Background Art As well known, star (Y)-delta (A) starters, which are used to start up an electric motor, serve to establish a star connection for the electric motor upon the start-up of the electric motor, thereby reducing starting current and starting torque required in the start-up of the electric motor to a 1/3 level, while switching the connection for the electric motor into a delta connection after completion of the start-up of the electric motor so that the electric motor is driven in the delta connection state. Such star-delta starters are widely used in a variety of industrial fields in order to protect electric motors and peripheral devices thereof from overload.

Star-delta starters are classified into a contact type using an electromagnetic switch device adapted to switch

electric contacts by use of electromagnets, and a non-contact type using a semiconductor switch device. The type using an electromagnetic switch device is more widely used.

Figs. la, lb and 2 illustrate a conventional electromagnetic switch device and a star-delta starter using the electromagnetic switch device, respectively. Fig. la is a perspective view illustrating the electromagnetic switch device, and Fig. lb is a cross-sectional view taken along the line A-A of Fig. la. Fig. 2 is an equivalent circuit diagram illustrating the star-delta starter.

As shown in Figs. la and lb, the conventional electromagnetic switch device, which is denoted by the reference character C, includes a body 1, and a cover 2 separably attached to an upper surface la of the body 1. Three pairs of terminals 3 are disposed on the upper surface la of the body 1 in such a fashion that the terminals of each terminal pair are arranged at opposite sides of the body 1, respectively, while being insulated from one another. Electric power lines not shown are connected to the terminals 3, respectively. Isolating plates 4 are arranged at opposite sides of the cover 2 to isolate adjacent ones of the terminals 3.

Three pairs of fixed contacts 5 are also provided. Each fixed contact 5 is arranged at an end of an associated one of the terminals 3 extending toward a central portion of the body 1. The fixed contacts 5 are insulated from one another. A

vertical moving member 6 is arranged at the central portion of the body 1 in such a fashion that it is upwardly and downwardly movable. Three pairs of moving contacts 7 insulated from one another are mounted to the vertical moving member 6 at opposite sides of the vertical moving member 6 in such a fashion that each of the moving contacts 7 selectively comes into contact with an associated one of the fixed contacts 5 so that it is short-circuited or opened with respect to the associated fixed contact 5. A compression coil spring 8 is arranged around the vertical moving member 6 between the upper surface la of the body 1 and the moving contacts 7 in such a fashion that it always urges the vertical moving member 6 upwardly.

A fixed core 9 is arranged at a lower portion of the body 1. A coil 10 is wound around the fixed core 9 in order to form an electromagnet. Above the fixed core 9, a moving core 11 is arranged in such a fashion that it moves vertically along with the vertical moving member 6 in accordance with a magnetization of the electromagnet.

The conventional star-delta starter using electromagnetic switch devices having the above mentioned configuration includes an electromagnetic switch device Cl for a main circuit, an electromagnetic switch device C2 for a star circuit, and an electromagnetic switch device C3 for a delta connection, which are connected together as shown in the equivalent circuit diagram of Fig. 2 and activated by a timer (not shown) to start

up a three-phase electric motor M.

When current flows through the coil 10 of the electromagnetic switch device C2 for the star circuit upon starting the three-phase electric motor M, the electromagnet formed by the fixed core 9 and coil 10 is magnetized by virtue of the current.

Accordingly, the electromagnet generates a magnetic force greater than the resilience of the spring 8, so that the vertical moving member 6 and moving core 11 are downwardly moved. As a result, the moving contacts 7, which also move downwardly, come into contact with the fixed contacts 5, respectively.

When the electromagnetic switch device Cl for the main circuit is activated in accordance with the same procedure as mentioned above, a star connection is established for the three- phase electric motor M, so that the three-phase electric motor M is started up using starting current and starting torque reduced to a 1/3 level. At the same time, the timer not shown begins to operate in order to count the drive time of the three-phase electric motor M.

After a predetermined period of time elapses, the current flowing through the coil 10 of the electromagnetic switch device C2 for the star connection is cut off by an operation of the timer. At the same time, current flows through the coil 10 of the electromagnetic switch device C3 for the delta connection.

