Electromagnetic actuating system

Abstract

Disclosed herein is an electromagnetic actuating system. The system comprises first (101) and second (102) polar plates having first (111) and second (112) head portions, a permanent magnetic element (104) disposed such that a first pole of the permanent magnetic element (104) is in contact with the first polar plate (101) and a second pole of the permanent magnetic element (104) is in contact with the second polar plate (102); an armature (103) comprising a contact portion (113) and a pivot point (123); and a biasing member (105) coupled to the armature and configured to exert a torque on the armature to urge the armature from the closed position to the open position, wherein The armature (103) is held in the closed position during normal operation by a magnetic holding force between the first and second head portions and the contact portion (113), and wherein the pivot point (123) of the armature (103) does not contact the first and second polar plates.

Description

[0001] Electromagnetic Actuating System

[0002] Circuit breaking devices are designed to trip a circuit on detection of a fault condition. For example, residual current circuit breakers cause tripping of a circuit on detection of a residual current in a main circuit. In residual current circuit breakers, an actuating mechanism, such as a relay device, is actuated on detection of a residual current in a main circuit order to disconnect the current path in the main circuit. One type of actuating mechanism is a permanent magnet relay device (or polarized relay device), in which a permanent magnet is used to hold an armature in a closed position. An electromagnetic coil may be provided to generate a magnetic field in a yoke of the permanent magnet relay device under fault conditions in order to cause movement of the armature, which results in disconnection of the circuit.

[0003] The permanent magnet relay device must be able to achieve a stable closed position to avoid nuisance tripping of the residual current circuit breaker while achieving fast and reliable actuation on detection of a fault condition.

[0004] An increasing variety of circuit protection devices are being used in modern electrical systems to achieve improved safety and in order to comply with increasingly stringent regulatory requirements. In order to accommodate additional circuit protection devices in electrical equipment, there is a need to produce smaller circuit protection devices capable of providing performance that is at least as reliable as known devices. There is also a need to decrease the size of circuit protection devices in order to reduce the volume of raw materials required for their construction.

[0005] As the operating principles of actuation devices of circuit protection devices are normally dependent on a particular scale of the device, it is not generally possible to reproduce performance achieved in a known device by producing miniaturized versions of the device according to the same operating principle.

[0006] In view of the above, there is a need for an electromagnetic actuation device having a smaller size than existing electromagnetic actuation devices that is capable of reliable performance.

[0007] Summary of Invention

[0008] Disclosed herein is an electromagnetic actuating system comprising: a first polar plate comprising a first head portion; a second polar plate spaced apart from the first polar plate and comprising a second head portion; a permanent magnetic element disposed such that a first pole of the permanent magnetic element is in contact with the first polar plate and a second pole of the permanent magnetic element is in contact with the second polar plate; an armature comprising a contact portion and a pivot point, wherein the armature is configured to be moveable about the pivot point between an open position in which the armature does not contact the first and second head portions and a closed position in which the contact portion of the armature contacts both the first and the second head portions, thereby generating a magnetic holding force between the first and second head portions and the contact portion of the armature in the closed position in the closed position; and a biasing member coupled to the armature and configured to exert a torque on the armature to urge the armature from the closed position to the open position, wherein the pivot point of the armature does not contact the first and second polar plates.

[0009] The contact between the contact portion of the armature creates a magnetic path between the poles of the permanent magnetic element via the first and second polar plates and the contact portion of the armature, which results in a holding force between the head portions of the polar plates and the contact portion of the armature. During normal operation of the device (i.e., in the absence of a fault condition), the armature is held in the closed position by a magnetic holding force between the first and second head portions and the contact portion.

[0010] In some examples, the armature extends beyond ends of the first and second polar plates such that the pivot point of the armature is disposed at a position beyond the ends of the first and second polar plates.

[0011] In some examples, a conductive coil is wound around part of the first and second polar plates such that a current in the conductive coil above a threshold value generates a magnetic field in the polar plates that reduces the magnetic holding force between the first and second head portions and the armature, such that the armature is moved by the biasing member from the closed position to the open position.

