FORM 2
THE PATENTS ACT, 1970 COMPLETE SPECIFICATION
(See Section 10)
MECHANICAL INTERLOCK FOR SWITCHING DEVICES
Numbered as dated
INVENTORS:
1. SANDEEP SINGH HARI RAWAT
APPLICANT:
M/s. LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No 278,
Mumbai, 400 001, Maharashtra,
INDIA


THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

MECHANICAL INTERLOCK FOR SWITCHING DEVICES
A) TECHNICAL FIELD OF THE INVENTION:
[0001] The present invention generally relates to switching devices such as fuses, circuit breakers etc to open or close the electrical circuit and more particularly the present invention relates to a mechanical interlock for Molded Case Circuit Breakers (MCCBs).
B) BACKGROUND OF THE INVENTION:
[0002] In order to open or close the electrical circuit, a switch device is required. An additional protective device is required to protect the electrical circuits. Usually the low voltage switches are commonly used in the industries, but the present trend is to use circuit breakers for overload and short-circuit protection in place of the fuse switch. There are various types of switches and protective devices used in industries for different applications. All these devices are generally called switchgear.
[0003] The term switchgear used in association with the electric power system, or grid refers to a combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults. Apart form switching "ON" and "OFF" any section of an electrical installation, the switchgear must include the necessary protective devices.


Generally the protective devices automatically isolate particular section of the installation under fault conditions.
[0004] In order to ensure the safe operation sequences of the switchgear a trapped key interlocking is used to provide predefined scenarios of operation. For example, if only one of two sources of supply are permitted to be connected at a given time, the interlock scheme may require that the first switch must be opened to release a key that will allow closing the second switch. An interlock governs succeeding operations of the same or allied devices and may be either electrical or mechanical.
[0005] Generally an interlock ensures that the circuit breaker cannot be raised or lowered unless its interrupter contacts are in open position. It ensures that the circuit breaker can only be closed when it is in the fully raised or lowered position. Most switchboards and motor control centers are fitted with a variety of electrical and mechanical safety interlock devices. The main purpose of the safety interlocks is to withdraw the switching device while it is carrying load or faulty current.
[0006] Mechanical interlocks eliminate the possibility of making or breaking the circuit under load or making an unplanned connection. A mechanism within the enclosure prevents the switch from being turned to the "ON" position until the plug is fully engaged into the receptacle. Once inserted, the plug is locked in place when the switch is turned "ON" and can't be removed until the switch is turned to the 'OFF" position. This prevents making or breaking the circuit under load.


[0007] The currently available interlocks also prevent the opening of access doors or panels before setting the switching device in it's "OFF" state. The interlocks generally used in above cases are mechanical latches, bolts and shutters. Electrical interlocks are used to ensure that the closing and tripping functions takes place in particular sequence.
[0008] In case of two circuit breakers, interlocking between the two circuit breakers should be provided to prevent both the circuit breakers from being in "ON" position at the same time. The design of the interlock system shall be such as to avoid removal of the interlock by unqualified or unauthorized personnel. The design shall lessen the convenience of removing the interlock either accidentally or intentionally. Interlocking also prevents the tripping of the relays due to gravitation or to prevent unauthorized operation of the breakers.
[0009] An interlock bar shall also be provided between the two main breakers to avoid both breakers from being in the "ON" position at the same time. Interlocking of circuit breakers shall be accomplished through a mechanical interlock.
[0010] The current available interlocks do not provide the solution for above mentioned problems. Further the previously available interlocks for circuit breakers are very costly and also the mechanical strength offered by it is very weak. Hence there is a need to develop a mechanical interlock system which is compact and which provides good mechanical strength to the switching devices.


[0011] Prior art discloses a locking arrangement for switchgear wherein a blocking body couples the switchgear in such a way that upon activation of the first one the other switchgear, which acts upon the blocking body in an opposite sense as compared to the first, is blocked in the activated mode.
[0012] None of the prior arts discloses an integral locking model to provide a common interlocking between two Molded Case Circuit Breakers (MCCBs) and to prevent paralleling of switching devices. It is also necessary to prevent the falling of electrical switch due to virtue of gravity and hence there is a need to ensure safety of the human beings while maintenance of downstream equipment.
[0013] Hence there is a further need to develop an improved mechanical interlock for molded case circuit breakers which are less costly as compared to available interlocks and durable with a good mechanical strength and avoids the paralleling of switching devices.
C) OBJECTIVES OF THE INVENTION:
[0014] The primary objective of the present invention is to design a common mechanical interlock for two MCCBs placed adjacent to each other.