In this state, the magnetic force of the electromagnet formed by the fixed core 9 and coil 10 of the electromagnetic switch device C2 for the star connection disappears. As a result, the vertical moving member 6 is upwardly moved along with the moving core 11 and moving contacts 7 by virtue of the resilience of the spring 8, thereby causing the moving contacts 7 to be separated from the fixed contacts 5.

Meanwhile, the electromagnet formed by the fixed core 9 and coil 10 of the electromagnetic switch device C3 for the delta connection is magnetized by virtue of the current flowing through the coil 10. As a result, the moving contacts 7 are downwardly moved, so that they come into contact with the fixed contacts 5, respectively.

Accordingly, the electromagnetic switch device C3 for the delta connection is short-circuited to electric power lines at its one-side terminals 3. As a result, the three-phase electric motor M is switched to the star connection state to a delta connection state, so that it is driven at a full speed.

In the star-delta starter having the above mentioned configuration, each of its electromagnetic switch devices is used only for a single purpose, that is, a star connection or a delta connection. For this reason, the conventional star-delta starter cannot implement a desired system unless at least two electromagnetic switch devices are used, even when those used for the main circuit are not taken into consideration.

As a result, the conventional star-delta starter involves high manufacturing and installing costs and a large occupation space.

The conventional star-delta starter also involves a complex wiring for the connection between the electric motor and the electromagnetic switch device used. Such a complex wiring may result in a possibility of erroneous connections. In particular, such a wiring may be easily damaged by an external force applied thereto, thereby resulting in an erroneous operation of the starter or a damage of the electric motor.

Disclosure of Invention Therefore, an object of the invention is to solve the above mentioned problems involved in the prior art, and to provide an electromagnetic switch device for star-delta connections which includes two electromagnets arranged in its body and two switching units operating in accordance with respective magnetization states of the electromagnets in order to selectively establish a star connection or a delta connection for a three-phase electric motor, so that it can reduce installation costs and an occupation space when it is applied to a star-delta starter while using no unnecessary wiring, thereby reducing erroneous connections and erroneous operations.

In accordance with the present invention, this object is accomplished by providing an electromagnetic switch device for

star-delta connections comprising: a body; three power terminals arranged at one side of the body and respectively connected to three-phase power lines, the power terminals being insulated from one another; three main starting terminals arranged at the other side of the body and respectively connected to one-side terminals of a three-phase electric motor, the main starting terminals being insulated from one another; three star-delta terminals arranged at the other side of the body outside the main starting terminals and connected to the other-side ends of the three-phase electric motor, respectively, the star-delta terminals being insulated from one another; an electromagnet for a main circuit and an electromagnet for star-delta connections disposed at a lower portion of the body in such a fashion that they are laterally aligned with each other while being insulated from each other, each of the electromagnets including a fixed core and a coil wound around the fixed core; a main circuit switching unit arranged near the main circuit-end electromagnet in the interior of the body, the main circuit switching unit serving to selectively connect each of the main starting terminals to an associated one of the power terminals in accordance with a magnetization of the main circuit-end electromagnet; and a star-delta connection switching unit arranged near the star-delta connection-end electromagnet in the interior of the body, the star-delta connection switching unit serving to selectively connect the star-delta terminals to one

another or to the main starting terminals, respectively, in accordance with a magnetization of the star-delta connection-end electromagnet.

Preferably, the electromagnetic switch device further comprises a timer arranged in the interior of the body and adapted to count an activation time of the main circuit-end electromagnet, thereby determining a point of time when the star-delta connection-end electromagnet is to be activated.

The electromagnetic switch device may further comprise isolating plates arranged between adjacent ones of the power terminals, between adjacent ones of the main starting terminals, and between adjacent ones of the star-delta terminals to isolate the adjacent power terminals, the adjacent main starting terminals, and the adjacent star-delta terminals, respectively.

The main circuit switching unit may comprise: a moving core vertically movable in accordance with a magnetization of the main circuit-end electromagnet; a vertical moving member integrally coupled to the moving core in such a fashion that it is moved along with the moving core; three pairs of fixed contacts arranged at desired positions within a vertical movement zone of the vertical moving member in such a fashion that the fixed contacts included in each of the fixed contact pairs are disposed at opposite sides of the vertical moving member, respectively, the fixed contacts arranged at one side of the vertical moving member being connected to the power

terminals, respectively, while being insulated from one another, and the fixed contacts arranged at the other side of the vertical moving member being connected to the main starting terminals, respectively, while being insulated from one another; and three pairs of moving contacts mounted to the vertical moving member in such a fashion that the moving contacts included in each of the moving contact pairs are disposed at opposite sides of the vertical moving member, respectively, the moving contacts arranged at one side of the vertical moving member being insulated from one another, the moving contacts arranged at the other side of the vertical moving member being insulated from one another, and the moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the power terminal-end fixed contacts to be selectively connected to the starting terminal-end fixed contacts.