[0012] In some examples, the electromagnetic actuating system comprises a residual current detection element configured to generate a current above the threshold value in the coil when a residual current is detected in a main circuit. In some examples, the first and second polar plates respectively comprise first and second cut-out portions positioned adjacent to each other, and wherein the coil is wound through the cut-out portions.

[0013] In some examples, the first and second head portions are disposed adjacent to the first and second cut out portions respectively.

[0014] In some examples, the contact portion is disposed at a first end of the armature and the pivot point is disposed at a second end of the armature opposite the first end.

[0015] In some examples, the electromagnetic actuating system further comprises a housing surrounding the first and second polar plates, the permanent magnet, the armature and the biasing member, wherein the pivot point engages a support surface extruded from the housing or a support surface formed from non-magnetic steel and coupled to the housing.

[0016] In some examples, the first and second polar plates and the armature are formed of a ferromagnetic material.

[0017] In some examples, the first and second polar plates are separated by an air gap or a non-ferromagnetic layer.

[0018] In some examples, the first and second polar plates each have a length, PL, and where the pivot point of the armature extends beyond the polar plates by an overhang length, OL, and wherein OL = MF x PL, where MF is a multiplying factor between 0.7 and 1.7.

[0019] In some examples, the electromagnetic actuating system of any preceding claim, further comprises a pin coupled to the armature, wherein the pin is configured to activate a circuit breaking mechanism when the armature is in the open position.

[0020] In some examples, the armature has a Y-shaped structure with a main portion and two branch portions, wherein an end of the main portion comprises the contact portion and each of the two branch portions comprises a pivot point.

[0021] In some examples, the permanent magnetic element is arranged such that a first pole of the permanent magnetic element is in contact with an end portion of the first polar plate and a second pole of the permanent magnetic element is in contact with an end portion of the second polar plate.

[0022] In some examples, the first head portion is arranged directly adjacent to the second head portion.

[0023] Brief Description of the Figures

[0024] The detailed description is with reference to the following figures.

[0025] Fig. 1 is a sectional line drawing of an example embodiment of the disclosure.

[0026] Fig. 2 is a wireframe drawing of elements of an example embodiment of the disclosure.

[0027] Figs. 3a and 3b illustrate the magnetic field strength in elements of an example embodiment of the disclosure while the armature is in a closed position and while the armature is in an open position respectively.

[0028] Fig. 4 is an illustration of elements of an example embodiment of the disclosure including a schematic depiction of magnetic flux paths.

[0029] Fig. 5 is an illustration of elements of an example embodiment of the disclosure.

[0030] Detailed Description

[0031] The embodiments discussed herein relate to an electromagnetic actuating system comprising a permanent magnet relay mechanism. The electromagnetic actuating system is particularly advantageous when used in a circuit breaking device in order to disconnect a power source from a load on detection of a fault condition. The embodiments described in detail below relate in particular to an electromagnetic actuating system used in a residual current circuit breaker. However, the skilled person should understand that the actuation of the device could be triggered by the detection of other fault conditions, such as an overcurrent, short circuit or arcing fault.

[0032] An embodiment of the electromagnetic actuation system is described with reference to Figs. 1 to 6. The electromagnetic actuating system 100 comprises a first polar plate 101, a second polar plate 102, an armature 103, a permanent magnetic element 104, a biasing member 105, a conductive coil 106, a housing 107 and a pin 108. The first polar plate 101 is formed of a ferromagnetic material, such as magnetic iron, steel or nickel. The first polar plate 101 forms part of a yoke of the electromagnetic actuation system 101 along with a second polar plate 102. The first polar plate 101 comprises a substantially planar main section 121 having main faces extending in a first direction DI and a second direction D2 which is perpendicular to the first direction DI. The main faces of the first polar plate 101 are normal to a third direction D3 (i.e. the thickness direction), parallel to each other, and separated from each other in the third direction D3. In the example shown in Fig. 1, the main section 121 of the first polar plate has a substantially rectangular profile, with edges extending in the first direction DI and the second direction D2, though the shape of the first polar plate 101 may be different in other embodiments. The first polar plate 101 extends from a first end 101a to a second end 101b in the first direction DI. The first polar plate 101 comprises a first flange section 141 at the second end 101b. The first flange section 141 projects from the end of the main section 121 in the third direction D3 such that, when viewed along the second direction D2, the first polar plate 101 has a substantially L-shaped cross-section.

