DESC:TECHNICAL FIELD OF THE INVENTION

The present invention relates to switching devices. More particularly, the present invention provides a contact erosion indication arrangement used in switchgear for indicating the status of contact condition.

BACKGROUND AND THE PRIOR ART

In Industrial, residential or commercial applications, huge number of switching device are used. Devices like contactors, MCB, MCCB, ACB, etc may be subjected to many intended and/or unintended switching operations in normal and/or in abnormal conditions irrespective of load.

During such switching operations unwanted arcing occurs, which in most of the cases unintended/unintentional. Arcing, which occurs due to breakdown of dielectric strength of the medium between the two contacts of the switching device, accompanies generation of high temperatures and transfer of material from contact system to component/parts surrounding it, leading to erosion of material from the main contact surface of the switchgear.

Erosion of main contact material leads to rise in temperature of the contact systems during passage of normal operating current which is not desirable and leads to furthermore problems.

US2005224331 disclosed a switch contact arrangement with a first moving switch contact, with a second switch contact, provided for the first switch contact and with an erosion display, for the switch contacts. The erosion display comprises an erosion pointer and a display surface or display edge. The display pointer follows the movement of the first switch contact and, on closing the contacts, then only extends over the display surface or display edge when the value for the erosion of the switch contacts is less than a given maximum value.; In order to be able to shorten the display pointer in the unused condition without a special tool to give a separation from the display surface or display edge, the value of which corresponds to the value of the maximum permitted erosion of the switch contacts, at least one marking for the cutting of the display pointer is provided, whereby the marking is separated from the display surface or display edge by the maximum permitted erosion of the switch contacts.
Disadvantages/drawbacks of current arrangement :
· The current arrangement needs pointer component as indicator and also tool to cut the extra pointer component.
· The pointer is connected to one of the fingers (group of contacts in moving contact) used in moving contact and it will not indicate erosion of other fingers/moving contact where pointer is not attached.
· Need to adjust the pointer by cutting it on every fresh sample.

The present invention provides a contact erosion indication arrangement intimating the user about contact maintenance and replacement condition.
OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide a contact erosion indication arrangement used in switchgear for indicating the status of contact condition.

Another object of the present invention is to provide a contact erosion indicator which indicates the Electrical life of the contacts i.e. threshold limit of erosion beyond which the switchgear fails to carry rated current.

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.

In an aspect of the present invention, there is provided an arrangement for indicating the condition of a main contact(s) in switchgear, said arrangement comprising:
a contact system comprising:
a fixed terminal/contact;
a distinct moving terminal/contact assembly;
an indicator having a substantially step structure depicting desired number of regions/bands indicating the condition of said contact(s);
wherein said indicator positioned in the switchgear so as to measure the position of a moving contact surface of the moving contact from a desired reference surface for determining the condition of said main 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.

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 erosion indication window 4 in switchgear and moving contact assembly inside the switchgear.

Figure 2 illustrates the exploded view of contact erosion indicator 5 arrangement on moving contact assembly 8.

Figures 3, 4 and 5 illustrate the different position of moving contact surface 3 indicated by indicator 5.

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 INVENTION

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.

Accordingly, present invention provides a contact erosion indication arrangement used in switchgear for indicating the status of contact condition. The indicator 5 consists of an arrangement similar to one shown in figure 2. The different bands of the indicator 5 indicate contact condition from good to bad. The indicator 5 indicates the condition of contacts by taking surface 2 as reference surface. The position of indicator 5 in switchgear may vary with respect to application of switchgear. The indicator 5 has steps as shown in figure 2 and so irrespective of ash deposition on indicator it will give clear indication.

The range of the indication Good to Bad is totally depend on the allowable limit of the erosion of the switchgear contacts and it may be depend on the application of the switchgear. The indicator may be of any material depending on the application.

This type of indicator has following advantages:
· Clear and easy indication.
· Multiple number of indication ranges possible between good to bad i.e. 20% erosion, 40% erosion, etc.
· Fixed and steady reference.
· No specific material requirements.
· No electronic circuit require for indication.

Such advantages are available from a very simplified design which meets up to the industrial working standards and has a more professional approach compared to the existing solutions available.

