Thomson coil actuator

Abstract

A Thomson coil actuator comprises a plate which is at least partially conductive (or a "conductive plate") and at least two conductive coils (or "windings"). The at least two coils are arranged around an axis, wherein a centre of each conductive coil is offset from the axis. The at least two coils are configured to drive the plate in a first direction along the axis when an electric current is provided to the at least two conductive coils. The actuator also comprises a driver circuit configured to provide an electric current to each of the at least two conductive coils independently. The driver circuit is configured to provide the electric currents to the respective coils simultaneously. An electrical switching apparatus comprising said actuator is also disclosed, along with a method of detecting a fault in a plate of a Thomson coil using said coil arrangement.

Description

[0001] Thomson coil actuator

[0002] Field

[0003] This relates to a Thomson coil actuator, and an electrical switching apparatus comprising said Thomson coil actuator.

[0004] Background

[0005] Thomson coil actuators are used in electrical switching apparatus, such as circuit breakers. In applications which require a rapid opening time, such as a hybrid circuit breaker, high rated capacitors (e.g., high voltage and / or high capacitance) are needed. The rapid acceleration of the Thomson coil actuator plate (or disc) as a result of these high rated capacitors can lead to very large bending stresses within the plate. The lifetime of the plate, and thus of the Thomson coil actuator itself, may therefore be reduced. For example, there may be failure of the plate, such as the formation of faults or cracks. Moreover, there can be challenges in incorporating a higher rated capacitor into electrical switching apparatus, both from a safety point of view and due to size constraints (since higher rated capacitors are larger and need to be charged to a higher voltage after every discharge).

[0006] It is therefore desirable to provide a Thomson coil actuator which addresses some of these challenges and which is able to detect failure of the plate.

[0007] Summary

[0008] Disclosed herein is a Thomson coil actuator, and an electric switching apparatus comprising said actuator.

[0009] In a first aspect, a Thomson coil actuator comprises a plate which is at least partially conductive (also called herein a "conductive plate") and at least two conductive coils (also called herein "windings"). The at least two coils are arranged around an axis, wherein a centre of each conductive coil is offset from the axis. The at least two coils are configured to drive the plate in a first direction along the axis when an electric current is provided to the at least two conductive coils. The actuator also comprises a driver circuit configured to provide an electric current to each of the at least two conductive coils independently. The driver circuit is configured to provide the electric currents to the respective coils simultaneously.

[0010] In this way, a conventional single coil winding can be replaced with at least two separate coil windings arranged around and offset from an axis. The use of multiple coils arranged around the axis and synchronized to operate at the same time can generate the same I similar acceleration as a single coil, whilst reducing the peak current discharge. Smaller capacitors or a less powerful driving circuits may therefore be used. This can be beneficial from a safety point of view.

[0011] The centres of the coils can be offset from the axis in different directions by an equal amount. In some implementations, the centres of the at least two conductive coils are arranged evenly around the axis. In some implementations, the centres of the at least two conductive coils are arranged evenly around a circumference of a circle, where the axis passes through a centre of the circle. With two coils, the coils may be arranged opposite each other, one either side of the axis. In an example, for n coils, the centre of each coil may be offset a predetermined distance from the axis and the centre of each coil may be located at regular intervals around the axis, for example at intervals of 360 / n degrees around the axis.

[0012] In some examples, the at least two conductive coils are arranged in a first plane. In some examples, the plate is arranged in a second plane, wherein the axis passes through a centre of the plate. In some examples, the first and second planes are parallel. In some examples, the axis is perpendicular to the first and second planes. These arrangements can maximise the transfer of force to the plate, improving the operation of the Thomson coil actuator.

[0013] In some examples, the driver circuit comprises at least two capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least two coils. As discussed above, the arrangement of the coils allows that smaller capacitors may be used as compared to a conventional single winding. This can be beneficial from a safety point of view.

[0014] The driver circuit can be configured to simultaneously discharge the at least two capacitors. This can allow the capacitors to operate simultaneously, providing an even acceleration to the plate. The driver circuit can be configured to synchronize the charging of the at least two capacitors.

[0015] The actuator can further comprise a sensing circuit configured to identify a crack in the plate based on the electric current passing through each of the at least two conductive coils. In other words, the specific arrangement of the coils can be used to detect a fault or failure of the plate at the same time as driving the plate. In some implementations, the sensing circuit is configured to identify a difference between the current discharge curves for each of the at least two capacitors, the difference indicative of a crack in the plate. Optionally, the sensing circuit is configured to measure the current discharge curve for each of the at least two capacitors and compare each measured current discharge curve with a reference value to identify the difference.

[0016] In one example, the sensing circuit is configured to: measure a peak of a current discharge curve for each of the at least two capacitors; compare each measured peak with a reference value to identify a difference; and identify a crack in the plate based on the difference. This can allow the discharge curve of the respective capacitors to be used to detect a fault or failure of the plate at the same time as driving the plate with the conductive coils.

[0017] In another example the sensing circuit comprises a transformer. Where there are an even number of coils (e.g. two coils, or four coils), a respective current path of each of the conductive coils passes through the transformer, wherein the sensing circuit is configured to identify a crack in the plate based on a voltage induced in the transformer. In this way, a single sensing element can be used to detect the fault or failure of the plate. The sensing circuit may therefore be more resource efficient.

