EP2940708A1

EP2940708A1 - Tripping mechanism and electrical installation device

Info

Publication number: EP2940708A1
Application number: EP14001524.9A
Authority: EP
Inventors: Günther MECHLER; Alexander Wachter; Markus Schneider
Original assignee: ABB AG Germany
Current assignee: ABB AG Germany
Priority date: 2014-04-30
Filing date: 2014-04-30
Publication date: 2015-11-04

Abstract

The invention is about a tripping mechanism (1), which has a double-armed armature (2) that is rotatably mounted to a rotation axis (12), and which has driving means (3, 4) for driving the armature (2) to alternate between two stable positions, whereby each arm (2.1, 2.2) is provided with a contact arrangement (7', 8') that allows, by tripping operations of the driving means (3, 4), to connect pairs of phase contacts (5, 5'; 6, 6') in a closing position of the arm and to disconnect pairs of phase contacts (5, 5'; 6, 6') in an opening position of the arm. A first arm (2.1) of the armature is functionally coupled to a first electromagnetic driving unit (4), the second arm (2.2) of the armature is functionally coupled to a second electromagnetic driving unit (3), on activation of the first electromagnetic driving unit (4) the first arm (2.1) is rotated to its closing position and the second arm (2.2) is rotated to its opening position, on activation of the second electromagnetic driving unit (3) the second arm (2.2) is rotated to its closing position and the first arm (2.1) is rotated to its opening position, and that the tripping mechanism is provided with retaining means (13) which retain the first arm (2.1) in its closing position after deactivation of the first electromagnetic driving unit (4) and which retain the second arm (2.2) in its closing position after deactivation of the second electromagnetic driving unit (3).

