FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - A MECHANICAL SYSTEM FOR PREDICTING THE EROSION EXTENT OR THE REMAINING LIFE OF CONATCTS IN SWITCHING DEVICES CONSISTING OF CONTACTS IN AN ENCLOSED CHAMBER
2. Applicant(s)

(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company.
(c) ADDRESS: L & T House, Ballard Estate, Mumbai 400 001,
State of Maharashtra, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to switching devices having vacuum contactors. More particularly, the invention relates to a mechanical system for providing an indication of wear out or erosion of contacts inside a vacuum interrupter and predicting the remaining life time of the contactors.
BACKGROUND AND THE PRIOR ART
Switching devices such as vacuum contactors consist of vacuum interrupters which house the moving as well as the fixed contacts. In the event of continuous operation, these contacts are subjected to erosion. As both of these contacts are enclosed in an evacuated chamber, visual inspection of the contacts for the extent of erosion becomes impossible. Thus, a lever mechanism needs to be developed to facilitate the visual inspection of erosion of these contacts.
Vacuum Contactors, in general, are very reliable and exhibit very high electrical life. Thus, the interrupters, once installed, do not require frequent replacement. The frequency of replacement of coil is comparatively more. Hence coil on top design of contactor is the philosophy used here as reference. Generally contactors are mounted in vertical condition. Thus for the indication to be conspicuous and easy to interpret, it is necessary for it to be on top.
Another reason for the location of erosion indicator on top is due to the fact that vacuum interrupters comprise of very small contact gaps of the order of 2 to 4 mm. If the mechanism to indicate erosion directly uses this travel, it will be neither conspicuous nor the travel sufficient enough to interpret.
The conventional method to check for erosion is to look for the extent by which the contact spring pressure has changed. When this force decreases beyond a certain value, the interrupter needs to be replaced. However, this method is very cumbersome and inaccurate at times. Measurement of spring force in the assembled condition of the interrupter becomes extremely difficult.

US patent 4479042 discloses a mechanism which uses an arrangement of two nuts used to adjust the contact overtravel to depict the extent of erosion. However, in this particular scenario, with the vacuum interrupters enclosed inside housing, visual inspection will be possible only after the housing is opened and since the travels are extremely small, it will be very difficult to measure the extent of erosion. This particular method is also not very suitable because it depends upon the manual adjustment of nuts at a distance equal to the overtravel of the contact which is highly susceptible to human error.
The mechanism described in US patent 6150625 uses an erosion gauge tool for measuring the erosion of movable contact. This erosion gauge consists of a pointer has a handle and a pointer that moves closer to the erosion mark as the movable contact erodes. This erosion gauge is sized to indicate when the movable contact needs to be replaced. The disadvantage of this system is that it consists of too many linkages. Malfunctioning of one can lead to wrong display of the erosion extent. Also a very high precision is required to establish the erosion mark otherwise it may lead to wrong interpretation.
All these disadvantages stated above have been overcome in the present invention.
OBJECTS OF THE INVENTION
One object of the invention is to overcome the disadvantages/drawbacks of the prior art.
A basic object of the present invention is to provide an accurate and conspicuous erosion or remaining life time indicator.
Another object of the present invention is to provide an easy to interpret mechanism comprising of a leverage mechanism.
Another object of the present invention is to convert the very small travel at the vacuum interrupter level to a travel which is long enough to be noticeable.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
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.
There is provided a system to provide an erosion or life time indicator for vacuum interrupters in vacuum contactors.
In one aspect of the present invention, there is provided a system for indicating the extent of erosion of contacts in switching devices. The system comprises:
an erosion indicator shaft(s) (Al, A2, A3) coupled with a vacuum interrupter (s) (A6) by a connecting means;
a coupling mechanism comprising a contact spring support (A4) and a contact spring (A5) for connecting said connecting means with a movable driving shaft;
a spring means (A9) for connecting said indicator shaft (s) (Al, A2, A3) with said movable driving shaft coupled with said connecting means (AS);
a clamp means (A7) for clamping the said indicator shaft(s) to a terminal;
a cap means (A11) at the top of said erosion indicator shaft(s) (Al, A2, A3) comprising color coded bands for indicating extent of erosion of said contact(s);
wherein said system provides a leverage mechanism for indicating the erosion of said contact(s).

