated and the plunger 21 returns to its retracted position, the latch member 14 will maintain the carrier 11 in its second position.

Note that while a laterally moving latch member 14 is shown in the embodiments, many variations of such a mechanism can be employed, for example, with the latch member engaging the end wall 7 of the supporting element 4, rather than the side wall 8. A releasing solenoid actuator 40 is disposed on the side of the supporting member in which the slot 16 is defined (again the solenoid winding for delivering the energizing current is not shown in the drawings). The releasing actuator 40 includes a plunger 41 which is actuable against the bias of a compression spring 42 to move between a retracted state and an extended state, where it extends into the slot 16 defined in the supporting element 4.

With reference to Figure 1, in a starting condition, the movable contact 2 is held in the open state with respect to the contact 3. In this condition, the closing actuator 20 is de-energized, so that its plunger 21 is biased into the retracted state by the spring 22, and the movable carrier 11 is biased in the first position by the opening spring 12. As illustrated in Figure 1, the latch member 14 stays in an unlatched state where it bears against the side wall 8 of the second cavity 6 so as to keep the leaf spring 15 compressed.

As such, in the situation illustrated in Figure 1 the latching mechanism 10, considered as a whole, stays in a first stable unlatched state without consuming any electrical power.

Figure 1 further illustrates the releasing solenoid actuator 40 associated with the latching mechanism 10, which is also deactivated, so that its plunger 41 is biased in a retracted state by the spring 42.

When closure of the device 10 is required, an electrical pulse of short duration is applied to energize the closing actuator 20. Upon receiving the pulse, the closing actuator 20 is energized to move its plunger 21 from the retracted state to an extended state. Thus, the plunger 21 pushes the carrier 11 against the opening spring 12, from the first position illustrated in Figure 1 to the second position illustrated in Figures 2 and 3.

During this movement of the carrier 11, the latch member 14 slides on a surface of the side wall 8 until reaching the corresponding slot 16 defined through the side wall 8 when the carrier 11 reaches the second position.

As this point, as illustrated in Figure 2, the leaf spring 15 can release and push the latch member 14 into a latched state where it locates into the slot 16.

Furthermore, when the movable carrier 11 reaches the second position, the movable contact 2 couples with the contact 3. As illustrated in Figures 1-3, in the embodiment the contact 3 is resiliently connected to an end wall 9 of the supporting element 4 through a compression spring 17, so that the spring 17 biases the contact 3 towards the coupled movable contact 2.

In this way, the movable contact 2 is not pushed by the carrier 11 against a completely rigid structure, thus facilitating a small amount of over-travel by the movable carrier 11. As such, the contact 3 can be considered a normally fixed contact 3 which can be subject to a small amount of over-travel on impact with the movable contact 2, as allowed by its resilient connection to the supporting element 4. This minimizes the risk of contact bouncing and resultant arcing, as well as other unwanted effects. Furthermore, it will be seen that in the embodiment, the contact 3 comprises a plate extending transversely (the need for which will be explained below) and in a plate a button contact is formed or mounted in order to make a point connection with the contact 2.

As illustrated in Figure 2, on expiry of the short duration energizing pulse applied to closing actuator 20, the spring 22 allows the plunger 21 to revert to its retracted state. However, the locating of the latch member 14 into the slot 16 retains the movable carrier 11 in the second position against the force exerted by the opening spring 12 which has been compressed during the movement of the carrier 11. Thus, the latch member 14 in the latched state can hold the movable contact 2 coupled to the contact 3, despite the strong pressure exerted by the compressed spring 12 against the movable carrier 11. Thus, a strong pressure is stably maintained between the contacts 2, 3, also with the contribution of the spring 17, so as to ensure a good conductivity between the contacts 2, 3.

As such, in the situation illustrated in Figure 2 the latching mechanism 10, considered as a whole, stays in a second stable latched state without consuming any electrical power.

When opening of the device 10 is required, an electrical pulse of short duration can be applied to the releasing actuator 40.

With reference to Figure 3, upon receiving the pulse the releasing actuator 40 is energized to move its plunger 41 from the retracted state to an extended release state. In particular, the actuator 40 is arranged with respect to the supporting element 4 so that the plunger 41 moving towards the release state intercepts and disengages the latch member 14 from the slot 16. As a result, the compressed opening spring 12 pushes the movable carrier 11 back to the first position illustrated in Figure 1, where the movable contact 2 is held in the open state with respect to the contact 3. Further, on expiry of the short duration energizing pulse applied to releasing actuator 40, the spring 42 reverts the plunger 41 to its released state as illustrated in Figure 1.