[0018] In some implementations, a geometry of the plate mirrors the arrangement of the at least two coils. An edge or perimeter of the plate comprises at least two protrusions and indents between adjacent ones of the protrusions. By mirroring the geometry between the plate and the conductive coils, more efficient acceleration of the plate may be provided, since the coils can induce a driving force in the plate more efficiently and effectively.

[0019] In some examples, the plate comprises one or more ribs, each rib extending between the axis and one of the indents. These rib(s) can strengthen the plate, reducing or avoiding the formation of cracks or faults in locations between coils. This can be beneficial because the sensing element may be unable to identify a crack or fault at this location.

[0020] Optionally, there are at least three coils. Optionally there are at least four coils.

[0021] Optionally there are at least five coils. Optionally there are at least six coils.

[0022] Optionally there are at least seven coils. Also disclosed here is an electrical switching apparatus comprising: a first electrical contact; a second electrical contact; and a Thomson coil actuator as described herein. The plate is coupled to the second electrical contact in order to move the second electrical contact into or out of electrical contact with the first electrical contact when the at least two coils drive the plate in the first direction along the axis.

[0023] Also disclosed is a method of detecting a fault in a plate of a Thomson coil actuator. The detecting can be performed using said coil arrangement described herein. The method comprises independently providing an electric current to each of at least two conductive coils, wherein the at least two conductive coils are arranged around an axis and a centre of each conductive coil is offset from the axis, wherein the electric current is provided simultaneously to each of the at least two conductive coils. The method further comprises, in response to providing the electric current, driving, by the at least two conductive coils, an at least partially conductive plate in a first direction along the axis. The method further comprises identifying, based on the electric current passing through each of the at least two conductive coils, a fault or crack in the plate.

[0024] Optionally identifying, based on the electric current passing through each of the at least two conductive coils, a fault in the plate can comprise: measuring a current peak; comparing each measured peak with a reference value to identify a difference; and identifying the fault in the plate based on the difference.

[0025] In some specific implementations, providing an electric current to each of the at least two conductive coils comprises simultaneously discharging at least two capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least two coils. In this example, identifying, based on the electric current passing through each of the at least two conductive coils, a fault in the plate comprises: measuring a peak of a current discharge curve for each of the at least two capacitors (an example of a measured current peak); comparing each measured peak with a reference value to identify a difference; and identifying the fault in the plate based on the difference.

[0026] In another example, a respective current path of each of the at least two conductive coils passes through a transformer of the sensing circuit. In some implementations, identifying, based on the electric current passing through each of the at least two conductive coils, a fault in the plate comprises identifying the fault in the plate based on a voltage induced in the transformer. In a second aspect, a Thomson coil actuator comprises a plate which is at least partially conductive (also called herein a "conductive plate") and at least three conductive coils (also called herein "windings"). The at least three coils are arranged around an axis, wherein a centre of each conductive coil is offset from the axis. The at least three coils are configured to drive the plate in a first direction along the axis when an electric current is provided to the at least three conductive coils. The actuator also comprises a driver circuit configured to provide an electric current to each of the at least three conductive coils independently. The driver circuit is configured to provide the electric currents to the respective coils simultaneously.

[0027] In this way, a conventional single coil winding can be replaced with at least three separate coil windings arranged around and offset from an axis. The use of multiple coils arranged around the axis and synchronized to operate at the same time can generate the same I similar acceleration as a single coil, whilst reducing the peak current discharge. Smaller capacitors or a less powerful driving circuits may therefore be used. This can be beneficial from a safety point of view. Moreover, the use of three coils can improve a stability of the motion of the plate during actuation of the Thomson coil actuator (e.g. as compared to an arrangement with two coils, as in the first aspect).

[0028] The centres of the coils can be offset from the axis in different directions by an equal amount. In some implementations, the centres of the at least three conductive coils are arranged evenly around the axis. In some implementations, the centres of the at least three conductive coils are arranged evenly around a circumference of a circle, where the axis passes through a centre of the circle. For example, for n coils, the centre of each coil may be offset a predetermined distance from the axis and the centre of each coil may be located at regular intervals around the axis, for example at intervals of 360 / n degrees around the axis.

[0029] Where there are three coils, it will be understood that the coils can be arranged such that there are three lines of symmetry (the lines passing through the axis and a centre of each coil). Where there are n coils, the coils can be arranged such that there are n lines of symmetry. In some specific examples, there are three, four, five, six or seven coils. Any suitable number of coils may be provided. In some examples, the at least three conductive coils are arranged in a first plane. In some examples, the plate is arranged in a second plane, wherein the axis passes through a centre of the plate. In some examples, the first and second planes are parallel. In some examples, the axis is perpendicular to the first and second planes. These arrangements can maximise the transfer of force to the plate, improving the operation of the Thomson coil actuator.

[0030] In some examples, the driver circuit comprises at least three capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least three coils. As discussed above, the arrangement of the coils allows that smaller capacitors may be used as compared to a conventional single winding. This can be beneficial from a safety point of view.

[0031] The driver circuit can be configured to simultaneously discharge the at least three capacitors. This can allow the capacitors to operate simultaneously, providing an even acceleration to the plate. The driver circuit can be configured to synchronize the charging of the at least three capacitors.

[0032] The actuator can further comprise a sensing circuit configured to identify a crack in the plate based on the electric current passing through each of the at least three conductive coils. In other words, the specific arrangement of the coils can be used to detect a fault or failure of the plate at the same time as driving the plate.