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.
DETAILED DESCRIPTION OF THE INVENTION
According to one embodiment of the present invention, there is provided a mechanical system which couples itself with the vacuum interrupter by means of a stud which is attached to the movable driving shaft by means of a coupling mechanism comprising of the contact springs and the contact spring support. Also a part of this mechanism is the retainer pin, which is attached to the stud.
Other embodiment of the present invention provides another mechanical system which consists of the erosion indicator shaft, coupled to the shaft of the above mechanical system by means of a compression spring, which rests on one end at the surface of the erosion indicator shaft and at the other end on the housing which houses this mechanism.
The present invention provides a mechanical system that successfully exhibits the erosion of the vacuum interrupters with a lot of clarity. The object is achieved in accordance with the invention, by providing an erosion indicator shaft, coupled to the vacuum interrupter by means of a stud, and is attached to the terminal at a suitable point to act as fulcrum, thus bringing the advantage of mechanism of leverage to depict the erosion of each of the contacts in the three poles with sufficient travel and clarity.
In normal operating conditions, that is, the contacts have not shown any signs of any erosion whatsoever, the erosion indicator shaft remains in its position, under the effect of the assembled compression spring. As the contacts start eroding, the contacts exhibit larger travels, thus forcing the erosion indicator shaft to travel along with it, under the effect of the compression spring, causing the erosion indicator shaft to move around the fulcrum obtained due to its strategic clamping at the terminal level, causing a

subsequent displacement in the opposite direction as that of the contacts, at the top level, that is, the point where the cap of the erosion indicator is attached with the erosion indicator shaft.
The greater the extent of erosion, the more is the displacement at the contacts , causing a larger displacement at the cap of the erosion indicator level, due to the mechanical advantage is lieu of the mechanism of levers, making the entire mechanism to depict erosion far more easy to visualize and interpret.
Key features of the present invention:
• Easy in construction as the mechanism consists of simple components which work in tandem to provide the desired result.
• Concept of leverage used to provide a mechanism which converts very small travels due to erosion to large displacement, ensuring that the extent of erosion is more clearly visible at the top and hence making it very easy to visualize and interpret.
• An accurate method to predict the remaining life time of the vacuum interrupters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Figure 1 illustrates the entire mechanism
Figure 2 illustrates the per pole assembly of this mechanism with the contacts in healthy condition that is no erosion.

Figure 3 illustrates the per pole assembly of this mechanism with the contacts in fully eroded.
Figure 4 illustrates the top view of the cap of erosion indicator which consists of various colored bands encoding the extent of erosion of contacts.
Figure 5 illustrates the top view of the mechanism as seen from the top clearly indicating the easy visibility of the erosion of each of the contacts inside the interrupter.
Figure 6 illustrates the view of the erosion indicator as seen from the top with the switching device, particularly vacuum contactor mounted in vertical condition.
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 numerals are used to depict the same or similar elements, features and structures.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.
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 and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

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.
It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
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.
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.
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.
Reference is first invited to Fig I where the entire mechanism is shown.
Referring to figure 1, Al, A2 and A3 are the erosion indicator shafts, which are coupled to the vacuum interrupters A6 by means of a stud A8 which serves as a means of coupling at both the ends. The contact spring support A4 is used to hold and locate the contact spring A5. Each of the erosion indicator shafts Al, A2 and A3 is coupled to the terminal by means of a clamp A7. This clamping ensures that a fulcrum is created at the point where the clamp A7 holds the erosion indicator shafts Al, A2 and A3. The