Description

The invention is about a tripping mechanism, which has a double-armed armature that is rotatably mounted to a rotation axis, and which has driving means for driving the armature to alternate between two stable positions, whereby each arm is provided with a contact arrangement that allows, by tripping operations of the driving means, in a closing position of the arm to connect pairs of phase contacts and in an opening position of the arm to disconnect pairs of phase contacts, according to the preamble of claim 1.
Such a tripping mechanism is shown, for example, in DE 10 2009 043 105 A1 . In this document an electrical overload relay with a contact bridge is shown, where a tripping mechanism according to the preamble of claim1 is contained.
An overload relay is used for the protection of motors and other electrical devices from overloads caused by short circuits or load imbalances. Typical components of an overload relay are (1) a voltage transformer to detect if the condition for relay operation is fulfilled, (2) a current transformer to extract energy from the magnetic field caused by the phase current, (3) a DC supply unit consisting of a capacitor that is loaded by the current from the current transformer using an AC/DC converter, (4) an electronic unit in form of a circuit board controlling the DC supply for (5) an electromechanical tripping arrangement driving an armature to alternate between two stable positions. Armature motion can be linear or rotational; (6) a contact arrangement that allows connecting or disconnecting pairs of phase contacts by tripping operations. The said armature is in most cases stiffly connected with a tripping body that holds the contact springs and contact bridges.
A number of problems are known with respect to state of the art tripping mechanisms. For example, in state-of-the-art tripping solutions the electromagnetic energy is transferred to the tripping lever indirectly using a coil that changes the magnetization of a ferromagnetic core that is already magnetized by a permanent magnet that holds a movable armature, which is a part of the magnetic circuit, in a stable position.
A spring that guarantees a well-defined contact force that the armature excites on the phase contacts is oriented opposite to the magnetic holding force but weak enough to allow the switch staying in a stable position even under the condition of external mechanical shocks or vibrations.
As soon as the magnetic flux that excites the holding force on the armature is reduced by the magnetic flux from the said coil, the holding force drops below the spring force, the contact springs will repel the armature from the contacts. The inertia of the armature and attractive forces at other gaps of the magnetic circuit support the armature movement that should end in another end position that is stable even though the coil excitation will be removed. In some cases the middle position is also a stable position, due to a minimum of potential energy. To prevent the armature from being trapped in this middle position, it needs to be accelerated to a sufficient kinetic energy to be able passing the mid position trap.
In some existing solutions the second stable position is physically symmetric to the first stable position while the same permanent magnet causes the holding force in both positions.
In a gap of a magnetic circuit the forces are always attractive. If the circuit has two air gaps, the magnetic holding force in a stable position is the big attractive force of the small gap minus the small attractive force of the big gap. In an intermediate position both attractive gap forces are small, so that the inertia of the armature and spring or friction forces is dominant. Friction will be negligible in most cases, but spring forces strongly contribute to the acceleration of the armature. A sufficiently high mass or moment of inertia is required to guarantee the arrival at the other stable position.
If the current of the switching coil has reduced the magnetic holding force or torque in the small air gap, the armature is already moving due to the contact spring driving force. If the current of the coil is further increasing, the magnetic force in the small gap will increase again, because the magnetic force is proportional to the square of the magnetic flux density that has inverted the spacial orientation but is increasing strongly. This could stop the armature motion and bring it back to the starting position, especially if the contact spring force is too small.
As soon as a gap at a stable position is opening, the magnetic force excited on the armature is decreasing fast with distance. The consequence is that at intermediate positions the motion control by electromagnetic forces becomes more difficult, because motion is governed by spring forces and inertial forces.
If the magnetic circuit has a topology with two or more coupled magnetic loops with more than two air gaps, the magnetic holding force in two closed air gaps is not automatically compensated simultaneously. It can happen that once the force in one closed gap is compensated, the force in the second closed gap is still high. Furthermore if the force in the second closed air gap is compensated, the holding force in the first air gap is already growing again.
A big share of the magnetic flux generated by the coils is not contributing to the gap forces especially in open gaps, because it is leaving the core at other locations as leakage flux. The magnetic energy of that leakage field is lost.
If the magnetic core is not laminated but massive, the ohmic eddy current losses due to electrical current in the core contribute significantly to the overall energy losses. Due to back-emf the eddy currents also increase the losses in the exciting coil
In the light of the state of the art it is the objective of the present invention to provide an energy efficient tripping mechanism that avoids the drawbacks of the prior art, and also an improved electrical installation device.
The object of the current invention is achieved by a tripping mechanism with the characterizing features of claim 1.
According to the invention, a first arm of the armature is functionally coupled to a first electromagnetic driving unit, the second arm of the armature is functionally coupled to a second electromagnetic driving unit, on activation of the first electromagnetic driving unit the first arm is rotated to its closing position and the second arm is rotated to its opening position, on activation of the second electromagnetic driving unit the second arm is rotated to its closing position and the first arm is rotated to its opening position, and the tripping mechanism is provided with retaining means which retain the first arm in its closing position after deactivation of the first electromagnetic driving unit and which retain the second arm in its closing position after deactivation of the second electromagnetic driving unit.