It will be appreciated that variations can be applied to the embodiment illustrated for exemplary purposes in Figures 1-3.

For example, although in Figures 1-3 the carrier 11 is arranged to move inside the supporting element 4, it will be appreciated that the carrier 11 and the supporting element 4 can be reversed with the carrier sliding over the support element.

Although in Figures 1-3 the latch member 14 directly engages the supporting element 2 by inserting into the slot 16, a different stable mechanical engagement can be devised between the plunger 14 (or another latching element) and the supporting element 4. For example, the engagement can occur with an element of the switching device 1 which is directly or indirectly connected to the supporting element 2. For example, the latch member 14 can insert into a corresponding slot defined in a plate positioned inside the cavity 6 and connected to the case of the switching device 10. The movable carrier can comprise more elements or components operatively connected to each other. For example, the movable carrier can comprise a first carrier for supporting the moving contact 2 and another carrier for supporting the latching element 14, wherein such carriers are operatively connected to each other so as to move together upon the actuation by the actuators 20, 40.

Furthermore, although it is maintained that short duration pulses applied to the actuators 20, 30 ensure that the latching mechanism 10 is always trip free and that it can be reliably closed and released when required, it will be appreciated that the latching mechanism 10 could be also operated manually in addition or as an alternative to electrical actuation using the solenoid coils. For example, the carrier 11 can be manually pressed in the second position illustrated in Figure 2, e.g. by pressing the plunger 21 of the closing actuator 20. The mechanism 10 can be also released by manually pressing the plunger 41 of the releasing actuator 40.

Because the device 10 is stable both in the open and closed states, it can be useful to determine if the release mechanism 40 in particular is working, but without having to break an electrical supply being provided through the device 10.

Referring now to Figures 4-6, there is shown the device 10 according to the first embodiment including a further auxiliary contact 50. The auxiliary contact is cooperable with the contacts 2, 3 and latching mechanism 10 illustrated in Figures 1-3 as explained in more detail below. A carrier 51 supports the auxiliary contact 50 and is movable, under the control of an auxiliary solenoid actuator 60 (again, the solenoid windings are not shown), with respect to the supporting element 4 between a first position (illustrated in Figures 4 and 6) and a second position (illustrated in Figure 5). The auxiliary actuator 60 comprises a plunger 61 biased by a compression spring 62 and operatively coupled to the movable carrier 51, so that when the actuator 60 is deactivated, the plunger 61 is moved into a retracted state by a spring 62; and when enough energy is provided to the auxiliary actuator 60, the plunger 61 is moved to an extended state against the bias of the spring 62. Movement of the plunger 61 from the retracted state to the extended state causes a corresponding movement of the carrier 51 from the first position to the second position.

When the movable carrier 51 is in the first position, the auxiliary contact 50 is in a normally open state where it is separated from the contact 3 housed into the cavity 5 of the supporting element 4. When the movable carrier 51 is in the second position, the auxiliary contact 50 is in the closed state where it passes through a slot 52 defined in the supporting element 4 for coupling with the contact 3. At the same time, the auxiliary contact 50 is permanently electrically connected to the movable contact 2 through a flexible wire or lead 53.

Note that while in the embodiment movement of the auxiliary contact is shown as being transverse to the movement of the carrier 11, the auxiliary actuator 60 could alternatively be located to move in a direction parallel to the movement of the carrier. Any such variations may be employed, especially where these might provide a more compact implementation. A detector 80 is operatively associated with the movable contact 2 for detecting a movement thereof from the closed state to the open state. For example, the detector 80 can be an electronic detector, an optical detector, a magnetic detector or a mechanical microswitch.

Figure 4 shows the latching mechanism 10 stably latching the movable contact 2 in its closed position and the carrier 51 biased into the first position by the spring 62 of the auxiliary actuator 60.

After the closure of the auxiliary contact 50, the releasing actuator 40 can be actuated, so as to cause a release of the latched mechanism 10 as previously disclosed with reference to Figure 3. In this way, the movable contact 2 can reach its open state, while an electrical connection is maintained between a circuit supply and load through the conductive path provided by the closed auxiliary contact 50. A detector 80 is arranged to detect the presence of the movable contact 2 to its open state, so that after such detection, the closing actuator 20 can be activated so as to cause a return of the movable contact 2 to the closed state.

The auxiliary actuator 60 can then be deactivated to cause a return of the plunger 61 to the retracted position and, therefore, a return of the carrier 51 in the second position where the auxiliary contact 50 is separated from the contact 2 as illustrated in Figure 4.

