ELECTROMAGNETIC ACTUATOR

Abstract

 The invention relates to an electromagnetic actuator (1) for an electrical switching apparatus (2), the electromagnetic actuator (1) comprising an actuator housing (8) defining a longitudinal axis (9) and having an upper inner housing surface (15) and a lower inner housing surface (13), an armature (3) comprising ferromagnetic material and arranged within the actuator housing (8) axially movable between a first position and a second position, whereby the armature (3) in the first position contacts the upper inner housing surface (15) and in the second position contacts the lower inner housing surface (13), at least one electromagnetic coil (10, 11) coaxially arranged within the actuator housing (8) in respect to and for actuating the armature (3), and a damping element (16) arranged on a bottom end of the armature (3) facing the lower inner housing surface (13) or arranged on the lower inner housing surface (13) facing the bottom end of the armature (3).

Description

Technical Field

[0001] The invention relates to an electromagnetic actuator for an electrical switching apparatus, the electromagnetic actuator comprising an actuator housing defining a longitudinal axis and having an upper inner housing surface and a lower inner housing surface, an armature comprising ferromagnetic material and arranged within the actuator housing axially movable between a first position and a second position, and at least one electromagnetic coil coaxially arranged within the actuator housing in respect to and for actuating the armature.

Background Art

[0002] Electromagnetic actuators due to their simplicity and high efficiency are widely used for providing motion in electrical switching apparatuses, such as for example MV, medium voltage, circuit breakers, reclosers, switches and contactors. Commonly, such electromagnetic actuators comprise a permanent magnet with either a single or double electromagnet coil for driving a movable contact of the electrical switching apparatus for closing and tripping respectively opening. Both alternative designs provide high reliability and fast operation with contact speeds reaching at least 1 m/s, which is critical for proper operation of the electrical switching apparatus in some electrical applications, such as for example capacitor switching.

[0003] Those high speeds combined with high masses, which are usually typical in MV electrical switching apparatuses, result in high kinetic energy being involved in switching operations. Each time the electrical switching apparatus is closed or opened, the complete assembly, consisting of the moving contact, a drive rod, and an armature with stems weighting usually more than 1,6 kg, travels with around 1 m/s. A final position is achieved by instantly decelerating thereby creating high mechanical tensions and vibrations.

[0004] In most cases the drive rod is equipped with an overtravel spring, which works like a bumper and decreases shocks being generated during closing, thereby changing some of the kinetic energy into potential energy that provides additional opening speed during tripping. However, for opening the whole kinetic energy is instantly discharged by the armature while hitting a housing of the actuator. Said operation is a source of massive tensions, vibrations and noise and may lead to premature mechanical failures of the device due to material fatigue.

Summary of invention

[0005] It is therefore an object of the invention to provide an improved electromagnetic actuator for an electrical switching apparatus characterized by extended mechanical life and reduced material fatigue.

[0006] The object of the invention is solved by the features of the independent claim. Preferred implementations are detailed in the dependent claims.

[0007] Thus, the object is solved by an electromagnetic actuator for an electrical switching apparatus, the electromagnetic actuator comprising

an actuator housing defining a longitudinal axis and having an upper inner housing surface and a lower inner housing surface,

an armature comprising ferromagnetic material and arranged within the actuator housing axially movable between a first position and a second position, whereby the armature in the first position contacts the upper inner housing surface and in the second position contacts the lower inner housing surface,

at least one electromagnetic coil coaxially arranged within the actuator housing in respect to and for actuating the armature, and

a damping element arranged on a bottom end of the armature facing the lower inner housing surface or arranged on the lower inner housing surface facing the bottom end of the armature.

[0008] The damping element in particular for tripping operation constitutes a key point of the proposed solution. Said damping element reduces mechanical shocks generated during switch tripping. During a tripping operation, moving mass kinetic energy may compress the damping element so that at least a part of the kinetic energy will be transformed directly into potential energy, which will be then available when the electrical switching apparatus will be requested to close. Thus, the proposed solution decreases significantly mechanical shock generated during tripping of electrical switching apparatus, reduces noise and extends mechanical life due to reduced material fatigue. The damping element is not intended to provide a permanent separation between the armature and the actuator housing, as in the second position the armature preferably tangentially contacts the lower inner housing surface. Thus, the damping element dissipates energy when the armature moves into the second position, whereby the damping element becomes in particular fully compressed. With a metallic actuator housing magnetic latching can be achieved in said second position. In result electrical switching apparatus lifetime is significantly extended.