The star-delta connection switching unit may comprise: a moving core vertically movable in accordance with a magnetization of the star-delta connection-end electromagnet; a vertical moving member integrally coupled to the moving core in such a fashion that it is moved along with the moving core; three pairs of fixed contacts for star-delta connection arranged at desired positions within a vertical movement zone of the

vertical moving member in such a fashion that the fixed contacts included in each of the fixed contact pairs are disposed at opposite sides of the vertical moving member, respectively, the fixed contacts arranged at one side of the vertical moving member being connected to the main starting terminals, respectively, while being insulated from one another, and the fixed contacts arranged at the other side of the vertical moving member being connected to the star-delta terminals, respectively, while being insulated from one another; three pairs of moving contacts for delta connection mounted to the vertical moving member in such a fashion that the moving contacts included in each of the moving contact pairs are disposed at opposite sides of the vertical moving member, respectively, the moving contacts arranged at one side of the vertical moving member being insulated from one another, the moving contacts arranged at the other side of the vertical moving member being insulated from one another, and the moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the star-delta connection-end fixed contacts to be selectively connected to the starting terminal- end fixed contacts so as to achieve a delta connection; and three moving contacts for star connection mounted to the vertical moving member at a position vertically shifted from the

delta connection-end moving contacts near the star-delta connection-end fixed contacts, the star connection-end moving contacts being short-circuited together, and the star connection-end moving contacts being vertically moved in accordance with a vertical movement of the vertical moving member, so that they selectively come into contact with respective associated ones of the fixed contacts, thereby causing the fixed contacts to be selectively connected together so as to achieve a star connection, the star connection by the star connection-end moving contacts being achieved when the delta connection by the delta connection-end moving contacts is released.

Each of the main circuit switching unit and star-delta connection switching unit may further comprise a return springs adapted to provide a return force for returning the associated vertical moving member to an original position thereof at which the associated moving contacts are separated from respective associated ones of the fixed contacts.

Each of the main circuit switching unit and star-delta connection switching unit may further comprise an arc prevention spring arranged in the associated vertical moving member and adapted to always urge the associated moving contacts toward the associated fixed contacts, thereby increasing the contact force of the moving contacts when the moving contacts come into contact with the fixed contacts, so as to suppress generation of

arc at regions where the moving contacts come into contact with the fixed contacts, respectively.

Brief Description of Drawings The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which: Figs. la, lb and 2 illustrate a conventional electromagnetic switch device and a star-delta starter using the electromagnetic switch device, respectively, wherein Fig. la is a perspective view illustrating the electromagnetic switch device, Fig. lb is a cross-sectional view taken along the line A -A of Fig. la, and Fig. 2 is an equivalent circuit diagram illustrating the star-delta starter; and Figs. 3a, 3b and 4 illustrate an electromagnetic switch device according to the present invention and a star-delta starter using the electromagnetic switch device, respectively, wherein Fig. 3a is a perspective view illustrating the electromagnetic switch device, Fig. 3b is a cross-sectional view taken along the line A-A of Fig. 3a, and Fig. 4 is an equivalent circuit diagram illustrating the star-delta starter using the electromagnetic switch device according to the present invention.

Best Mode for Carrying Out the Invention Figs. 3a, 3b and 4 illustrate an electromagnetic switch device according to the present invention and a star-delta starter using the electromagnetic switch device, respectively.

Fig. 3a is a perspective view of the electromagnetic switch device, and Fig. 3b is a cross-sectional view taken along the line A-A of Fig. 3a. Fig. 4 is an equivalent circuit diagram of the star-delta starter using the electromagnetic switch device according to the present invention.