According to the invention, the driving means for driving the double-armed armature is split into two electromagnetic driving units, one associated with each of the arms. This allows for a more energy efficient design and operation of the driving of the armature.
According to an advantageous aspect of the invention, the double-armed armature is made of a ferromagnetic material. It is especially advantageous if the double armed armature is made of a laminated ferromagnetic material.
According to an advantageous aspect of the invention, the first and second electromagnetic driving unit is an air core coil each, and the first arm is coupled to a first plunger, and the second arm is coupled to a second plunger, and in the activated state of the first coil the flux in the air core pulls the first plunger into the air core of the first coil which makes the first arm rotate, and in the activated state of the second coil the flux in the air core pulls the second plunger into the air core of the second coil which makes the second arm rotate. Activated state of a coil is the state when an electric current is flowing in the coil winding of a size that the resulting magnetic flux in the air core is sufficiently large to exert an attractive force on the plunger associated with that coil to attract the plunger into the air core. The functional coupling of the double armed armature to the electromagnetic driving units is thus realized by the plungers, which can be realized as extensions to the armature.
According to an advantageous aspect of the invention, the first arm is provided with a first retaining extension and the second arm is provided with a second retaining extension, and the retaining means for retaining the first or second arm execute a holding force on the second retaining extension or the first retaining extension.
According to an advantageous aspect of the invention, the first arm is provided with a first contact spring which is guided in a first frame and which is exerting a contact force on a first contact bridge, and the second arm is provided with a second contact spring which is guided in a second frame and which is exerting a contact force on a second contact bridge.
According to an advantageous aspect of the invention, the retaining means contains a permanent magnet.
According to an advantageous aspect of the invention, the retaining means contains a permanent magnet with flux guides, whereby at least one of the flux guides gets in contact with the first or second retaining extensions for retaining the second or first arm.
According to an advantageous aspect of the invention, one of the flux guides gets in contact with the first or second retaining extensions for retaining the second or first arm, and in the contact position of one of the flux guides there is an air gap between the non-contacting flux guide and the first or second retaining extensions.
According to an advantageous aspect of the invention, each air core coil is provided with a ferromagnetic yoke around the coil for increasing the amount of flux inside the air core.
According to an advantageous aspect of the invention, activation of each of the air core coils is achieved through a pulsed activation current regime through the coils.
An electrical installation device according to the invention has a housing and a tripping mechanism according to the invention as described above. The rotation axis, the phase contacts and the retaining means are mounted in a fixed position relatively to the housing.
In a tripping mechanism according to the invention, the holding force acting on the armature is generated by a permanent magnet, thereby guiding the magnetic flux locally through a ferromagnetic core like in a magnetic short circuit, so no remagnetization of a long core is to be expected. The core parts excited by the permanent magnet are always excited in the same direction. Thus high hysteresis losses are avoided.
The magnetic circuit can also comprise one or two ferromagnetic plates covering one or both sides of the permanent magnet. Said plates are called the first and second flux guide, as they can guide the flux of the permanent magnet to the ferromagnetic core. This has an advantage in respect to the brittleness of the permanent magnet material. The impact with the first and second retaining extensions of the armature in contact position is then not directly with the brittle permanent magnet material, but with the flus guide plate, which can be made of a more robust material. The two small plates could also be used to fix the permanent magnet at the stator parts.
If one of the plates is kept shorter than the other plate, an artificial gap can be introduced to the magnetic short circuit. With the width of this gap the magnetic holding force acting on the movable armature can be adjusted to a requested value.
A high percentage of the flux generated in the air core coils is contributing directly to the force acting on the coil plunger. The plunger force is directly transferred to the tripping lever, the double armed armature, that is moved to external contact pins either on one or the other side. Leakage, i.e. mechanically non-active flux, is avoided. Once the movement due to direct acting the plunger coils has started, the accelerating force is not reduced like in an opening gap. Thus the acceleration can be controlled by the length of the coil current pulse.
The force acting on the plunger can according to the invention be increased adding a housing or a yoke made of ferromagnetic material to each air core coil. The housing or yoke then needs an aperture where the plunger can enter the coil core. Summarizing the advantages of the invention, it describes a solution with a balanced ferromagnetic plate rotatable about an axis with multiple functionality. Firstly, the double armed armature plate has two extensions that can be used as plunger of plunger coils thus exciting a torque on the plate with all attached parts. Secondly, the contour of the double armed armature ferromagnetic plate has two retaining extensions, which each define a contact line in its contour that allow the contact to a permanent magnet that is fixed at a stator frame or at the housing of the electrical switching device where the tripping device according to the invention is inserted, with or without flux guide plates at two holding positions. Thirdly, the double armed armature plate has attached contact springs, a spring frame, contact bridges and contact pins attached that are moved and compressed when they are moved to external line contact pins while rotating the balanced plate from the first to the second stable position or vice versa. In an advantageous embodiment, the double armed armature plate is balanced out, the attached parts are then considered as integral parts of the rotatable double armed armature plate.
The invention will be described in greater detail by description of an embodiment with reference to the accompanying drawings, wherein

