Apparatus for an electromagnetic switching device The present invention relates to an apparatus for driving a coil of an electromagnetic switching device.

An electromagnetic switching device is typically used for controlling flow of electrical current in an electrical circuit. The electromagnetic switching device is controllable for switching between on and off states for closing and breaking a power supply circuit. The electromagnetic

switching device may be manually or electrically controlled. To control the electromagnetic switching device electrically, magnets may be employed to actuate a movable contact element for breaking and closing the power supply circuit.

Typically, the movable contact element is moved to engagement with a stationary contact element for closing the power supply circuit. The stationary contact element is

electrically connected to the power supply. Thus, the power supply circuit is closed when movable contact element is in engagement with the stationary contact element. The magnets employed to actuate the movable contact element are energized by a coil. The coil is energized by a current flowing through the coil.

It is an object of the embodiments of the invention to measure to reduce electrical losses occurring at a switch driving the coil in an electromagnetic switching device.

The above object is achieved by an apparatus for driving a coil of an electromagnetic switching device according to claim 1.

The first switch supplies the pick-up current to the coil and the second switch supplies the hold-on current to the coil. The pick-up current is the current required for energizing the coil for the circuit closing motion of the contact element. The hold-on current is the current required for maintaining the contact element in the circuit closing position. The first switch and the second switch may be controlled responsive to a current flowing through the coil. Providing the pick-up current using the first switch and the hold-on current using the second switch enables in reducing the electrical losses at the switches as the heat dissipation is reduced at the switches. According to another embodiment, the first switch and the second switch are different with respect to a switching frequency. As the pick-up current is typically of a higher value than the hold-on current, the switches having different switching frequencies enable in efficient operation of the switches.

According to yet another embodiment, wherein the first switch and the second switch are solid state switches. According to yet another embodiment, the first switch and the second switch being connected in parallel to each other.

Connecting the first switch and the second switch in parallel enables in achieving two different current paths from the supply source. This enables in controlling the pick-up current and the hold-on current provided to the coil.

According to yet another embodiment, the first switch and the second switch connected in parallel is connected in series to the coil. Connecting the parallel connected first switch and the second switch in series with the coil enables in

providing the pick-up current and the hold-on current over two different current paths.

According to yet another embodiment, the apparatus may further comprises a controller configured to provide a fist control signal to the first switch and a second control signal to the second switch responsive to the current flowing through the coil. The controller responsive to the current flowing though the coil may provide the first control signal to the first switch and the second control signal to the second switch for controlling the switches respectively.

According to yet another embodiment, the first control signal is provided to the first switch for providing the pick-up current the coil. The first control signal is provided to the first switch responsive to the current flowing through the coil. This enables in controlling the first switch for providing the pick-up current to the coil .

According to yet another embodiment, the first switch is adapted to be in an on state during a circuit closing motion of a contact element. The first switch adapted to be in an on state during the circuit closing motion enables in providing the pick-up current to the coil.

According to yet another embodiment, the second control signal is provided to the second switch for providing the hold-on current to the coil. The second control signal is provided to the second switch responsive to the current flowing through the coil. This enables in controlling the second switch for providing the hold-on current to the coil.

According to yet another embodiment, the second switch is adapted to perform a high frequency switching responsive to the second control signal. Performing a high frequency switching responsive to the second control signal enables in reducing the current provided to the coil and thus, provide the hold-on current to the coil.

According to yet another embodiment, wherein the second control signal is a pulse width modulated signal. The pulse width modulated signal enables the switch to perform high frequency switching based responsive to the widths of the pulses.

According to yet another embodiment, the switching frequency of the first switch is less than the second switch. The first switch providing the pick-up may not be required to perform high frequency switching. Thus, the switching frequency of the first switch may be lower than the switching frequency of the second switch. This enables in reducing the electrical losses at the first switch.

According to yet another embodiment, wherein the first switch is selected from the group consisting of a transistor, and an IGBT. The first switch being a transistor or an IGBT may operate efficiently to supply the pick-up current as the pick-up current is of a higher value than the hold-on current .

