Drive mechanism for switchgear The present invention relates to a drive mechanism for switchgear and more particularly to a drive mechanism for a circuit breaker.

Switchgear is a combination of electrical disconnect

switches, fuses or circuit breakers for controlling,

protecting and isolating electrical equipment. A circuit breaker is designed to protect an electrical circuit from an overload or short-circuit. Typically, the circuit breakers are automatically operated electrical switch. The circuit breaker responds to a fault condition and immediately

discontinues electrical flow by interrupting continuity in the electrical flow.

Circuit breakers use drive mechanism to tension a relatively strong spring, with sufficient energy potential to turn the circuit breaker open and close again either manually or with an aid of a motor. The drive mechanism can function as a step drive in which after the motor is turned on, the spring is tensioned far enough to store the required energy for the subsequent release of a switch mechanism. Alternatively the drive mechanism can operate as a storage drive, in which the energy stored by the spring can be released in any desired manner at a desired moment for switching. Drive mechanism typically use a free-wheel which is a subassembly used to operate a high voltage circuit breaker. In the drive mechanism, closing spring is charged by the motor by means of free-wheel assembly. Initially closing spring is in discharged condition. A charging shaft is rotated by means of the motor connected to a shaft and gear, through a gear train to charge the closing spring. A transport lever, engages in the cam on the charging shaft and rotates the cam till the transport lever reaches the upper dead center. At this point transport lever gets disengaged from the cam due to the positioning of a triangular plate on fixed drive housing. Thus the motor is disengaged from the cam after the spring is charged.

Such an arrangement typically employs a number of components thereby increasing the cost.

It is therefore an object of the present invention to provide a drive mechanism for switchgear and particularly for a circuit breaker which employs less components and is

additionally cost effective.

The object is achieved by providing a drive mechanism for a switchgear according to claim 1.

According to the invention a drive mechanism for switchgear is provided. The drive mechanism includes a first gear wheel having a first gear ratio, the first gear wheel having a protrusion along a radius of the first gear wheel, a second gear wheel having a second gear ratio, the second gear wheel having a groove along a radius of the second gear wheel, and a charging shaft having a first end and a second end wherein the first gear wheel and the second gear wheel are mounted coaxially on the charging shaft at the first end, such that the protrusion in the first gear wheel engages with the groove on the second gear wheel to rotate the second gear wheel and the charging shaft and wherein the charging shaft is coupled to a spring at the second end of the charging shaft, such that the spring is compressed by rotation of the charging shaft. By having different gear ratios for the first gear wheel and the second gear wheel, the second gear wheel rotates faster thereby rotating the charging shaft which in turn compresses the spring. The engagement of protrusion in the first gear wheel with the second gear wheel enables the second gear wheel to rotate to a desired position in order to charge the spring. In one embodiment, the first gear wheel is mounted on a bearing of the charging shaft such an arrangement enables rotation of the first gear wheel even when the charging shaft is stationary.

In one embodiment, the first gear wheel comprises a first rim having teeth thereon. The teeth on the rim enable engagement of the first gear wheel with a second shaft which in turn is driven by a motor.

In another embodiment, the second gear wheel includes a second rim having teeth on at least a portion of the rim. By having partial teeth on the rim, the second gear wheel is engaged with the second shaft for a desired angle

irrespective of the engagement of the first gear wheel with the second shaft. Thus, the partial teeth move the second gear wheel by a particular angle.

In one embodiment, the second shaft is engaged with the first gear wheel and second gear wheel enabling rotation of the first gear wheel and the second gear wheel .

In one embodiment, the charging shaft is a crankshaft.

Crankshaft enables reciprocating rotary motion into a linear motion thereby enabling rotation of crankshaft to charge and discharge the spring attached at the second end of the shaft.

In one embodiment, the first gear wheel includes a first side and a second side wherein the protrusion is present on the second side. Additionally, the second gear wheel includes a first side and the second side wherein the groove is present on the first side. Such an arrangement enables engagement of the protrusion on the first gear wheel with the groove on the second gear wheel .

In one embodiment, the span of teeth on the second rim of the second gear wheel is about 120 degrees. Such an arrangement enables the second gear wheel to be rotated for a certain extent only, which is about 120 degrees due to the span of teeth .

The above-mentioned and other features of the invention will now be addressed with reference to the accompanying drawings of the present invention. The illustrated embodiments are intended to illustrate, but not limit the invention. The drawings contain the following figures, in which like numbers refer to like parts, throughout the description and drawings.