Figure 1 shows schematically the embodiment of a tripping mechanism with the left pair of contacts connected,
Figure 2 shows schematically the embodiment of a tripping mechanism in the neutral position with none of the contact pairs connected,
Figure 3 shows schematically the embodiment of a tripping mechanism with the right pair of contacts connected.

Figure 1 shows a tripping mechanism 1 comprising a laminated ferromagnetic rotational plate 2 and a first air coil 4 that is fixed at the housing of an electromagnetic switching device (not shown in the figure) where the tripping mechanism is inserted. The rotational plate 2 has the basic form of a double-armed armature 2. It has a first arm 2.1 and a second arm 2.2. The first arm 2.1 is provided with a first retaining extension 22 and the second arm 2.2 is provided with a second retaining extension 23. Both retaining extensions 22, 23 are facing downwards, in a direction opposite the rotation axis 12. A central bar portion 24 of the double armed armature is showing upwards from the rotational axis. It carries at its upper free end a first extension in form of a first plunger 17. On the side of the second arm 2.2, and a second extension in form of a second plunger 18, on the side of the first arm 2.1. The first and second plungers 17, 18 have a slightly bent shape. The central bar portion 24 with the two plungers 17,18 attached has the form approximately of an anchor.
In the space between the first and second retaining extensions 22, 23 there is located a permanent magnet 13, forming the retaining means, with an upper, first flux guide plate 14 and a lower, second flux guide plate 15. The first flux guide plate 14 is larger in diameter than the second flux guide plate 15, it overlaps the second flux guide plate.
The first arm 2.1 is provided at its free end, upward looking side, with a first contact arrangement 7', and at its second arm 2.2, free end, upward looking side, with a second contact arrangement 8'. The first contact arrangement 7' comprises a frame-type arrangement, a first frame 11, which is guiding a first contact spring 9 and a first contact bridge 7. The contact first bridge 7 carries two movable contact pieces 7a, 7b.
The second contact arrangement 8' comprises a frame-type arrangement, a second frame 11', which is guiding a second contact spring 10 and a second contact bridge 8. The second contact bridge 8 carries two movable contact pieces 8a, 8b.
The first air coil 4 can attract the first plunger 17, when there is an electric current flowing through the first coil 4. The first coil 4 is in its activated state when the electrical current is flowing through the coil windings. In its activated state, the first coil 4 is drawing this first plunger 17 into the coil aperture 20 of the first coil 4, thus rotating the plate 2 around the rotational axis 12 in a clockwise direction. The rotational axis 12 is as well fixed at the housing of the electromagnetic switching device where the tripping mechanism is inserted.
The rotational movement of the plate 2 comes to an end when the second retaining extension 23 gets in touching contact with the first flux guide plate 14. This situation is shown in figure 1. A holding force is caused by the magnetic flux 16 of the permanent magnet 13 and guided by the flux guides 14 and 15 to the second retaining extension 23. This holding force holds the plate 2 in its position as shown in figure 1 even when the first coil 4 is deactivated again, i.e. when the current flow through the coil windings is stopped.
The rotated position as shown in figure 1 is called a first stable position of the double-armed armature 2. The first contact bridge 7 with the two movable contact pieces 7a, 7b is pressed against a first pair of phase contacts 5, 5', closing a signal current path between the two phase contacts 5, 5' via the contact bridge 7. The first contact spring 9 is compressed, exerting an additional contact force onto the first contact bridge 7.
There is a second air coil 3 that is fixed at the housing of the electrical switching device and which can attract the second plunger 18 of said plate 2, drawing this plunger 18 into the coil aperture 19 of the second coil 3, when the second coil 3 is activated, thus rotating the plate 2 around the rotational axis 12 in anti-clockwise direction. The drawing force of the second coil 3 on the plate 2 is big enough so that the plate 2 is overcoming the holding force at the second retaining extension 23, caused by the magnetic flux 16 of the permanent magnet 13.
The anti-clockwise rotational movement of the plate 2 is stopped when the double-armed armature 2 reaches its second stable position, shown in figure 3.
