WO2013164027A1

WO2013164027A1 - Electrical switch and electromagnetic assembly therefor

Info

Publication number: WO2013164027A1
Application number: PCT/EP2012/058109
Authority: WO
Inventors: Waseem MOHAMMAD; Vikalp SAXENA; Vikrant Jain
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-05-03
Filing date: 2012-05-03
Publication date: 2013-11-07

Abstract

Electrical switch and electromagnetic assembly therefor The present invention discloses an electromagnetic assembly (100) suitable for use with an electrical switch (200). The electromagnetic assembly (100) includes a yoke (104), an excitation coil (106), and an armature (108). The excitation coil (106) is mounted on said yoke (104), and is configured for establishing a magnetic flux through said yoke (104). The armature (108) is mounted on a clapper (110), which is configured for pivotal movement about a pivot axis (P) such as to move said armature (108) between an unactuated position and an actuated position relative to said yoke (104).

Description

Electrical switch and electromagnetic assembly therefor The present invention relates to an electrical switch used for opening and closing an electrically conductive path between an electric supply and an electric load. In

particular, the present invention relates to an

electromagnetic assembly suitable for operating such an electrical switch.

In conventional electrical switches, a set of movable

contacts is displaced relative to a set of stationary

contacts to establish or interrupt an electrically-conductive path between supply-side and load-side stationary contacts. The supply-side and load side stationary contacts are

connected to an electrical supply and an electrical load respectively. An electromagnetic assembly is included to provide a driving force such as to cause desired displacement of the movable contacts from an open position to a closed position to operate the electrical switch.

A typical electromagnetic assembly includes a magnet frame, which includes a stationary portion referred to as 'yoke' and a movable portion referred to as 'armature' (sometimes also referred to as 'anker' ) . The yoke and the armature have complementary construction with air gaps in between

confronting ends. The yoke is associated with an excitation coil, which is energized to establish magnetic flux through the yoke and consequently, through the armature such that the armature moves towards the yoke under the influence of magnetic force. The armature of the electromagnetic assembly is coupled to a carrier assembly supporting the movable contacts. The movement of the armature from an unactuated position to an actuated position provides a driving force to displace the carrier assembly from an open position to a closed position thereof. During a closing stroke, the electromagnetic assembly

provides driving force to the carrier assembly such that the movable contacts are displaced from the open position to the closed position. During the closing stroke, the

electromagnetic assembly must initially overcome impeding force of biasing springs, which bias the carrier assembly towards the open position thereof. As the carrier assembly is displaced further, at a point during the closing stroke, the movable contacts come into an initial engagement with the stationary contacts, and subsequently, contact springs, which bias the movable contacts against the carrier assembly, also start resisting further displacement of the carrier assembly during the closing stroke. Thus, subsequent to initial contact engagement, the electromagnetic assembly must

overcome combined impeding forces of biasing springs and contact springs. Hence, the electromagnetic assembly should be capable of exerting correspondingly higher driving force thereafter. Also, the electromagnetic assembly is required to exert a linearly increasing driving force until the carrier assembly finally reaches the closed position.

When the carrier assembly is in the closed position, the corresponding position of the electromagnetic assembly is referred to as the actuated position. The driving force provided by electromagnetic assembly in the actuated position has influence on temperature rise of the movable contacts. It is observed that for a given construction, increase in temperature varies inversely with respect to increase in contact force between the stationary and the movable

contacts. Thus, it is desirable to achieve an electromagnetic assembly design in which high driving force is provided during the actuated position.

In the prior art, one of the approaches is to use large-sized electromagnetic assemblies to achieve higher driving force during the actuated position. However, such designs adversely impact compactness of the electrical switch. Moreover, such electromagnetic assemblies are prone to high power losses during the actuated position due to high demand of excitation current .

Another approach is to use clapper arrangements, such as that disclosed in US 3,525,059. While such clapper arrangements ensure desirable high contact force during the actuated position, the force versus air-gap characteristics, in such designs with pivotally-mounted armature, are not

satisfactory. In electromagnetic assemblies based on such designs, the armature contacts various portions of the yoke at different time instants leading to very undesirable force versus air-gap characteristics.