[0015] Another object of the invention is to provide an interlocking between two breakers such that only one breaker can be switched in "ON" position at any particular time and hence avoids the paralleling of switching devices.
[0016] Yet another objective of the invention is to design a tamper-proof interlock for MCCBs to prevent the access of unauthorized person.
[0017] Yet another objective of the invention is to design an interlock device which has good mechanical strength and cannot be tampered easily.
[0018] Yet another object of the invention is to ensure that both the breakers are locked while in "OFF" position or either one of the breaker is in "ON" position at any point of time, to ensure the safety of human beings while maintenance of downstream equipments.
[0019] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0020] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood from the following specification.


[0021] The present invention provides an interlocking device with slider for adjacent placed circuit breakers. It prevents the simultaneous switching "ON" of the two MCCBs placed adjacent to each other. The mechanical interlock for switching devices is a new product developed to control the switching action of the two circuit breakers. The design is suitable for two breakers mounted adjacent to each other. It is particularly designed to provide a tamper proof interlock for molded case circuit breakers.
[0022] The mechanical interlock decides the operating positions of the two circuit breakers. It ensures that both the circuit breakers should not be switched "ON" simultaneously. The various operating positions of the switches are decided by the slider. Accordingly only one of the two circuit breakers should be switched "ON" at any point of time or both the circuit breakers could be switched "OFF" at the same time. The aim is to prevent both switches to be switched "ON" simultaneously.
[0023] According to one embodiment of the invention the interlocking module includes two plates: a moving plate and a base plate. The moving plate and the base plate are riveted to each other. The moving plate is fixed to a hinge so that it can be moved flexibly to cover the base plate.
[0024] The fixed plate acts as a bridging plate between the breakers with two fixing points on either breaker. A position interlock is provided inside the moving plate, wherein a protruding part of the moving plate comes and interlocks with the slider on the base plate.


[0025] The interlock assembly includes a sliding component with slots wherein a protruding part of the moving plate comes and interlocks. At this position the interlock is locked. The three required positions are decided by the slots on the slider. The slider is free to move on the slot provided on base late.
[0026] According to the other embodiment of the invention the punches are provided on both ends of the slider providing dual action on the base plate. Though the slider is free to move in the slot provided on the base plate, the punch protrusion helps the slider to be locked with in the assembly. The two locking positions are directly decided by the punch protrusions. Holes are provided on the front ends of both the base plate and moving plate with the provision for locking the base plate and moving plate to prevent it from tampering. A window is provided on the moving plate to have access to thermal adjustment and push to trip button.
[0027] According to another embodiment of the invention the interlocking is done independent of the distance between the two switching device. The design is suitable for two breakers mounted adjacent to each other but, can be customized for a few millimeter gap between the breakers.
E) BRIEF DESCRIPTION OF THE DRAWINGS:
[0028] FIGURE 1 shows the slider with three slots and punch protrusions.


[0029] FIGURE 2 shows moving plate with the position interlock and holes.
[0030] FIGURE 3 illustrates the moving plate with the position interlock and holes.
[0031] FIGURE 4 illustrates base plate with slots provided for slider on both sides. It also shows the double locking holes on either side of the plate.
[0032] FIGURE 5 shows the top view of the base plate
[0033] FIGURE 6 shows the overall integrated interlock assembly with the moving plate, fixed plate and slider.
[0034] FIGURE 7 illustrates a position interlock in the middle of the slider slot.
[0035] FIGURE 8 illustrates the mechanism of adjusting a position interlock between the three slots on the slider.
[0036] FIGURE 9 illustrates a top view of the two circuit breakers placed adjacent to each other with the interlocking module mounted in between the two circuit breakers in closed position.
[0037] FIGURE 10 illustrates another top view of the interlocking module assembly place above the circuit breakers.


[0038] FIGURE 11 illustrates a side view of the circuit breakers and interlocking assembly showing a hinge point, provision for locking and the mounting screws.
F) DETAILED DESCRIPTION OF THE INVENTION
[0039] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments which may be practiced is shown by way of illustration.
[0040] FIGURE 1 shows slider 100 with three slots 102A, 102B, 102C and two punch protrusions 104A and 104B on either ends of the slider. Punches 104A and 104B on both side of slider 100 provide dual action. Punch protrusions 104A and 104B facilitates slider 100 locking in the assembly and the locking position is decided by the stopping point of the punch position.
[0041] FIGURE 2 illustrates moving plate 200 with position interlock and holes. It includes top portion 210 and bottom portion 212A and 212B, which prevents the tampering of interlocking module screws 1002A, 1002B, 1002C, 1002D (as shown in FIGURE 10). It includes a locking holes 206A and 206B which interfaces with locking holes 410A and 410B (as shown in FIGURE 4) of base plate 400 (as shown in FIGURE 4), with the provision for final locking to prevent tampering. Position interlock 204 interlocks with the slots provided on slider 100 to prevent the simultaneous switching