[0009] The actuator housing may be made of metal and/or may comprise a closed tube-like and/or cylinder-like shape, in particular with openings only at deck surfaces for a rod and/or a stem mentioned below. The upper inner housing surface and/or the lower inner housing surface may thus be defined by an inner deck surface of the cylinder. The armature may also comprise a respective closed tube-like and/or cylinder-like shape, in particular sharing the axis of the actuator housing. The term that the armature in the first position contacts the upper inner housing surface and in the second position contacts the lower inner housing surface means preferably that at least a part of a deck surface of the armature contacts the respective inner housing surface in a touching manner. Thereby, in the second position, preferably at least a part of the deck surface of the armature contacts the lower inner housing surface, for example 10, 20, 30 or 50% of the deck surface of the armature facing the lower inner housing surface.

[0010] The armature can be understood as an electrically conducting member of which a part is adjacent to the electromagnetic coil such that the armature is subject to a repulsive force upon application of a current pulse to the electromagnetic coil. The current pulse in the electromagnetic coil generates a varying magnetic flux, which in turn generates a current with opposite direction in the armature, which generates a magnetic force between the electromagnetic coil and the armature for effecting movement of the armature relatively to the electromagnetic coil. The armature may comprise a continuous aluminium body, since aluminium has a relatively good conductivity and also a relatively light but robust structure.

[0011] Ferromagnetic material means that the material comprises a kind of magnetism that is associated with materials such as for example iron, cobalt, nickel, and some alloys or compounds containing one or more of these elements. The at least one electromagnetic coil may radially surround the armature such that, when a current is applied to the least one electromagnetic coil, the armature is axially moved within the actuator housing from the first position into the second position. The damping element may be provided as a flat pad, may be permanently attached to the bottom end of the armature or to the lower inner housing surface and/or may comprise a round diameter extending around the longitudinal axis.

[0012] According to a preferred implementation the bottom end of the armature or the lower inner housing surface comprises a recess and the damping element is provided in the recess. The recess may be provided as an opening, as a cavity, as a gap and/or as a notch, in which the damping element is arranged. Thereby, the recess preferably comprises an axial depth smaller than an axial extension of the damping element. In other words, the recess is preferably dimensioned such that the damping element axially overtops the recess.

[0013] In another preferred implementation the recess extends ring-like, rectange-like or square-like around the longitudinal axis. The recess may comprise a shape in a form of a flat washer. The recess may comprise an axial depth or 2, 5, 10 or 20 mm, with a width being 2, 5 or 10 times the depth. The recess may comprise, in a side view, a rectangle-like shape, a V-shape or a rounded shape.

[0014] According to a further preferred implementation the recess comprises a radially extending surface smaller than a radially extending surface of the bottom end of the armature. In other words, the recess is preferably smaller in size than the bottom end of the armature so that in the second position at least a part of the armature contacts the lower inner housing surface. Preferably, the radially extending surface of the recess is 50, 70, 80 or 90% of the radially extending surface of the bottom end of the armature. Such way on one hand it can be ensured that the damping element sufficiently decelerates a movement of the armature from the first position into the second position, while on the other hand in the second position the armature reliably contacts the actuator housing.

[0015] In another preferred implementation at least a part of the bottom end or the lower inner housing surface is provided damping element-free and, in the second position, the damping element-free part tangentially contacts the lower inner housing surface or the bottom end. In other words, it is preferred that at least the damping element-free part, in the second position, is in preferably touching contact between the armature and the lower inner housing surface. In even other words, at the damping element-free part no damping element is present. The part preferably extends radially. The part may have a ring-like or square-like shape extending around the damping element. The part may have the same outer form as the axial side of the armature.

[0016] Generally, the damping element may be provided as any kind of shock absorber for converting kinetic energy of the moving armature into another form of energy. According to a further preferred implementation the damping element comprises a pad made of compressible porous material. The damping element and/or the pad may comprise an axial thickness of 0.2, 0.5, 1, 2, 5 or 10 cm. The damping element may consist of a microcellular foam, such as for example urethane foam, a viscoelastic PUR-material, nitrile, polyurethane, polyvinyl chloride, rubber or a combination thereof.

