Electrical switch assembly adapted for electrical loads drawing high transient currents

The present invention generally relates to electrical

switches. More specifically, the present invention relates to an electrical switch assembly adapted for use with electrical loads prone to drawing high transient currents during

switching operations. Still more specifically, the present invention relates to an electrical switch assembly based on an auxiliary switch adapted for use in conjunction with a main switch such that a desired sequence of operating states of said main and said auxiliary switches is achieved during switching operations in a simple yet effective manner.

Electrical switches are employed to establish or interrupt an electrically-conductive path between an electrical supply and an electrical load. In such 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

respectively connected to an electrical supply and an

electrical load.

In a first state of equilibrium, when a movable contact is not in contact with a corresponding pair of stationary contacts, the electrically-conductive path between the electrical supply and the electrical load is interrupted. In this position, the movable contact is said to be in "open position" and the electrical switch is said to be is "open state". On the other hand, in a second state of equilibrium, when the movable contact is in contact with the corresponding pair of stationary contacts, the electrically-conductive path between the electrical supply and the electrical load is established. In this position, the movable contact is said to be in "closed position" and the electrical switch is said to be is "closed state". Thus, an electrical switch is

configured to operate in two distinct operating states - namely, the open state and the closed state. In order to bring the electrical switch from the open state to the closed state, the set of movable contacts are

displaced from an open position to a closed position. This is referred to as "switching-on" operation. Similarly, in order to bring the electrical switch from the closed state to the open state, the movable contacts are displaced from an open position to a closed position. This is referred to as

"switching-off" operation. The switching-on and switching-off operations may be collectively referred to as Switching' operations. The operation of the electrical switch subsequent to the switching-on operation and before initiation of the switching-off operation, wherein the movable contacts is stably in contact with corresponding pairs of stationary contacts, is referred to as a steady-state operation of the electrical switch.

An electrical switch is designed to conduct a rated

electrical current during a steady state operation, which defines an electrical rating thereof, that is, magnitude of an operating current and/or an operating voltage that the electrical switch may be subjected to during the steady state operation. Accordingly, an electrical switch with a suitable electrical rating is selected based on an electrical rating of a particular electrical load required to be connected thereto .

It is well-known in the state-of-the-art that certain

electrical loads, such as capacitive banks, and so on, are prone to drawing high transient currents during switching operations. Such transient currents are much higher than rated currents drawn during a steady-state operation of the electrical switch. In such cases, it is not economically feasible to use an electrical switch that has electrical ratings commensurate to magnitude of transient currents drawn during the switching operations. Hence, it is a common practice to select an electrical switch based on magnitude of rated currents drawn during the steady-state operation, and provide special arrangements to facilitate an alternative high-resistance electrically-conductive path during a

switching operation.

According to one technique known in the art, an auxiliary switch is used in conjunction with a main switch to form a switch assembly. The auxiliary switch is coupled to the main switch using suitable coupling means such that a movable carrier assembly supporting a set of movable contacts in the auxiliary switch is coupled to a movable carrier assembly supporting a set of movable contacts in the main switch. In addition, the supply-side and load-side stationary contacts of the auxiliary switch are respectively connected to

corresponding supply-side and load-side stationary contacts of the main switches through current-limiting resistors. The respective distances between movable contact and

corresponding stationary contact, referred to as respective "contact gaps", in the main and the auxiliary switches are such that during the switching-on operation, the auxiliary switch reaches the closed state prior to the main switch. Thus, the electrical current during the switching operations flows through the current-limiting resistors and the

auxiliary switch.

To ensure satisfactory operation and sufficient operational life of such switch assembly, it is desirable that the auxiliary switch returns to the open state after the main switch reaches the closed state during the switching-on operation such that only the transient current during the switching-on operation flows through the current-limiting resistors, while the transient current during the switching- off operation flows through the main switch.