In light of the above, there is a need for an improved electromagnetic assembly for use in electrical switches. It is desirable that the improved electromagnetic assembly should provide high driving force in the actuated position such as to ensure high contact force between the stationary and the movable contacts, and yet be compact and energy efficient.

Accordingly, an object of the present invention is to provide an electromagnetic assembly suitable for use in electrical switches such that the electromagnetic assembly is effective, compact, and energy efficient.

The object of the present invention is achieved by an

electromagnetic assembly according to claim 1 and an

electrical switch according to claim 6. Further embodiments of the present invention are addressed in the dependent claims .

In accordance with the aforementioned object, an

electromagnetic assembly suitable for use with an electrical switch is provided. The electrical switch comprises at least one pair of stationary contacts, and at least one carrier assembly, which supports at least one movable contact

thereon. The carrier assembly is displaceable between an open position and a closed position. The electromagnetic assembly comprises a yoke, an excitation coil, and an armature. The yoke is mounted on a stationary base and comprises a set of pole legs. The excitation coil is mounted on the yoke, and is configured for establishing a magnetic flux through the yoke based on circulation of an excitation current through the excitation coil. The armature is configured for providing a return path to the magnetic flux. The armature is mounted on a clapper, which is configured for pivotal movement about a pivot axis such as to move the armature between an unactuated position and an actuated position relative to the yoke. The armature moves between the unactuated position and the actuated position such that a radial orientation of the armature relative to the pivot axis remains substantially constant. Further, the yoke and the armature are arranged such that when the armature moves from the unactuated

position to the actuated position, the armature symmetrically engages each pole leg. The present invention provides an electromagnetic assembly based on a clapper design which is configured to provide desirable force versus air-gap characteristics. The

electromagnetic assembly of the present invention also provides high contact force during an actuated position with minimum energy consumption. Further, the electromagnetic assembly of the present invention is highly compact. Thus, the electromagnetic assembly of the present invention is effective, efficient, and compact. In accordance with an embodiment of the present invention, the yoke and the armature are arranged such that a first longitudinal plane corresponding to a path of the magnetic flux through the yoke, and a second longitudinal plane corresponding to the return path of the magnetic flux through the armature are parallel to the pivot axis. According to this technical feature the yoke and the armature are arranged such that during movement towards the actuated position, the armature engages the yoke in a symmetric manner, and hence, the electromagnetic assembly provides desired force versus air-gap characteristics.

In accordance with another embodiment of the present

invention, the yoke is substantially E-shaped such that the yoke comprises three pole legs, and two cross-legs

interconnecting the pole legs, wherein the excitation coil is mounted on middle pole leg. In accordance with another embodiment of the present

invention, the base comprises one or more support arms and the clapper comprises one or more pivoting arms. The pivoting arms are configured for pivotally engaging the support arms. According to this technical feature, the clapper is engaged with the base in pivotal manner.

In accordance with another embodiment of the present

invention, the clapper comprises one or more coupling arms configured for engaging the carrier assembly such that pivotal movement of the clapper from the unactuated position to the actuated position displaces the carrier assembly from the open position to the closed position thereof. According to this technical feature, the clapper is configured to operate the electrical switch in a desired manner.

In accordance with another embodiment of the present

invention, an electrical switch comprising the

electromagnetic assembly, as described above, is provided. The present invention is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawings, in which:

FIGS 1A-1D illustrate a perspective view, two side views, and a partial cross-sectional view respectively of an electromagnetic assembly in accordance with an embodiment of the present invention, FIG 2 illustrates a partially cut-away perspective view of an electrical switch in accordance with an embodiment of the present invention, and FIG 3 illustrates a graphical representation of force versus air-gap characteristics of three

electromagnetic assemblies.

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details.

FIGS 1A through ID illustrate a perspective view, two side views, and a partial cross-sectional view respectively of an electromagnetic assembly 100 in accordance with an embodiment of the present invention.