WORKING
The faults and switching operations of switchgear will lead to erosion of the contacts and it will reduce the contacts life. During ON operation, moving contact 8 travels towards the fixed contact 7 and, the relative distance between the two contacts keeps on decreasing which leads to breakdown of dielectric strength of the medium when gap decreases to a certain minimum value leading to generation of arc. Similarly during OFF operation, moving contact 8 travels away from the fixed contact 7 and, the relative distance between the two contacts keeps on increasing. In this case, due to opening of the contacts arcing occurs and it gets extinguished with the increasing distance as dielectric strength is regained by the medium.

The switching operations in faulty conditions [e.g. Short Circuit] generates heavy arcing at high temperatures in switchgears which reduces the contact life. Thus to find out the erosion and/or the remaining life of the contact, some type of indication is required to indicate safe operating range.

The arrangement can be located such that any surface 2 can be taken as reference. The arrangement should be located such that the indication should be clearly visible from indication window 4 or from outside. The arrangement will locate the position of the moving contact surface 3 with respect to the reference surface 2 on the steps of indicator 5.

When the switchgear is turned ON, the condition of moving contact assembly 8 would be as depicted in figure 2. Now as contacts get eroded, the moving contact finger 6 will move towards the fixed contact 7 and so the position of the moving contact surface3, which moves away from reference surface 2 will be taken for indication. The moving contact surface3 will take different positions as the main contact 1 is eroded. The different position of moving contact surface 3 will be indicated by indicator 5 as in Figures 3, 4 and 5.

As shown in figure 3 the main contact 1 has good/healthy thickness to make and break the rated current and so the moving contact surface 3 is in the good region of indicator 5.

As shown in figure 4 the main contact 1 is eroded up to some extent as a result moving contact surface 3 gets displaced correspondingly forward towards fixed contact 7. In this range the thickness of the main contact 1 gets reduced by extent such that it may carry the rated current but may fail in breaking and/or making operation in rated or fault condition. Thus in this range, contact quality starts deteriorating and it indicates maintenance requirements of contacts. This range indicates threshold limits for the breakers that beyond this range breaker may fail to break and/or make fault current.

As shown in figure 5 the main contact 1 is eroded totally and so the moving contact surface 3 come into contact replacement zone which means contact life is over.

ADVANTAGES:
· Simple Design and cost effective solution
· Clear visibility in indication
· Clear indication even after ash and carbon deposition from arcing.
· Multiple stage indications like contacts are in 1) Good, 2) Intermediate, 3) Bad condition.
· Easy to understand/interpret.
· No effect of vibration and ON-Off operations on indicator position.
,CLAIMS:1. An arrangement for indicating the condition of a main contact(s) in switchgear, said arrangement comprising:
a contact system comprising :
a fixed terminal/contact (7);
a distinct moving terminal/contact assembly (8);
an indicator (5) having a substantially step structure having desired number of regions/bands indicating the condition of said contact(s) (1);
wherein said indicator (5) positioned in the switchgear so as to measure the position of a moving contact surface (3) of the moving contact (6) from a reference surface (2) for determining the condition of said main contact(s) (1).

2. The arrangement as claimed in claim 1, wherein said indicator (5) having desired number of steps for good region, intermediate region and bad region depending on allowable limit of erosion of said switchgear for determining the condition of said main contact(s) (1).

3. The arrangement as claimed in claim 1, wherein said moving contact surface (3) is adapted to move with respect to said reference surface (2) in said good region of said indicator indicating good condition of said main contact (s) (1) thereby determining the thickness of said main contact(s) (1) in good limit.

4. The arrangement as claimed in claim 1, wherein said moving contact surface (3) is adapted to move with respect to said reference surface (2) in intermediate region of said indicator indicating the eroded condition of said main contact(s) (1).

5. The arrangement as claimed in claim 4, wherein said intermediate region of said indicator (5) determines a threshold limit of reduction in thickness of said moving contact surface (s) (3) thereby facilitating the failure of said main contact (1) to make and/or break contact beyond said threshold limit in normal and/or faulty operation.

6. The arrangement as claimed in claim 1, wherein said moving contact surface (3) is adapted to move with respect to said reference surface (2) in said bad region of said indicator (5) indicating the complete eroded condition of said main contact (s) (1).