As shown in Figs. 3a and 3b, the electromagnetic switch device of the present invention, which is denoted by the reference character C, includes a body 110, and three power terminals 121a, 121b, and 121c arranged at one side of the body 110 and respectively connected to three-phase power lines R, S, and T. The power terminals 121a, 121b, and 121c are insulated from one another. The electromagnetic switch device also includes three main starting terminals 122a, 122b, and 122c arranged at the other side of the body 110 and respectively connected to one-side terminals u, v, and w of a three-phase electric motor M. The main starting terminals 122a, 122b, and 122c are insulated from one another. Three star-delta terminals 123a, 123b, and 123c are arranged at the other side of the body 110 outside the main starting terminals 122a to 122c. The star- delta terminals 123a, 123b, and 123c are connected to the other- side ends Z, X, and Y of the three-phase electric motor M,

respectively. The star-delta terminals 123a, 123b, and 123c are insulated from one another.

An electromagnet 130 for a main circuit and an electromagnet 140 for star-delta connections are disposed at a lower portion of the body 110 in such a fashion that they are laterally aligned with each other while being insulated from each other. The electromagnet 130 includes a fixed core 131 and a coil 132 whereas the electromagnet 140 includes a fixed core 141 and a coil 142.

The electromagnetic switch device also includes a main circuit switching unit 150 arranged above the main circuit-end electromagnet 130 in the interior of the body 110. The main circuit switching unit 150 serves to selectively connect the main starting terminals 122a, 122b, and 122c to respective power terminals 121a, 121b, and 121c in accordance with a magnetization of the main circuit-end electromagnet 130.

The main circuit switching unit 150 includes a main circuit-end moving core 151 and a main circuit-end vertical moving member 152 integrally coupled together and arranged above the main circuit-end electromagnet 130 near the main circuit-end electromagnet 130. The moving core 151 and vertical moving member 152 are adapted to be moved together in accordance with a magnetization of the electromagnet 130. The main circuit switching unit 150 also includes three pairs of main circuit-end fixed contacts 153a, 153b, and 153c arranged at desired

positions within a vertical movement zone of the main circuit- end vertical moving member 152 in such a fashion that the fixed contacts of each fixed contact pair are disposed at opposite sides of the vertical moving member 152, respectively. The fixed contacts 153a, 153b, and 153c arranged at one side of the vertical moving member 152 are connected to the power terminals 121a, 121b, and 121c, respectively, while being insulated from one another. The fixed contacts 153a, 153b, and 153c arranged at the other side of the vertical moving member 152 are connected to the main starting terminals 122a, 122b, and 122c, respectively, while being insulated from one another. Three pairs of moving contacts 154a, 154b, and 154c are mounted to the main circuit-end vertical moving member 152 in such a fashion that the moving contacts of each moving contact pair are disposed at opposite sides of the vertical moving member 152, respectively. The moving contacts 154a, 154b, and 154c arranged at one side of the vertical moving member 152 are insulated from one another. In similar, the moving contacts 154a, 154b, and 154c arranged at the other side of the vertical moving member 152 are insulated from one another. The moving contacts 154a, 154b, and 154c are vertically moved in accordance with a vertical movement of the vertical moving member 152, so that they selectively come into contact with respective associated ones of the fixed contacts 153a, 153b, and 153c, thereby causing the power terminal-end fixed contacts 153a, 153b, and 153c to be

selectively connected to the starting terminal-end fixed contacts 153a, 153b, and 153c.

Return springs 155 are arranged around the moving core 151 between the upper surface of the main circuit-end electromagnet 130 and the lower surface of the main circuit-end vertical moving member 152 in order to provide a return force for returning the vertical moving member 152 to its original position at which the moving contacts 154a, 154b, and 154c are separated from respective associated ones of the fixed contacts 153a, 153b, and 153c. An arc prevention spring 156 is arranged in the main circuit-end vertical moving member 152 in order to always urge the moving contacts 154a, 154b, and 154c toward the fixed contacts 153a, 153b, and 153c, thereby increasing the contact force of the moving contacts 154a, 154b, and 154c when the moving contacts 154a, 154b, and 154c come into contact with the fixed contacts 153a, 153b, and 153c, so as to suppress generation of arc at those contacts.

The electromagnetic switch device further includes a star- delta connection switching unit 160 arranged above the star- delta connection-end electromagnet 140 in the interior of the body 110. The star-delta connection switching unit 160 serves to selectively connect the star-delta terminals 123a, 123b, 123c to one another or to respective main starting terminals 122a, 122b, and 122c in accordance with a magnetization of the star- delta connection-end electromagnet 140.