[0017] In another preferred implementation the damping element comprises a foamed EPDM and/or rubber elastomeric material, in particular with closed or open structures filled with air. EPDM, ethylene propylene diene monomer rubber, is usually known as a type of synthetic rubber comprises elastomers having a saturated chain of the polyethylene type. EPDM is typically made from ethylene, propylene, and a diene comonomer that enables crosslinking via sulfur vulcanization, and often has a hardness, Shore A, between 30 to 90. Rubber is typically referred to a material consisting of polymers of an organic compound isoprene, with minor impurities of other organic compounds.

[0018] According to a further preferred implementation the electromagnetic actuator comprises two electromagnetic coils arranged axially distant to each other. Thereby, the coil adjacent to the damping element can be referred to as open and/or trip coil, as said coil is intended for opening the electrical switching apparatus. The other coil can be referred to as closing coil being intended for closing the electrical switching apparatus. The respective coil is preferably arranged such that, exemplary to the open and/or trip coil, in the first position the open and/or trip coil and the armature axially only slightly overlap, while in the second position the armature axially preferably fully overlaps the open and/or trip coil. The coils preferably circumferentially extends around a lateral surface of the armature.

[0019] In another preferred implementation the electromagnetic actuator comprises a permanent magnet coaxially arranged within the actuator housing in respect to and for actuating the armature and arranged axially distant to the at least one electromagnetic coil. Said at least one electromagnetic coil and/or permanent magnet are intended for driving the armature and subsequently a movable contact connectable to the armature as described below for closing and tripping the electrical switching apparatus. The at least one electromagnetic coil and/or permanent magnet are preferably designed such that the actuator provide high reliability and fast operation with armature and/or movable contact speeds reaching at least 1m/s. On the other side the damping element is preferably designed to effectively damp and/or decelerate such speeds thereby avoiding noise and/or vibrations.

[0020] In another preferred implementation the electromagnetic actuator comprises a connecting rod extending along the longitudinal axis, fixed to the armature and configured for moving a moveable contact of the electrical switching apparatus in order to open and close the electrical switching apparatus. In a further preferred implementation, the electromagnetic actuator comprises an overtravel spring axially connected to the connecting rod and configured for connecting the movable contact. Such way the overtravel spring is preferably connected in between the connecting rod and the movable contact in axial extension of the connecting rod. For close operation the connecting rod, also referred to as drive rod, can be equipped with such overtravel spring which role is to maintain contacts pressure and assists in building up opening speed for faster contact separation for electric current breaking. Additionally, the overtravel spring can work as a bumper reducing mechanical stresses on mechanical components of the electrical switching apparatus.

[0021] In another preferred implementation the electromagnetic actuator comprises a stem extending along the longitudinal axis such that the armature is arranged between the stem and the connecting rod. The stem is preferably fixed to the armature and/or extends in parallel to the connecting rod. The connecting rod and/or the stem may axially extend through an opening within the upper inner housing surface and/or the lower inner housing surface of the actuator housing. In another preferred implementation the electromagnetic actuator comprises a trip assisting spring arranged between the stem and the actuator housing. Said trip assisting spring is preferably connected with one end to the actuator housing and with and never opposite end to an end of the stem facing away from the armature.

[0022] The object is further solved by an electrical switching apparatus comprising a fixed contact, a movable contact and the electromagnetic actuator as described before, whereby the armature is connected to the movable contact in order to open and close the electrical switching apparatus. In another preferred implementation the electrical switching apparatus is provided as medium voltage circuit breaker, recloser, switch or contactor. The term medium voltage is preferably understood as 1 and 50 kV or lower than 72 kV AC and 100 kV DC. So-called protection devices, typically circuit breakers, are basically suitable for carrying, for a specified time, and breaking currents under specified abnormal circuit conditions, namely short circuits. So called maneuvering switching devices, such as contactors, are capable of making, carrying and breaking currents under normal circuit conditions including overload conditions. Such contactors are widely used for example to switch on/off electric motors, are required to satisfy a number of conditions which are important to guarantee the proper functional performances during their service life in electrical networks.

Brief description of drawings

[0023] These and other aspects of the invention will be apparent from and elucidated with reference to the implementations described hereinafter.

