FIELD OF THE NVENTION

The present invention relates to an interlock mechanism for switching devices. More particularly, the invention is concerned about an improved interlock system for switching devices having flexible cable type interlock arrangement that allows various combinations between multiple switching devices for interlocking.

BACKGROUND OF THE INVENTION

There are various types of mechanical interlock mechanisms available for switching devices. Walking beam type interlock applicable for only two switching devices, only one switching device is ON at any time. The interlock includes a pivoting rocker arm and a linkage assembly associated with each switching device. Another type of interlock using sliding bar arrangement fitted on switching devices. It prevents simultaneous closing of two switching devices. Interlock using key locks also available. Cable type Interlock system used if there is a need for variable distance between switches and interlock system.

US 5814777 entitled "Cable interlock system for circuit breakers" discloses that a cable interlock system for preventing at least two circuit breakers from being closed at the same time, comprising a first circuit breaker having a first operating handle, wherein the first operating handle is adapted to close or open the first circuit breaker, a second circuit breaker having a second operating handle, wherein the second operating handle is adapted to close or open the second circuit breaker, a first mounting bracket that is attached or secured to or otherwise associated with the first circuit breaker, a first lever arm movably attached or secured to or otherwise associated with the first mounting bracket, a second mounting bracket that is attached or secured to or otherwise associated with the second circuit breaker, a second lever arm movably attached or secured to or otherwise associated with the second mounting bracket, a cable assembly having one end adapted to be connected to the first lever arm of the first mounting bracket and having another end adapted to be connected to the second lever arm of the second mounting bracket, wherein said cable assembly and the first lever arm and the second lever arm operate together so as to prevent the first operating handle and the second operating handle from both being in the closed position.

US 5726401 entitled "Cable/crossbar interlock system for circuit breakers" discloses that a cable interlock system is provided for preventing at least two circuit breakers from both being closed, comprising: a first circuit breaker assembly comprising a first main contact, a first cross bar, a first cross bar plunger, a first transfer assembly and a first operating handle, wherein the first operating handle is adapted to close or open the first circuit breaker assembly, and wherein the first cross bar plunger is adapted to contact the first cross bar, and wherein the first transfer assembly is adapted to move the first cross bar plunger; a second circuit breaker assembly comprising a second main contact, a second cross bar, a second cross bar plunger, a second transfer assembly and a second operating handle, wherein the second operating handle is adapted to close or open the second circuit breaker assembly, and wherein the second cross bar plunger is adapted to contact the second cross bar, and wherein the second transfer assembly is adapted to move the second cross bar plunger; a cable assembly having one end adapted for association with the first transfer assembly and having another end adapted for association with the second transfer assembly, wherein the one end of the cable assembly and the first transfer assembly cooperate with the first cross bar and the first cross bar plunger, and the another end of the cable assembly and the second transfer assembly cooperate with the second cross bar and the second cross bar plunger so as to prevent the first main contact and the second main contact from both being closed.

US 4400599 entitled "Flexible cable mechanical interlock for electrical control devices" discloses that an interlock assembly for preventing two electrical control devices from simultaneously assuming a closed or "ON" position. The assembly comprises two subassemblies which are operably connected by a push/pull flexible cable. Each subassembly includes a frame member which carries a reciprocally movable plunger unit. A stop link is pivotally connected to the plunger unit at one end and carries a guide rod at its opposite end. The guide rod is retained within a guideway formed in the frame member which has a main longitudinally extending portion and an offset portion. The plunger unit is prevented from reciprocal movement to a depressed position when the guide rod is in the offset portion whereas reciprocal movement of the plunger unit to a depressed position is permitted when the guide rod is in the main portion of the guideway. The cable connects the respective guide rods in a manner which prevents both rods from being positioned in the main portion of the respective guideways, whereby only one plunger unit is able to assume a depressed position at any given time