In the transition phase between the first and second stable positions of the double-armed armature 2, the contact spring 9 is expanding and contributing to the angular acceleration of the plate 2, removing subsequently the first contact bridge 7 from the first pair of phase contacts 5, 5'. Expansion of the contact spring 9 is stopped when the contact bridge 7 gets contact to the upper part of the first frame 11 that is fixed at the first arm 2.1 of the plate 2.
In the second stable position, see figure 3, the second contact bridge 8 with the movable contact pieces 8a, 8b gets contact with the second pair of phase contacts 6, 6', whereupon the second contact spring 10 is compressed until the rotation of the double armed armature 2 is stopped. The rotational movement is stopped when the first retaining extension 22 gets contact with the first flux guide 14 of the permanent magnet 13. The resulting magnetic flux 29 excites a holding torque on plate 2 in the second stable position, which is lasting even when the activation of the second coil 3 is stopped.
On its way from the first stable position, figure 1, to the second stable position, figure 3, the double armed armature 2 is passing over a neutral position in the middle, figure 2, when none of the contact bridges 7, 8 is in contact with any of the pairs of phase contacts 5, 5', 6, 6'.
When in the second stable position, figure 3, the first coil 4 is activated again, the plate 2 is being rotated back to the first stable position. The second contact spring 10 supports the rotation by expanding and contributing to the angular acceleration of plate 2 until the second contact bridge 8 gets contact with the upper end of the second frame 11' that is fixed at the second arm 2.2 of plate 2 and removes subsequently the second contact bridge 8 from the second pair of phase contacts 6, 6', and after continued rotation the first contact bridge 7 gets again in contact with the first pair of phase contacts 5, 5', whereupon the first contact spring 9 is again compressed until the rotation of plate 2 is stopped when the second retaining extension 23 of plate 2 again gets in contact with the flux guide plate 14 of the permanent magnet 13 while the magnetic flux 16 excites a holding torque on plate 2.
The flux guides 14 and 15 are attached to the permanent magnet 13 and they hold the permanent magnet in a fixed position with respect to the housing of the installation device, not shown in the figures.
The extension of the first and second flux guides 14 and 15 have different length in the direction normal to the first and second retaining extensions 22 or 23, while only the longer flux guide 14 will get contact with one of the first and second retaining extensions 22 or 23, whereas between the shorter flux guide 15 and one of the first and second retaining extensions 22 or 23 an air gap 26 will exist with a magnetic reluctance that limits the magnetic holding force exerted on plate 2 to the required value that is high enough to keep the plate angular position-stable against external shocks and vibration and low enough to allow for the first and second air coils 4 and 3 an energy efficient tripping operation.
The bobbins of the first and second coils 4 and 3 are designed in a way that the coil apertures 19 and 20 and the extensions 17 and 18 are fitting well together when moving against each other with a sufficient play that accounts for the bearing tolerances between the plate 2 and the rotational axis 12.
The coil current control scheme for activating the first and second coils 4 and 3 generates coil current pulses, that are designed in a way that the resulting magnetic force function exerted on the first and second plungers 17, 18 is sufficient to achieve an angular acceleration on the double-armed armature plate 2 that is sufficient to transport the plate 2 and all attached bodies from one angular end position in the first stable position to the other angular end position in the second stable position without bouncing back and without being trapped at another intermediate angular position. So the neutral position in the middle, figure 2, is passed and the double-armed armature 2 will not stop there.
Figure 3 shows a variant of the first and second coils arrangements 4, 3 in that ferromagnetic solid or laminated housings or frames 27 and 28 are arranged around the coils 4 and 3 to increase the amount of magnetic flux that will penetrate the attracted end of the plungers 17 or 18 when entering the respective coils 4, 3, thus getting a higher torque on the double-armed armature plate 2.
The outer contours of the double-armed armature plate 2 are designed in a way that the center of mass of the double-armed armature plate 2 including the weight of the contact springs 9 and 10, frames 11 and 11' and contact bridges 7 and 8, is exactly matching the position of the rotational axis 12.