The star-delta connection switching unit 160 includes a star-delta connection-end moving core 161 and a star-delta connection-end vertical moving member 162 integrally coupled together and arranged above the star-delta connection-end electromagnet 140 near the star-delta connection-end electromagnet 140. The moving core 161 and vertical moving member 162 are adapted to be moved together in accordance with a magnetization of the electromagnet 140. The star-delta connection switching unit 160 also includes three pairs of fixed contacts 163a, 163b, and 163c for star-delta connection arranged at desired positions within a vertical movement zone of the star-delta connection-end vertical moving member 162 in such a fashion that the fixed contacts of each fixed contact pair are disposed at opposite sides of the vertical moving member 162, respectively. The fixed contacts 163a, 163b, and 163c arranged at one side of the vertical moving member 162 are connected to the main starting terminals 122a, 122b, and 122c, respectively, while being insulated from one another. The fixed contacts 163a, 163b, and 163c arranged at the other side of the vertical moving member 162 are connected to the star-delta terminals 123a, 123b, and 123c, respectively, while being insulated from one another. Three pairs of moving contacts 164a, 164b, and 164c for delta connection are mounted to the star-delta connection-end vertical moving member 162 in such a fashion that the moving contacts of each moving contact pair are disposed at

opposite sides of the vertical moving member 162, respectively.

The moving contacts 164a, 164b, and 164c arranged at one side of the vertical moving member 162 are insulated from one another.

In similar, the moving contacts 164a, 164b, and 164c arranged at the other side of the vertical moving member 162 are insulated from one another. The moving contacts 164a, 164b, and 164c are vertically moved in accordance with a vertical movement of the vertical moving member 162, so that they selectively come into contact with respective associated ones of the fixed contacts 163a, 163b, and 163c, thereby causing the star-delta connection- end fixed contacts 163a, 163b, and 163c to be selectively connected to the starting terminal-end fixed contacts 163a, 163b, and 163c.

Three moving contacts 167a, 167b, and 167c for star connection are also mounted to the star-delta connection-end vertical moving member 162 above the delta connection-end moving contacts 164a, 164b, and 164c near the fixed contacts 163a, 163b, and 163c connected to the star-delta terminals 123a, 123b, and 123c. The star connection-end moving contacts 167a, 167b, and 167c are short-circuited together. The moving contacts 167a, 167b, and 167c are vertically moved in accordance with a vertical movement of the vertical moving member 162, so that they selectively come into contact with respective associated ones of the fixed contacts 163a, 163b, and 163c, thereby causing the fixed contacts 163a, 163b, and 163c to be selectively

connected together. The star connection by the star connection- end moving contacts 167a, 167b, and 167c and the delta connection by the delta connection-end moving contacts 164a, 164b and 164c are achieved in an alternating fashion. For example, the star connection by the star connection-end moving contacts 167a, 167b, and 167c is achieved when the delta connection by the delta connection-end moving contacts 164a, 164b and 164c is released.

Return springs 165 are arranged around the star-delta connection-end moving core 161 between the upper surface of the star-delta connection-end electromagnet 140 and the lower surface of the star-delta connection-end vertical moving member 162 in order to provide a return force for returning the vertical moving member 162 to its original position at which the delta connection-end moving contacts 164a, 164b, and 164c are separated from respective associated ones of the fixed contacts 163a, 163b, and 163c. An arc prevention spring 166 is arranged in the star-delta connection-end vertical moving member 162 in order to always urge the delta connection-end moving contacts 164a, 164b, and 164c and the star connection-end moving contacts 167a, 167b, and 167c toward respective corresponding portions of the fixed contacts 163a, 163b, and 163c, thereby increasing the contact force of the delta connection-end moving contacts 164a, 164b, and 164c or the star connection-end moving contacts 167a, 167b, and 167c when the delta connection-end moving contacts

164a, 164b, and 164c or the star connection-end moving contacts 167a, 167b, and 167c come into contact with the fixed contacts 153a, 153b, and 153c, so as to suppress generation of arc at those contacts.