US 6060668 entitled "Set of switches with means of mutual locking is applicable for three breakers" discloses that set of switches mutual locking devices, comprising switches with actuator toggles and locking elements, each of the switches having a rocker supported by an elastic element and having Bowden type cables to be connected to the two arms of the rockers, the free end of a first cable of a switch being operationally connected to elements of actuation of a second switch and the free end of a second cable being operationally connected to the elements of actuation of a third switch, and the rockers being loaded at their ends to come into operational contact with the locking elements

US 6225581 entitled "Installation comprising an electrical switchgear apparatus and a cable interlock" discloses that an installation comprises at least one electrical switchgear apparatus a movable mechanism which is interlocked with a device such as an access door by a kinematic transmission cable comprising a flexible sheath and a core designed to slide in the sheath. The ends of the sheath and of the core are respectively fixed to a fixed part of the apparatus and to the movable mechanism by fixing apparatus comprising an end-piece operating in conjunction with the corresponding part of the cable, a housing designed to receive the end-piece, and a locking device with dead point passage designed to oppose insertion of the end-piece in the housing when the force exerted on the locking device in an insertion direction remains lower than an insertion threshold and to enable insertion of the end-piece in the housing when the force exerted on the device means in an insertion direction is greater than the insertion threshold. US 6388214 entitled "Mechanical AND gate for interlocking electric power switches and distribution system incorporating same" discloses that a mechanical AND gate has a pivot plate with an elongated slot engaged by an output coupling formed by a pair of pins radially offset from the end of an output shaft. A pair of input couplings secured to the pivot plate at points laterally offset on opposite sides of the elongated slot couple first and second elongated actuators to the pivot plate. Movement of only one of the elongated actuators to an ON position causes the pivot plate to translate relative to the output coupling, but not to rotate. However, when the second actuator is moved to an ON position in a direction parallel but opposite to the movement of the first actuator, the pivot plate rotates to rotate the output coupling, and therefore, the output shaft. This mechanical AND gate has particular application to interlocking three electric power switches such as circuit breakers so that any two, but not all three, circuit breakers may be on at one time US 5227952 entitled "Interlock device for circuit breakers" discloses that A mechanical interlock device for preventing simultaneous operation of two 3 -phase vacuum interrupter- type circuit breakers is provided. The device operates with the floor tripper and the Mechanism Operated Control ("MOC") driver of each vacuum circuit breaker. The device includes a retainer member mounted at the base of each circuit breaker. Each retainer member includes two levers. The first lever is a trip lever which engages the floor tripper of the associated circuit breaker. The second lever is driven by the MOC driver of the associated circuit breakers. The two levers are preferably mounted on a common pivot bar located at one end the retainer member. Cabling is provided between the trip lever on the first circuit breaker and the MOC driver lever on the second circuit breaker. Similarly, a cable is provided between the MOC driver lever of the first circuit breaker and the trip lever of the second circuit breaker. When either circuit breaker is in normal operation, its MOC driver is in a downward position. This forces the MOC driver lever downward which in turn rotates the trip lever in the opposite breaker upwards. The trip lever thereby acts to engage the floor tripper of the opposite circuit breaker which in turn forces the circuit breaker open and prevents it from operating while the other circuit breaker is on.

The existing types of interlocks mechanism have drawbacks such as complex mechanism, the switching devices must be partially dismantled to install interlock systems, switching devices must be mounted at predefined distance, limited to use with two or three switching devices, more number of flexible cable used and possible combinations of operation are limited. Thus, there is a need to overcome the problems of the prior art. Therefore, inventors have developed an improved flexible cable interlocks arrangement for allowing various combinations between multiple switching devices.

OBJECTS OF THE INVENTION

An object of the present invention is to overcome the problems/disadvantages of the prior art. Another object of the present invention is to provide an improved interlock system for switching devices.

Another object of the present invention is to provide an improved main module assembly. Another object of the present invention is to provide an improved sub module assembly. Yet, another object of the present invention is to provide an improved link assembly.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 illustrates an isometric view of flexible cable used in the system

Figure 2 illustrates an assembly view of sub module Figure 3 illustrates front and side view of assembled sub module.

Figure 4 illustrates an isometric view of assembled sub module.