The electromagnetic assembly 100 comprises a stationary base 102, a yoke 104, an excitation coil 106, an armature 108, and a clapper 110. The clapper 110 includes one or more pivoting arms 112 and one or more coupling arms 114. The pivoting arms 112 include one or more coupling slots 116 and the coupling arms 114 include one or more coupling slots 118. The base 102 includes one or more support arms 120. The clapper 110 is pivotally coupled to the support arms 112 extending from the base 102 using a pivoting rod 122. The clapper 110 is coupled to a carrier assembly (not shown) of an electrical switch (not shown) through a coupling rod 124.

The yoke 104 is mounted on the base 102. It should be noted that when electromagnetic assembly 100 is integrated with the electrical switch, as will be discussed in conjunction with FIG 2, the base 102 is an optional element, that is to say, a part of housing of the electrical switch may serve as the base 102 and various constituent elements of the

electromagnetic assembly 100, other than the base 102, may be directly assembled on such part, in the manner as described herein .

The yoke 104 includes a set of pole legs (PI, P2, and P3) , as shown in the adjoining figures. In the exemplary embodiment depicted in the adjoining figures, the yoke 104 is

substantially E-shaped such that the yoke 104 includes three pole legs (PI, P2, and P3) , and two cross-legs (CI and C2). The cross-legs (CI and C2) interconnect the pole legs (PI, P2, and P3) . The excitation coil 106 is mounted on middle pole leg (P2) . Thus, the yoke 104 provides mechanical support for excitation coil 106 and also, serves to intensify a magnetic flux established by the excitation coil 106. In various embodiments of the present invention, the yoke 104 is manufactured using any suitable ferromagnetic material and has a laminar construction, as known in the art.

It should be noted that the particular design of the yoke 104, as mentioned above constitutes only one embodiment of the present invention. In various alternative embodiments of the present invention, the yoke 104 may be constructed based on any suitable design known in the art. In one example, the yoke 104 is substantially U-shaped such that the yoke 104 comprises only two pole legs, and one cross-leg

interconnecting the pole legs. In this example, the

excitation coil 106 is mounted on each pole leg.

As described above, the excitation coil 106 is mounted on the yoke 104. The excitation coil 106 is configured for

establishing a magnetic flux through the yoke 104 based on circulation of an excitation current through the excitation coil 104. The path of magnetic flux through the yoke 104 is best depicted through the dashed lines passing there-through in FIG ID. A control unit (not shown) is provided for switching the excitation current through the excitation coil 106.

The armature 108 is configured for providing a return path to the magnetic flux established in the yoke 104. The path of magnetic flux through the armature 108 is best depicted through the dashed lines passing there-through in FIG ID. The armature 108 is mounted on the clapper 110. The clapper 110 includes the pivoting arms 112 and the coupling arms 114. Each of the pivoting arms 112 and the coupling arms 114 include coupling slots 116 and 118

respectively. The pivoting arms 112 pivotally couple the clapper 110 to the support arms 112 extending from the base 102 through a pivoting rod 122. Thus, the clapper 110 is engaged with the base 102 in a pivotal manner. The coupling arms 114 engage the carrier assembly (not shown) through the coupling rod 124 such that the pivotal movement of the clapper 110 from the unactuated position to the actuated position displaces the carrier assembly from the open

position to the closed position thereof. Thus, the coupling arms 114 operatively couple the clapper 110 to the carrier assembly of the electrical switch. This feature will be explained more in conjunction with FIG 2.

The operation of the electromagnetic assembly 100 will now be briefly explained.

The excitation coil 106 is configured to provide a magneto- motive force to establish a magnetic circuit through the yoke 104 and the armature 108. The armature 108 is configured to provide an actuating force to the carrier assembly of the electrical switch. The magneto-motive force is provided in response to application of an excitation current to the excitation coil 106. Thus, a magnetic flux is established in the yoke 104. The armature 108 serves to complete the

magnetic circuit by providing the return path to the magnetic flux in the yoke 304. In absence of the excitation current, the armature 108 is separated from the yoke 104 due to biasing means, described in conjunction with FIG 2. This position of the armature 108 is referred to as the unactuated position, as shown in FIG

IB. As the excitation current is applied, due to formation of magnetic flux through the yoke 104, the armature 108 is magnetically pulled towards the yoke 104, and consequently, the armature 108 moves towards the yoke 104, until the armature 108 clacks onto the yoke 104. This position of the armature 108 is referred to as the actuated position, as shown in FIG 1C.