One such switch assembly is known from EP 0 545 745 Bl . The patent discloses a multi-pole switch device including at least one switch having at least one fixed contact member and a cooperating mobile contact member operated by a mobile assembly, and an operating member adapted to perform a forward and a return stroke to actuate the mobile assembly. The operating member is coupled to the mobile assembly of the switch by a mechanical coupling including a disengageable coupling adapted to assume a disengaged position during the forward travel of the operating member when the resisting force exerted by the mobile assembly rises above a

predetermined threshold and then to return to the engaged position during the return stroke of the operating member. The disengageable coupling is preferably implemented using magnetic coupling means. One of the inherent disadvantages of using magnetic coupling means is reduced precision and reliability of operation due to manufacturing tolerances. Also, the magnetic coupling means in such switch assemblies are subjected to mechanical shocks during operation, which adversely impact corresponding magnetic properties. Furthermore, it is well-known in the art that during operation, high temperatures exist in the

vicinity of stationary and movable contacts. Such high temperatures also adversely affect magnetic properties, and thereby leading to deterioration in performance of such switch assemblies. Moreover, there is easy accumulation of dust on various magnetic surfaces leading to hindrance in effective operation. Thus, such switch assemblies need to be regularly overhauled and also, require replacement of magnets at frequent intervals.

Although some solutions have been proposed in the state of the art to implement a mechanical latching mechanism, such known mechanical latching mechanisms suffer from various disadvantages such as complex mechanical designs based on excessive number of structural elements; and difficult and cumbersome production process leading to undesirable

investment of time and effort, and consequently, high

manufacturing costs. Moreover, due to ageing of various structural elements, such electrical switches suffer from lack of accuracy, high cost of maintenance, and frequent field failures. In light of the foregoing, there is a need for an improved electrical switch adapted for use with electrical loads prone to drawing high transient currents during switching

operations. Such electrical switch should provide sufficient ease of manufacturing and maintenance; and should provide benefit of low rates of field failures.

Accordingly, an object of the present invention is to provide an electrical switch assembly adapted for use with electrical loads prone to drawing high transient currents during

switching operations such that the electrical switch is based on a simple, efficient, and reliable design.

The object of the present invention is achieved by an

electrical switch assembly according to claim 1 and an auxiliary switch according to claim 9. Further embodiments of the present invention are addressed in the dependent claims.

In accordance with a first aspect of the present invention, an electrical switch assembly is provided. The electrical switch assembly comprises at least one housing and at least one carrier assembly. The housing supports at least one pair of main stationary contacts and at least one pair of

auxiliary stationary contacts. The carrier assembly extends along a longitudinal axis and comprises at least a first portion and at least a second portion. The first portion is configured for supporting at least one auxiliary movable contact. The second portion is configured for supporting at least one main movable contact. Each portion is displaceable along the longitudinal axis in a first direction and a second direction. The second direction is substantially opposite to the first direction. The first and the second portions of the carrier assembly are detachably coupled to each other. One of said portions of the carrier assembly comprises a resilient member, wherein at least a portion of the resilient member is resiliently deformable substantially along a transverse axis. The transverse axis is substantially perpendicular to the longitudinal axis. The other of said portions comprises retaining means and triggering means . The retaining means are configured for retaining the resilient member during a coupled state of the carrier assembly. The triggering means are configured for deforming the resilient member to permit release thereof from the retaining means resulting in a decoupled state of the carrier assembly.

Thus, the present invention provides an electrical switch assembly based on a simple, efficient, and reliable design. The electrical switch assembly is configured such that said main and the auxiliary movable contacts contact respective pair of stationary contacts in a desired sequence during a switching-on operation. Further, said auxiliary movable contacts are opened at the end of switching-on operation, thus, ensuring that said main movable contacts interrupt an electrically-conductive path between an electric supply and an electric load during a switching-off operation. The present invention facilitates coupling and decoupling of different portions of the carrier assembly carrying the main and the auxiliary movable carriers in an effective and reliable manner to achieve a desired sequence of operating states of said main and said auxiliary switches during switching operations.

In accordance with an embodiment of the present invention, the retaining means comprise a cavity and a retaining seat. The cavity is suitable for receiving the resilient member therein. The resilient member comprises a mating shoulder suitable for engaging the retaining seat. In accordance with another embodiment of the present

invention, the resilient member is substantially U-shaped, and comprises a first leg and a second leg. The first leg is rigidly coupled to said one portion. The second leg comprises the mating shoulder and is elastically deformable relative to the first leg in a longitudinal plane containing the first and second legs . In accordance with another embodiment of the present

invention, the first and the second portions of the carrier assembly are configured to cooperate in a sliding manner along the longitudinal axis such that the carrier assembly transitions from the decoupled state to the coupled state. According to this technical feature, the carrier assembly achieves a coupled state at the end of switching-off

operation. Thus, the electrical switch assembly becomes suitable to begin next set of switching-on and switching-off operations .