[0033] The first polar plate 101 has a first cut-out portion 131 passing therethrough. The first cut-out portion 131 may be a rectangular gap passing through the thickness of the first polar plate 101. The first cut-out portion 131 provides a gap through which part of a conductive coil 106 can be wound. The first polar plate 101 comprises a first head portion 111 for contacting a contact portion 113 of the armature 103. The first head portion 111 comprises a protrusion on an upper surface (where the "upwards" direction is considered to correspond to the D2 direction of Fig. 1) of the main section 121 of the first polar plate 101. Preferably, the first head portion 111 is disposed above the first cut-out portion 131. In this embodiment, the first head portion 111 and first the cut-out 131 portion are separated by a narrow bridge portion 115 of the main section 121 of the first polar plate 101. The provision of the head portion 111 on a narrow bridge portion 115 allows concentration of magnetic fields in the yoke due to the coil 106 and the permanent magnetic element 104 in the vicinity of the first head portion 111. Preferably, the main section 121, the first head portion 111 and the first flange section 141 are integrally formed. In some embodiments, such as the examples shown in Figs. 3a, 3b, 4 and 5, the first polar plate 101 comprises a further cut-out portion, which may be used to secure the first polar plate 101 to the housing 107.

[0034] The second polar plate 102 is formed of a ferromagnetic material, such as magnetic iron, steel or nickel, and is preferably formed from the same material from which the first polar plate 101 is formed. The second polar plate 102 corresponds substantially to the first polar plate 101 other than that a second flange section 142 of the second polar plate 102 extends in an opposite direction to that of the first flange section 142. In other words, the second polar plate 102 is a mirror image of the first polar plate 101 in the planes of the main faces of the first polar plate 101. In embodiments where neither the first or the second polar plates have flange sections, the first polar plate 101 and the second polar plate 102 may be identical. To avoid unnecessary repetition, features previously described in detail with respect to the first polar plate 101 will not be discussed in detail.

[0035] As shown in Fig. 2, the second polar plate 102 is disposed adjacent to the first polar plate 101 and is separated from the first polar plate 101 in the second direction D2 such that main faces of the first polar plate 101 and the second polar plate 102 face each other but are not in contact. Preferably, the main faces of the first and second polar plates are parallel to each other. In some examples, there is an air gap in the region between the first polar plate 101 and the second polar plate 102, while in other examples there is a layer or film of non-ferromagnetic material 109, such as nonmagnetic steel between the first and second polar plates. A second head portion 112 of the second polar plate 102 is adjacent to the first head portion of the first polar plate 101, and a second cut-out portion of the second polar plate 102 is adjacent to and aligned with the first cut-out portion 131 such that a continuous gap passes through both the first 101 and second 102 polar plates. In embodiments where a nonferromagnetic film is disposed between the first and second polar plates 101, there is also a cut-out portion in the non-ferromagnetic film corresponding to the first and second cut-out portions.