As the carrier assembly is coupled to the clapper 110 through coupling arms 114, the movement of the clapper 110 causes a corresponding displacement of the carrier assembly from an open position to a closed position.

As understood from the preceding description, the clapper 110 is configured for pivotal movement about a pivot axis (P) such as to move the armature 108 between the unactuated position, as shown in FIG IB, and the actuated position, as shown in FIG 1C, relative to the yoke 104. As the armature 108 is rigidly mounted on the clapper 110, which undergoes pivotal motion about the pivot axis (P) , the radial orientation of the armature 108 with respect to the pivot axis (P) remains substantially constant. As shown in FIG IB, in the unactuated position, the armature 108 is oriented such that a longitudinal axis L thereof is at an angle Θ with respect to radial direction Rl . Similarly, as shown in FIG 1C, in the actuated position, the armature 108 is oriented such that a longitudinal axis L thereof is at the same angle Θ with respect to radial direction R2. Therefore, as apparent from FIGS IB and 1C, the armature 108 moves between the unactuated position and the actuated position such that the radial orientation of the armature 108 relative to the pivot axis (P) remains substantially constant.

In accordance with an important technical feature of the present invention, the yoke 104 and the armature 108 are so arranged that when the armature 108 moves from the unactuated position to the actuated position, the armature 108

symmetrically engages each pole legs (PI, P2, and P3) . In particular, as evident from adjoining figures, a first longitudinal plane (x-z plane) , corresponding to the cross- sectional plane shown in FIG ID, which includes the path of the magnetic flux through the yoke 104 is parallel to the pivot axis (P) . Similarly, a second longitudinal plane (x-z plane) , corresponding to the cross-sectional plane shown in FIG ID, which includes the return path of the magnetic flux through the armature 104 is also parallel to the pivot axis (P) . As the radial orientation of the armature 108 remains substantially constant during the pivotal movement from the unactuated to the actuated position, the second longitudinal plane also remains parallel to the pivot axis (P) at all times .

Due to the arrangement described above, the yoke 104 and the armature 108 are arranged such that during movement towards from the unactuated position to the actuated position, the armature 108 engages the yoke 104, in particular, the pole legs (PI, P2, and P3) in a symmetric manner, that is to say, at substantially same time instant. This, in turn,

advantageously leads to desirable force versus air-gap characteristics. The force versus air-gap characteristics of the electromagnetic assembly 100 will be described in

conjunction with FIG 3. It should be further understood that due to inherent

characteristics of a clapper arrangement, the electromagnetic assembly 100 advantageously provides a high contact force during the actuated position while requiring minimum energy consumption. Also, the clapper-based design advantageously aids in achieving a more compact form factor for the

electromagnetic assembly 100. FIG 2 illustrates a partially cut-away perspective view of an electrical switch 200 in accordance with an embodiment of the present invention.

The electrical switch 200 includes a set of pairs of

stationary contacts 202 and a set of movable contacts 204.

The movable contacts 204 are supported on a carrier assembly 206. The carrier assembly 206 is displaceable between an open position and a closed position. The electrical switch 200 also includes a mid-cover 208 and biasing means 210. In addition, the electrical switch 200 includes the

electromagnetic assembly 100, described in conjunction with the preceding figures.

The set of stationary and movable contacts 202, 204 are enclosed in a housing, which includes a mid-cover 208. The housing, except for the mid-cover 208, is not shown in the adjoining figure. The mid-cover 208 provides physical and electrical isolation of various constituent elements enclosed therein. In the example shown in the adjoining figure, the electromagnetic assembly 100 is mounted on the mid-cover 208, and is coupled to the carrier assembly 206. Thus, the mid- cover 208 serves as the base 102, described in conjunction with the preceding figures. It should be noted that the number of pairs of stationary contacts 202, a corresponding number of movable contacts 204, included in the electrical switch 200 may be varied as desired . As well-known in the art, the carrier assembly 206 is

dispaceable between an open position and a closed position for respectively opening and closing an electrically- conductive path between an electrical supply and an electrical load (not shown in the figure) . The

electromagnetic assembly 200 provides an actuating force to effect displacement of the carrier assembly 206 for opening and closing the electrically-conductive paths through the electrical switch 200.