The embodiment shown in the figures is of an exemplary character. Other variants are possible and included in the scope of the invention. Such possible variants are for example, and not meant to be limiting,

coils

4 and 3 with or without further encapsulation, :permanent magnet 13 without flux guides 14, 15, or with only one flux guide on one side, or with two evenly long flux guides, or with flux guides of diferent length that allow for calibrating the holding force.

List of reference signs

1	tripping mechanism	18	second plunger
2	double-armed armature	19	air core of first coil
2.1	first arm	20	air core of second coil
2.2	second arm	22	first retaining extension
3	driving means, second electromagnetic driving unit	23	second retaining extension
3	driving means, second electromagnetic driving unit	24	central bar
4	driving means, first electromagnetic driving unit	26	air gap
4	driving means, first electromagnetic driving unit	27	yoke, frame
5, 5'	first pair of phase contacts	28	yoke, frame
6, 6'	second pair of phase contacts	29	flux path
7'	first contact arrangement
8'	second contact arrangement
7	first contact bridge
7a	movable contact piece
7b	movable contact piece
8	second contact bridge
8a	movable contact piece
8b	movable contact piece
9	first contact spring
10	second contact spring
11	first frame
11'	second frame
12	rotation axis
13	retaining means, permanent magnet
14	first flux guide
15	second flux guide
16	flux path
17	first plunger

Claims

A tripping mechanism (1), which has a double-armed armature (2) that is rotatably mounted to a rotation axis (12), and which has driving means (3, 4) for driving the armature (2) to alternate between two stable positions, whereby each arm (2.1, 2.2) is provided with a contact arrangement (7', 8') that allows, by tripping operations of the driving means (3, 4), to connect pairs of phase contacts (5, 5'; 6, 6') in a closing position of the arm and to disconnect pairs of phase contacts (5, 5'; 6, 6') in an opening position of the arm,
characterized in that a first arm (2.1) of the armature is functionally coupled to a first electromagnetic driving unit (4), the second arm (2.2) of the armature is functionally coupled to a second electromagnetic driving unit (3), on activation of the first electromagnetic driving unit (4) the first arm (2.1) is rotated to its closing position and the second arm (2.2) is rotated to its opening position, on activation of the second electromagnetic driving unit (3) the second arm (2.2) is rotated to its closing position and the first arm (2.1) is rotated to its opening position, and that the tripping mechanism is provided with retaining means (13) which retain the first arm (2.1) in its closing position after deactivation of the first electromagnetic driving unit (4) and which retain the second arm (2.2) in its closing position after deactivation of the second electromagnetic driving unit (3).
A tripping mechanism according to claim 1, characterized in that the double-armed armature is made of a ferromagnetic material.
A tripping mechanism according to claim 2, characterized in that the first and second electromagnetic driving unit (4, 3) is an air core coil each, that the first arm (2.1) is coupled to a first plunger (17), and the second arm (2.2) is coupled to a second plunger (18), that in the activated state of the first coil (4) the flux in the air core pulls the first plunger (17) into the air core (20) of the first coil (4) which makes the first arm (2.1) rotate, and that in the activated state of the second coil (4) the flux in the air core pulls the second plunger (18) into the air core (19) of the second coil (4) which makes the second arm (2.1) rotate.
A tripping mechanism according to claim 3, characterized in that the first arm (2.1) is provided with a first retaining extension (22) and the second arm (2.2) is provided with a second retaining extension (23), and that the retaining means (13) for retaining the first or second arm (2.1, 2.2) execute a holding force on the second retaining extension (23) or the first retaining extension (22).
A tripping mechanism according to claim 4, characterized in that the first arm (2.1) is provided with a first contact spring (9) which is guided in a first frame (11) and which is exerting a contact force on a first contact bridge (7), and that the second arm (2.2) is provided with a second contact spring (10) which is guided in a second frame (11') and which is exerting a contact force on a second contact bridge (8).
A tripping mechanism according to claim 4, characterized in that the retaining means (13) contains a permanent magnet.
A tripping mechanism according to claim 6, characterized in that the retaining means (13) contains a permanent magnet with flux guides (14,15), whereby at least one of the flux guides (14,15) gets in contact with the first or second retaining extensions (22, 23) for retaining the second or first arm (2.2, 2.1).
A tripping mechanism according to claim 7, characterized in that one of the flux guides gets in contact with the first or second retaining extensions (22, 23) for retaining the second or first arm (2.2, 2.1), and that in the contact position of one of the flux guides there is an air gap between the non-contacting flux guide and the first or second retaining extensions (22, 23).
A tripping mechanism according to claim 3, characterized in that each air core coil (3, 4) is provided with a ferromagnetic yoke (27, 28) around the coil for increasing the amount of flux inside the air core.
A tripping mechanism according to claim 3, characterized in that activation of each of the air core coils is achieved through a pulsed activation current regime through the coils.
Electrical installation device with a housing and a tripping mechanism according to one of the preceding claims, characterized in that the rotation axis (12), the phase contacts (5, 5'; 6, 6') and the retaining means (13) are mounted in a fixed position relatively to the housing.