[0036] The permanent magnetic element 104 is disposed at the second end 101b of the polar plates such that the permanent magnetic element 104 is in contact with both the first polar plate 101 and the second polar plate 102. The permanent magnetic element 104 has a north pole and a south pole and is arranged such that one pole of the permanent magnetic element 104 is in contact with the first polar plate 101 while the other pole of the permanent magnetic element 104 is in contact with the second polar plate 102. Preferably, the permanent magnetic element 104 is disposed to be in contact with the first and second flange sections of the first and second polar plate respectively. A bracket (not illustrated) may be used to fasten the permanent magnetic element 104 to the first and second flange sections of the first and second polar plate. The permanent magnetic element 104 may be formed of a permanent magnetic material, such as Ferrite, Alnico, Sm-CO, NdFeB-type magnets. The armature 103 is formed of a ferromagnetic material and may be formed of the same material as the first 101 and second 102 polar plates. The armature comprises an elongate body having a contact portion 113 at one end and a pivot point 123 at the opposite end. In the embodiments described in detail, the armature 103 has a Y- shaped structure with a main portion and two branch portions. The end of the main portion comprises the contact portion 113 and the opposite ends of each of the two branch portions comprises a pivot point 123. The pivot point 123 of each of the branch portions engages a respective support surface 110. The support surfaces 110 may be extruded from the housing 107. In other examples, the support surfaces 110 may be formed from a non-magnetic steel hinge inserted into the housing 107. The use of non-magnetic steel in forming the support surface 110 can prevent generation of dust from erosion of the support surface 110 which could interfere with the contact between the armature 103 and the first and second polar plates. The support surface 110 may have the shape of a concave right-angled surface. The armature 103 is able to rotate around the pivot point 123 against the support surface. The support surfaces 110 and the pivot points 123 are disposed beyond an end of the polar plates and are not in contact with the polar plates, as discussed in more detail below. Where the armature comprises two or move pivot points 123, these may be separated from each other along an axis of rotation of the armature 103 (that is, in the third direction D3 in the illustrated embodiment).

[0037] The armature 103 is moveable between a closed position and an open position by rotation around the pivot point 123. In the closed position, the contact portion 113 of the armature 103 is in contact with both the first head portion 111 of the first polar plate 101 and the second head portion 112 of the second polar plate 102. The contact of the contact portion 113 with both the first head portion 111 and the second head portion 112 creates a low reluctance path between the first polar plate 101 and the second polar plate 102 and thereby creates a low reluctance magnetic path between the north and south poles of the permanent magnetic element via the first and second polar plates. When the armature is in the closed position, a magnetic holding force is generated between the contact portion 113 of the armature 103 and the first and second head portions. In the open position, no part of the armature is in contact with either the first polar plate 101 or the second polar plate 102.

[0038] Fig. 3a illustrates the magnetic field strength throughout the first 101 and second 102 polar plates and the armature 103 when the armature 103 is in the closed position. Fig. 3b illustrates the magnetic field strength throughout the first 101 and second 102 polar plates and the armature 103 when the armature 103 is in the open position.

[0039] Fig. 4 illustrates a low reluctance magnetic path 401 between the north and south poles of the permanent magnetic element 104 via the armature 103 when the armature 103 is in the closed position. Because the pivot points 123 of the_armature 103 are not in contact with the first polar plate 101 or the second polar plate 102, there is minimal magnetic flux in the armature 103 at the pivot points 123. This results in a large concentration of magnetic flux at the contact portion 113 of the armature 103 when in contact with the first and second contact portions. This arrangement allows the use of a smaller permanent magnetic element 104 to generate a similar magnetic holding force in comparison to permanent magnetic relay devices in which a pivot point of an armature is in contact with polar plates.

[0040] A biasing member 105 is coupled to the armature 103 and exerts a torque on the armature 103. The torque exerted on the armature by the biasing member 105 biases the armature 103 from the closed position to the open position. The biasing member 105 may, for example, be a spring or another resilient component capable of exerting a torque on the armature 103. Under normal operating conditions (i.e., in the absence of a detected fault) when the armature 103 is in the closed position, the torque produced on the armature 103 by the biasing member 105 is not sufficient to overcome the torque in the opposite direction produced by the magnetic holding force between the contact portion 113 of the armature and the head portions of the polar plates. The biasing member 105 may be coupled to armature at a coupling protrusion 114 extending from the main body of the armature 103 for increasing the torque resulting from the force of the biasing member 105.