According to yet another embodiment, the second switch is an MOSFE . The second switch being an MOSFET may operate efficiently to supply the hold-on current as MOSFET operate efficiently at high switching frequency.

Another embodiment includes, an electromagnetic switching device comprising the apparatus according to any of the claims 1 to 14.

Embodiments of the present invention are further described hereinafter with reference to illustrated embodiments shown in the accompanying drawings, in which:

FIG la illustrates a carrier of an electromagnetic

switching device according to an embodiment herein,

FIG lb illustrates an assembly of an electromagnet system and the carrier 1 of FIG la according to an embodiment herein, and

FIG 2 FIG 2 illustrates a schematic diagram of an

apparatus for supplying the pick-up current and the hold-on current to the coil according to an embodiment herein.

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 FIG. la, a carrier 1 of an electromagnetic switching device is illustrated according to an embodiment herein. A contact element 3 is supported in the carrier to be movable form a circuit breaking position to a circuit closing position, wherein the contact element 3 is moved to be in contact with a stationary contact element to be in the circuit closing position. The stationary contact may be connected to the input power supply.

FIG lb illustrates an assembly of an electromagnet system and the carrier 1 of FIG la according to an embodiment herein. In the shown example of FIG lb, the carrier 1 comprises a column 7 extending vertically upwards. The electromagnet system 8 is supported on the column 7 to actuate the carrier. In the present embodiment, the electromagnet system 8 is shown as comprising electromagnetic armatures 9, 13. However, the electromagnet system 8 may be designed in another way comprising fewer or more electromagnetic armatures.

Typically, the electromagnetic armatures 9, 13 are adapted to actuate the carrier 1. The electromagnetic armature 9 engages the column 7 via a member 11 for transferring the armature 9 movement to the carrier 1. The carrier 1 in turn moves the contact element 3 into the circuit closing position. In the shown example of FIG lb, the electromagnetic armature 9 is in engagement with the column mechanically via the member 11. However, the electromagnetic armature 9 may be engaged with the column 7 using other known mechanical means. Another electromagnetic armature 13 comprising coils 17 is also supported on the column 7. In the shown example of FIG lb two coils 17 have been illustrated. However, in certain

implementations the magnetic armature may comprise only a single coil 17. The coils 17 are energized by supplying a current provided by a supply source. On the coils 17 being energized, the electromagnetic armature 9 is drawn towards the electromagnetic armature 13. This movement of the armature 9 is transferred to the carrier 1 and to the contact element 3 for the circuit closing motion. However, in other embodiments, the carrier 1 may comprise a column extending vertically downwards and the electromagnetic armature 9 and the electromagnetic armature 13 may be supported on the column . In the circuit closing motion, the contact element 3 is moved to be in contact with the stationary contact element. The contact element 3 in contact with the stationary contact element is said to be in the circuit closing position. The current required for energizing the coil 17 for the circuit closing motion of the contact element 3 is hereinafter referred to as a pick-up current. Once the contact element 3 is moved to the circuit closing position, the current required for energizing the coil 17 such that the contact element 3 is maintained at the circuit closing position is referred to as a hold-on current.

FIG 2 illustrates a schematic diagram of an apparatus 18 for supplying the pick-up current and the hold-on current to the coil according to an embodiment herein. In the example of FIG 2, a pick-up current for energizing the coil 17 is provided to the coil 17 using a switch 19 and a hold-on current is provided by a switch 21. The switch 19 is operable for providing the pick-up current to the coil 17 during circuit closing motion and the switch 21 is operable for providing the hold-on current to the coil 17 for maintaining the contact element 3 of FIG la in a circuit closing position. For example, the switch 19 and the switch 21 may be solid state static switches. Still referring to FIG 2, a controller 23 is configured to control the switch 19 for providing the pick-up current to the coil 17 during circuit closing motion and the switch 21 for providing the hold-current to the coil 17 for maintaining the contact element 3 of FIG 1 at the circuit closing position. The controller 23 controls the switch 19 and switch 21 responsive to the current flowing in the coil 17. The current flowing in the coil 17 is provided to the controller 23 by a conditioning circuit 25. The controller 23 may be a processor, a microcontroller, and the like.

