DESC:TECHNICAL FIELD

[001] The present subject matter described herein, in general, relates to an electrical switching device and more particularly to a tripping assembly in the electrical switching device that is operational when an overcurrent relay senses a fault in a circuit.

BACKGROUND

[002] An electrical switching device may be defined as a unit designed to connect, carry and disconnect electrical supply so as to protect the equipment connected in the electrical circuit from damage caused by overload, under-voltage or short circuit etc. Circuit breakers are well-known devices used to provide automatic circuit interruption, to a monitored circuit, when circuit fault conditions occur. Fault conditions include, but are not limited to, current overload, ground faults, over voltage conditions and arcing faults. The release or disengaging of circuit breaker contacts to interrupt a monitored circuit is commonly referred to as tripping. In other words, a circuit breaker must be able to be switched on and off, and it must open automatically during a fault condition. In order to open automatically, circuit breakers are equipped with some type of tripping mechanism.

[003] The operating mechanism of a circuit breaker in case of a current interruption is usually achieved by having a movable contact that separates from a stationary contact The movable contact is under considerable spring tension to move away from the stationary contact to open the circuit. When the movable contact separates from the stationary contact, it is important that this physical action occurs quickly and reliably to minimize arcing. If the arcing is too intense, it can affect the ability of the circuit breaker to open the faulted circuit. It is also important, in the design of circuit breaker trip mechanisms, that the force required to trip or open the circuit breaker mechanism is minimized. In typical circuit breakers a latching mechanism is used to provide engagement of the circuit breaker contacts. When the circuit breaker contacts are closed or engaged, energy is stored in the contact spring. This energy is locked with the latching mechanism that holds the spring-loaded circuit breaker contacts together through set of linkages. When the latching assembly is de-latched by moving the linkages, the energy stored in the springs is released to trip the breaker. However, the latching mechanism in the circuit breakers must be sensitive enough to trip and open the contacts with minimal force.

[004] Some circuit breakers employ electromechanical tripping mechanisms, some use hydro mechanical tripping mechanisms and some use electronic tripping mechanisms. The existing switchgear products include a tripping assembly with journal bearing at its pivot. However, journal bearings are more susceptible to adhesive wear and experiences high static friction. The use of deep groove ball bearings for tripping purpose is more costly as compared to the other tripping assembly and also such ball bearings has limited dynamic load capacity.

[005] Thus, in view the drawbacks of the exiting tripping assembly in electrical switching devices, there exists a dire need to provide an enhance tripping assembly that provides better reliability of latching and load distribution with high factor of safety of static and dynamic loading.

SUMMARY OF THE INVENTION

[006] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[007] An object of the present invention is to provide a tripping assembly that obviates the drawbacks of the hitherto tripping assembly in an electrical switching device.

[008] Another object of the present invention is to provide a tripping assembly with improved reliability of latching and high dynamic load capability.

[009] Yet another object of the present invention is to provide tripping assembly with high factor of safety due to static and dynamic loading.

[0010] Accordingly, the present invention provides a tripping assembly for separating a pair of electrical contacts in an electrical switching device when a fault is detect in a monitored circuit. The tripping assembly comprises a cam-follower type roller bearing member, bearing housing assembly, and a tripping shaft wherein the cam-follower type roller bearing member further comprises free rollers which forms a contact with the tripping shaft. The present invention provides an arrangement which has a cam-follower type roller bearing in electrical switch, hence stress is given to the said bearing’s usage and unique advantage is achieved because of the same.

[0011] In one implementation, a tripping system to be used in a switching device is disclosed. The tripping system comprises at least one bearing member enclosed in a bearing housing assembly mounted on at least one side plate, wherein said bearing member comprises at least one roller surrounded by an outer ring and rigidly held by at least one stopper plug. Further, the tripping system comprises at least one tripping shaft adapted to transfer force to at least one pole assembly when rotated.

[0012] In one implementation, the present invention provides an improved tripping mechanism using a tripping assembly that separates a pair of electrical contacts in an electrical switching device by rotating a tripping shaft guided using a bearing housing assembly.

[0013] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0014] Figure 1 illustrates a tripping assembly without an engagement of a tripping shaft in a bearing housing assembly, in accordance with an embodiment of the present subject matter.

[0015] Figure 2 illustrates a cam follower type roller bearing member, in accordance with an embodiment of the present subject matter.

[0016] Figure 3 illustrates a bearing holder assembly to be mounted on a tripping mechanism side plate, in accordance with an embodiment of the present subject matter.