FIG. 1 is a schematic diagram depicting an exemplary drive mechanism,

FIG. 2 is a schematic diagram of a first gear wheel of the drive mechanism of FIG. 1,

FIG. 3 is a schematic diagram of a second gear wheel of the drive mechanism of FIG. 1, FIG. 4 is a schematic diagram depicting a view of the drive mechanism with a spring in discharge state, and

FIG. 5 is a schematic diagram depicting a view of the drive mechanism with the spring in charge state, in accordance with aspects of the present technique.

Embodiments of the present invention relate to a drive mechanism for switchgear, such as but not limited to gas insulated switchgear. The exemplary drive mechanism may also be used in circuit breakers, such as but not limited to a high voltage circuit breaker or a medium voltage circuit breaker. Typically, these circuit breakers are employed in switchgears as mentioned above. Referring to FIG. 1, a drive mechanism 1 for switchgear and particularly for a circuit breaker is depicted. The drive mechanism includes a first gear wheel 4 and a second gear wheel 6 adjacent each other and mounted on a charging shaft 10.

The charging shaft 10 has a first end 12 and a second end 14. At the first end 12, the first gear wheel 4 and the second gear wheel 6 are mounted.

In accordance with aspects of the present technique, the first gear wheel 4 is mounted on a bearing 18 of the charging shaft 10. The second gear wheel 6 is mounted directly onto the charging shaft 10. More particularly, the second gear wheel 6 is splined to the charging shaft 10.

In the presently contemplated configuration, the charging shaft 10 includes ridges or teeth that mesh with ridges or teeth in the second gear wheel 6. Such an arrangement enables transfer of torque from the second gear wheel 6 to the shaft 10, thereby rotating the charging shaft 10. The second end 14 of the charging shaft 10 is connected to a spring 20, which is a charging spring according to the present configuration. More particularly, the second end 14 of the charging shaft 10 is coupled to a tie bar 16, which moves linearly along an axis perpendicular to a linear axis of the charging shaft 10.

It may be noted that the charging shaft 10 is a crankshaft, which rotates around the linear axis. The second end 14 of the shaft 10 while rotating, transfers the rotating motion into linear motion of the tie bar 16 connected to it. The linear motion of the tie bar 16 compresses or charges the spring 20.

In accordance with the aspects of the present technique, the drive mechanism 1 further includes a second shaft 22 engaged with the first gear wheel 4 and the second gear wheel 6, a motor (not shown) may be used to drive the second shaft 22. The spring 20 is pre-compressed due to the rotation of the shaft 22 manually or by a motor.

The first gear wheel 4 includes teeth 26 which are engaged with the ridges in the second shaft 22 enabling rotation of the first gear wheel 4. It may be noted that the second gear wheel 6 is engaged with the first gear wheel 4 due to an arrangement which will be described in more detail with reference to FIG. 2 and FIG. 3.

Referring now to FIG 2 and FIG. 3, the first gear wheel 4 has a first side 30 and a second side 32, a first rim 25 having teeth 26 thereon. The teeth 26 are present on the entire rim 25. A protrusion 34 is present along the radius of the first gear wheel 4. More particularly, the protrusion 34 is located at a particular radial distance from the center of the first gear wheel 4. The second gear wheel 6 also has a first side 44 and a second side 46, a second rim 40 which includes teeth 42 on a portion of the second rim 40. A groove 48 is present on the first side 44 of the second gear wheel 6 at a second radial distance from the center of the second gear wheel 6, such that the first radial distance of the first gear wheel 4 and the second radial distance of the second gear wheel 6 are same .

In accordance with aspects of the present technique, the first gear wheel 4 and the second gear wheel 6 are mounted on the charging shaft 10 adjacent one another. Particularly, the second side 32 of the first gear wheel 4 is adjacent the first side 44 of the second gear wheel 6. The protrusion 34 on the first gear wheel 4 engages with the groove 48 on the second gear wheel 6. The engagement enables rotation of the second gear wheel 6 with the first gear wheel 4. It may be noted that the groove 48 has an extent of about 270 degrees from the center, however, the extent of the

protrusion 34 on the first gear wheel 4 is about 15 to about

20 degrees, which is quite small as compared to the groove 48. Upon engagement of the protrusion 34 with the groove 48, there is a formation of a buffer space in the groove.

Additionally, the first gear wheel 4 and the second gear wheel 6 have a first gear ratio and a second gear ratio respectively. The first gear ratio of the first gear wheel 4 is higher than the second gear ratio of the second gear wheel 6. Such an arrangement enables a faster rotation of the second gear wheel 6 than the first gear wheel 4. Due to this faster rotation of the second gear wheel 6, the buffer space is provided.