Figure 5 illustrates an isometric view of 'C shaped slider.

Figure 6 illustrates an assembling of flexible cable with sub module.

Figure 7 illustrates an assembling of sub module with switching devices.

Figure 8 illustrates an isometric view of switching device assembled with sub module and flexible cable.

Figure 9 illustrates an isometric view of base plate.

Figure 10 illustrates top and side view of top plate.

Figure 11 illustrates an isometric view of cable holder.

Figure 12 illustrates an isometric view of stepped pins.

Figure 13 illustrates top view of link assembly (Case 1).

Figure 14 illustrates top view of link assembly (Case 2).

Figure 15 illustrates an assembling of main module (Case 1).

Figure 16 illustrates an isometric view of partially assembled main module (Case 1).

Figure 17 illustrates an assembling of link assembly (Case 1).

Figure 18 illustrates an isometric view of fully assembled main module (Case 1).

Figure 19 illustrates an isometric view of full mechanical interlock system with four switching devices (Case 1).

Figure 20 illustrates an assembling of main module (Case 2).

Figure 21 illustrates an isometric view of partially assembled main module (Case 2).

Figure 22 illustrates an assembling of link assembly (Case 2).

Figure 23 illustrates an isometric view of fully assembled main module (Case 2).

Figure 24 illustrates an isometric view of full mechanical interlock system with three switching devices (Case 2).

Figure 25 illustrates a links arrangement of main module corresponding to [0000] combination. (Case 1)

Figure 26 illustrates links arrangement of main module corresponding to [0001] combination. (Case 1) Figure 27 illustrates links arrangement of main module corresponding to [0010] combination. (Case 1)

Figure 28 illustrates links arrangement of main module corresponding to [0100] combination. (Case 1)

Figure 29 illustrates links arrangement of main module corresponding to [ [11000] combination. (Case 1)

Figure 30 illustrates links arrangement of main module corresponding to [000] combination. (Case 2)

Figure 31 illustrates links arrangement of main module corresponding to [001] combination. (Case 2)

Figure 32 illustrates links arrangement of main module corresponding to [010] combination. (Case 2)

Figure 33 illustrates links arrangement of main module corresponding to [011] combination. (Case 2)

Figure 34 illustrates links arrangement of main module corresponding to [100] combination. (Case 2)

Figure 35 illustrates links arrangement of main module corresponding to [101] combination. (Case 2)

Figure 36 illustrates links arrangement of main module corresponding to [110] combination. (Case 2)

Figure 37 illustrates application of two switching devices interlock system.

Figure 38 illustrates application of four switching devices interlock system.

Figure 39 illustrates interlocking of three breakers and their truth table. DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

According to the invention there is provided an improved interlock system for switching devices having flexible cable interlocks arrangement for switching devices. It is common to restrict switching device movement, particularly, to prevent unintended operation of one or more of the individual switching devices. Limiting of switching devices from OFF to ON, is desirable in situations where multiple power sources are used to supply a limited number of energy consuming devices.

According to one embodiment of the invention only one switching device can be ON, out of 'N' numbers of switching device (Case 1). Certain industrial application may require two switching devices to be interlocked to prevent them from being closed at the same time. In that case one switching device is used to connect with electricity board and another switching device used to connect with backup power supply. Figure 37 illustrates the application of two switching device interlock system. Here A and B cannot be switched ON at the same time. Some critical loads need two or more backup power supplies. So there is a need to have an interlocking system, which allows only one switching device to ON, out of 'N' numbers of switching devices.

For example if there is a load which is normally supplied with EB supply and use three backup supplies as shown in figure 38. If EB supply fails S2 switched ON. If S2 also fails S3 or S4 switched ON. Here we need to have an interlock system which allows only one switching device to ON at any time. So far the necessity of interlocking system, which allows only one breaker ON, out of 'N' breakers [N=2, 3, 4 ...] is explained. According to another embodiment of the invention any two switching devices can be ON, out of '3' switching devices (Case 2). To better understand the necessity of interlocking three breakers, consider the figure 39, this is a typical case in many of the industries. Here two sources SI, S2 are used to power two loads LI, L2. Here T represents ON state of breaker; Ό' represents OFF state of breaker. The table shows seven required combinations for interlocking three breakers as shown in figure 39.