[0024] In the drawings:

Fig. 1 shows an electromagnetic actuator for an electrical switching apparatus with three different axial positions of an armature in a schematic sectional view according to a preferred implementation,

Fig. 2 shows the electromagnetic actuator for the electrical switching apparatus with three different axial positions of the armature in the schematic sectional view according to a further preferred implementation, and

Fig. 3 shows the electromagnetic actuator for the electrical switching apparatus with three different axial positions of the armature in the schematic sectional view according to an even further preferred implementation.

Description of implementations

[0025] Figs. 1 to 3 each show an electromagnetic actuator 1 for an electrical switching apparatus 2, only partially shown, with three different axial positions of an armature 3 made of a ferromagnetic material in a schematic sectional view according to different implementation. The electrical switching apparatus 2 is provided as medium voltage circuit breaker, recloser, switch or contactor.

[0026] The electromagnetic actuator 1 is part of electrical switching apparatus 2, which comprises a two current carrying contacts, namely a fixed contact part 4 and a movable contact part 5. A connecting respectively pull rod 6 connects the movable contact 5 via an overtravel spring 7 to the actuator 1 in order to open and close the electrical switching apparatus 2. The pull rod 6 is made of an electrically insulating material in order to electrically insulate the contacts 4, 5 from the actuator 1.

[0027] The actuator 1 comprises a tube-like actuator housing 8 surrounding the tube-like armature 3 and defining a longitudinal axis 9. The actuator housing 8 has two axial openings along the longitudinal axis 9, one upper opening where the pull rod 6 extends along the longitudinal axis through the actuator housing 8 being connected to an upper axial end of the armature 3 and one lower opening where a stem 10 extends along the longitudinal axis through the actuator housing 8 being connected to a lower axial end of the armature 3.

[0028] The actuator 1 further comprises at least one electromagnetic coil 11, 12 arranged within the actuator housing 8 coaxially in respect to the armature 3. The actuator 1 of Figs. 1 and 2 comprise one electromagnetic coil 11 arranged close to a lower inner housing surface 13 of the actuator housing 8, whereby the actuator 1 of Fig. 3 comprises two electromagnetic coils 11, 12 arranged axially distant to each other. Axially between and distant to the two electromagnetic coils 11, 12 a permanent magnet 14 is coaxially arranged within the actuator housing 8 in respect to the armature 3.

[0029] The armature 3 is axially movable along the longitudinal axis 9 between a first position, shown in Figs. 1 to 3 in the left, and a second position, shown in Figs. 1 to 3 in the right. In the first position the movable contact 5 electrically contacts the fixed contact 4 and the overtravel spring 7 is compressed, while the armature 3 tangentially contacts an upper inner housing surface 15 of the actuator housing 8.

[0030] In the second position the movable contact 5 does not electrically contact the fixed contact 4 and the overtravel spring 7 is expanded, while the armature 3 tangentially contacts the lower inner housing surface 13 of the actuator housing 8. In a middle position, shown in Figs. 1 to 3 in the middle, the movable contact 5 still electrically contacts the fixed contact 4, while the overtravel spring 7 becomes expanded as the armature 3 is not in contact anymore with the upper inner housing surface 15, but also not yet in contact with the lower inner housing surface 13.

[0031] The actuator 1 further comprises a damping element 16, which is attached in Fig. 1 to the lower inner housing surface 13 thereby facing a bottom end of the armature 3. In Figs. 2 and 3 the damping element 16 is attached to the bottom end of the armature 3 thereby facing the lower inner housing surface 13. The damping element 16 comprises a ring-like radially extending shape arranged around the stem 10 respectively the longitudinal axis 9. Thereby a radially extending surface of the damping element 16 is smaller than a radially extending surface of the bottom end of the armature 3. The damping element 16 is provided as a pad made of compressible porous material, such as a foamed EPDM and/or rubber elastomeric material with closed or open structures filled with air. A trip assisting spring 19 is arranged in Figs. 1 and 2 between the stem 10 and the actuator housing 8, whereby the trip assisting spring 19 is most compressed in the first position and expanded in the second position.

[0032] In Fig. 1 the lower inner housing surface 13 and in Figs. 2 and 3 the bottom end is provided with a radially extending recess 17 having a ring-like shape. The damping element 16 is provided in the recess such that the damping element 16, as shown in Figs. 1 to 3 in the left and in the middle, overtop the recess 17. During a tripping operation, i.e. when the armature 3 moves from the first position shown in the left to the right position shown in the right, moving mass kinetic energy compresses the damping element 16 until the armature 3 rests touching on the lower inner housing surface 13. Therefore, at least a part 18 of the bottom end or of the lower inner housing surface 13 is provided damping element-free so that, in the second position, the damping element-free part 18 tangentially contacts lower inner housing surface 13 or the bottom end of the armature 3.