In an example, the conditioning circuit 25 is connected at A across a resistor R27 on the circuit providing the current to the coil 17. A voltage across A is conditioned by the conditioned circuit 25 and is thereafter, provided to the controller 23. The controller 23 determines the current flowing through the coil 17 responsive to the output of the conditioning circuit 25. For example, during a circuit closing motion, the pick-up current is to be provided to the coil 17 for energizing the coil 17. During the circuit closing motion, the switch 19 is turned on to provide the pick-up current to the coil 17. The controller 23 may control the switch 19 by providing a first control signal. Once, the contact element 3 is in contact with the stationary contact element, the current flowing through the coil 17 decreases. This decrease in the current flowing through the coil 17 is detected by the controller 23. The controller 23 in response to the decrease in the current turns off the switch 19 and turns on the switch 21. The switch 21 is operable for high frequency switching to provide the hold-on current to the coil 17. The switch 21 performs the high frequency switching responsive to a second control signal, such as a PWM pulse, provided by the controller 23. The high frequency switching performed by the switch 21 reduces the current flowing through the coil 17 and thus provides the hold-on current to the coil 17 to maintain the contact element 3 in the circuit closing position. The use of two switches 19, 21 for providing the pick-up current and the hold-on current to the coil 17 respectively reduces

electrical losses occurring at the switches 19, 21.

The switch 19 may be a solid state static switch selected such that it is suitable for carrying high currents and the switch 21 may be a solid state static switch selected such that it is capable of performing high frequency switching with minimum switching loses. The switching frequency of the first switch 19 may be less than the switching frequency of the second switch 21. In an embodiment, the switch 19 may be a transistor, such as an IGBT and the switch 21 may be an MOSFE . An IGBT is capable of carrying high currents and an MOSFET is capable of performing high frequency switching with minimum switching loses.

As the switch 19 is suitable for carrying high currents and the switch 21 is suitable for high frequency switching with minimum switching loses, the electrical losses occurring at the switches 19, 21 are reduced, thus reducing the heat dissipation at the switches 19, 21. This enables in

eliminating the requirement of using bulky heat sinks and thus reduction in size of the electromagnetic switching device. Additionally, the longevity of the switches 19, 21 is increased due to the reduction in heat generated.

In an alternate embodiment, during the circuit closing motion, the switch 19 may be turned on to provide the pick-up current to the coil 17 and the switch 21 also may be turned on to carry a fraction of the pick-up current. The controller 23 may provide control signals to the first switch 19 and the second switch 21 respectively to turn on both the switches 19, 21 during circuit closing motion. This enables in further reducing the electrical losses at the switch 19, thus reducing the heat generated at the switch 19. Similarly, for maintaining the contact element 3 of FIG la in circuit closing position, the switch 21 may be turned on to provide the hold-on current to the coil 17 and the switch 19 may also be turned on to carry a fraction of the hold-on current. The controller 23 may provide control signals to the first switch 19 and the second switch 21 respectively to turn on both the switches 19, 21 for maintaining the contact element 3 in circuit closing position. This enables in further reducing the electrical loses at the switch 21, thus reducing heat generated at the switch 21. The embodiments described herein enable reducing electrical losses occurring at the switch, thereby reducing the heat dissipation at the switch. This enables in eliminating the requirement of using bulky heat sinks and thus reduction in size of the electromagnetic switching device. Additionally, the longevity of the switches is increased due to the reduction in the heat dissipated. This enables in providing efficient switching in order to provide the pick-up current and the hold-on current to the coil.

While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments. Rather, in view of the present disclosure which describes the current best mode for

practicing the invention, 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 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.