[0033] In some implementations, the sensing circuit is configured to identify a difference between the current discharge curves for each of the at least three capacitors, the difference indicative of a crack in the plate. Optionally, the sensing circuit is configured to measure the current discharge curve for each of the at least three capacitors and compare each measured current discharge curve with a reference value to identify the difference.

[0034] In one example, the sensing circuit is configured to: measure a peak of a current discharge curve for each of the at least three capacitors; compare each measured peak with a reference value to identify a difference; and identify a crack in the plate based on the difference. This can allow the discharge curve of the respective capacitors to be used to detect a fault or failure of the plate at the same time as driving the plate with the conductive coils. In another example the sensing circuit comprises a transformer. Where there are an even number of coils (e.g., four or six coils), a respective current path of each of the conductive coils passes through the transformer, wherein the sensing circuit is configured to identify a crack in the plate based on a voltage induced in the transformer. In this way, a single sensing element can be used to detect the fault or failure of the plate. The sensing circuit may therefore be more resource efficient.

[0035] In some implementations, a geometry of the plate mirrors the arrangement of the at least three coils. An edge or perimeter of the plate comprises at least three protrusions and indents between adjacent ones of the protrusions. By mirroring the geometry between the plate and the conductive coils, more efficient acceleration of the plate may be provided, since the coils can induce a driving force in the plate more efficiently and effectively.

[0036] In some examples, the plate comprises one or more ribs, each rib extending between the axis and one of the indents. These rib(s) can strengthen the plate, reducing or avoiding the formation of cracks or faults in locations between coils. The use of such ribs can also be beneficial because the sensing element may be unable to identify a fault or crack at the locations between coils.

[0037] Also disclosed here is an electrical switching apparatus comprising: a first electrical contact; a second electrical contact; and a Thomson coil actuator as described herein. The plate is coupled to the second electrical contact in order to move the second electrical contact into or out of electrical contact with the first electrical contact when the at least three coils drive the plate in the first direction along the axis.

[0038] Also disclosed is a method of detecting a fault in a plate of a Thomson coil actuator. The detecting can be performed using said coil arrangement described herein. The method comprises independently providing an electric current to each of at least three conductive coils, wherein the at least three conductive coils are arranged around an axis and a centre of each conductive coil is offset from the axis, wherein the electric current is provided simultaneously to each of the at least three conductive coils. The method further comprises, in response to providing the electric current, driving, by the at least three conductive coils, an at least partially conductive plate in a first direction along the axis. The method further comprises identifying, based on the electric current passing through each of the at least three conductive coils, a fault or crack in the plate. Optionally identifying, based on the electric current passing through each of the at least three conductive coils, a fault in the plate can comprise: measuring a current peak; comparing each measured peak with a reference value to identify a difference; and identifying the fault in the plate based on the difference.

[0039] In some specific implementations, providing an electric current to each of the at least three conductive coils comprises simultaneously discharging at least three capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least three coils. In this example, identifying, based on the electric current passing through each of the at least three conductive coils, a fault in the plate comprises: measuring a peak of a current discharge curve for each of the at least three capacitors (an example of a measured current peak); comparing each measured peak with a reference value to identify a difference; and identifying the fault in the plate based on the difference.

[0040] In another example, a respective current path of each of the at least three conductive coils passes through a transformer of the sensing circuit. In some implementations, identifying, based on the electric current passing through each of the at least three conductive coils, a fault in the plate comprises identifying the fault in the plate based on a voltage induced in the transformer.

[0041] List of Figures

[0042] The detailed description is with reference to the following Figures.

[0043] FIG. 1A shows a schematic top view of three conductive coils arranged around and offset from an axis; FIG. IB shows a schematic top view of an example plate for use with the coils of FIG. 1A; FIG. 1C shows a schematic top view of the example plate of FIG. IB showing one or more cracks of faults; and FIG. ID shows a schematic top view of the example plate of FIG. IB showing one or more strengthening ribs.

[0044] FIG. 2A shows a perspective view of an actuator having four conductive coils arranged around and offset from an axis and a plate, where the coils and plate are arranged in separate, but parallel, planes; FIG. 2B shows a top view of the actuator of FIG. 2B, showing the coils and the plate, where the plate is beneath the coils; FIG. 2C shows a schematic top view of the example plate of FIG. 2B showing one or more cracks of faults; and FIG. 2D shows a schematic top view of the example plate of FIG. 2B showing one or more strengthening ribs.

[0045] FIG. 3 shows a table with example simulated values of the peak current in the coils during operation of the actuator in the presence and absence of a crack or fault.

[0046] FIG. 4 shows a circuit diagram of an example sensing circuit. FIG 5. shows a table with example simulated values of the peak current in the coils and peak voltage in a transformer during operation of the actuator in the presence and absence of a crack or fault.

[0047] FIG. 6 shows a schematic illustration of a switching apparatus comprising an actuator as described herein.

[0048] FIG. 7 shows a flow chart of an example method of determining the presence of a fault or crack.

[0049] FIG. 8A shows a schematic top view of two conductive coils arranged around and offset from an axis; and FIG. 8B shows a schematic top view of an example plate for use with the coils of FIG. 8A.

[0050] Like reference numerals apply to like features.

