Claims:1. A switchgear with extensibility interlock, wherein the switchgear is a Ring Main Unit (RMU) (4) comprising:
a ring switch;
a ring switch fascia (3) provided on the front outer surface of the RMU (4);
a first lock (2) positioned on the ring switch fascia (3);
a key (1) disposed in the first lock (2);
an extensible bushing box (5) positioned atop the RMU (4);
a second lock (10) positioned on the extensible bushing box (5);
wherein the key (1) transition from the first lock (2) of the ring switch fascia (3) to the second lock (10) of the extensible bushing box (5) takes place only when the ring switch is put to earth position to avoid access to the extensible bushing in operating condition.

2. The switchgear as claimed in claim 1, wherein the key from the first lock (2) is released once the ring switch is in earth position.

3. The switchgear as claimed in claim 1, wherein the position of the ring switch cannot be changed until the key (1) is trapped in the second lock (10) of the extensible bushing box.

4. The switchgear as claimed in claim 1, wherein the extensible bushing box (5) comprises a housing (7), a front bracket (6) and a rear bracket (8).

5. The switchgear as claimed in claim 1, wherein the extensible bushing box (5) comprises a locking mechanism (9) adapted to lock the extensible bushing box (5) in closed position to avoid access to unearthed extensible bushing.
, Description:TECHNICAL FIELD OF THE INVENTION
The present invention relates to an interlock device of switchgear, and more particularly, to an interlock device of switchgear in which an extensible bushing/PDS can be accessed only after the functional unit (incomer) is in earth position & vice versa.

BACKGROUND OF THE INVENTION
In the electric power switchgear art, it is customary practice to house removable circuit breaker units in individual cells or compartments of a grounded sheet-metal enclosure. The current-conducting parts of the circuit breaker are connected for energization to associated supply and load circuits by means of cooperating, separable disconnect members, with suitable means being provided for racking the breaker unit to and from its connected or fully inserted position within the compartment. Thus the breaker unit can be readily withdrawn from its housing for repair or maintenance purposes.

The document CN203573857U discloses a solid insulating ring network cabinet, particularly to metal-enclosed solid insulation RMU interlocking means. At present load switches, circuit breakers, fuses Switchgear and more into a single product, a combination of switchgear become a trend. The combined operation panel appears multiple windows, likely to cause malfunction, causing the circuit grid fault. Thus, the interlocking solid insulated metal-enclosed RMU respective switches on the panel operation, a key safe operation.

The document CN103943391B discloses, a ring counter, and more particularly to a novel locking ring counter structure) At this stage, with the handlebar switch RMU with very common, which is a technique using epoxy board blocks handlebar switch after closing, insertion switch movement between the contacts, and impinges interlocking block, by interlocking block and a series of links, to convey it to the hook of the door hook decoupling, this time can be open, the switch cannot be blocked by closing disconnectors; open the door, the door hit the block from interlocking pieces, the interlock tension spring go back sheet slot epoxy boards, epoxy boards not to lock out, so as to achieve the door is not closed, not closing purposes, we can see a conventional RMU interlocking structure is extremely complex, difficult to install, multi-material cost.

The document CN104377073A relates to the field of electrical equipment, electric power applied particularly to a device and to a solid insulated grounding switch RMU. It RMU solid insulation grounding switch is often used on the market of formula grounding switch, through the ground switch operating mechanism to drive the grounding switch quickly closing operation, when a charging load, short-circuit current generated closing , while using the grounding switch is applied with a blade rotation speed constant closing, which operating mechanism and the transmission portion generates a very high demand, most of the times do not have the ground fault current closing capacity, or current turn is barely twice the number of co-ground short of the requirements of national standards, which brings great risks to the operation of the distribution network, causing severe casualties occurred.