As shown in adjoining figure, the coupling arms 114 of the clapper 110 are coupled to the carrier assembly 206 through a connecting rod 124.

The electrical switch 200 includes biasing means 210 that bias the electromagnetic assembly 100 and the carrier

assembly towards an unactuated position. In case the

electrical switch 200 is normally-open, the carrier assembly 206 is an open position when the electromagnetic assembly 100 is in the unactuated position. Similarly, in case the

electrical switch 200 is normally-closed, the carrier

assembly 206 is a closed position when the electromagnetic assembly 100 is in the unactuated position.

It should be noted that the electrical switch 200, as

described herein, is a normally-open electrical switch.

However, various embodiment of the present invention are equally applicable to normally-closed electrical switch with appropriate modification in the relative positions of the stationary and the movable contacts, as will be apparent to a person ordinarily skilled in the art.

In accordance with the exemplary embodiment of the present invention as shown in the adjoining figure, the biasing springs 210 engage the coupling arms 114 of the

electromagnetic assembly 100. In various alternative

embodiments of the present invention, it is possible to couple the biasing springs 210 with other movable components of the electrical switch 200, such as the carrier assembly 206. The operation of the electrical switch 200 will now be briefly explained.

In order to switch-on the electrical switch 200, an

excitation current is applied to the excitation coil 106.

When the excitation current is applied to the excitation coil 106, a magnetic flux is established. Subsequent to

application of the magnetic flux, the armature 108, along with the clapper 110, of the electromagnetic assembly 100 undergo pivotal movement about the pivot axis (P) and

accordingly, the carrier assembly 206 undergoes a movement in a first direction. As a result, the movable contacts 204 come in contact with the respective pairs of stationary contacts 202, thereby establishing an electrically-conductive path between the two stationary contacts in each pair of

stationary contacts 202.

Subsequently, in order to switch off the electrical switch 200, the excitation current in the excitation coil 106 is removed. The biasing means 210 will cause movement of the clapper 110 of the electromagnetic assembly 100, and hence, the carrier assembly 206 in a second direction, which is substantially opposite to the first direction. As a result, the electrically-conductive path between the two stationary contacts in each pair of stationary contacts 202 is

interrupted .

FIG 3 illustrates a graphical representation of force versus air-gap characteristics of three electromagnetic assemblies.

The curve A provides variation of an impeding force created due to movement of the electromagnetic assembly 100 from the unactuated position to the actuated position. The x-axis denotes the displacement of a carrier assembly within an electrical switch. The y-axis denotes magnitude of force.

As well-known in the art, the impeding force is created due to action of biasing means and contact springs. As explained earlier, the biasing means bias a carrier assembly towards an unactuated position. The contact springs are included within the carrier assembly to bias movable contacts against the carrier assembly. The contact springs, ultimately, serve to create required contact force during contact engagement between a set of stationary contacts and corresponding movable contacts.

Thus, curve A essentially depicts the impeding force that an electromagnetic assembly must overcome to operate an

electrical switch. During a closing stroke, the impeding force gradually increases as shown by the portion of curve A between XI and X2. Subsequent to engagement between the stationary and the movable contacts, an abrupt increase in the impeding force occurs, as depicted by curve A in vicinity of X2. Thereafter, the impeding force again increases

linearly for the remaining part of the closing stroke from X2 to X3. The curves B and C correspond to driving forces provided by electromagnetic assemblies based on two exemplary designs available in the state of the art. The curve D corresponds to driving force provided by the electromagnetic assembly 100 of the present invention. The x-axis denotes the displacement of an armature with respect to a yoke within an electromagnetic assembly. The y-axis denotes magnitude of force.

As apparent from the adjoining representation, the driving force does not remain sufficiently strong throughout the closing stroke in case electromagnetic assemblies of the prior art.