[0051] Detailed description

[0052] Disclosed herein is a Thomson coil actuator which can provide benefits from a safety point of view and facilitate provision of smaller and optionally more compact driver circuitry. It will be understood that the size and compactness / footprint of the driver circuitry can depend on the specific number of coils being used and the desired force to be applied by the Thomson coil actuator. The specific arrangements of the coils or windings of the actuator can also be used to detect a fault or failure of the plate at the same time as driving the plate. In this way, long term monitoring of the health of the plate and actuator can be performed, and faults or cracks can be detected before failure occurs, improving the lifetime of the actuator.

[0053] With reference to FIGs. 1A to ID, a first example Thomson coil actuator is described. The Thomson coil actuator 100 comprises a plate 104 which is at least partially conductive (also called herein a "conductive plate"). The conductive plate 104 may be made of metal, optionally sheet metal. Although the plate 104 may not be made entirely of a uniformly conductive component (and part of the plate may not be conductive), the plate 104 is structured to allow for proper operation in a switching apparatus comprising the actuator.

[0054] The actuator comprises at least three conductive coils 102a, 102b, 102c arranged around an axis 106. These conductive coils, or conductive coil windings, are also referred to herein as "windings". The coils 102a, 102b, 102c (referred to collectively as 102n) are configured to drive the plate 104 in a first direction (not shown) along the axis 106 when an electric current is provided to the at least three conductive coils. A driver circuit (not shown here, see 120 of FIG. 6) is configured to provide an electric current to each of the at least three conductive coils 102n independently to cause them to drive the plate 104 up and down, thereby assisting the Thomson coil actuator 100 in closing and opening electrical contacts of a switching mechanism (not shown). In particular, an electric current applied to the coils 102n by the driver circuit (optionally from discharge of a capacitor) induces a first magnetic field. The induced magnetic field causes an eddy current with the plate 104. In accordance with Lenz's law, a second magnetic field is induced in response to the eddy current, the second magnetic field opposing the first magnetic field. These opposing magnetic fields repel the plate 104 away from the coils 102n, thereby driving the plate 104 in the first direction. The driver circuit 120 is configured to provide the electric currents to the coils 102n simultaneously so as to provide an even force to the plate 104.

[0055] As shown in FIG. 1A, a centre 110a of conductive coil 102a is offset from the axis 106. Centres of the other coils 102b, 102c can be similarly offset. The centres of the coils can be offset from the axis 106 in different directions by an equal amount. In some implementations, the centres of the at least three conductive coils are arranged evenly around the axis 106. For example, the centres of the at least three conductive coils 102n are arranged evenly around a circumference of a circle (not shown), where the axis 106 passes through a centre of the circle.

[0056] In this way, a conventional single coil winding can be replaced with at least three separate coil windings arranged around and offset from an axis. The use of multiple coils arranged around the axis and synchronized to operate at the same time can generate the same I similar acceleration as a single coil, whilst reducing the peak current discharge. Smaller capacitors or a less powerful driving circuits may therefore be used. This can be beneficial from a safety point of view.

[0057] In some implementations of the actuator 100, the driver circuit comprises at least three capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least three coils. As discussed above, the arrangement of the coils allows that smaller capacitors may be used as compared to a conventional single winding. This can be beneficial from a safety point of view. Moreover, this arrangement can allow for smaller driving circuitry for each individual coil. By reducing the size of the driver circuit, a smaller actuator may be provided.

[0058] The driver or driving circuit 120 can be configured to simultaneously discharge the at least three capacitors. This can allow the capacitors to operate simultaneously, providing an even acceleration to the plate. The driver circuit can be configured to synchronize the charging of the at least three capacitors. Synchronized discharging of energy sources (such as capacitors) can be controlled using multiplexer switches or any other suitable configuration. Any switching method and driver circuit 120 can be used. One example driver circuit 120 is described with reference to Figure 3 of UK patent application GB2408829.6, the description of which driver circuit is hereby incorporated by reference. However, this circuit is an example only, and any suitable circuit can be used, as will be understood by the skilled person.

[0059] In the specific example of FIG. 1A there are three coils, and the coils 102n are arranged such that there are three lines of symmetry (the lines passing through the axis 106 and a centre of each coil, e.g. centre 110a of coil 102a and the same for each other coil). The centre of each coil is offset a predetermined distance from the axis 106 and the centre of each coil is located at regular intervals around the axis 106, i.e. at intervals of 360 / 3 degrees around the axis (at 0 degrees, 120 degrees and 240 degrees). It will be understood that where there are n coils, the coils can be arranged such that there are n lines of symmetry, and the centre of each coil may be located at intervals of 360 / n degrees around the axis 106. Any suitable number of coils may be provided.

[0060] With reference to the alternative example Thomson coil actuator shown in of FIGS. 2A to 2D, the actuator 100 comprises four coils 102n. The coils 102n are arranged such that there are four lines of symmetry (the lines passing through the axis 106 and a centre llOn of each coil). The centre of each coil is offset a predetermined distance from the axis 106 and the centre of each coil is located at regular intervals around the axis 106, i.e. at intervals of 360 / 4 degrees around the axis (at 0 degrees, 90 degrees, 180 degrees and 270 degrees).