A timer 170 is arranged beneath the main circuit-end electromagnet 130 and star-delta connection-end electromagnet 140 in the interior of the body 110. The timer 170 serves to count an activation time of the main circuit-end electromagnet 130, thereby determining a point of time when the star-delta connection-end electromagnet 140 is to be activated. Isolating plates 180 are also arranged to isolate adjacent ones of the power terminals 121a, 121b, and 121c, adjacent ones of the main starting terminals 122a, 122b, and 122c, and adjacent ones of the star-delta terminals 123a, 123b, and 123c, respectively.

In the drawings, the reference numeral 191 denotes terminals to which power lines are coupled in order to supply current to the coils 132 and 142. The reference numeral 192 denotes bolts respectively coupled to the terminals 191 in order to provide an easy connection of the power lines to the terminals 191.

The electromagnetic switch device C for star-delta connections having the above mentioned configuration operates in a connection state, as shown in the equivalent circuit diagram of Fig. 4, in such a fashion that it establishes a star connection, when it is desired to start up the electric motor M,

in order to achieve a start-up of the electric motor M using starting current and starting torque reduced to a 1/3 level while switching the connection of the electric motor M to a delta connection after completion of the start-up of the electric motor M. For the best understanding of the present invention, elements of Fig. 4 respectively corresponding to those in Figs. 3a and 3b are denoted by the same reference numerals.

Now, the operation of the electromagnetic switch device C for star-delta connections according to the present invention will be described.

When current flows through the coil 132 of the main circuit-end electromagnet 130, which is constructed by the fixed core 131 and the coil 132, upon starting the three-phase electric motor M, the electromagnet 130 is magnetized by virtue of the current. Simultaneously with the magnetization of the electromagnet 130, the timer 170 begins to count the activation time of the electromagnet 130.

As the electromagnet 130 is activated, it generates a magnetic force greater than the resilience of the return spring 155, so that the moving core 151 and vertical moving member 152 are downwardly moved. At the same time, the main circuit-end moving contacts 154a, 154b, and 154c are downwardly moved, so that they come into contact with the main circuit-end fixed contacts 153a, 153b, and 153c, respectively.

In such an initial state, the star-delta connection-end electromagnet 140 is maintained under a non-magnetization condition, that is, a condition in which no current flows through the coil 142. Accordingly, the star-delta connection- end moving coil 161 and star-delta connection-end vertical moving member 162 are maintained in a state in which they are spaced away from the coil 142 by virtue of the resilience of the return spring 165. In this state, the delta connection-end moving contacts 164a, 164b, and 164c are separated from the associated fixed contacts 163a, 163b, and 163c whereas the star connection-end moving contacts 167a, 167b, and 167c are in contact with the associated fixed contacts 163a, 163b, and 163c, that is, in a state short-circuited to the associated fixed contacts 163a, 163b, and 163c.

Accordingly, the three-phase electric motor M is in a star connection state, so that it is started up by electric power supplied via the three-phase power lines R, S, and T respectively connected to the power terminal 121a, 121b, and 121c.

After a predetermined period of time elapses, the timer 170 operates to allow current to flow through the coil 142 of the star-delta connection-end electromagnet 140. By virtue of the current, the star-delta connection-end electromagnet 140 is magnetized.

As the electromagnet 130 is activated, it generates a

magnetic force greater than the resilience of the return spring 165, so that the moving core 161 and vertical moving member 162 are downwardly moved.

At the same time, the star connection-end moving contacts 167a, 167b, and 167c are downwardly moved, so that they are separated from the associated fixed contacts 163a, 163b, and 163c, respectively. Also, the delta connection-end moving contacts 164a, 164b, and 164c are downwardly moved, so that they come into contact with the associated fixed contacts 163a, 163b, and 163c, respectively.

As a result, the main starting terminals 122a, 122b, and 122c are connected with the star-delta terminals 123a, 123b, and 123c, respectively, so that the three-phase electric motor M is switched to a delta connection state in which it is driven at a full speed.

Industrial Applicability As apparent from the above description, the present invention provides an electromagnetic switch device for star- delta connections which includes two electromagnets arranged in its body and two switching units operating in accordance with respective magnetization states of the electromagnets in order to selectively establish a star connection or a delta connection for a three-phase electric motor. The electromagnetic switch device of the present invention can reduce installation costs

and an occupation space when it is applied to a star-delta starter. In addition, there is no unnecessary wiring.

Accordingly, it is possible to reduce erroneous connections and erroneous operations.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.