erosion indicator shaft is kept attached with the stud A8 by means of a compression spring A9. This assembly thus brings into picture the mechanism of leverage.
Referring to Figure 2, it shows the per pole assembly of the mechanism. During normal operating conditions, the shaft Al is as shown in the above figure, pivoted by means of the clamp A7. When the contactor is energized, the stud A8 which is attached to the interrupter starts moving. At the end of contact travel, starts the over travel, where the contact spring A5 starts getting compressed. However since the contacts are healthy, the stud would not move ahead during over travel, indicating that there is no need for replacement and the interrupters are healthy. This indication is achieved by means of the cap of the erosion indicator Al 1 which is color coded to indicate the extent of erosion.
Figure 3 depicts the scenario where the contacts have completely eroded. Here the stud A8 will now travel an additional distance corresponding t o over travel and along with it will also cause displacement of the erosion indicator shaft Al. The upper half of Al will move in the opposite direction taking the advantage of the leverage provided in the system to produce corresponding displacement of the cap of the erosion indicator at the top, clearly stating the extent of erosion.
Figure 4 shows the cap of erosion indicator Al 1, which comprises of color coded bands, signifying the extent of erosion. Green color indicates that the interrupters are healthy and the contacts show no or very little sign of erosion (0 to 25%). Yellow color shows that the contacts are eroded from 25 to 50%. Orange color indicates that the erosion level is from 50 to 75%. And finally, the red color states that the erosion has exceeded 75% and the interrupter needs immediate replacement.
As and when the contacts show erosion due to continuous operation, the erosion indicator shaft moves about the fulcrum, and with it moves the cap of the erosion indicator but in a different direction indicating the extent of erosion.
Referring to figure 5 the figure shows the top view of the entire mechanism in which the mechanism is adapted at all the three poles.

Figure 6 shows the top view of the mounted switching device, here contactor. A10 is the slot provided in the top cover to provide for the visibility of cap of erosion indicator A7 consisting of various color encoding the extent of erosion as described above.
The invented system is thus a mechanical system used to indicate the extent of erosion of contacts in switching devices with enclosed contacts, particularly vacuum switching devices.

WE CLAIM:
1. A system for indicating the extent of erosion of contacts in switching devices,
said system comprising:
an erosion indicator shaft(s) (Al, A2, A3) coupled with a vacuum interrupter(s) (A6) by a connecting means(A8);
a coupling mechanism comprising a contact spring support (A4) and a contact spring (A5) for connecting said connecting means (A8)with a movable driving shaft;
a spring means (A9) for connecting said indicator shaft (s) (Al, A2, A3) with said movable driving shaft coupled with said connecting means (A8);
a clamp means (A7) for clamping the said indicator shaft(s) to a terminal; and
a cap means (All) at the top of said erosion indicator shaft(s) ( Al, A2, A3) comprising color coded bands for indicating extent of erosion of said contact(s),
wherein said system provides a leverage mechanism for indicating the extent of erosion of said contact(s).
2. The system as claimed in claim 1, wherein said clamp means (A7) provides a fulcrum where said clamp means (A7) holds said erosion indicator shaft(s) (Al, A2, A3).
3. The system as claimed in claim 1, wherein said contact spring support (A4) is adapted to hold and locate said contact spring (A5) in said coupling mechanism.
4. The system as claimed in claim 1 wherein said connecting means comprises a stud.
5. The system as claimed in claims 1 & 4, wherein said connecting means (A8) attached to said vacuum interrupter (A6) starts moving resulting in compressing of said contact spring (A5) when the system is energized.

6. The system as claimed in claims 1,4 & 5, wherein when said contacts are healthy, said stud moves to an extent which is incapable of displacing said erosion indicator shaft (Al, A2, A3) resulting into no displacement of said cap means (Al 1) indicating said contact(s) are healthy.
7. The system as claimed in claims 1 and 4, 5, wherein when said contacts are eroded, said contacts travel a larger extent than when healthy resulting into travelling a larger distance by said stud leading to displacement of said erosion indicator shaft(s) (Al, A2, A3).
8. The system as claimed in claim 1, wherein said erosion indicator shaft(s) (Al, A2, A3) moves about the fulcrum resulting movement of upper part of said erosion indicator shaft (s) (Al, A2, A3) in opposite direction providing displacement of said cap means (Al 1) which indicate the extent of erosion of said contact(s).
9. The system as claimed in claim 1, wherein said cap indicates by means of different colours different states of the contact(s), namely healthy with erosion up to 25%, unhealthy state with erosion from 25 to 50%, unhealthy state with erosion from 25 to 50%, unhealthy state with erosion from 50 to 75%, and erosion exceeded 75% and the contact(s) requiring immediate replacement.
10. The system as claimed in claim 1, further comprising a slot (A10) in the top cover of said erosion indicator shaft for visibility of said cap means (Al 1).