[0061] In this way, a conventional single coil winding can be replaced with at least three (here four) separate coil windings arranged around and offset from an axis. The use of multiple coils arranged around the axis and synchronized to operate at the same time can generate the same I similar acceleration as a single coil, whilst reducing the peak current discharge. Smaller capacitors or a less powerful driving circuits may therefore be used. This can be beneficial from a safety point of view. Moreover, the use of four coils can provide a beneficial balance between capacitor volume (size), displacement of the plate and applied force.

[0062] As an example, in simulations it has been found that a conventional single coil winding driven with a capacitor rating of 16,000uF, 410V, results in a peak current of 9.08kA and a peak force on the plate of 37.68kN. In contrast, in simulations of the arrangement of FIG. 2A, the coils can each be driven with a capacitor rating of 4,700uF, 360V, which results in a peak current of 7.14kA and a peak force on the plate of 40.11kN. It is therefore apparent that the arrangement described herein is a suitable replacement for a conventional coil winding.

[0063] As can be seen in e.g. FIGs. 1A, IB and FIGs. 2A, 2B, the at least three conductive coils 102n (here four coils) can be arranged in a first plane. The plate 104 can be arranged in a second plane, wherein the axis 106 passes through a centre of the plate. In this example, the first and second planes are parallel. Moreover, the axis 106 is perpendicular or substantially perpendicular to the first and second planes. This arrangement can maximise the transfer of force to the plate 104, improving the operation of the Thomson coil actuator 100.

[0064] With further reference to FIG. IB and FIG. 2A, it can be seen that a geometry of the plate 104 mirrors the arrangement of the at least three coils 102n. An edge or perimeter (P) of the plate 104 comprises at least three protrusions 114a, 114b, 114c (i.e. 114n protrusions) and there are indents 116 between adjacent ones of the protrusions 114n. By mirroring the geometry between the plate 104 and the conductive coils 102, more efficient acceleration of the plate 104 may be provided, since a driving force can be induced in the plate more efficiently and effectively.

[0065] Moreover, this arrangement can facilitate detection of one or more faults, failures or cracks within the plate. As shown in FIG. 1C and FIG. 2C, a crack or fault 112a may form in plate 104 under one of the coils 102n. A crack or fault 112b may also form between adjacent coils. The presence of a crack or fault 112a can be identified or detected using a sensing circuit (not shown here, see 122 of FIG. 6). In particular, a sensing circuit 122 is configured to identify a crack 112a in the plate 104 based on the electric current passing through each of the at least three conductive coils 102n. In other words, the specific arrangement of the coils 102n can be used to detect a fault or failure of the plate 104 at the same time as driving the plate in the first direction 108 (see FIG. 2A).

[0066] In one example, for a driving circuit comprising capacitors configured to provide electric current to the respective coils 102a, it will be understood that the current discharge curves from each capacitor will be the same if the plate 104 is in healthy state (i.e. without a crack or fault). However, the initiation of crack (or another change in material properties of the plate 104) will affect the eddy current generation in the plate 104, and hence the mutual inductance observed in the coil 102n. Any difference in the current curves can indicate a start of failure. This can provide an early diagnosis of a fault, allowing suitable maintenance and therefore improving the lifetime of the actuator 100. In other words, the sensing circuit 122 can be configured to identify a difference between the current discharge curves for each of the at least three capacitors, the difference indicative of a crack in the plate 104. In some examples, sensing results from one or more sensors, detectors or measurement units of the sensing circuit may be passed to a controller of the sensing circuit 122, where the controller performs the identification of the crack / fault in the plate.

[0067] For example, the sensing circuit 122 can be configured to measure the current discharge curve for each of the at least three capacitors and compare each measured current discharge curve with a reference value to identify the difference. In some specific examples, the sensing circuit is configured to: measure a peak of a current discharge curve for each of the at least three capacitors; compare each measured peak with a reference value to identify a difference; and identify a crack in the plate based on the difference. The reference value can be the expected peak value in the absence of a fault. This can allow the discharge curve of the respective capacitors to be used to detect a fault or failure of the plate 104 at the same time as driving the plate with the conductive coils. In another example, the sensing circuit can be configured to measure only a peak current in the coil winding 112n (i.e. rather than the entire current curve).

[0068] An example of the difference in peak current that can be observed is now discussed with reference to the table in FIG. 3, which shows a table with example values of the peak current in the coils during operation of the actuator in the presence and absence of a crack or fault. These example values are obtained using finite element modelling and so are simulated values, provided for explanatory purposes only.

[0069] The current within each coil 102n is proportional to the capacitor value which is used to drive the coil. Therefore, it has been recognised that there can be a perceived reduction in peak current due to inherent capacitor variation, which reduction is not associated with a fault or crack. As such, a reference value is used, corresponding to the current peak provided for that capacitor in the absence of a fault. This can be determined during e.g. an initial calibration step. As can be seen in FIG. 3, there can be a difference of between 80A and 140A between the measured current peak in event of a crack and the measured current peak without a crack. This difference is indicative of a crack. In this way, a crack or fault 112a can be detected by the sensing circuit 120 using the current through the coil or winding. This approach incorporates tolerance of variation in capacitance in the detection of failure in the Thomson plate.

