Fast bypass relay

Abstract

A relay 1 comprises a first fixed contact 7,15 (figure 1), a contact arm 8 having a first movable contact 9,14, and an electromagnetic drive unit 2 having an armature 3 and a yoke 4. A connector 10 (f

Description

Field of invention The present disclosure relates to an electromagnetic relay. More specifically, the disclosure relates to an electromagnetic relay for use as a bypass relay in a hybrid circuit breaker. Background Electromagnetic relays are used in electrical devices such as hybrid circuit breakers, in which an electromagnetic relay is disposed in parallel with a semiconductor switching apparatus. An example of an electromagnetic relay suitable for use in a hybrid circuit breaker is the bistable relay using a polarized magnetic actuator described in EP4000085B1. An important feature of bypass relays in hybrid circuit breakers is the time required to achieve contact separation during switching operations. In known circuit breakers, a degree of overtravel, in which part of an actuator travels beyond the range of motion of the movable electric contact, ensures reliable contact between the movable and fixed electric contacts when in an on-state. Overtravel can be achieved by a deformable connection between electric contacts and part of the actuator, which allows the actuator to move beyond the range or motion of the electric contacts. When switching to an off-state, the delay during which the actuator moves back through the overtravel region before the fixed and movable electric contacts begin separation contributes to the total duration of the switching operation. In view of the above, there is a need for an improved electromagnetic relay device that is able to achieve reliable electric contact between fixed and moving electric contacts while achieving improved opening speeds. Summary In one aspect of the disclosure, a relay is provided. The relay comprises: an electromagnetic drive unit with an armature and a yoke; a first fixed electric contact; a contact arm comprising a first movable electric contact; and a connector coupling the armature to the contact arm. The armature and the yoke are both displaceable with respect to the first fixed electrical contact. By allowing the armature and the yoke both to be displaced with respect to the first electrical contact, overtravel of the armature is in the on-position achieved with respect to the fixed electrical contact by movement of the yoke towards the armature. As such, when the relay is switched-off, movement of the armature achieved immediate movement of the movable electric contact away from the fixed electric contact without the armature first being required to move through an overtravel distance. In some examples, the first fixed electrical contact remains stationary with respect to a housing of the relay during switching operations. In some examples, the yoke and armature are both rotatable with respect to the first fixed electrical contact. As such, displacement of the yoke and armature with respect to the fixed electric contact is achieved via rotation. In some examples, the electromagnetic drive unit is configured such that the armature moves between an on-state, in which a first magnetic contact region of the armature contacts a second magnetic contact region of the yoke, and an off-state, in which the first magnetic contact region of the armature contacts a third magnetic contact region of the yoke, wherein the first movable electric contact is in contact with the first fixed electric contact when the armature is in the on-state. In some examples, the yoke and the armature rotate in opposite directions during transitions between the on-state and the off-state. In some examples, the relay comprises at least one biasing element configured to oppose the direction of displacement of the yoke during a switching-on operation. In some examples, the relay further comprises at least one biasing element configured to bias the yoke in a first rotational direction. In some examples, the at least one biasing element causes the first movable electric contact to the pressed into the first fixed electrical contact when the armature is in the on-state. In some examples, wherein the at least one biasing element comprises a spring coupled to the yoke. In some examples, the connector comprises a rigid shaft with the armature and the contact arm arranged at different positions on the shaft. In some examples, the armature is rotatable about the rigid shaft, and wherein the yoke is rotatable about an axis parallel with the shaft. In some examples, the rigid shaft is formed integrally with the armature. In some examples, the electromagnetic drive unit further comprises at least one permanent magnet and at least one coil disposed around part of the yoke, wherein energization of the at least one coil causes the armature to move between bistable states of the electromagnetic drive unit. In some examples, the relay further comprises: a second fixed electrical contact, wherein the contact arm comprises a second movable electric contact, wherein a current path is formed between the first and second fixed electric contacts via the first and second movable electric contacts when the relay is in an on-state. In an aspect of the disclosure, a hybrid circuit breaker is provided. The hybrid circuit breaker comprises a semiconductor switching unit and the relay of any preceding claim arranged in parallel with the semiconductor switching unit. Brief Description of Figures Fig. 1 shows an open front side of part of a bistable electrical switching device suitable for use in embodiments of the disclosure in the first stable position; Fig. 2 shows an open front side of the relay according Fig. 1 in the second stable position; Fig. 3 shows a back side of the relay