In accordance with another embodiment of the present

invention, the triggering means comprise a trigger arm pivoted about a pivot axis located intermediate between a head-end and a tail-end thereof. The pivot axis is

substantially orthogonal to the longitudinal and the

transverse axes. This technical feature ensures that the triggering means are capable of disengaging the resilient member to permit release thereof from said retaining means. In accordance with another embodiment of the present

invention, the tail-end is configured to engage a portion of the at least one housing while the carrier assembly is displaced along the first direction, such that the trigger arm rotates about the pivot axis and the head-end deforms the resilient member to permit release thereof from the retaining means, whereby the first portion becomes decoupled from the second portion. According to this technical feature, the triggering means release the resilient member through

engaging a portion of the housing of the electrical switch assembly. Thus, this technical feature enables easily

regulating time of decoupling during the switching-off operation, as may be desired, based on position of the portion of the housing of the electrical switch assembly. In accordance with another embodiment of the present

invention, the electrical switch assembly further comprises biasing means coupled to the first portion. The biasing means are configured to bias the first portion in the second direction, such that subsequent to the first portion becoming decoupled from the second portion, the carrier assembly transitions from the coupled state to the decoupled state. Thus, according to this technical feature, the auxiliary movable contact returns to an open state after the main movable contact has effectively achieved a closed state.

In accordance with another embodiment of the present

invention, the carrier assembly transitions from the coupled state to the decoupled state subsequent to contact between each of the movable contacts and corresponding pair of stationary contacts while the first and the second portions are displaced in the first direction. Further, the carrier assembly is configured to transition from the decoupled state to the coupled state while the second portion is displaced towards the first portion in the second direction. This technical feature facilitates achieving a desired sequence of operating states of said main and said auxiliary switches during switching operations.

In according with a second aspect of the present invention, an auxiliary switch is provided. The auxiliary switch is suitable for being operationally coupled to a main switch. The main switch comprises a main housing, which supports at least one pair of main stationary contacts. The main switch further comprises a main carrier assembly, which extends along a longitudinal axis and is configured for supporting at least one main movable contact. The auxiliary switch

comprises an auxiliary housing, which supports at least one pair of auxiliary stationary contacts. The auxiliary switch further comprises an auxiliary carrier assembly, which extends along a longitudinal axis, and comprises at least a first portion configured for supporting at least one auxiliary movable contact; and at least a second portion configured for coupling to the main carrier assembly. Each portion is displaceable in a first direction and a second direction along the longitudinal axis. The second direction is substantially opposite to the first direction. The first and the second portions of the auxiliary carrier assembly are detachably coupled to each other. One of said portions of the auxiliary carrier assembly comprises a resilient member, at least a portion of the resilient member being resiliently deformable substantially along a transverse axis, the

transverse axis being substantially perpendicular to the longitudinal axis. The other of said portions of the

auxiliary carrier assembly comprises retaining means and triggering means . The retaining means are configured for retaining the resilient member during a coupled state of the carrier assembly. The triggering means are configured for deforming the resilient member to permit release thereof from the retaining means resulting in a decoupled state of the carrier assembly.

According to the second aspect of the present invention, the main and the auxiliary switches are independently

manufactured. The auxiliary switch is coupled to the main switch, as and when required. Thus, the second aspect of the present invention provides a modular approach for

manufacturing desired electrical switch assemblies. Various other technical features disclosed in dependent claims with respect to the second aspect of the present invention are similar to those disclosed with respect to the first aspect of the present invention.

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, a first cross- sectional view, a second cross-sectional view, and an exploded view respectively of an electrical switch assembly in accordance with an embodiment of the present invention,

FIGS 2A-2E illustrate a first cross-sectional view of the electrical switch assembly in five different stages during switching-on and switching-off operations in accordance with an embodiment of the present invention, FIGS 3A-3E illustrate a second cross-sectional view of the electrical switch assembly in five different stages during switching-on and switching-off operations in accordance with an embodiment of the present invention, and

FIGS 4A-4B illustrate graphical representations of electric currents and stroke traces respectively, through a main switch and an auxiliary switch in five different stages during switching-on and

switching-off operations in accordance with an embodiment of the present invention.