[0070] However, it has been recognised that a crack located between windings, as in the location of crack 112b in FIG. 1C and FIG. 2C, does not produce an observable difference in the peak current. In other words, the current peak deviation is not significant if the crack initiates in this region. Therefore, in some examples, as shown in FIG. ID and FIG. 2D, the plate 104 can comprises one or more ribs 118. Each rib can extend between the axis 106 and one of the indents 116. These rib(s) 118 can strengthen the plate 104, reducing or avoiding the formation of cracks or faults in locations between coils. In this way, faults or failures in areas which cannot be easily detected can be reduced or avoided. The ribs can be any suitable structure element designed to provide increased strength to the plate 104 in these regions. The ribs can also be termed herein "strengthening ribs", since they act to strengthen the plate and reduce or avoid failures initiating in the plate as a result of the high forces and stresses experienced during acceleration of the plate.

[0071] In another example, as discussed with reference to FIG. 4 (which shows a circuit diagram of an example sensing circuit), a single sensing element can be used. This can avoid the need to monitor the current within each coil 102n individually. Using a single sensing element to detect the fault or failure of the plate may therefore be more resource efficient.

[0072] In one specific example, the sensing circuit 122 comprises a transformer 450. This arrangement can be used where there are an even number of conductive coils 102, e.g. two coils, four coils, etc. A respective current path of each of the conductive coils (in FIG. 4, four coils are shown, 102a, 102b, 102c, 102d) passes through the transformer 450. In the example of FIG. 4, two coils are wound on one side of an iron core, and two coils are wound in the opposite direction on the other side of the iron core (two parallel and two anti-parallel). If the current through each coil is equal, the magnetic fields induced on either side of the core of the transformer 450 will cancel each other out (since they are of an equal magnitude but in opposite directions. Therefore, no magnetic field will be sensed by the sensing coil.

[0073] In other words, if all currents are equal, it can be considered that there is no "residual" current. Therefore, there is no net magnetic flux induced in the core material of the transformer 450 and there will be no induced voltage at the sensing coil or secondary winding. However, if the current through one coil 102n is lower than the others, then the "residual" current would rise from zero. This "residual" current would cause a voltage to be induced at the secondary winding of the transformer, since the magnetic fields or fluxes from the respective conductive coils will not completely cancel out or nullify one another. The sensing circuit 122 is thus configured to identify a crack in the plate based on a voltage induced in the transformer 450; a fault can therefore be detected using only one sensing element. This may be more space and resource efficient than alternative approaches.

[0074] However, as discussed above with respect to FIG. 3, the currents within each coil may not be equal due to inherent variations in the capacitance used to provide electric current to the coils 102n. For example, each capacitor has an associated capacitance and tolerance. Therefore, even in a normal situation without cracks in the plate 104, it may be expected that there is some "residual" current. A threshold value for the peak induced voltage can be defined, where the threshold is used to indicate whether a crack / fault has occurred or initiated.

[0075] An example of the difference in peak induced voltage that can be observed is discussed below with reference to the table in FIG. 5, which shows a table with example values of the peak current in the coils and peak voltage in a transformer during operation of the actuator in the presence and absence of a crack or fault. These example values are obtained using a numerical approach, and so are approximated values, provided for explanatory purposes only. It can be seen that, without a crack, there may be a peak of e.g. 303 mV due to inherent capacitor variation, which reduction is not associated with a fault or crack. As such, a reference value is used when assessing whether there are cracks in the plate, e.g. corresponding to the voltage peak at the transformer 450 in the absence of a fault. This reference value can be determined during e.g. an initial calibration step. Peak voltages higher or lower than this reference value can be indicative of a fault under one of the windings (or coils). In this way, a crack or fault 112a can be detected. This approach also allows for a single sensing element to be used, while also incorporating tolerance of variation in capacitance into the detection of failure in the Thomson plate.

[0076] With reference to FIG. 6, an electrical switching apparatus 600 is illustrated comprising an actuator 100 as described herein. The apparatus 600 comprises a first electrical contact 660 and a second electrical contact 662. The plate 104 of the Thomson coil actuator 100 is coupled to the second electrical contact 664 in order to move the second electrical contact into or out of electrical contact with the first electrical contact when the at least three coils 102a, 102b, ... 102n drive the movable assembly in the first direction 108 along the axis 106. The plate 104 can be fixedly coupled to a rod 666 to form an axially movable assembly. The at least three coils 102n are configured to drive the movable assembly in the first direction 108 along the axis 106. The rod 666 of the movable assembly is coupled to the second electrical contact 664 in order to move the second electrical contact into or out of electrical contact with the first electrical contact 662 when the at least three coils drive the movable assembly in the first direction 108.

[0077] The at least three coils 102 are energised by the driving circuit 120, as discussed above. Optionally, a sensing circuit 122 (configured to operate as discussed above) can also be provided within the apparatus 600. In other examples (not shown), the sensing circuit 122 can be remote from the apparatus 600 but connected to the coils 102n in order to facilitate identification of a fault based on the electric current passing through the coils or windings.

[0078] With reference to FIG. 7, a method of detecting a fault in a plate of a Thomson coil actuator is now described. In other words, the approach of FIG. 7 is an example of a method of determining the presence of a fault or crack. The fault can be detected using the sensing circuit 122 described above.

[0079] The method comprises at operation 770 independently providing an electric current to each of at least three conductive coils 102n. As described with reference to FIGs. 1A- 1D and 2A-2D, the at least three conductive coils are arranged around an axis 106 and a centre llOn of each conductive coil is offset from the axis 106. The electric current is provided simultaneously to each of the at least three conductive coils. The method further comprises, at operation 775 (in response to providing the electric current) driving, by the at least three conductive coils 102n, the at least partially conductive plate 104 of the actuator 100 in a first direction 108 along the axis 106. Operation 775 can comprise driving, with the coils, the plate in a first direction along the axis to thereby open the switching apparatus 600 by separating the first and second electrical contacts 662, 664.