according Figs. 1 and 2; Fig. 4 shows the back side of the relay according to Fig. 3 in an off-position, an on-position, and a transition between the off- and on-positions. Fig. 5 shows a sectional view according the cutting plane A - A according Fig. 2; Fig. 6 schematically illustrates the effect of changing the polarity of an actuation signal on the magnetic field in an electromagnetic drive unit; Fig. 7 shows an examples of an armature, connector and contact arm of the relay. Detailed Description The disclosure relates to a relay device. The relay is particularly suited for use in apparatuses and systems in which fast separation of electric contacts is advantageous, such as in hybrid circuit breaker devices. However, the relay device described herein can be used in other applications for which relays are required. The relay device includes a bistable polarized magnetic actuator including a movable armature and a movable yoke. The armature is coupled via a shaft to a contact arm having movable electric contacts. Opening and closing of the relay is performed by controlling the armature to move the contact arm between positions in which movable electric contacts of the contact arm are in contact or separated from fixed electrical contacts. Effective overtravel of the armature with respect to the contact arm during switch-on is achieved through displacement of the yoke of the relay towards the armature when the contact arm has reached the end of its range of motion. This effective overtravel ensures reliable electric contact between movable electric contacts of the contact arm and fixed electric contacts of the relay. Because the effective overtravel of the armature results from the movement of the yoke towards the armature, there is no need for the armature to move through an overtravel distance before contact separation is initiated during a switch-off operation. When the relay is switched off, the rigid connection of the armature to the movable electrical contacts causes contact separation to begin as soon as the armature begins to move. In the embodiments described in detail below, displacement of the armature and the yoke are achieved by rotation of the armature and yoke respectively. In other examples, the operating principles of the devices described in detail below may be applied to devices in which the armature and / or yoke undergo different modes of displacement, such as translational movement. Figs. 1 to 6 illustrate aspects of a relay 1 comprising an electromagnetic drive unit 2 with a rotatable armature 3 and a rotatable yoke 4. In other examples, the yoke 4 may be displacement according to other degrees of freedom, such as through a translation. The rotatable armature 3 of the electromagnetic drive unit is coupled to a contact arm 8 via a connector 10. The connector is preferably a shaft 10, though other connections means such as a rod or gears could be used in other embodiments. The shaft 10 is preferably rigid, though in some examples the shaft 10 may have some degree of torsional elasticity. When the shaft 10 is rigid, the armature 3 and the contact arm 8 corotate. Rotation of the armature 3 between a first state (the switched-on state) and a second state (the switched-off state) causes the contact arm 8 to move between a first position in which movable electric contacts 9,14 of the contact arm 8 are in contact with fixed electric contacts 7,15 of the relay device 1 and a second position in which the movable electric contacts 9,14 of the contact arm 8 are separated from the fixed electric contacts 7,15 of the relay device. Fig. 1 shows the contact arm 8 in the second state where the movable electric contacts 9,14 of the contact arm 8 are separated from fixed electric contacts 7,15 of the relay device. Fig. 2 illustrates the contact arm 8 in the first state where the movable electric contacts 9,14 of the contact arm 8 are in contact with the fixed electric contacts 7,15 of the relay device. The fixed electric contacts 7,15 of the relay 1 are fixed relative to a housing 18 of the relay 1. The fixed electric contacts 7,15 may be directly mounted on the housing 18 or may be mounted on separate contact pieces 25,26 that are fixed directly or indirectly to the housing 18. The contact pieces 25,26 are electrically connected to terminals of the relay 1. The relay-housing 18 comprises two bushings for supporting the shaft 10. The shaft 10 is floating mounted in the relay-housing 18. In the illustrated embodiment, the electromagnetic switching device 1 comprises at least one auxiliary spring 19, 20, which is also an electric contact element. The auxiliary spring 19, 20 biases the contact arm 8 in direction to the first electric contact. The electromagnetic drive unit 2 is a bistable polarized magnetic actuator. Both the yoke 4 and the armature 3 are rotatable with respect to the fixed electrical contacts 7,15 of the relay 1. The electromagnetic drive unit 2 comprises a first coil 21 wound around a first part of the yoke 4. In the illustrated embodiment, the electromagnetic drive unit 2 further comprises a second coil 22 wound around a second part of the yoke 4. The electromagnetic drive unit 2 comprises a first permanent magnetic element 23, which is arranged between two parts of the yoke 4. In the illustrated embodiment, the electromagnetic drive unit 2 further comprises a second permanent magnetic element 24, which is also arranged between two parts of the yoke 4. Figs. 5 and 6, described in more detailed below, illustrate the arrangement of the first and second coils 21 and 22. The relay 1 is able to change between two distinct stable states by actuation of the electromagnetic drive unit 2. The first state a switched-on state. In the first state, a first fixed electric contact 7 of the relay is in contact