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.

Referring to FIGS 1A through ID, an electrical switch

assembly 100 is shown, in accordance with a first embodiment of the present invention. FIG 1A illustrates a perspective view of the electrical switch assembly 100. As shown in FIG 1A, the electrical switch assembly 100 includes a main switch 102 and an

auxiliary switch 104. FIG IB shows a first cross-sectional view depicting the electrical switch assembly 100 including the main switch 102 and the auxiliary switch 104 along cross-section B-B

indicated in FIG 1A. FIG 1C shows a second cross-sectional view depicting the auxiliary switch 104 along cross-section C-C indicated in FIG 1A. FIG ID shows an exploded view of the electrical switch assembly 100.

As depicted in adjoining figures, the main switch 102

includes a main housing 106, three pairs of main stationary contacts 108a-108c, a main carrier assembly 110, and three main movable contacts 112a-112c. Similarly, the auxiliary switch 104 includes an auxiliary housing 114, three pairs of auxiliary stationary contacts 116a-116c, an auxiliary carrier assembly 118, and three auxiliary movable contacts 120a-120c. In addition, the auxiliary switch 104 also includes a

projection 132, biasing means 134. The electrical switch assembly 100 includes multiple current-limiting resistors 144.

The main housing 106 supports the three pairs of main

stationary contacts 108 and the main carrier assembly 110. The main carrier assembly 110 extends along a longitudinal axis (z-axis) and is configured to supports the three main movable contacts 112.

In a similar manner, the auxiliary housing 114 supports the three pairs of auxiliary stationary contacts 108 and the auxiliary carrier assembly 118. The auxiliary carrier

assembly 118 extends along a longitudinal axis (z-axis) and is configured to supports the three auxiliary movable

contacts 120. It should be noted that the number of pairs of stationary contacts 108, 116, as mentioned herein are only exemplary in nature. The number of pairs of stationary contacts 108, 116, can be independently selected, as required. Thus, in one example, the number of pairs of main stationary contacts 108 is four while the number of auxiliary stationary contacts 116 is three. The number of movable contacts 112, 120 corresponds respectively to number of stationary contacts 108, 116.

The auxiliary switch 104 will now be described in more detail .

The auxiliary carrier assembly 118 includes a first portion 122 and a second portion 124. The first portion 122 supports the auxiliary movable contacts 120. The second portion 124, interfaces with the first portion 122 at a first end 124a and couples the auxiliary carrier assembly 118 to the main carrier assembly 110 at a second end 124b.

As indicated in the adjoining figure, each of said portions 122, 124 of the auxiliary carrier assembly 118 is

displaceable in a first direction (F) ; and in a second direction (S) along said longitudinal axis (z-axis) . As evident from the figure, the second direction (S) is

substantially opposite to the first direction (F) .

The first and the second portions 122, 124 are adapted to be coupled to and decoupled from each other during different stages of switching-on and switching-off operations of the electrical switch assembly 100. Accordingly, the auxiliary carrier assembly 118 is configured to operate in two distinct states a coupled state and a decoupled state. The first portion 122 includes a resilient member 126. The resilient member 126, in turn, includes a first leg 126a, a second leg 126b and a mating shoulder 136. The second portion 124 includes retaining means 128 and triggering means 130. The retaining means 128 include a cavity 138 and a retaining seat 140. The triggering means 130 include a trigger arm 142, which has a head-end 142a and a tail-end 142b. The first portion 122 includes the resilient member 126 at one end thereof. The resilient member 126 is such that at least a portion of the resilient member 126 is resiliently deformable substantially along a transverse axis (x-axis) . As evident from the figure, the transverse axis (x-axis) is substantially perpendicular to said longitudinal axis.

In one embodiment of the present invention, as depicted in the adjoining figure, the resilient member 126 is

substantially U-shaped such that the resilient member 126 includes the first leg 126a and the second leg 126b

interconnected to each other at one end. The first leg 126a, at the other end thereof, is rigidly coupled to the first portion 122. On the other hand, the second leg 126b, at the other end thereof, is elastically deformable relative to the first leg 126a in a longitudinal plane (x-z plane) containing the first leg 126a and the second leg 126b. Further, the second leg 126b includes the mating shoulder 136. The purpose of the mating shoulder 136 will be explained in detail later in the following description.