[0080] The method further comprises, at operation 780, identifying, based on the electric current passing through each of the at least three conductive coils, a fault in the plate 104. In this way, long term monitoring of the health of the plate and actuator can be performed, and faults or cracks can be detected before failure occurs, improving the lifetime of the actuator. The operation 780 of identifying, based on the electric current passing through each of the at least three conductive coils, a fault in the plate can comprise an operation 782 of measuring a current peak, an operation 784 of comparing each measured peak with a reference value to identify a difference, and an operation 786 of identifying a crack (in the plate) based on the difference.

[0081] In some examples, the electric current can be provided to each of the at least three conductive coils by simultaneously discharging at least three capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least three coils 102n. In these examples, operation 782 can comprise measuring a peak of a current discharge curve for each of the at least three capacitors (an example of a measured current peak), operation 784 comprises comparing each measured peak of the current discharge curve with a reference value to identify a difference, and operation 786 comprises identifying a crack in the plate based on the difference. In other examples, the current can be a peak current through the coil or winding.

[0082] In other examples, a respective current path of each of the at least three conductive coils passes through a transformer of the sensing circuit 122. In these examples, the operation 780 of identifying (based on the electric current passing through each of the at least three conductive coils) a fault in the plate can comprise an operation 788 of identifying a fault in the plate based on a voltage induced in the transformer.

[0083] As discussed above, the fault or crack identification described above can be performed by the sensing circuit. The sensing circuit can comprise any suitable components to facilitate identification of a fault in the plate. In some examples, sensing results from one or more sensors or measurement units may be passed to a controller of the sensing circuit 122, where the controller performs the identification.

[0084] With reference to FIGs. 8A and 8B, another example Thomson coil actuator is described. The Thomson coil actuator 100 comprises a plate 104 which is at least partially conductive (also called herein a "conductive plate"). The conductive plate 104 may be made of metal, optionally sheet metal. Although the plate 104 may not be made entirely of a uniformly conductive component (and part of the plate may not be conductive), the plate 104 is structured to allow for proper operation in a switching apparatus comprising the actuator. The actuator comprises two conductive coils 102a, 102b arranged around an axis 106. These conductive coils, or conductive coil windings, are also referred to herein as "windings". The coils 102a, 102b (referred to collectively as 102n) are configured to drive the plate 104 in a first direction (not shown) along the axis 106 when an electric current is provided to the two conductive coils. A driver circuit (not shown here, see 120 of FIG. 6) is configured to provide an electric current to each of the two conductive coils 102n independently to cause them to drive the plate 104 up and down, thereby assisting the Thomson coil actuator 100 in closing and opening electrical contacts of a switching mechanism (not shown), as discussed above. The driver circuit 120 is configured to provide the electric currents to the two coils 102n simultaneously so as to provide an even force to the plate 104.

[0085] As shown in FIG. 8A, a centre 110a of conductive coil 102a is offset from the axis 106. Centres of the other coil 102b can be similarly offset. The centres of the coils can be offset from the axis 106 in different directions by an equal amount. In this example, the two coils are arranged on opposite sides of axis 106 from each other.

[0086] In this way, a conventional single coil winding can be replaced with at least two separate coil windings arranged around and offset from an axis. The use of multiple coils arranged around the axis and synchronized to operate at the same time can generate the same I similar acceleration as a single coil, whilst reducing the peak current discharge. Smaller capacitors or a less powerful driving circuits may therefore be used. This can be beneficial from a safety point of view.

[0087] In some implementations of the actuator 100, the driver circuit comprises two capacitors, each capacitor configured to provide a respective electric current to a respective one of the two coils. As discussed above, the arrangement of the coils allows that smaller capacitors may be used as compared to a conventional single winding. This can be beneficial from a safety point of view. Moreover, this arrangement can allow for smaller driving circuitry for each individual coil. By reducing the size of the driver circuit, a smaller actuator may be provided.

[0088] The driver or driving circuit 120 can be configured to simultaneously discharge the two capacitors. This can allow the capacitors to operate simultaneously, providing an even acceleration to the plate. The driver circuit can be configured to synchronize the charging of the two capacitors. This charging and discharging is discussed above. In the specific example of FIG. 8A there are two coils, and the coils 102n are arranged such that there is one line of symmetry (the line passing through the axis 106 and between a centre of each coil, e.g. centre 110a of coil 102a and centre 110b of coil 102b). The centre of each coil is offset a predetermined distance from the axis 106 and the centre of each coil is located at regular intervals around the axis 106, i.e. at intervals of 360 / 2 degrees around the axis (at 0 degrees and 180 degrees). However, any suitable number of coils may be provided such that there are two or more coils, in accordance with the appended claims.

[0089] The use of multiple coils as described herein can allow to reduce peak discharge current value, thus reducing the ratings of components handling this current (e.g. the capacitors or the like). Moreover, failure in the Thomson plate (which sees the maximum stress) can be detected by comparing the current discharge curve through all coils in a manner which incorporates tolerance of variation in capacitance. In addition, a potential blind spot of the sensing approach has been identified and risk of failure in that spot mitigated by the optional use of ribs to strengthen the plate and avoid failure in these regions. In this way, a Thomson coil actuator is provided which can predict failure of the most stressed part in the product based on current discharge curve of coils. This can improve the lifetime of the device. At the same time, safety can be improved due to a reduction in capacitor ratings (capacitance and initial voltage levels) and peak discharge current values.