As previously noted, the second gear wheel 6 has a portion of the second rim 40 with teeth 42 thereon. The extent of the teeth 42 may be about 120 degrees and in one embodiment, the teeth may be about 37 in number. The teeth 42 on the second gear wheel 6 engage with the ridges on the second shaft 22 enabling rotation of the second gear wheel 6 till the

engagement of the teeth 42 with the second shaft 22.

Furthermore, the groove 48 in the second gear wheel 6 extends from a first end 49 to a second end 50. During operation the protrusion 34 on the first gear wheel 4 is engaged to the groove 48 on the second gear wheel 6. When the protrusion 34 on the first gear wheel 4 comes in contact with the first end 49 of the groove 48 on the second gear wheel 6, the second gear wheel 6 is rotated along with the first gear wheel 4, which is continuously engaged with the second shaft 22 along the first rim 25, as previously noted.

Referring now to FIG. 4 and FIG. 5, the drive mechanism 1 with the spring 20 in discharged condition and charged condition respectively is depicted. In FIG. 4 and FIG. 5 the front view of the drive mechanism 1 is depicted alongwith various components such as the first gear wheel 4, the second gear wheel 6, the charging shaft 10, the protrusion 34 and the groove 48. In the presently contemplated configuration, the second end 14 of the charging shaft 10 is connected to the spring 20 via the tie bar 16. As previously noted, the first end 12 of the charging shaft 10 is splined with the second gear wheel 6 and the first gear wheel 4 adjacent the second gear wheel 6. The first gear wheel 4 is mounted on the bearing 18 of the charging shaft 10.

As depicted in FIG. 4, the charging shaft 10 is at a first position 50, which is at an angle of about 5 degrees to about 10 degrees from a vertical axis ^λ Υ' . The spring 20 is pre- compressed either manually or by the motor (not shown) , resulting in the deviation of charging shaft 10 from the vertical axis ^λ Υ' during the discharged condition.

The second shaft 22 which is coupled to the motor is rotated as soon as the motor is switched on. The protrusion 34 on the first gear wheel 4 engages at the first end 49 of the groove 48 on the second gear wheel 6.

As previously noted, the first gear wheel 4 is continuously engaged with the second shaft 22. Hence, as the second shaft 22 rotates, the first gear wheel 4 is also rotated which causes the spring 20 to compress or charge further. The second gear wheel 6 is rotated alongwith the first gear wheel 4, but initially the second gear wheel 6 is not engaged with the second shaft 22 due to the presence of partial teeth 42 on the second rim 40. The second gear wheel 6 is rotated alongwith the first gear wheel 4, since the protrusion 34 in the first gear wheel 4 is in contact with the first end 49 of the groove 48 of the second gear wheel 6. The teeth 42 on the second gear wheel 6 get engaged with the second shaft 22, which rotates both the second gear wheel 6 and the first gear wheel 4

simultaneously. As previously noted, the first gear wheel 4 has the first gear ratio and the second gear wheel 6 has the second gear ratio, such that the first gear ratio of the first gear wheel is higher than the second gear ratio of the second gear wheel 6 thereby causing the second gear wheel 6 to rotate faster than the first gear wheel 4.

The spring 20 is further compressed or charged due to the rotation of the charging shaft 10 which is splined with second gear wheel 6. The second rim 40 of the second gear wheel 6 includes teeth 42 only partially or in a portion of the second rim 40, hence the second gear wheel 6 is engaged to the second shaft 22 for a limited extent. As depicted in FIG. 5, the charging shaft 10 rotates counter clockwise in the present configuration and passes the

vertical axis ^λ Υ' , which is typically a top dead center, to move to a second position 52 where the spring 20 is

compressed or charged.

The charging shaft 10 typically rotates about 180 degrees from the first position 50 to the second position 52 to compress or charge the spring 20. After passing the vertical axis ^λ Υ' the charging shaft 10 further rotates and the spring 20 gets relaxed by about 6 degrees to 10 degrees, due to which the second gear wheel 6 is disengaged with the second shaft 22. However, the first gear wheel 4 is engaged with the second shaft 22 which is driven by the motor. With continuing reference to FIG. 5, the buffer space 56 in the groove 48 is present after the rotation of the second gear wheel 6 and the first gear wheel 4. The second gear wheel 6 comes back to the first position 50 as depicted in FIG. 4 as soon as the spring 20 is discharged. The

discharging of spring 20 rotates the charging shaft 10 in counter clockwise direction to bring it to the first position 50 as depicted in FIG. 4. Again the first gear wheel 4 rotates due to engagement with the second shaft 22 driven by the motor to charge the spring 20 as described above.

Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the embodiments of the present

invention as defined.