FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10; rule 13) 1. Title of the invention. - AN IMPROVED SWITCHGEAR PANEL STRUCTURE WITH IMPROVED MECHANICAL JOINTS 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: FIELD OF THE INVENTION The present invention relates to an improved switchboards/panel structure which is capable to withstand higher dynamic force occurred during the transient conditions. More particularly, the invention relates to an improved panel structure with improved mechanical joints which can withstand high forces without any additional operation like welding resulting in a clean, less time consuming and cost effective assembly. BACKGROUND OF THE INVENTION In the prior art arrangements of switchboards/panel sheet metal type construction are used. In order to enhance the strength of the panel during normal and transient state material of higher thickness are used with rigid (welding) mechanical joints. In the earlier version of panel the sheet metal use to bear the load of the equipments installed, hence the load bearing was prominent in the prior case. It has been found that in the existing arrangements sheet metal of the panel structure are used to bear the entire equipment load which is not rigid enough to bear the load of the installed equipments. When it came to panel assembly it is cumbersome to assemble at the later stage of the assembly because of the accessibility issue which led to higher material/manufacturing cost and assembly time which in totality resulted in the higher product cost leading ineffective optimized product in terms of cost. Further the existing arrangements are not capable to withstand higher dynamic forces resulting in possibility of failure during transient state. The materials used are not optimized and thus resulting in a non cost effective product. The welding of the mechanical joints are done so as to enhance the strength of the panel during norma! and transient conditions but does not provide flexible/adjustable arrangements and results in not clean, time consuming and not cost effective assembly. US 5,901,868 disclose switchgear is provided including an enclosure for pad-mounted installation. The enclosure includes large lift-up cover panels in combination with removable front panels so as to provide unobstructed access to the interior of the enclosure. In a preferred arrangement, the enclosure houses switchgear that includes low-voltage control and viewing arrangements that are operable from a first side of the switchgear and medium-voltage cable terminations that are accessible from a second side of the switchgear opposite the first side, the enclosure providing access to the low-voltage arrangements while providing isolation from the medium-voltage arrangements. The enclosure also includes protection from the environment in the area of the lift-up cover panels while also providing collapsible lifting members. US 3,573,561 discloses metallic housing for pad-mounted high voltage switches and fuses has sliding top panel which must be shifted forward or back to permit removal of back and front sliding access panels. A lock prevents movement of the top panel from overlying relation to the front and rear panels. Fuses are mounted in a drawer which is locked closed and can only be opened when the lock under the top panel is uncovered. Access to the manual operator for the switch assembly or assemblies is accessible only when the top panel is shifted back. A mechanical maze construction between exposed movable panels reduces likelihood of entrance of wire and the like. US 6,769,749 disclose a switchgear cabinet with a cuboid rack assembled from frame legs, wherein free spaces are formed in areas of outer corner edges for receiving folded edges of meeting panel elements. If at least the folded edges of the vertical panel elements have at least two folded sections, which adjoin the panel elements whose insides are located directly, or via sealing elements, on the outer levels of the rack, and protrude into the free space of the facing frame leg, and the folded end sections extend parallel with respect to the median line of the outer levels meeting each other and their outsides are at the preset distance from the median line, then a transition which is symmetrical to the median line and has a narrow gap in the area of the outer corner edges and increased vandalism proofing is accomplished. JP 2002262414 discloses a box for a switchgear that eliminates the need for welding work in a manufacturing process, reduces time for bending a component member and carries mechanical strength equivalent to that of a usual one. The box is assembled such that a frame and a panel constituting the box for the switchgear are formed by bending a rectangular steel plate in one direction, and each component member is joined using a rivet. In none of the existing arrangements/assemblies and the prior art as discussed hereinabove mechanically riveted joints which overlap in four layers are found. Thus there is a need to provide with an improved switchgear panel structure with improved mechanical joints that would bear the equipment load more efficiently. It is necessary to provide with an improved panel which will have a rigid structure during normal and transient conditions so as to withstand higher dynamic forces. Further there is a need to provide a panel structure that is having an ease in manufacturability of components and assembly in less time, the material used should be such that it is cost effective, a panel structure which is rigid and also light weight that will result into ease of transportation and installation, where no installation of wire duct is required, to provide complete isolation and ingress protection, Further there is a need to manufacture an improved switchgear panel structure where there is no need of a person to enter in the cubicle during assembly. Further to provide with improved mechanically riveted joints which will withstand high forces without any additional operation like welding resulting in a clean, less time consuming and cost effective assembly. OBJECTS OF THE INVENTION The basic object of the present invention is to overcome the disadvantages of the prior art. Another object of the present invention is to provide an improved switchgear panel structure adapted to bear equipment load more efficiently. Yet another object of the present invention is to provide an improved switchgear panel structure improved mechanically riveted joints that overlap in four layers adapted to have clean, less time consuming and cost effective assembly. Yet another object of the present invention is to provide an improved switchgear panel structure improved mechanical joints (riveted joints) adapted to form a rigid structure during normal and transient conditions so as to withstand higher dynamic forces and provide best possible strength. Yet another object of the present invention is to provide an improved switchgear panel structure improved mechanical joints (riveted joints) adapted to develop a rigid and also light weight structure that will result in easy transportation and installation. Yet another object of the present invention is to provide an improved switchgear panel structure with sheet metal forming a layered sandwich joint making the structure more rigid and light weight. Yet another object of the present invention is to provide an improved switchgear panel structure improved mechanical joints (riveted joints) adapted to where no installation of wire duct is required, to provide complete isolation and ingress protection. SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided An improved switchgear panel structure (P) with improved mechanical joints adapted to withstand high forces to enhance the rigidity of the panel structure, said structure comprising : plurality of vertical frame assembly (2) comprising : plurality of horizontal bar means (H) and plurality of vertical bar means (V) wherein said horizontal bar means (H) having a base portion(B1) being profiled on its two lateral sides(S1 ,S2) so as to form a pair of substantially L- shaped bracket means (L) defining a predetermined space for disposition of said vertical bar means (V); wherein said L- shaped bracket means (L) being provided with a slot means (S) of predetermined depth so as to allow accommodating a predetermined portion of said vertical bar means (V); wherein said vertical bar means (V) comprises a substantially C-shaped profile