[0090] List of reference numerals

[0091] 100 Thomson coil actuator 116 indents

[0092] 102, 102a, 102b, 102c, 102d, 102n 118 rib(s) conductive coil(s) 120 d river circuit

[0093] 104 plate 122 sensing circuit

[0094] 106 axis 450 transformer

[0095] 108 first direction 600 electrical switching apparatus

[0096] 110, 110a, 110b, llOn centre(s) of 662 first electrical contact conductive coil 664 second electrical contact

[0097] 112, 112a, 112b crack 666 road

[0098] 114, 114a, 114b, 114c, 114n P perimeter of the plate protrusion(s)

Claims

1. Claims1. A Thomson coil actuator (100), comprising: a plate (104) which is at least partially conductive; at least two conductive coils (102n) arranged around an axis (106) and configured to drive the plate (104) in a first direction (108) along the axis (106) when an electric current is provided to the at least two conductive coils (102n), wherein a centre (llOn) of each conductive coil (102n) is offset from the axis (106); and a driver circuit (120) configured to provide an electric current to each of the at least two conductive coils (102n) independently, the driver circuit (120) configured to provide the electric currents simultaneously.

2. The actuator of claim 1, wherein : the at least two conductive coils (102n) are arranged in a first plane; and / or the plate (104) is arranged in a second plane, wherein the axis passes through a centre of the plate (104).

3. The actuator of claim 2, wherein the first and second planes are parallel, and optionally, wherein the axis (106) is perpendicular to the first and second planes.

4. The actuator of any preceding claim, wherein the centres (llOn) of the at least two conductive coils (102n) are arranged evenly around the axis (106), optionally, wherein the centres (llOn) of the at least two conductive coils are arranged evenly around a circumference of a circle, where the axis (106) passes through a centre of the circle.

5. The actuator of any preceding claim, the driver circuit (120) comprising at least two capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least two coils (102n), wherein the driver circuit (120) is configured to simultaneously discharge the at least two capacitors.

6. The actuator of claim 5, the driver circuit (120) further configured to synchronize the charging of the at least two capacitors.

7. The actuator of any preceding claim, further comprising a sensing circuit configured to identify a crack (112a) in the plate (104) based on the electric current passing through each of the at least two conductive coils (102n).

8. The actuator of claim 7 when dependent on claim 5, wherein the sensing circuit (122) is configured to: measure a peak of a current discharge curve for each of the at least two capacitors; compare each measured peak with a reference value to identify a difference; and identify a crack in the plate based on the difference.

9. The actuator of claim 7, wherein the sensing circuit (122) comprises a transformer (450), a respective current path of each of the at least two conductive coils passing through the transformer (450), wherein the sensing circuit is configured to identify a crack in the plate (104) based on a voltage induced in the transformer (450).

10. The actuator of any preceding claim, wherein a geometry of the plate (104) mirrors the arrangement of the at least two coils (102n), such that a perimeter (P) of the plate comprises at least two protrusions (114n) and indents (116) between adjacent ones of the protrusions (114).

11. The actuator of claim 10, the plate further comprising one or more ribs (118), each rib (118) extending between the axis (106) and one of the indents (116).

12. An electrical switching apparatus (600) comprising: a first electrical contact (662); a second electrical contact (664); and the Thomson coil actuator (100) of any preceding claim, wherein the plate (140) is coupled to the second electrical contact (664) in order to move the second electrical contact (664) into or out of electrical contact with the first electrical contact (662) when the at least two coils (102n) drive the plate (104) in the first direction (108) along the axis (106).

13. A method of detecting a fault in a plate of a Thomson coil actuator (100), the method comprising: independently providing (770) an electric current to each of at least two conductive coils (102n), wherein the at least two conductive coils (102n) are arranged around an axis (106) and a centre (llOn) of each conductive coil (102n) is offset fromthe axis (106), wherein the electric current is provided simultaneously to each of the at least two conductive coils (102n); in response to providing the electric current, driving (775), by the at least two conductive coils (102n), an at least partially conductive plate (104) in a first direction (108) along the axis (106); identifying (780), based on the electric current passing through each of the at least two conductive coils (102n), a fault (112a) in the plate (104).

14. The method of claim 13, wherein : providing an electric current to each of the at least two conductive coils (102n) comprises simultaneously discharging at least two capacitors, each capacitor configured to provide a respective electric current to a respective one of the at least two coils (102n); and identifying (780), based on the electric current passing through each of the at least two conductive coils (102n), a fault in the plate comprises: measuring (782) a peak of a current discharge curve for each of the at least two capacitors; comparing (784) each measured peak with a reference value to identify a difference; and identifying (786) the fault (112a) in the plate (104) based on the difference.

15. The method of claim 13, wherein a respective current path of each of the at least two conductive coils (102n) passes through a transformer (450), and wherein identifying (780), based on the electric current passing through each of the at least two conductive coils (102n), a fault in the plate comprises identifying (788) a fault in the plate (104) based on a voltage induced in the transformer (450).

Images