Let loads LI, L2 powered separately with two sources SI, S2 via Ά', 'B' respectively. At this state the 'C should not be able to ON, otherwise dead shot of SI, S2 will happen. If source SI is sufficient to power the loads LI and L2, breakers A and C are switched to ON. Now switching ON the third breaker 'B' should be restricted to avoid dead shot if S2 is live. From this the necessity of interlocking three breakers is clearly understood.

The invention disclosed here is a common interlock system which applicable to,

Case 1: Only one switching device can be ON, out of 'N' numbers of switching devices.

Case 2: Any two switching device can be ON, out of '3' switching devices.

The mechanical interlock system has link assembly which differs slightly for both the cases. For easy understanding the case 1 illustrated for four numbers of switching devices, even though the system can be extended to any number of switching devices.

The interlock system comprises a sub module fitted on each switching device and only one common main module. Connection between each sub module and main module is made by means of flexible cable. Main module can be fixed anywhere near to the switching devices depending on the length of the flexible cable. While operating the switching devices, knob movement transferred to main module through flexible cable, which correspondingly makes changes in the link assembly to achieve desired interlocking combinations. As shown in figure 1, flexible cable mentioned above is used to transmit mechanical force or energy by the movement of an inner cable (most commonly of steel or stainless steel) relative to hollow outer cable housing. The housing is generally of composite construction, consisting of a helical steel wire, often lined with plastic, and with a plastic outer sheath. Both ends of the cable have fixing means by which the cable can be fixed between a sub module and main module. One end of the cable has threads and lock nuts as fixing means and another end has stepped portion as fixing means. Fixing means of the cable is made of steel. This invention uses three flexible cables for interlocking three switching devices [case 2], four flexible cables for interlocking four switching devices [case 1]. As shown in figures 2, 3, 4 & 5, each switching device is fitted with a sub module on top of it. Sub module consists of substantially 'U' shaped guide, and substantially 'C shaped slider. Guide has two slots and one opening hole in its center limb. Slider has one opening, two fixing holes in its center limb and two cut outs in its side limb. Slider fixed with guide by suitable rivet pin in such a way that center limb of guide and slider is mating. After fixing, slider can move freely within the slots of guide.

As shown in figures 6, 7 & 8, sub modules fitted on switching devices by screws through fixing holes. Sub module is assembled on each switching devices in such a way that slider holds the knob of switching device in its center limb opening. So while operating the breaker, slider and knob moves together. The function of sub modules is to produce a linear motion of some desired distance from the movement of knob during breaker operation. Slider of sub module is itself acting as operating knob. Guide of sub module has upward projected limb with two slots for fixing one end of flexible cable. Fixing can be done on either right or left side slot depending upon our convenience.

Main module comprises base plate, top plate, link assembly, cable holder, stopper pin and stepped pin. Out of which base plate, top plate, cable holder and stepped pins are common for both case 1 and case 2.

As shown in figure 9, base plate is a sheet metal part, which has base limb [Horizontal portion] and upward projected limb [vertical portion]. Base limb has step in its center, on which stepped pin, top plate and link assembly are assembled. Upward limb has five substantially 'U' shaped openings in which one end of cable fixed.

As shown in figure 10, Top plate is a sheet metal part which has one stepped center portion. Center portion has seven oblong holes. Out of seven two are closed and five are opened at one end as shown below. These oblong holes acts as guide for stepped pins. Top plate assembled on base plate in such a way that horizontal portion of base plate mating with two side portions of top plate.

As shown in figure 11, cable holder of main module is substantially 'L' shaped sheet metal part. It has fixing holes in horizontal limb and cable fixing slots in vertical limbs.