Note that in Figure 6, each of the contacts 2, 3 as well as the contact 50 are shown in their open states, this would only be the case where it is desired to have the device 10 in an open state, for example, in response to a fault condition having been detected by a fault monitoring system incorporating the device 10.

The above described embodiments have involved a single pair of contacts 2, 3 and a corresponding contact 50. It will be appreciated that the switch mechanism 10 can be extended to include multiple pairs of contacts 2, 3 each with a corresponding auxiliary contact 50. Such an implementation might still only require a single detector 80 so that the mechanism can for example, be used with multi-phase supplies. Still, such implementations would only require a single closing, releasing and auxiliary actuator 20, 40, 60.

Alternatively, the supporting element 4 and/or housing for the device can be arranged so that multiple single contact devices can be readily fitted together as required. While the devices 10 have many possible applications, one particularly suitable application is within a fault monitoring system 1, for example, a residual current switching device (RCD), such as shown in Figure 7. In this case, the switching device 10 includes 2 pairs of contacts 2, 3, each with an auxiliary contact 50. A neutral line N and a live line L are provided to the system 1 from an AC supply and delivered to a circuit load (“LD”). The system 1 comprises two movable contacts 2 associated respectively with the N line and the L line. The movable contacts 2 can be actuated to move from a closed state, where they are coupled to corresponding contacts 3, to an open state where they are separated from the contacts 3 so as to electrically disconnect the circuit load from the AC supply. Each movable contact 2 is incorporated within the bistable latching device 10 configured to cause the closure and latching of the movable contacts 2.

The RCD 1 further comprises a fault monitoring circuitry 30 for controlling the releasing actuators 40 to open the movable contacts 2 upon a detection of a residual current fault.

In particular, the fault monitoring circuity 30 comprises a current transformer 31 operatively coupled to the N and L lines so as to output a signal depending on a current imbalance between the N and L lines. The fault monitoring circuitry 30 further comprises detection circuitry 32 configured for: receiving the output signal of the current transformer 31, detecting a presence of a residual current fault in case a current difference between the lines N and L is above a fault threshold, and generating a release signal R in case of residual current fault detection.

Although Figure 7 illustrates a residual current switching device 1, a switching device according to the present invention can be any type of bistable electrical switching device, such as a circuit breaker, an RCBO or an AFCI. As such, the fault monitoring circuitry 30 can be configured to detect a residual current, an overload or short-circuit current, an arc fault, or any combination thereof.

As illustrated in Figure 7, the switching device 1 further comprises a self-test circuity 70 configured to generate an electrical signal AUX to be applied to the auxiliary actuators 60 for closing the auxiliary contacts 50.

The detection circuitry 32 can be further configured to generate a test signal T periodically or when an opening test for the movable contacts 2 is requested.

Upon receiving the signal test T, the self-test circuit 70 can generate the AUX pulse to activate the auxiliary actuators 60. Upon activation, the auxiliary actuators 60 close the normally opened auxiliary contacts 50. In the closed state, the auxiliary contacts 50 are arranged to provide a parallel conductive path between the corresponding couple of contacts 2, 3. After the activation of the auxiliary solenoid actuators 60 and the closure of the auxiliary contacts 50, the detection circuitry 32 can apply a release pulse R to the actuators 40 to attempt a test opening movement of the closed contacts 2.

If the contacts 2 correctly open, the detector 80 generates a signal D indicative of such opening and sends this signal D to the self-test circuitry 70.

Note that even when the movable contacts 2 correctly open, the AC supply and load remain electrically connected to each other through the conductive path(s) provided by the closed auxiliary contacts 50. Thus, the auxiliary contacts 50 may be suitably rated for making and breaking the load current, but they can also be derated if it is not required to make or break the load current. In this case the composition of the auxiliary contacts 50 can be simpler and of lower cost than the main contacts 2, 3.

If the self-test circuitry 70 does not receive the signal D from the detector 80 after a predetermined time from the activation of the auxiliary actuators 60, the self-test circuitry 70 can generate an alert, such as an electrical signal A sent to the detection circuitry 32.

If the signal D is received, the self-test circuitry 70 can prompt the detection circuitry 32 to apply a closure pulse C to the closing actuators 20 for causing a return of the movable contacts 2 to their closed state. After this closure, the self-test circuitry 70 can interrupt the application of the AUX signal to the auxiliary solenoid actuators 60 so as to cause a return of the auxiliary contacts 50 to their normally open state.

It will be appreciated that variations are applicable to the arrangement illustrated for exemplary purposes in Figure 7.

For example, the self-test circuitry 70 can be configured to apply the AUX signal to the auxiliary actuators 60, independently of the detection circuitry 32, periodically or when an opening test for the movable contacts 2 is required, and signaling this generation to the detection circuitry 32. After receiving such a signal, the detection circuitry 32 can apply the closing pulse C to the closing actuators 20.