[0017] Figure 4 illustrates a final tripping assembly showing an engagement of a tripping shaft in a bearing housing assembly, in accordance with an embodiment of the present subject matter.

[0018] Figure 5 illustrates a cross sectional view of an operating tripping mechanism, in accordance with an embodiment of the present subject matter.

[0019] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0020] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0021] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0022] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0023] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0024] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0025] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0026] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0027] In one implementation, the present invention comprises of a tripping arrangement compassing a bearing housing assembly 2 which includes a cam-follower type roller bearing member 1 rigidly contained in housing 21. Bearing member 1 comprises of series of rollers 12 surrounded by an outer ring 11 rigidly held together by a stopper plug 13 for storage purpose only. These rollers are not having any axial sideways support. Bearing housing assembly 2 once assembled in mechanism side plate, stopper plug 13 is being removed and shaft gets into direct contact with the rollers 12. The sideways axial movement of rollers 12 is restricted by bearing housing and countersunk side plate slot. The system is made OFF by rotating tripping shaft 41 which is guided by the said bearing member 1 on both sides of mechanism. Since there is no inner bearing cage, it has a high dynamic load capability.

[0028] In one implementation, the present invention overcomes the limitation of dynamic load capacity of ball and guided roller bearing. Within the space constraints, this arrangement provides high factor of safety for loading and eliminates the problem of bearing cage breakage issue in impact loading.

[0029] In one implementation, cam follower type bearing has free rollers of 60 Rc hardness which comes directly in contact with the shaft. Since there is no guiding part in the bearing itself, any impact on shaft will be directly transferred to the rollers and finally will be absorbed in the side plate assembly. Hence bearing breakage on its own can be eliminated.

[0030] In one implementation, cam follower type roller bearing member 1 as shown in figure 2 which has a stopper plug 13 is contained in its housing 21 and bearing- holder assembly 2 as shown in figure 3 is mounted in the mechanism side plate 31 (figure 1). Tripping shaft 41 is guided by bearing element on both ends and rollers 12 are in direct contact with the shaft around its periphery. While assembling trip shaft 41 on side plate 31, the stopper plug 13 is taken out. Final assembly is shown in figure 4. Figure 5 shows the cross section of operating mechanism. Tripping shaft 41 has a latched kinematic linkage which, transfer force to the Pole assembly when shaft 41 is rotated. Hence the tripping shaft feels a dynamic loading and in the loaded condition it has to oscillate. The dimensions of the bearing are as follows: Outer diameter 17mm, inner diameter 8mm, bearing width 4.5mm.

[0031] In one implementation, a tripping arrangement 1 is pivoted rigidly on the pivot shaft 41 conforming only single degree of freedom on its own axis. The bearing member 1 ensures proper engagement of the bearing needle rollers on the Tripping shaft 41. Hence there is no need for lubrication needed at the interaction. On rotation of tripping arrangement on its axis ensures change in position of individual needle rollers on the direction of force every time hence overcomes phenomenon of stiction when mechanism is latched for longer period. The consistency in the torque transmission could be achieved by reducing the static friction losses of the joint by introducing the bearing member 1 in the closing circuit which has 0.005 coefficient of static and rolling friction as against 0.1 in case of journal bearing.

[0032] Figure 1 illustrates a tripping assembly without an engagement of a tripping shaft in a bearing housing assembly. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0033] Figure 2 illustrates a cam follower type roller bearing member. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0034] Figure 3 illustrates a bearing holder assembly to be mounted on a tripping mechanism. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0035] Figure 4 illustrates a final tripping assembly showing an engagement of a tripping shaft in a bearing housing assembly. A person skilled in the art will appreciate that for understanding purpose the present invention is explained with the help of electronic protection relay however the disclosed method shall not be considered as the limiting factor for the scope of present invention.

[0036] Referring now to figure 1, in one implementation, a tripping assembly encompassing a bearing housing assembly (2) mounted on a mechanism side plate (31) and a tripping shaft (41). The arrangement indicates the tripping assembly when the tripping shaft (41) is not engaged in the bearing housing assembly (2).

[0037] Referring now to figure 2, in one implementation, a cam follower type roller bearing member (1) comprises series of rollers (12) surrounded by outer ring (11) rigidly held together by a stopper plug (13) for storage purposes.

[0038] Referring now to figure 3, in one implementation, a cam follower type roller bearing member (1) is rigidly contained in a housing (21).

[0039] Referring now to figure 4, in one implementation, the final tripping assembly that causes a pair of contacts in a electrical switching device to open by rotating tripping shaft (41) guided by the said cam follower type roller bearing member (1) on both sides of mechanism side plate (31).