[0041] A conductive coil 106 is wound around a portion of both the first polar plate 101 and the second polar plate 102. The conductive coil 106 is wound through the first and second cut-out portions and around edge portions of the first and second polar plates. The conductive coil 106 is coupled to an electric fault detection device which causes a current to be produced in the conductive coil 106 in the event of a detected electrical fault. For example, the electric fault detection device may cause a current to be generated in the conductive coil 106 in the event of a residual current being detected in a main circuit. The conductive coil 106 is configured such that, when a current is generated in the conductive coil 106 due to the detection of an electric fault, a magnetic field is generated in the first and second polar plates that opposes the magnetic field generated by the permanent magnetic element 104. The magnetic field generated by the conductive coil 106 causes a reduction in the magnetic holding force between the contact portion 113 of the armature 103 and the first and second head portions of the polar plates. The reduction in the magnetic holding force between the armature 103 and the polar plates allows the torque due to the biasing member 105 to overcome the opposing torque due to the magnetic holding force, causing the armature 103 to rotate around the pivot point 123 from the closed position to the open position.

[0042] Preferably, in the absence of a current in the conductive coil 106, the magnetic holding force is greater than 400 mN. Preferably, in the absence of a current in the conductive coil 106, the holding torque is greater than 5 mNm. Preferably, when the conductive coil 106 is excited during a fault condition, the magnetic holding force is less than 200 mN. Preferably, when the conductive coil 106 is excited during a fault condition, the holding torque is less than 2 mNm. The biasing member 105 is configured to exert a torque on the armature 103 in the closed position that is greater than the holding torque when the conductive coil 106 is excited but less than the holding torque when no current is present in the conductive coil 106. Preferably, the biasing member 105 is configured to exert a torque on the armature 103 in the closed position that is greater than 2 mNm and less than 5 mNm.

[0043] The armature 103 is coupled to a pin 108, which extends through a wall of the housing 107. When the armature 103 rotates from the closed position to the open position, movement of the pin 108 activates a circuit breaking mechanism causing disconnection of the main circuit from a power supply.

[0044] When the armature 103 is in the closed position, the armature 103 extends substantially along the first direction DI. The magnetic holding force between the contact portion 113 and the first and second head portions of the polar plates is substantially parallel with the second direction D2. The contact between the contact portion 113 of the armature 103 is separated from the pivot points 123 of the armature 103 in substantially the first direction DI in the closed position. The pivot points 123 of the armature 103 are disposed beyond the ends of the first polar plate 101 and the second polar plate 102 in the first direction DI. The distance in the first direction DI between the pivot points 123 of the armature 103 and the ends of the polar plates is defined in this disclosure as the overhang length, OL, as illustrated in Fig. 5. Because the pivot points 123 of the armature 103 are disposed beyond the ends of the polar plates, the holding torque produced for a given magnetic holding force is greater than would be the case for comparable devices in which the pivot point 123 is in contact with the polar plates.

[0045] Preferably, the overhang length, OL, is related to the overall length of the polar plates, PL, in the first direction by a multiplying factor, MF between 0.7 and 1.7. Preferably, the polar plate length, PL, is between 5mm and 11mm. Preferably, the overhang length, OL, is between 3mm and 8mm.

[0046] In order to achieve reliable functioning of the device, the holding torque due to magnetic holding force should be sufficient to overcome the biasing torque due to the biasing member 105 in the absence of a fault condition in order to avoid nuisance tripping. The holding torque should also exhibit a sharp decrease as current is introduced into the conductive coil 106 in order to achieve reliable tripping under fault conditions.

[0047] Embodiments of the disclosure provide electromagnetic actuation devices capable of improved miniaturization in comparison with known permanent magnet relay based electromagnetic actuation devices. The placement of the pivot points 123 of the armature 103 beyond the end points of the first and second polar plates allows the length of the polar plates to be reduced in comparison to known devices while maintaining suitably high holding torque. By decreasing the length of the first and second polar plates in comparison to known devices, the permanent magnetic element 104 is brought closer to the contact area between the first and second polar plates and the armature 103, which allows a smaller permanent magnetic element to be used in comparison to known devices. Furthermore, because the pivot points 123 of the armature 103 are not in contact with the first and second polar plates, a low reluctance path between the north and south poles of the permanent magnetic element 104 via the pivot points 123 is avoided. This arrangement concentrates the magnetic flux at the contact portion 113 of the armature 103, allowing a suitable holding force to be achieved using a smaller permanent magnetic element 104 in comparison to devices in which the pivot points 123 of the armature 103 are in contact with the first and second polar plates.