with a first movable electric contact 9 of the contact arm 8 and a second fixed electric contact 15 of the relay 1 in contact with a second movable electric contact 14 of the contact arm 8. The contact arm 8 comprises a conductive path between the first and second movable electric contacts and may be formed entirely of a conductive material. The fixed electric contacts 7,15 are connected (directly or indirectly) to terminals of the relay 1. In the switched-on state, current is able to flow between the first and second fixed electrical contacts via the contact arm 8. The second state is a switched-off state. In the second state, the first and second movable electric contacts are respectively separated from the first and second fixed electric contacts, and an electric current is not able to flow through the relay 1. The armature 3 is rotatably mounted with respect to the housing 18. The armature 3 comprises at least a first arm, with a first magnetic contact region 5. Rotation of the armature 3 moves the armature between a first position, in which the first magnetic contact region 5 of the armature 3 is in contact with a second magnetic contact region 6 of the yoke 4, and a second position, in which the first magnetic contact region 5 of the armature 3 is in contact with a third magnetic contact region 27 of the yoke 4. The first magnetic contact region 5 preferably includes at least two sides of the first arm of the armature 3. Preferably, the armature 3 comprises a second arm that is substantially symmetric with the first arm and comprising a fourth magnetic contact region. In this embodiment the yoke 4 further comprises a fifth magnetic contact region 31 and a sixth magnetic contact region 32. In the first position, the fourth magnetic contact region of the armature 3 is in contact with the fifth magnetic contact region 31 of the yoke 4. In the second position, the fourth magnetic contact region of the armature 3 is in contact with the sixth magnetic contact region 32 of the yoke 4. In some examples, the first and second arms of the armature 3 may comprise opposite ends of one continuous piece. The armature 3 and the yoke 4 may both be formed of a low reluctance material, such as iron or ferromagnetic steel. The yoke 4 is rotatably mounted within the housing and is coupled directly or indirectly to the housing 18 of the relay 1 by cylindrical compression spring elements 29. Other biasing means may be used, such as a leaf spring. The magnetic force between the yoke 4 and the armature 3 that biases the armature 3 to rotate in one rotational direction biases the yoke 4 to rotate in the opposite rotational direction. Rotation of the yoke 4 in relation to the housing 18 during a switch-on operation causes compression the spring element 29 that biases the yoke 4 against its rotation. Fig. 3 illustrates an example of the mounting of the yoke 4 with two cylindrical compression springs 29. Fig. 4 illustrates the positions of the yoke 4, the armature 3, the contact arm 8 and the movable electric contacts 9,14 in the second state (switched-off state) and the first state (switched-on state). The images provide cross-sectional views along the direction of the rotational axes of the yoke 4 and the armature 3 and the contact arm 8. The portion of the images outside the dotted lines illustrate the part of the relay comprising the contact arm 8 and the electrical contacts 9,14,7,15. The portion of the images inside the dotted line illustrate the part of the relay comprising the armature 3 and the yoke 4. Because the armature 3 is coupled to the contact arm 8 via a rigid shaft, the range of rotation of the armature 3 is limited to the range of rotation of the contact arm 8. When the electromagnetic drive unit 2 is in the first state (the switched-on state), the extent of rotation of the armature 3 is limited by the position at which the movable electric contact 11 of the contact arm reaches the fixed electrical contacts 7,15 of the relay 1. During a switch-on operation, the armature 3 rotates until the movable electric contacts 9,14 reach the fixed electric contacts 7,15 of the relay 1. In order for the armature 3 to make contact with the yoke 4, the yoke 4 rotates in the opposite rotational direction (to that of the armature) against the biasing force of the spring elements 29. The additional rotation of the yoke 4 against the spring elements 29 beyond the range of rotation available for the contact arm 8 provides an overtravel range in the electromagnetic drive unit 2, which ensures reliable electric contact between the fixed electric contacts 7 and the movable electric contacts 9 in the first state (switched-on state). In this state, the springs 29 bias the yoke 4 and the armature 3 in a first rotational direction that causes the movable electric contacts 9,14 of the contact arm 8 to the pressed into the fixed electrical contacts 7 of the relay 1. When the electromagnetic drive unit 2 receives an actuation signal to move the armature 3 from the first state (the switched-on state) to the second state (the switched-off) state, the first magnetic contact region armature 3 begins to be attracted towards the third magnetic contact region of the yoke 4 rather than the second magnetic contact region of the yoke 4. As such, the armature 3 immediately begins to rotate towards the second position in which the first magnetic contact region of the armature 3 is in contact with the third magnetic contact region 27 of the yoke 4. The release of the attractive magnetic force between the first magnetic contact region 5 of the armature 3 and the second magnetic contact region of the yoke 4 causes the yoke 4 to rotate in the opposite direction to the direction of rotation of the armature 3 due to the biasing force of the compression spring elements 