As shown in figure 12, there are two types of stepped pins are used in this invention. First type pins are used to connect first stage links with second stage links. Second type pins are used to connect second stage links with inner core of flexible cable. Second type pins have semi-slots in its bottom portion especially made for this purpose. The stepped pins are assembling in such a way that it moves freely within the oblong hole of the top cover. The force applied to switching device knob is transmitted to main module via flexible cable. So any changes in switching device knob position cause changes in links arrangement in the main module.

As shown in figure 13, for case 1, the link assembly of main module comprises, 9 links assembled in two stage hierarchy as shown below. It has three different sized links. Link assembly fixed with base plate through cylindrical pin. Links assembly is arranged in such a way that it allows closing of only one switching device.

As shown in figure 14, for case 2, the link assembly of main module comprises, 6 links assembled in two stage hierarchy as shown below. It has three different sized links. Link assembly fixed with base plate through cylindrical pin. Links assembly is arranged in such a way that it allows closing of any two switching devices. Switching ON three breakers is not at all possible. Hence desirable interlocking between three breakers is achieved. The SEVEN possible combinations are shown in table.

As shown in figure 15, the present invention is applicable for both case 1 and case 2. As link assembly is different for both the cases Links movement distance also different for both the cases. Links movement distance is lower for case 1 and higher for case 2. Substantially Oblong holes are dimensioned for allowing maximum Links movement distance (case 2) and while using the mechanical interlock for case 1 stopper pins are provided to restrict additional possible link movement. Stopper pins fixed on base plate if we need to use the interlocking system for case 1. Otherwise these pins are not used.

WORKING OF THE INVENTION

According to one aspect of the invention, there is only one switching device can be ON, out of 'N' numbers of switching devices (Case 1). Though this concept is explained for 4 switching devices in the present invention, but it can be extended to N number of switching devices. Considering initially all four switching devices [A, B, C&D] are in the contact opening position. Any Interlock mechanism will require that all switches are in the contact opening position. In this state closing of any switch [A or B or C or D] is possible. Now if 'A' (out of four switches) is closed, force applied to close the switching devices is transmitted via flexible cable to the main module and it rearranges the link assembly. At this state, closing of 'B' or 'C or 'D' [remaining switches] is not possible. There are five possible combinations and its corresponding link arrangements are given below. [0 represents OFF position; 1 represents ON position] Combination 1: All four switches are in OFF position [0000]. At this state all links are free to move as shown in figure 25.

Combination 2: Switches A, B and C are in OFF position and switch D is in ON position [0001]. At this state no links are free to move as shown in figure 26.

Combination 3: Switches A, B and D are in OFF position and switch C is in ON position [0010]. At this state no links are free to move as shown in figure 27.

Combination 4: Switches A, C and D are in OFF position and switch B is in ON position [0100]. At this state no links are free to move as shown in figure 28.

Combination 5: Switches B, C and D are in OFF position and switch 'A' is in ON position [1000]. At this state no links are free to move as shown in figure 29. According to one aspect of the invention, there are any two switching device can be ON, out of '3' switching devices (Case 2). Considering initially all three switching devices [A, B, C] are in the contact opening position. Any Interlock mechanism will require that all switches are in the contact opening position. In this state closing of any switch ['Α' or 'B' or 'C'] is possible. Now if 'A' (out of three switches) is closed, force applied to close the switching devices is transmitted via flexible cable to the main module and it rearranges the link assembly. At this state, closing of either 'B' or 'C [remaining switches] is possible. Now if 'B' (out of remaining two switches) is also closed, link assembly once again rearranged. But in this state, closing of 'C [third switch] is not possible. Switching sequence can vary depending upon the requirement. There are seven possible combinations and its corresponding link arrangements are given below. [0 represents OFF position; 1 represents ON position} Combination 1 : All three switches are in OFF position [000]. At this state all links are free to move as shown in figure 30.

Combination 2: Switches 'A' and 'B' are in OFF position and switch 'C is in ON position [001]. At this state links corresponding to 'A' and 'B' are free to move as shown in figure 31. Combination 3: Switches 'A' and 'C are in OFF position and switch 'B' is in ON position [010]. At this state links corresponding to 'A' and 'C are free to move as shown in figure 32.