The document CN101916680A discloses, a mechanical linkage mechanism, in particular a mechanical RMU chain, in particular an operating mechanism for chain RMU, belongs to the field of control RMU. As RMU ring power supply, the ring counter structure is relatively simple, the price is relatively low, and the distribution is the most widely used protection circuit electrically controlled; the RMU addition power, long life, open breaking the vacuum load switch resistance and other common advantages, its advantage is easy to implement three operating position (ON, OFF and ground) and a small current (inductance, capacitance) breaking, and having the ability of anti-severe ambient conditions strong. RMU optimum voltage distribution network in the urban and rural application; RMU requires more reliability in operation, to avoid the failure of the power supply apparatus caused by erroneous operation. Currently, RMU operations do not have a chain of operations, easily lead to erroneous operation of the RMU, cannot guarantee the safe use of RMU.

In an electrical power distribution system, switchgear is a factory assembled, metal enclosed panel used at the various transmission and distribution level of an electrical power system. The growing need of the electrical power demands an efficient way for power distribution. As a result of this the extensibility feature in switchgear is introduced. The extensibility enables easy distribution of electrical power. For safety purpose the extensibility requires an interlock in such a manner that the extension bushing/PDS can be accessed only after the incomer is earthed. The extensible bushing/PDS is used to couple two switchgears. Currently there is no such invention to prevent access of the extensible bushing during general operating condition.

For the reasons mentioned above, keeping human safety in mind, earthing the live components before handling is of utmost importance. So for the purpose of coupling, the extensible bushing needs to be earthed.

SUMMARY OF THE INVENTION
The following disclosure 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.

An object of present invention is to overcome the problems of prior art.

Another object of the present invention is to provide switchgear with extensibility interlock which ensures proper earth of the extensible bushing box before it can be accessed, making the extensible bushing safe for coupling.

Another object of present invention to provide switchgear with extensibility interlock having easy and simple design.

Yet another object of present invention is to provide highly reliable switchgear with extensibility interlock.

Yet another object of present invention is to provide switchgear with extensibility interlock having antitheft feature.

Yet another object of present invention is to provide switchgear with extensibility interlock which is less expensive.

The present disclosure provides switchgear with extensibility interlock which ensures proper earth isolation of the extensible bushing box before it can be accessed, making the extensible bushing safe for coupling. It discloses switchgear having an extensibility interlock, where the switchgear is a Ring main unit (RMU). The ring switch facia of the RMU is provided with a lock having a castle key disposed in it. The extensible bushing box is positioned on the top of the RMU and an another lock is provided on the front bracket of the extensible bushing box where the key transition from the first lock of the ring switch fascia to the second lock of the extensible bushing box takes place only when the ring switch(incomer) of the RMU is put to earth position to avoid access to the extensible bushing in operating condition.

One aspect of the present invention is to provide switchgear with extensibility interlock where the key from the first lock of the ring switch fascia releases only when the ring switch(incomer) is in earth position.

Another aspect of the present invention is to provide switchgear with extensibility interlock where the position of the ring switch(incomer) cannot be changed until the key is trapped in the lock of the extensible bushing box.

Yet another aspect of the present invention is to provide switchgear with extensibility interlock where the extensible bushing box has a locking mechanism to lock the extensible bushing box in closed position to avoid access to non-isolated extensible bushing.

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 ACCOMPANYING DRAWINGS
The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 illustrates the schematic view of the ring switch fascia (3) according to one of the embodiments of the present invention.

Figure 2 illustrates the schematic view of the Ring Main Unit (4) according to one of the embodiments of the present invention.

Figure 3 illustrates the schematic view of the exploded Ring Main Unit (4) according to one of the embodiments of the present invention.

Figure 4 illustrates the schematic view of the circuit diagram of the Ring Main Unit (4) according to one of the embodiments of the present invention.

Figure 5(a) - 5(c) illustrates the flowchart of the working according to one of the embodiments of the present invention.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have 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
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure 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 various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be 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 present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

The present disclosure provides switchgear with extensibility interlock which ensures proper isolation of the extensible bushing before it can be accessed, making the extensible bushing safe for coupling. It discloses switchgear having an extensibility interlock, where the switchgear is a Ring main unit (RMU). The ring switch facia of the RMU is provided with a lock having a castle key disposed in it. The extensible bushing box is positioned on the top of the RMU and an another lock is provided on the front bracket of the extensible bushing box where the key transition from the first lock of the ring switch fascia to the second lock of the extensible bushing box takes place only when the ring switch (incomer) of the RMU is put to earth position to avoid access to the extensible bushing in operating condition.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "a component surface" includes a reference to one or more of such surfaces.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, Expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.