[0040] Referring now to figure 5, in one implementation, said tripping shaft (41) has a latched kinematic linkage which, transfer force to the pole assembly when the tripping shaft (41) is rotated. Hence the tripping shaft (41) feels a dynamic loading and in the loaded condition it oscillates.

[0041] In one implementation, said cam follower type roller bearing member (1) is pivot rigidly on the tripping shaft (41) conforming only single degree of freedom on its own axis. The cam follower type roller bearing member bearing (1) ensures proper engagement of the bearing needle rollers on the Tripping shaft (41). On rotation of tripping shaft (41) on its axis, change in position of individual needle rollers on the direction of force is ensured every time which overcomes phenomenon of stiction when tripping shaft (41) is latched for longer period. The consistency in the torque transmission is achieved by reducing the static friction losses of the joint by introducing the cam follower type roller bearing member(1) in the closing circuit which has 0.005 coefficient of static and rolling friction as against 0.1 in case of journal bearing.

[0042] In one implementation, the dimensions of a cam follower type roller bearing member (1) includes outer diameter 17mm, inner diameter 8mm and bearing width 4.5mm.

[0043] In one implementation, series of rollers (12) does not having axial sideways support. The bearing housing assembly (2) once mounted on the mechanism side plate (31), storage plug (13) is being removed and tripping shaft (41) comes into direct contact with the rollers (12).

[0044] In one implementation, cam follower type roller bearing member (1) has free rollers of 60 Rc hardness which comes directly in contact with the tripping shaft (41). This prevents bearing leakage by transferring an impact on the tripping shaft (41) to the roller and later gets absorbed by the side plate assembly.

[0045] In one implementation, the cam-follower type roller bearing member (1) and the bearing housing assembly (2) is mounted on at least one side of a tripping mechanism side plate (31).

[0046] Some of the important features of the present invention, considered to be noteworthy are mentioned below:
1. The present invention provides enhanced reliability in transmission of direction of forces.
2. The present invention provides enhanced reliability of operation even under no lubrication.
3. The present invention provides an economical option as compact size of needle roller bearing which can be fitted easily into a compact mechanism assembly.
4. The present invention provides a dynamic load carrying capacity as high as 4.8 kN as against 1.4 kN in case of ball bearing.
5. Needle roller and cage assembly bearings differ from general bearings in that, if the shaft and bearing housing can be made to a specific hardness, accuracy, and surface roughness, the needle roller and cage assemblies can function as independent bearings without inner and outer rings.
,CLAIMS:1. A tripping system to be used in a switching device, CHARACTERIZED IN THAT comprising:
at least one roller bearing member (1) having at least one free roller (12) enclosed in a bearing housing assembly (2) mounted on at least one side plate (31) of a mechanism, wherein said bearing member (1) comprises at least one roller (12) surrounded by an outer ring (11) and rigidly held by at least one stopper plug (13);
at least one tripping shaft (41) adapted to transfer force to at least one pole assembly when rotated.

2. The tripping system as claimed in claim 1, wherein said bearing housing assembly (2) is comprises a housing (21) at one end and at least one slot at other end, said slot is used to mount/fix said bearing housing assembly (2) on said side plate (31) of mechanism .

3. The tripping system as claimed in claim 1 and 2, wherein said roller bearing member (1) is a cam-follower type roller bearing member (1) enclosed in a housing (21) of said bearing housing assembly (2).

4. The tripping system as claimed in claim 1, said tripping shaft (41) is adapted to pass through said bearing member (1) and contact said roller (12) around its periphery.

5. The tripping system as claimed in claim 4, wherein said tripping shaft (41) is adapted to rotate under guidance of said bearing member (1) on both sides.

6. The tripping system as claimed in claim 1, wherein said roller (12) has a specific hardness, preferably of 60 Rc hardness.

7. The tripping system as claimed in claim 1, wherein said bearing member (1) comprises:
an outer diameter, preferably of 17mm;
an inner diameter, preferably of 8mm; and
said bearing width, preferably of 4.5mm.

8. The tripping system as claimed in claim 1, wherein said bearing member (1) is adapted to achieve 0.005 coefficient of static and rolling friction.

9. The tripping system as claimed in claim 1, wherein when said stopper plug (13) is removable, on removal of which said tripping shaft is in direct contact with said roller (12).

10. The tripping system as claimed in claim 1, wherein said tripping system is pivoted rigidly on said tripping shaft (41) conforming only single degree of freedom on its own axis.