For example, the signal D generated by the detectors 80 can be provided to the detection circuitry 32 in addition or alternatively to the self-test circuitry 70.

Although in Figure 7 the self-test circuitry 70 is external to the device 10, the self-test circuitry 70 and indeed the circuitry 30 can be incorporated within a housing with the switching device 10.

Also, although in Figure 7 the detection circuitry 32 provides the signals C and R to the closing and releasing actuators 20, 40 through two independent signal lines, such signals C, R can be provided to the actuators 20, 40 through a single port. Furthermore, although the detection circuitry 32 and the self-test circuitry 70 are illustrated in Figure 7 as separate electronic blocks operatively connected to each other, these circuitries 30, 70 can be implemented in a same electrical unit, such as a microprocessor.

Claims

1. A bistable electrical switching (1) device comprising: - a supporting element (4) housing at least one first electrical contact (3); - at least one movable electrical contact (2) which can move between a closed state where it is coupled to a corresponding first electrical contact and an open state where it is separated from the corresponding first electrical contact; - a latching mechanism (10) comprising: o a carrier (11) for said at least one movable contact, said carrier being movable relative to said supporting element, o a closing actuator (20) operatively coupled to said carrier so as to cause said carrier to move upon activation of the closing actuator from a first position, where said at least one movable contact is in the open state, to a second position, where said at least one movable contact is in the closed state, said carrier being resiliently connected to the supporting element to bias said carrier towards said first position; and o a latch (14) operatively connected to the carrier and arranged to engage said supporting element to maintain the carrier in the second position when said closing actuator is deactivated; and - a releasing mechanism (40) actuable to disengage the latch from said supporting element so as to cause a return of the carrier from the second position to the first position.

2. The switching device according to claim 1, further comprising an auxiliary contact (50) and an auxiliary actuator (60) operatively connected to said auxiliary contact so as to cause said auxiliary contact to move upon actuation of the auxiliary actuator from a normally open state to a closed state, wherein in the closed state the auxiliary contact is arranged to provide a parallel conductive path between said at least one movable contact and corresponding first contact.

3. The switching device according to claim 2, wherein said auxiliary contact (50) is operatively electrically connected to said at least one movable contact (2) through a flexible conducting element (53) and is arranged to couple with said first contact (3) when it reaches the closed state.

4. The switching device according to claim 2, further comprising a detector (80) for detecting a movement of said at least one movable contact (2) from the closed state to the open state.

5. The switching device according to claim 1, wherein said latch (14) is operatively connected to the carrier (11) through a resilient member (15), wherein, - when the carrier is not in the second position, the latch is arranged to stay in an unlatched state where the latch contacts the supporting element (4) and compresses the resilient member; and - when the carrier reaches the second position, the resilient member is arranged to push the latch into a latched state where the latch locates in a corresponding slot (16) defined in the supporting element.

6. The switching device according to claim 1, wherein said first contact (3) is resiliently connected to the supporting element (4) to bias the first contact towards the movable contact (2), when the movable contact couples with the first contact.

7. A system comprising: - at least one switching device (1) according to claim 4; and - fault monitoring circuitry (30), said fault monitoring circuity being operatively connected to and configured to activate said closing actuator (20) of the switching device, and being operatively connected to and configured to actuate said releasing mechanism (40) of the switching device.

8. The system of claim 7, further comprising a self-test circuitry (70) operatively connected to and configured to activate said auxiliary actuator (60) of the switching device (1).

9. The system of claim 8, wherein the fault monitoring circuitry (30) is configured to actuate said releasing mechanism (40) for attempting a test opening movement of said at least one movable contact (2) after an activation of said auxiliary actuator (60) through the self-test circuitry (70) for closing the auxiliary contact (50).

10. The system of claim 9, wherein at least one of said self-test circuitry (70) and said fault monitoring circuity (30) is: - operatively connected to said detector (80) to receive a signal (D) from the detector indicative of an opening movement of said at least one movable contact (2), and - configured to generate an alert (A) in response to no signal being received from the detector after said actuation of the releasing mechanism (40).

11. The system of claim 10, wherein said fault monitoring circuitry (30) and said selftest circuitry (70) are responsive to receiving the signal (D) from the detector indicative of the opening movement of said at least one movable contact (2), to activate said closing actuator (20) through the fault monitoring circuitry (30) for causing a return of said at least one movable contact (2) into the closed state and to deactivate said auxiliary actuator (60) to cause a return of the auxiliary contact (50) to the normally open state.