Claims

Claims1. An electromagnetic actuating system comprising: a first polar plate (101) comprising a first head portion (111); a second polar plate (102) spaced apart from the first polar plate and comprising a second head portion (112); a permanent magnetic element (104) disposed such that a first pole of the permanent magnetic element is in contact with the first polar plate and a second pole of the permanent magnetic element is in contact with the second polar plate; an armature (103) comprising a contact portion (113) and a pivot point (123), wherein the armature (103) is configured to be moveable about the pivot point between an open position in which the armature does not contact the first and second head portions and a closed position in which the contact portion of the armature contacts both the first and the second head portions, thereby generating a magnetic holding force between the first and second head portions and the contact portion of the armature in the closed position; and a biasing member (105) coupled to the armature and configured to exert a torque on the armature to urge the armature from the closed position towards the open position, wherein the pivot point of the armature does not contact the first and second polar plates.

2. The electromagnetic actuating system of claim 1, wherein the armature extends beyond ends (101b) of the first and second polar plates such that the pivot point of the armature is disposed at a position beyond the ends of the first and second polar plates.

3. The electromagnetic actuating system of claim 1 or claim 2, further comprising a conductive coil (106) wound around part of the first and second polar plates such that a current in the conductive coil above a threshold value generates a magnetic field in the polar plates that reduces the magnetic holding force between the first and second head portions and the armature such that the armature is moved by the biasing member from the closed position to the open position.

4. The electromagnetic actuating system of claim 3, further comprising a residual current detection element configured to generate a current above the threshold value in the conductive coil when a residual current is detected in a main circuit.

5. The electromagnetic actuating system of claim 3 or claim 4, wherein the first and second polar plates respectively comprise first and second cut-out portions (131) positioned adjacent to each other, and wherein the conductive coil is wound through the cut-out portions.

6. The electromagnetic actuating system of claim 5, wherein the first and second head portions are disposed adjacent to the first and second cut-out portions respectively.

7. The electromagnetic actuating system of any preceding claim, wherein the contact portion is disposed at a first end of the armature and the pivot point is disposed at a second end of the armature opposite the first end.

8. The electromagnetic actuating system of any preceding claim, further comprising a housing (107) surrounding the first and second polar plates, the permanent magnet, the armature and the biasing member, wherein the pivot point engages a support surface (110) extruded from the housing or a support surface (110) formed from a non-magnetic material and coupled to the housing.

9. The electromagnetic actuating system of any preceding claim, wherein the first and second polar plates and the armature are formed of a ferromagnetic material.

10. The electromagnetic actuating system of any preceding claim, wherein the first and second polar plates are separated by an air gap or a non-ferromagnetic layer.

11. The electromagnetic actuating system of any preceding claim, wherein the first and second polar plates each have a length, PL, and where the pivot point of the armature extends beyond the polar plates by an overhang length, OL, and wherein OL = MF x PL, where MF is a multiplying factor between 0.7 and 1.7.

12. The electromagnetic actuating system of any preceding claim, further comprising a pin (108) coupled to the armature, wherein the pin is configured to activate a circuit breaking mechanism when the armature is in the open position.

13. The electromagnetic actuating system of any preceding claim, wherein the armature has a Y-shaped structure with a main portion and two branch portions, wherein an end of the main portion comprises the contact portion and each of the two branch portions comprises a pivot point.

14. The electromagnetic actuating system of any preceding claim, wherein the permanent magnetic element is arranged such that a first pole of the permanent magnetic element is in contact with an end portion (101b) the first polar plate and a second pole of the permanent magnetic element is in contact with an end portion of the second polar plate.

15. The electromagnetic actuating system of any preceding claim, wherein the first head portion is arranged directly adjacent to the second head portion.

Images