It should be noted that while one exemplary construction of the resilient member 126 has been described above, various alternative constructions are readily applicable. For

example, it is possible to construct the resilient member 126 including only one leg, which is rigidly coupled to the first portion 122 at one end, and is resiliently deformable

substantially along the transverse axis (x-axis) at the other end. In this case, the mating shoulder 136 is formed at said other end of said one leg. All such variations of the

resilient member are intended to be covered under the scope of the present invention.

As mentioned earlier, the second portion 124 includes

retaining means 128 and triggering means 130. The retaining means 128 are configured for retaining the resilient member 126 during a coupled state of the auxiliary carrier assembly 118. The triggering means 130 are configured for deforming said resilient member 126 to permit release thereof from the retaining means 128 resulting in a decoupled state of the auxiliary carrier assembly 118. Thus, as evident from the preceding description, one of portions 122, 124 of the auxiliary carrier assembly 118 includes the resilient member 126; and the other of said portions 122, 124 includes the retaining means 128 and triggering means 130.

It should be understood that the present invention may be implemented in an alternative manner such that various technical features related to coupling and decoupling of the first portion 122 and the second portion 124, as described above and as will be described in more detail later, and in particular, the resilient member 126, the retaining means 128, and the triggering means 130, may be implemented in a reverse manner. Thus, in the alternative implementation, the resilient member 126 is associated with the second portion 124 while the retaining means 128 and the triggering means 130 are associated with the first portion 122. This

alternative implementation is intended to be well within the scope of the present invention. The coupling and decoupling mechanisms will now be described in more detail in the following description.

The first and the second portions 122, 124 are coupled through an interaction between the resilient member 126 and the retaining means 128.

The retaining means 128 include the cavity 138 and the retaining seat 140. The second portion 124, at its end 124a, has a parallelepiped box-shaped construction, which extends along the longitudinal axis (z-axis) and is devoid of one wall at an interface between the first and the second portions 122, 124 such as to form a cavity 138. The cavity 138 is suitable for receiving the resilient member 126 therein. In addition, as depicted in the adjoining figure, one of the walls of said parallelepiped box-shaped

construction is configured to form a retaining seat 140. In one example, the retaining seat 140 is located substantially near the interface between the first and the second portions 122, 124.

The resilient member 126 includes the mating shoulder 136. The mating shoulder 136 has a construction suitable for engaging said retaining seat 140. Thus, the construction of the resilient member 126 and the retaining means 128 is such that when the first and the second portions 122, 124 are brought closer to each other along the longitudinal axis (z- axis) , the resilient member 126 slides into the cavity 138 until the mating shoulder 136 click-fits into the retaining seat 140. Thus, the first and second portions 122, 124 are configured to cooperate in a sliding manner along the

longitudinal axis (z-axis) such that the auxiliary carrier assembly 118 transitions from the decoupled state to the coupled state.

In one embodiment of the present invention, the first and the second portions 122, 124 are brought closer when the

auxiliary movable contacts 120 are in the open position, and the main movable contacts 112 transition from the closed position to the open position. Thus, the first portion 122 is static while the second portion 124 is displaced towards the first portion 122 along the second direction (S) . The first and the second portions 122, 124 are decoupled primarily through an interaction between the triggering means 130 and the resilient member 126.

The triggering means 130 include the trigger arm 142. The trigger arm 142 includes a head-end 142a and a tail-end 142b. Further, the trigger arm 142 is pivoted about a pivot axis (y-axis) passing through point P, which is located

intermediate between the head-end 142a and the tail-end 142b. As evident from the adjoining figures, the pivot axis (y- axis) is substantially orthogonal to the longitudinal (z- axis) and the transverse axes (x-axis) . The trigger arm 142 is pivoted such that the trigger arm 142 is freely rotatable between a first and a second position. The first position corresponds to a position in which the head-end 142a of the trigger arm 142 is located away from the retaining means 128. On the other hand, the second position corresponds to a position in which the head-end 142a is located close to the retaining means 128 such as to deform the resilient member 126. The trigger arm 142 is pivoted in such manner that the trigger arm 142 tends towards in the first position in absence of an external force. However, the trigger arm 142 tends to rotate towards the second position when a tail-end 142b thereof is engaged by the projection, as will be

explained later.

