Spring operated actuator

1. A spring operated actuator for an electric switching apparatus including an actuation spring to provide an actuating movement of the switching apparatus and a rotary air damper connected to the actuation spring, the damper is arranged to decelerate the spring movement during at least an end portion of the actuating movement, the damper having a toroidal working chamber formed by first and second circumferential housing parts which are rotatable relative to each other, each housing part having internal walls which together define the working chamber, the first housing part having a rotatable displacement wall, sealingly rotatable in said working chamber, the second housing part having a stationary end wall of the working chamber, wherein at least one of said housing parts is provided with at least one recess in its internal walls, the recess when provided in the second housing part is located less than 90° ahead the end wall as seen is the rotational direction of the displacement wall at an actuating movement, and the recess in the second housing part has an extension in the circumferential direction that is larger than the effective thickness of the displacement wall, and the recess when provided in the first housing part is located less than 90° ahead the displacement wall as seen in the rotational direction of the displacement wall at an actuating movement, and the recess in the first housing part has an extension in the circumferential direction that is larger than the effective thickness of the end wall.

2. The spring operated actuator according to claim 1 , wherein said actuation spring is a closing spring and said actuating movement is a closing movement.

3. The spring operated actuator according to claim 1 , wherein said recess has an extension in the circumferential direction that is longer than its extension in a direction perpendicular to the circumferential direction.

4. The spring operated actuator according to claim 1 , wherein said recess has an extension in the circumferential direction that is 2-20 times longer than the effective thickness of the displacement wall or the end wall.

5. The spring operated actuator according to claim 1 , wherein said recess has an extension in the circumferential direction that is within the range of 5°-90°.

6. The spring operated actuator according to claim 1 , wherein said recess is arranged in a side wall of said internal walls.

7. The spring operated actuator according to claim 1 , wherein the recess has an elongated extension in the circumferential direction and has the shape of a circular curve around the axis of the toroidal working chamber.

8. The spring operated actuator according to claim 1 , wherein the depth of the recess is within the range of 0.5 to 5 mm.

9. The spring operated actuator according to claim 1 , wherein a plurality of recesses are arranged in the internal walls of said at least one of housing parts.

10. The spring operated actuator according to claim 1 , wherein the cross section of the toroidal working chamber is substantially rectangular.

11. The spring operated actuator according to claim 9 , wherein the recesses are arranged on the side wall, on the radially outer wall and/or on the radially inner wall of said internal walls.

12. The spring operated actuator according to claim 9 , wherein the recesses overlap each other, at least partly, in the angular direction.

13. An electrical switching apparatus including a spring operated actuator to provide an actuating movement of the switching apparatus and a rotary air damper connected to the actuation spring, the damper is arranged to decelerate the spring movement during at least an end portion of the actuating movement, the damper having a toroidal working chamber formed by first and second circumferential housing parts which are rotatable relative to each other, each housing part having internal walls which together define the working chamber, the first housing part having a rotatable displacement wall, sealingly rotatable in said working chamber, the second housing part having a stationary end wall of the working chamber, wherein at least one of said housing parts is provided with at least one recess in its internal walls, the recess when provided in the second housing part is located less than 90° ahead the end wall as seen is the rotational direction of the displacement wall at an actuating movement, and the recess in the second housing part has an extension in the circumferential direction that is larger than the effective thickness of the displacement wall, and the recess when provided in the first housing part is located less than 90° ahead the displacement wall as seen in the rotational direction of the displacement wall at an actuating movement, and the recess in the first housing part has an extension in the circumferential direction that is larger than the effective thickness of the end wall.

14. The electrical switching apparatus according to claim 13 , wherein the switching apparatus is a circuit breaker.

15. The spring operated actuator according to claim 1 , wherein said recess has an extension in the circumferential direction that is 5-10 times longer than the effective thickness of the displacement wall or the end wall, respectively.

16. The spring operated actuator according to claim 2 , wherein said recess has an extension in the circumferential direction that is longer than its extension in a direction perpendicular to the circumferential direction.

17. The spring operated actuator according to claim 1 , wherein said recess has an extension in the circumferential direction that is within the range of 15°-40°.

18. The spring operated actuator according to claim 2 , wherein said recess is arranged in a side wall of said internal walls.

19. The spring operated actuator according to claim 11 , wherein the recesses overlap each other, at least partly, in the angular direction.