[0033] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed implementations. Other variations to be disclosed implementations can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

Reference signs list

[0034] 

1

electrical vehicle

2

electrical switching apparatus

3

armature

4

fixed contact

5

movable contact

6

connecting rod

7

overtravel spring

8

actuator housing

9

longitudinal axis

10

stem

11

electromagnetic coil

12

electromagnetic coil

13

lower inner housing surface

14

permanent magnet

15

upper inner housing surface

16

damping element

17

recess

18

part

19

trip assisting spring

Claims

1. An electromagnetic actuator (1) for an electrical switching apparatus (2), the electromagnetic actuator (1) comprising

an actuator housing (8) defining a longitudinal axis (9) and having an upper inner housing surface (15) and a lower inner housing surface (13),

an armature (3) comprising ferromagnetic material and arranged within the actuator housing (8) axially movable between a first position and a second position, whereby the armature (3) in the first position contacts the upper inner housing surface (15) and in the second position contacts the lower inner housing surface (13),

at least one electromagnetic coil (10, 11) coaxially arranged within the actuator housing (8) in respect to and for actuating the armature (3), and

a damping element (16) arranged on a bottom end of the armature (3) facing the lower inner housing surface (13) or arranged on the lower inner housing surface (13) facing the bottom end of the armature (3).

2. The electromagnetic actuator (1) according to the previous claim, whereby the bottom end of the armature (3) or the lower inner housing surface (13) comprises a recess (17) and the damping element (16) is provided in the recess (17).

3. The electromagnetic actuator (1) according to the previous claim, whereby the recess (17) extends ring-like or square-like around the longitudinal axis (9).

4. The electromagnetic actuator (1) according to any of the two previous claims, whereby the recess (17) comprises a radially extending surface smaller than a radially extending surface of the bottom end of the armature (3).

5. The electromagnetic actuator (1) according to any of the previous claims, whereby at least a part (18) of the bottom end or the lower inner housing surface (13) is provided damping element-free and, in the second position, the damping element-free part (18) tangentially contacts lower inner housing surface (13) or the bottom end.

6. The electromagnetic actuator (1) according to any of the previous claims, whereby the damping element (16) comprises a pad made of compressible porous material.

7. The electromagnetic actuator (1) according to any of the previous claims, whereby the damping element (16) comprises a foamed EPDM and/or rubber elastomeric material, in particular with closed or open structures filled with air.

8. The electromagnetic actuator (1) according to any of the previous claims, comprising two electromagnetic coils (10, 11) arranged axially distant to each other.

9. The electromagnetic actuator (1) according to any of the previous claims, comprising a permanent magnet (14) coaxially arranged within the actuator housing (8) in respect to and for actuating the armature (3) and arranged axially distant to the at least one electromagnetic coil (10, 11).

10. The electromagnetic actuator (1) according to any of the previous claims, comprising a connecting rod (6) extending along the longitudinal axis (9), fixed to the armature (3) and configured for moving a moveable contact (5) of the electrical switching apparatus (2) in order to open and close the electrical switching apparatus (2).

11. The electromagnetic actuator (1) according to the previous claim, comprising an overtravel spring (7) axially connected to the connecting rod (6) and configured for connecting the movable contact (5).

12. The electromagnetic actuator (1) according to any of the previous two claims, comprising a stem (10) extending along the longitudinal axis (9) such that the armature (3) is arranged between the stem (10) and the connecting rod (6).

13. The electromagnetic actuator (1) according to the previous claim, comprising a trip assisting spring (19) arranged between the stem (10) and the actuator housing (8).

14. An electrical switching apparatus (2) comprising a fixed contact (4), a movable contact (5) and the electromagnetic actuator (1) according to any of the previous claims, whereby the armature (3) is connected to the movable contact (5) stem in order to open and close the electrical switching apparatus (2).

15. The electrical switching apparatus (2) according to the previous claim, whereby the electrical switching apparatus (2) is provided as medium voltage circuit breaker, recloser, switch or contactor.

Drawing