The construction of the triggering means 130 and the

resilient member 126 is such that when the second portion 124, along with the first portion 122 in the coupled state, is displaced along the longitudinal axis (z-axis) in the first direction (F) , the tail-end 142b engages a portion of the auxiliary housing 114, such as projection 132. As a result, the trigger arm 142 rotates about said pivot axis (y- axis) passing through point P and the head-end 142a deforms the resilient member 126 to permit release thereof from the retaining means 128. Thus, the first portion 122 becomes decoupled from the second portion 124. As mentioned earlier, the auxiliary switch 104 also includes the biasing means 134. In one example, the biasing means 134 are implemented through a compression spring. On one end, the biasing means 134 are coupled to the first portion 122, while on the other end, the biasing means 134 are coupled to the auxiliary housing 114. The biasing means 134 are configured to bias the first portion 122 towards the second direction (S) . Thus, the biasing means 134 urge the first portion 122 towards the open position of the auxiliary movable contacts 120. Hence, subsequent to the first portion 122 becoming decoupled from the second portion 124, the auxiliary carrier assembly 118 transitions from said coupled state to the decoupled state, whereby the first and the second portions 122, 124 are distanced from each other.

The auxiliary switch 104, as described above, is adapted for being operationally coupled to the main switch 102. The auxiliary switch 104 is coupled to the main switch 102 using suitable mechanical coupling means such that the auxiliary carrier assembly 118 is operationally coupled to the main carrier assembly 110. In addition, supply-side and load-side stationary contacts in the auxiliary switch 104 are

respectively connected to corresponding supply-side and load- side stationary contacts in the main switch 102 through current-limiting resistors 144.

The operation of the electrical switch assembly 100 will now be briefly described.

During the switching-on operation, as the auxiliary carrier assembly 118 is displaced along the longitudinal axis (z- axis) in the first direction (F) . It is generally known that the distance between a movable contact and corresponding stationary contact is referred to as "contact gap". The contact gap (Gl) in the main switch 102 and the contact gap (G2) in the auxiliary switch 104 are such that during the switching-on operation, the auxiliary switch 104 reaches a closed state prior to the main switch 102.

Thus, the transient current during the switching-on operation flows through the current-limiting resistors 144 and the auxiliary switch 104. As the auxiliary carrier assembly 118, along with the main carrier assembly 110, is further displaced along the

longitudinal axis (z-axis) in the first direction (F) , the auxiliary carrier assembly 118 transitions from the coupled state to the decoupled state, in the manner described

earlier. Such transition occurs after the main switch 102 reaches the closed state during the switching-on operation. During the switching-off operation, as the auxiliary switch 104 is in the open state, the transient current flows through the main switch 104. Thus, only the transient current during the switching-on operation flows through the current-limiting resistors 144 and the auxiliary switch 104, while the

transient current during the switching-off operation flows through the main switch 102.

As the main carrier assembly 110 moves along the longitudinal axis (z-axis) in the second direction (S) , the second portion 124 of the auxiliary carrier assembly 118 is also displaced in the same manner. Towards end of the switching-off

operation, the second portion 124 couples the first portion 122 such that the auxiliary carrier assembly 118 transitions from the decoupled state to the coupled state. Thus, the electrical switch assembly 100 becomes ready for the next set of switching-on and switching-off operations.

It should be understood that the present invention, as described above, facilitates a modular design of the

electrical switch assembly 100. Thus, it enables separately manufacturing the main switch 102 and the auxiliary switch 104, and coupling the auxiliary switch 104 to the main switch 102, as and when required. In a second embodiment of the present invention, the

electrical switch assembly 100 is provided as a single unit. In this design, essentially, the main housing 106 and the auxiliary housing 114 are manufactured as an integral

element. Similarly, the second portion 122 of the auxiliary carrier assembly 118 is integrated with the main carrier assembly 110 to provide a single carrier assembly. In this case, the carrier assembly includes two portions, a first portion and a second portion. The first portion is equivalent to the first portion 122, described in conjunction with the preceding embodiment. Similarly, the second portion is equivalent to a combination of the second portion 124 and the main carrier assembly 110, described in conjunction with the preceding embodiment. Therefore, in this embodiment, the electrical switch assembly 100 is manufactured as a single unit .