Figure 1 illustrates the schematic view of the ring switch fascia (3) according to one of the embodiments of the present invention and shows the ring switch fascia with the first lock (2) having the key (1) disposed in the first lock (2).

Figure 2 illustrates the schematic view of the Ring Main Unit (4) with the extensible bushing box (5) placed on the top of it where the extensible bushing box (5) shows the second lock (10) positioned on the extensible box front bracket (6) and Figure 3 shows the exploded Ring Main Unit (4) and the extensible bushing box (5) having the front bracket (6), main housing (7) and the rear bracket (8). Further, it also discloses the locking mechanism (9) of the extensible bushing box (5).

Figure 4 shows the circuit diagram of the Ring Main Unit (4) and it is clear in the circuit diagram that once the ring switch is earthed the supply to extensible bushing is cut off.

Figure 5(a) - 5(c) shows the complete flow chart of the working.The interlock works in such a way that no personnel could access the bushing until the ring switch is earthed. The castle key (1) from the fascia of RMU (4) is released only when ring switch is earthed. The key (1) then can be trapped in the lock of extensible bushing box (5), which allows the extensible bushing box to be opened in sequential manner. Extendible bushing box brackets (6, 7, 8) will open in the following sequence - 6, 7 & 8 as explained in the flow chart diagram. As long as the key (1) is trapped in the second lock (10) of extensible bushing box (5), ring switch cannot be put to other position from earth. The key transition from the first lock (2) of the ring switch fascia (3) to the second lock (10) of the extensible bushing box (5) takes place only when the ring switch of the RMU (4) is put to earth position to avoid access to the extensible bushing in the operating condition.

In one implementation, the present invention provides a switchgear with extensibility interlock, wherein the switchgear is a Ring Main Unit (RMU) (4) which comprises of a ring switch, a ring switch fascia (3) which is provided on the front outer surface of the RMU (4), a first lock (2) positioned on the ring switch fascia (3), a key (1) disposed in the first lock (2), an extensible bushing box (5) positioned atop the RMU (4), a second lock (10) positioned on the extensible bushing box (5), wherein the key (1) transition from the first lock (2) of the ring switch fascia (3) to the second lock (10) of the extensible bushing box (5) takes place only when the ring switch is put to earth position to avoid access to the extensible bushing in operating condition.

In one implementation, the present invention provides switchgear with extensibility interlock where the key from the first lock (2) is released once the ring switch is in earth position.

In one implementation, the present invention provide switchgear with extensibility interlock wherein the position of the ring switch cannot be changed until the key (1) is trapped in the second lock (10) of the extensible bushing box.

In another implementation, the present invention provide switchgear with extensibility interlock where the extensible bushing box (5) comprises a housing (7), a front bracket (6) and a rear bracket (8) and where the extensible bushing box (5) comprises a locking mechanism (9) adapted to lock the extensible bushing box (5) in closed position to avoid access to unearthed extensible bushing.

Stages of development: In switchgear are any other equipment major challenge is to provide human safety i.e. to protect operator from any electrical hazard while working on switchgear panel. This is because if any electrical hazard happens while operator is working on switchgear it may cost operator his precious life. This safety can be provided in many ways:

1) Isolating switchgear from electrical system before getting access to High voltage parts.
2) Cutting off main electrical supply.
3) By means of proper personal protective equipment.

So keeping the aforementioned problem in mind the idea is developed. The model of concept has been released for prototype, installed in gas insulated switchgear.

Some of the non-limiting advantages of the present invention are as follows:
1) There is guaranteed safety of human life.
2) Easy and simple design.
3) Can be mass-produced readily.
4) Highly reliable switchgear.
5) Cost is fairly very less than after mishap cost.
6) Anti-theft feature.

Although the essential features of the invention has been disclosed above, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific methods or devices described herein.