On the contrary, the electromagnetic assembly 100 of the present invention provides a driving force that remains sufficiently strong during the entire stroke length. More importantly, a desired final state, in terms of driving force, is achievable over much shorter displacement of the armature relative to the yoke based on the techniques of the present invention. This feature advantageously facilitates a compact design of the electromagnetic assembly 100 of the present invention. The present invention provides an electromagnetic assembly based on a clapper design which is configured to provide desirable force versus air-gap characteristics. The

electromagnetic assembly of the present invention also provides high contact force during an actuated position with minimum energy consumption. Further, the electromagnetic assembly of the present invention is highly compact. Thus, the electromagnetic assembly of the present invention is effective, efficient, and compact. While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those

embodiments. In view of the present disclosure, many

modifications and variations would present themselves, to those of skill in the art without departing from the scope and spirit of this invention. The scope of the present invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

LIST OF REFERENCES

100 ELECTROMAGNETIC ASSEMBLY

102 BASE

104 YOKE

106 EXCITATION COIL

108 ARMATURE

110 CLAPPER

112 PIVOTING ARMS

114 COUPLING ARMS

116 COUPLING SLOTS

118 COUPLING SLOTS

120 SUPPORT ARMS

122 PIVOTING ROD

124 COUPLING ROD

202 stationary contact

204 movable contact

206 carrier assembly

208 mid-cover

210 biasing means

Curve A, B, C, D

Stroke XI, X2, X3

Claims

Claims :

1. An electromagnetic assembly (100) suitable for use with an electrical switch (200), said electrical switch (200) comprising at least one pair of stationary contacts (202), and at least one carrier assembly (206) supporting at least one movable contact (204) thereon, said carrier assembly (206) being displaceable between an open position and a closed position, said electromagnetic assembly (100)

comprising:

- a yoke (104), said yoke (104) being mounted on a

stationary base (102), and said yoke (104) comprising a set of pole legs (PI, P2, P3) ,

- an excitation coil (106), said excitation coil (106) being mounted on said yoke (104), and configured for

establishing a magnetic flux through said yoke (104) based on circulation of an excitation current through said excitation coil (106) , and

- an armature (108), said armature (108) configured for providing a return path to said magnetic flux, said armature (108) being mounted on a clapper (110), said clapper (110) configured for pivotal movement about a pivot axis (P) such as to move said armature (108) between an unactuated position and an actuated position relative to said yoke (104),

said electromagnetic assembly (100) being characterized in that said armature (108) moves between said unactuated position and said actuated position such that a radial orientation of said armature (108) relative to said pivot axis (P) remains substantially constant, and wherein said yoke (104) and said armature (108) are arranged such that when said armature (108) moves from said unactuated position to said actuated position, said armature (108) symmetrically engages each of pole legs (PI, P2, and P3) .

2. The electromagnetic assembly (100) according to claim 1, characterized in that said yoke (104) and said armature (108) are arranged such that a first longitudinal plane (x-z plane) corresponding to a path of said magnetic flux through said yoke (104), and a second longitudinal plane (x-z plane) corresponding to said return path of said magnetic flux through said armature (108) are parallel to said pivot axis (P) .

3. The electromagnetic assembly (100) according to claims 1 or 2, characterized in that said yoke (104) is substantially E-shaped such that said yoke (104) comprises three pole legs (PI, P2, P3) , and two cross-legs (CI, C2) interconnecting said pole legs (PI, P2, P3) , wherein said excitation coil (106) is mounted on middle pole leg (P2) .

4. The electromagnetic assembly (100) according to any of the preceding claims, characterized in that said base (102) comprises one or more support arms (120) and said clapper

(110) comprises one or more pivoting arms (112), wherein said pivoting arms (112) are configured for pivotally engaging said support arms (120) .

5. The electromagnetic assembly (100) according to any of the preceding claims, characterized in that said clapper (110) comprises one or more coupling arms (114) configured for engaging said carrier assembly (206) such that pivotal movement of said clapper (110) from said unactuated position to said actuated position displaces said carrier assembly (206) from said open position to said closed position

thereof .

6. An electrical switch (200) comprising an electromagnetic assembly (100) in accordance with any of the preceding claims .