Various technical features described in conjunction with the preceding embodiment are applicable to this embodiment as well . The present invention will hereinafter be described with reference to the first embodiment of the present invention.

FIGS 2A through 2E illustrate a first cross-sectional view of the electrical switch assembly 100 in five different stages during switching-on and switching-off operations. FIGS 3A through 3E illustrate a second cross-sectional view of the auxiliary switch 104 in the five different stages during switching-on and switching-off operations. Also, FIGS 4A and 4B illustrate graphical representations of electric currents and stroke traces respectively, through a main switch (Curve I) and an auxiliary switch (Curve II) in the five different stages during switching-on and switching- off operations.

With reference to FIGS 4A and 4B, the switching-on operation begins at time instant TO and continues till time instant T3. The operation of electrical switch assembly 100 from time instant T3 to time instant T4 is said to be steady state operation. The switching-off operation begins at time instant T4 and continues till time instant T5. Referring now to FIG 2A and FIG 3A, the electrical switch assembly 100 is shown in Stage A. The electrical switch assembly 100 is in Stage A, before initiation of the

switching-on operation. Also, the electrical switch assembly 100 returns to Stage A after completion of the switching-off operation. In Stage A, the main movable contacts 112 and the auxiliary movable contacts 120 are in the open position.

Also, the auxiliary carrier assembly 118 is in the coupled state. Referring to FIG 4A, the electrical switch assembly 100 is in Stage A at time instant TO.

At time instant TO, the main carrier assembly 110 is actuated to displace along the longitudinal axis (z-axis) in the first direction (F) . The auxiliary carrier assembly 118 moves along with the main carrier assembly 110. As explained earlier, the contact gaps in the main and the auxiliary switches (Gl, G2) are such that the auxiliary movable contacts are closed before the main movable contacts are closed. Thus, at time instant Tl, the auxiliary movable contacts 120 are closed, resulting in Stage B of the electrical switch assembly 100.

As shown in FIG 4A, the electric current through the

auxiliary switch 104 increases significantly at time instant Tl, while the electric current through the main switch 102 remains zero. The relative displacements of the respective carrier assemblies in the main and the auxiliary switches 102, 104 is depicted through stroke trace curves I and II respectively from TO to Tl in FIG 4B. Referring to FIG 2B and FIG 3B, the electrical switch

assembly 100 is shown in Stage B. In Stage B, the main movable contacts 112 are in the open position, while the auxiliary movable contacts 120 are in the closed position. Also, the auxiliary carrier assembly 118 is in the coupled state.

As the switching-on operation continues after time instant Tl, the main carrier assembly 110 continues to displace along the longitudinal axis (z-axis) in the first direction (F) . The auxiliary carrier assembly 118 also moves along with the main carrier assembly 110. Eventually, at time instant T2, the main movable contacts 112 are closed, resulting in Stage C of the electrical switch assembly 100.

As shown in FIG 4A, the electric current (curve I) through the main switch 102 increases significantly at time instant T2, while the electric current (curve II) through the

auxiliary switch 104 continues to be at a non-zero value. The relative displacements of the respective carrier assemblies in the main and the auxiliary switches 102, 104 is depicted through stroke trace curves I and II respectively from Tl to T2 in FIG 4B.

Referring to FIG 2C and FIG 3C, the electrical switch

assembly 100 is shown in Stage C. In Stage C, the main movable contacts 112 as well as the auxiliary movable

contacts 120 are in the closed position. During Stage C, i.e. from time instant T2 to time instant T3, the auxiliary carrier assembly 118 transitions from the coupled state to the decoupled state.

As the switching-on operation continues after time instant T2, the main carrier assembly 110 continues to displace along the longitudinal axis (z-axis) in the first direction (F) . The auxiliary carrier assembly 118 also moves along with the main carrier assembly 110. Eventually, as the time instant T3 approaches, the triggering means 130 engage the projection 132 and begin to deform the resilient member 126, in the manner described in conjunction with the preceding figures. At time instant T3, the first portion 122 becomes decoupled to the second portion 124. The biasing means 134 urge the first portion 122 to return to the open position of the auxiliary movable contacts 120.