29. By allowing the yoke 4 to move with respect to the fixed electrical contacts, effective overtravel of the armature 3 with respect to the fixed electrical contacts is achieved through movement of the yoke 4 towards the armature 3. A biasing force exerted on the yoke 4 by biasing elements 29 in the opposite direction to the displacement of the yoke 4 is transmitted to the contact arm 8, causing the movable electric contacts to be pressed into the fixed electric contacts of the relay. The effective overtravel ensures a reliable electric contact between the fixed and movable electric contacts in the switched-on state. When transitioning from the switched-on and switched-off state, the effective overtravel is reversed by rotational movement of the yoke 4. Movement of the armature 3, and hence the movable electric contacts, begins instantaneously on receiving of the actuation signal and does not require completion the movement of the yoke 4. As such, the effective overtravel distance does not contribute to the contact separation time of the relay 1 during a switching off operation. Faster contact separation of electric contacts reduces the time during which current passes through solid-state components during a fault condition, thereby reducing heating of the solidstate components. The reduction in the delay until contact separation is initiated allows contact separation to begin at a lower current level during short-circuit conditions in comparison to devices in which the armature must move through an overtravel distance before contact separation is initiated. By reducing the current level at contact opening, the arcing energy at the contacts during a short-circuit condition is reduced. As overtravel during switch closing is achieved through movement of the yoke 4 rather than the actuator 3, increase in the overtravel distance of the yoke 4 as the electric contacts degrade over the lifecycle of the relay 1 does not result in an increased delay before contact separation to begins during switching operations. Figs. 5 and 6 illustrate how the provision of currents in the coils 21 and 22 causes the electromagnetic drive unit 2 to change between the first and second states. Movement of the armature 3 and yoke 4 is controlled by providing electric currents in coils 21 and 22 to induce magnetization of the yoke 4. When neither of coils 21 and 22 are energised, the magnetic fields between the permanent magnetic elements 23 and 24 (or between poles of one magnetic element) generates a holding force between the armature 3 and the surfaces of the yoke 4 that the armature 3 is in contact with. As such, when the armature 3 and yoke 4 are in a first stable position, the magnetic holding force biases the armature 3 to remain contact with the yoke 4 in the first stable position against external forces. Similarly, when the armature 3 and yoke 4 are in the second stable position, the magnetic holding force biases the armature 3 to remain in contact with the yoke 4 in the second stable position. The coils 21 and 22 are arranged such that when energized by current flow in a first current direction, only one of the first and second positions of the armature 3 and yoke 4 remains stable, and the armature 3 and yoke 4 are biased towards the stable position and away from the unstable position. In the situation, the second position of the armature 3 and yoke 4 is no longer stable and a torque is generated to cause rotational acceleration of the armature 3 (and rotational acceleration of the yoke 4 in the opposite direction) towards the first position. After the armature 3 has rotated to the first position, removing current from the coils 21 and 22 causes both the first and second positions to become stable, and the armature 3 and yoke 4 will remain in the first position. By introducing a current in the coils in a second direction opposite the first direction, magnetic fields in the yoke 4 and armature 3 can generated causing only the first position to remain stable, in which case the armature 3 and yoke 4 will accelerate towards the first position. As such, the electromagnetic drive unit 2 can be controlled to move the armature 3 from the second position to the first position by introducing current of a first direction into the coils, and the electromagnetic drive unit 2 can be controlled to move the armature from the second position to the first position by introducing current in a second direction into the coils (i.e. reversing the current of the first direction). Fig. 7 illustrates an example of an armature assembly suitable for use in examples of the disclosure. In this example the armature 3 and the shaft 10 form one single integral element. The contact arm 8 is mounted on the end of the shaft 10 via a hole passing through the contact arm 8. The two arms of the armature 3 comprise one single flat portion 5 configured to contact parts of the yoke 4 at opposite ends. The armature 3 and shaft 10 are entirely rigid. As such, all overtravel is achieved via rotation of the yoke 4 and compression of spring elements 29. In other examples, the shaft 10 may be flexible. When the shaft 10 is flexible, overtravel may be achieved via a combination of shaft 10 torsion and yoke 4 rotation. In this example, a lower degree of overtravel is required in comparison to devices in which the overtravel is entirely achieved via torsion of the shaft. List of elements and reference numerals: Relay: 1 Electromagnetic Drive Unit: 2 Armature: 3 Yoke: 4 Magnetic contact regions of the yoke: 6, 27, 31, 32. Magnetic contact regions of the armature: 5 Contact arm: 8 5 Connector: 10 Movable electric contacts: 9,14 Fixed electric contacts: 7,15 Housing: 18 Contact pieces: 25,26 10 Biasing element: 29 Coils: 21, 22 Permanent magnetic elements: 23,24 Auxiliary spring 19, 20 15