Combination 4: Switches 'B' and 'C are in ON position and switch 'A' is in OFF position [011]. At this state no links are free to move as shown in figure 33.

Combination 5: Switches 'B' and 'C are in OFF position and switch 'A' is in ON position [100]. At this state links corresponding to 'Β' and 'C are free to move as shown in figure 34. Combination 6: Switches 'A' and 'C are in ON position and switch 'B' is in OFF position [101]. At this state no links are free to move as shown in figure 35.

Combination 7: Switches 'A' and 'B' are in ON position and switch 'C is in OFF position [110]. At this state no links are free to move as shown in figure 36. As shown in figure 18 mechanical interlocking system of this invention comprises Main module [40], Sub modules [38a], [38b], [38c] [38d], switching devices [35a], [35b], [35c], [35d], and flexible cables [39a], [39b], [39c], [39d]. Switching devices [35a], [35b], [35c], [35d], fitted with sub modules [38a], [38b], [38c], [38d] respectively on top of it. Connection between sub modules [38a], [38b], [38c], [38d] and main module [40] is given by flexible cables [39a], [39b], [39c], [39d] respectively.

As shown in figures 1 & 6, switching devices of the invention essentially consists of operating knob [37] and mid cover [36]. In order to transmit mechanical movement from sub module [38] to main module [40] flexile cable composed of Outer Sheath [1], Inner Cable [2], Thread and lock nuts [3] and Stepped portion [4] is provided.

As shown in figures 2, 3, 4 & 6, each sub module assembly [38] consists of a guide [5] and slider [6]. Guide of sub module is 'U' shaped sheet metal part, which has one center limb [41] between two angular bended side portions [42a], [42b]. Guide has an opening hole [8] between two slots [7a], [7b] in the center limb. Guide also has an upward projected limb [12] in its center. Upward projected limb [12] has two open slots [13a], [13b] which can be used to fix threaded end [3] of the cable. Fixing can be done on either right [13a] or left side [13b] slot depending upon our convenience. Two side portions of guide [42a], [42b] have fixing holes [11], with which sub module [38] fitted to switching devices [35].

As shown in figures 4 & 5, slider [6] of sub module is 'C shaped sheet metal part. Slider has one opening hole [14] to hold operating knob [37], two fixing holes [10], in its center limb and two cut outs [9a], [9b] in its side limb. Slider [6] fixed with guide [5] by suitable rivet pin [10a], [10b] through fixing holes [10] in such a way that center limb of guide and slider is mating. Two side Cut-outs [9a], [9b] of slider, hold the inner core [2] of cable [39]. After fixing slider [6] with guide [5], it has to move freely within the slots of guide [7a], [7b]. As shown in figures 7 & 8, sub modules [38] fitted on switching devices [35] by screws [11a], [l ib], [11c], [l id] through fixing holes [11]. Sub module [38] is assembled on each switching devices [35] in such a way that slider [6] holds the knob [37] of switching device [35] in its center limb opening [8]. So while operating the breaker [35], slider [6] and knob [37] moves together. The function of sub modules [38] is to produce a linear motion of some desired distance from the movement of knob [37] during breaker operation. Slider [6] of sub module is also acting as operating knob to the switching devices [35].

Main module [40] comprises base plate [43], top plate [44], link assembly [45], cable holder [46], cylindrical pin [47], stopper pin [63] and stepped pins [32], [33].

As shown in figures 9 & 15, base plate is a sheet metal part, which has base limb (Horizontal portion) [15] and upward projected limb (vertical portion) [16]. Base limb has step in its center [17], on which stepped pin [32],[33], top plate [44] and link assembly [45] are assembled. Upward limb [16] has five 'U' shaped opening [18] in which one end of cable [4] fixed. Base plate [43] is a platform provided to assemble other components of main module [40]. Stepped portion [17] of base limb [15] has four holes [20] to fix top plate [44] using four fixing screws [60a], [60b], [60c], [60d]. Four more holes [21] provided on base limb [15] to fix cable holder [46] using fixing screws [61]. Horizontal portion of base plate [15] has a hole [19] in its center to fix cylindrical pin using fixing screw [62] three holes [59] of base limb [15] used to fix stopper pins [63].