As shown in FIG 4A, the electric current (curve II) through the auxiliary switch 104 decreases to zero, while the electric current (curve I) through the main switch 102 continues to be at a non-zero, at time instant T3. The relative displacements of the respective carrier assemblies in the main and the auxiliary switches 102, 104 is depicted through stroke trace curves I and II respectively between T2 and T3 in FIG 4B.

Subsequent to time instant T3 and before time instant T4, the electrical switch assembly 100 is said to be operating in Stage D.

Referring to FIG 2D and FIG 3D, the electrical switch

assembly 100 is shown in Stage D. In Stage D, the main movable contacts 112 are in the closed position while the auxiliary movable contacts 120 are in the open position.

Also, the auxiliary carrier assembly 118 is in the decoupled state .

Stage D corresponds to the steady-state operation of the electrical switch assembly 100 during the electrical switch assembly 100 provides a rated current to an electric load. Stage D ends at time instant T4, when the switching-off operation is initiated. As shown in FIG 4A, the electric current (curve I) through the main switch 102 decreases to zero, while the electric current (curve II) through the auxiliary switch 104 continues to be zero, at time instant T4. The relative displacements of the respective carrier assemblies in the main and the

auxiliary switches 102, 104 is depicted through stroke trace curves I and II from time instants T3 to T4 in FIG 4B.

Subsequent to time instant T4 and before time instant T5, the electrical switch assembly 100 is said to be operating in Stage E.

Referring to FIG 2E and FIG 3E, the electrical switch

assembly 100 is shown in Stage E. In Stage E, the auxiliary movable contacts 120 are in the open position, while the main movable contacts 112 are transitioning from the closed position to the open position. During this stage, the

auxiliary carrier assembly 118 transitions from the decoupled state to the coupled state.

During operation subsequent to time instant T4, the main carrier assembly 110 moves along the longitudinal axis (z- axis) in the second direction (S) . The second portion 124 of the auxiliary carrier assembly 118 also moves along with the main carrier assembly 110. Eventually, as the time instant T5 approaches, the first and the second portions 122, 124 cooperate in a sliding manner, wherein the resilient member 126 is engaged by the retaining means 128, such that at time instant T5, the auxiliary carrier assembly 118 transitions from the decoupled state to the coupled state.

Thus, the electrical switch assembly 100 becomes ready to begin the next set of switching-on and switching-off

operations, i.e. the next sequence of five stages described above .

Thus, the present invention provides an electrical switch assembly adapted for use with electrical loads prone to drawing high transient currents during switching operations. The electrical switch assembly of the present invention is based on a simple, efficient, and reliable design. The electrical switch assembly is configured such that said main and the auxiliary movable contacts contact respective pair of stationary contacts in a desired sequence during the

switching-on operation. The auxiliary movable contacts are opened at the end of switching-on operation, thus, ensuring that said main movable contacts interrupt an electrically- conductive path between an electric supply and an electric load during the switching-off operation.

The present invention facilitates coupling and decoupling of different portions of the carrier assembly carrying the main and the auxiliary movable carriers in an effective and reliable manner to achieve a desired sequence of operating states of said main and said auxiliary switches during switching operations.

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 ELECTRICAL SWITCH ASSEMBLY

102 MAIN SWITCH

104 AUXILIARY SWITCH

106 MAIN HOUSING

108 MAIN STATIONARY CONTACTS

110 MAIN CARRIER ASSEMBLY

112 MAIN MOVABLE CONTACT

114 AUXILIARY HOUSING

116 AUXILIARY STATIONARY CONTACTS

118 AUXILIARY CARRIER ASSEMBLY

120 AUXILIARY MOVABLE CONTACT

122 FIRST PORTION

124 SECOND PORTION

126 RESILIENT MEMBER

126A FIRST LEG

126B SECOND LEG

128 RETAINING MEANS

130 TRIGGERING MEANS

132 PROJECTION

134 BIASING MEANS

136 MATING SHOULDER

138 CAVITY

140 RETAINING SEAT

142 TRIGGER ARM

142A HEAD-END

142B TAIL-END

144 CURRENT-LIMITING RESISTORS

P PIVOT

Gl CONTACT GAP IN AUXILIARY SWIK

G2 CONTACT GAP IN MAIN SWITCH