Claims

1. A relay comprising:an electromagnetic drive unit (2) with an armature (3) and a yoke (4);a first fixed electric contact (7,15);a contact arm (8) comprising a first movable electric contact (9,14); and a connector (10) coupling the armature (3) to the contact arm (8);wherein the armature (3) and the yoke (4) are both displaceable with respect to the first fixed electrical contact (7,15).

2. The relay of claim 1, wherein the first fixed electrical contact (7,15) remains stationary with respect to a housing (18) of the relay (1) during switching operations.

3. The relay of claim 1 or claim 2, wherein the yoke (4) and armature (3) are both rotatable with respect to the first fixed electrical contact (7,15).

4. The relay of any preceding, wherein the electromagnetic drive unit (2) is configured such that the armature (3) moves between an on-state, in which a first magnetic contact region (5) of the armature (3) contacts a second magnetic contact region (6) of the yoke (4), and an off-state, in which the first magnetic contact region (5) of the armature (3) contacts a third magnetic contact region (27) of the yoke (4), wherein the first movable electric contact (9,14) is in contact with the first fixed electric contact (7,15) when the armature is in the on-state.

5. The relay of claim 4, wherein the yoke (4) and the armature (3) rotate in opposite directions during transitions between the on-state and the off-state.

6. The relay of any preceding claim, wherein the relay further comprises at least one biasing element (29) configured to oppose the direction of displacement of the yoke (4) during a switching-on operation.

7. The relay of any preceding claim, wherein the relay comprises at least one biasing element (29) configured to bias the yoke (4) in a first rotational direction.

8. The relay of claim 6 or claim 7, wherein the at least one biasing element (29) causes the first movable electric contact (9) to the pressed into the first fixed electrical contact (7) when the armature is in the on-state.

9. The relay of any of claims 6 to 8, wherein the at least one biasing element (29) comprises a spring coupled to the yoke (4).10.The relay of any preceding claim wherein the connector (10) comprises a rigid shaft, with the armature (3) and the contact arm (8) arranged at different positions on the shaft.11.The relay of claim 11, wherein the armature (8) is rotatable about the rigid shaft (10), and wherein the yoke (4) is rotatable about an axis parallel with the rigid shaft (10).

12. The relay of claim 11, wherein the rigid shaft (10) is formed integrally with the armature (3).13.The relay of any preceding claim, wherein the electromagnetic drive unit (20) further comprises at least one permanent magnet (23) and at least one coil (21) disposed around part of the yoke (4),wherein energization of the at least one coil (21) causes the armature (3) to move between bistable states of the electromagnetic drive unit (2).14.The relay of any preceding claim, further comprising: a second fixed electrical contact (15), wherein the contact arm (8) comprises a second movable electric contact (14), wherein a current path is formed between the first and second fixed electric contacts via the first and second movable electric contacts when the relay is in an on-state.

15. A hybrid circuit breaker comprising a semiconductor switching unit and the relay of any preceding claim arranged in parallel with the semiconductor switching unit.13

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