As shown in figure 10, top plate [44] is a sheet metal part which has one stepped center portion [22]. Center portion [22] has seven oblong holes. Out of seven two are closed [24] and five are opened [25] at one end as shown in figure. Closed oblong holes [24] receive first type stepped pin [32] whereas open oblong holes [25] receive second type stepped pin [33]. These oblong holes [24], [25] act as guide for the stepped pins [32], [33]. Top plate [44] has four fixing holes [27]; two for each bended side portions [23] to fix with base plate [43]. Top plate [44] assembled on base plate [43] in such a way that horizontal portion [15] of base plate [43] mating with two side portions [23] of top plate [44].

As shown in figure 11, cable holder [46] of main module [40] is 'L' shaped sheet metal part. It has fixing holes [30] in horizontal limb [28] and cable fixing slots [31] in vertical limbs [29]. After fixing cable holder [46] with base plate [43], it tightly holds the stepped portion [4] of cables [39].

As shown in figure 12, there are two types of stepped pins [32], [33] are used in this invention. First type pins [32] are used to connect first stage links [48] with second stage links [49]. It has two steps [50], [51] in it. It has thread in its center surface [52] through the whole length of the pin [32]. Second type pins [33] are used to connect second stage links [48] with inner core [2] of flexible cable [39]. It also has two steps [53], [54]. Second type pins have semi-slots [34] in its bottom portion especially made for terminating one end of the inner core [2]. It also has thread in its center surface [55]. Both the stepped pins [32], [33] are assembled in such a way that it moves freely within the oblong hole [24], [25] of the top cover [44]. The force applied to switching device knob [37] is transmitted to main module [40] via flexible cable [39]. So any changes in switching device knob [37] position cause changes in links arrangement [45] in the main module [40].

As shown in figures 13 & 17, for Case 1, the link assembly [45] of main module [40] comprises, 9 links assembled in two stage [48], [49] hierarchy as shown in fig. It has three different sized links. Link assembly [45] fixed with base plate [43] through cylindrical pin [47]. Links assembly assembled on stepped pins with fixing screws [64]. Links assembly [45] is arranged in such a way that it allows closing of only one switching device [35].

As shown in figure 14, for Case 2, the link assembly [56] of main module [40] comprises, 6 links assembled in two stage [57], [58] hierarchy as shown below. It has three different sized links. Link assembly [46] fixed with base plate [43] through cylindrical pin [47]. Links assembly [56] is arranged in such a way that it allows closing of any two switching devices [35]. Switching ON three breakers is not at all possible. Hence desirable interlocking between three breakers is achieved. The SEVEN possible combinations are shown in table.

The present invention is applicable for both case 1 and case 2. But Links movement distance is different for both the cases. Links movement distance is lower for case 1 and higher for case 2. Oblong holes are dimensioned for allowing maximum Links movement distance (case 2) and while using the mechanical interlock for case 1 stopper pins [63] are provided to restrict additional possible link movement.

ADVANTAGES OF THE INVENTION

1. It is simple mechanism.

2. This can be used for the system already in service.

3. Switching devices can be mounted anywhere within the length of the flexible cable.

4. This invention is applicable to use with multiple switching devices

5. It uses same number of flexible cables as number of switching devices.

6. It allows various combinations between multiple switching devices for interlocking.

7. It uses a sub module which can be fit with switching devices without disturbing its termination.

8. This system ensures easy site installation by customer.

9. This invention can be used for fixed, plug-in, withdraw able type of breakers as it gets actuation from operating knob.

The invention has been described in a preferred form only and many variations may be made in the invention which will still be comprised within its spirit. The invention is not limited to the details cited above. The structure thus conceived is susceptible of numerous modifications and variations, all the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which will still be comprised within its true spirit.