"ON" of the two circuit breakers 900A and 900B (as shown in FIGURE 9). Rectangular space 208 on moving plate 200 provides access to the thermal adjustment and push to trip button of the circuit breakers. Hinge points 202A and 202B (not shown in figure) of cover plate 200 engages with the base plate 400 (as shown in FIGURE 4) hinge points 402A and 402B (as shown in FIGURE 4) in order to ensure the flexible movement of the cover with respect to the base plate.
[0042] FIGURE 3 illustrates a side view of the cover plate 200, showing a hinge point 202A, a top portion of cover plate 212A, a position interlock 204, a locking hole 206A and a bottom plate 210. FIGURE 4 illustrates a top perspective view of the base plate 400 with the rectangular slots 408A and 408B provided for slider 100 (of FIGURE 1) on both sides. It includes locking holes 410A and 410B to provide a final locking arrangement with 206A and 206B of the cover plate 200. It includes four circular holes two at the top 404A and 404B and two at the bottom 406A and 406B for mounting the screws 1002A, 1002B, 1002C, 1002D (as shown in FIGURE 10) in to the holes. The mounting screw holds the interlock assembly rigidly between the circuit breaker. A rectangular space 412 is provided in the base plate which intern provides the access to thermal adjustment and push to trip button of the circuit breakers.
[0043] According to one embodiment of the invention punches 104A and 104B (of FIGURE 1) are provided on both ends of slider 100 (of FIGURE 1) providing dual action. Firstly, though slider 100 is free to move in the slot provided but, because of the punch protrusions it is locked in the assembly. Secondly, the punches gives a customer


friendly feature wherein two locking positions are directly decided by the stopping point achieved by the punch positions. FIGURE 5 illustrates the top view of base plate 400.
[0044] FIGURE 6 shows the integrated interlock assembly with moving plate 200, fixed plate 400 and slider 100. Moving plate 200 and base plate 400 are fixed at a common hinge point. The slider 100 is fixed in-between the rectangular holes of the base plate 400. The slider can be adjusted with the position interlock 204 in the cover plate 200 to prevent the paralleling of the two supply sources. Slider 100 is guided by the moving and the fixed plate with the definite positions 102A, 102B, and 102C for locking. The entire assembly is compact in size with lower material scrapping. It is very easy to manufacture with lesser critical dimensions to be maintained and the manufacturing cost is also low.
[0045] Slider 100 is guided by the moving 200 and base plated 400 with definite positions for locking. Once the interlock position is decided and adjusted, the moving plate 200 is closed with respect to the base plate 400. Once locked, the whole system is tamper proof that is an unauthorized person will not be able to unscrew it, or change the position of the slider or remove the interlock from breakers; as the mounting screws are inaccessible
[0046] The protruding part of moving plate 200 interlocks with middle slot 102B in slider 100 as shown in FIGURE 7. At this position, both the circuit breakers' switches are in "OFF" position. Further upper part 212A, 212B and lower part 210 of the moving plate 200 covers mounting screws 1002A, 1002B, 1002C, 1002D (as shown in FIGURE 10) on


the base plate 400 to prevent from unauthorized access to it. The design avoids the removal of interlock by unqualified or unauthorized personnel. The design lessens the convenience of removing the interlock either accidentally or intentionally. It prevents the tripping of the relays due to gravitation or to prevent unauthorized operation of the breakers. According to another embodiment of the invention a double locking arrangement has been made with a standardized hole requirement for the ratings. With this locking arrangement slider 100 is constrained from falling over by the virtue of gravity and is well guided by the moving and fixed plates with definite positions for locking. This type of arrangement provides a good mechanical strength to the interlock assembly.
[0047] FIGURE 8 illustrates a method of adjusting the position interlock with the three slots on slider. Protruding part 204 of moving plate 200 can be adjusted for slots 102A, 102B and 102C in slider 100 to avoid the paralleling of the two supply sources. As shown in FIGURE 8 the protruding part 204 of moving plate 200 interlocks with the sliding component at slot 102C. In this position, circuit breaker 900A will be switched 'OFF" and the other circuit breaker 900B can be adjusted in the desired position that is either ON/OFF. Hence it ensures that both circuit breakers are not switched "ON" simultaneously.
[0048] FIGURE 9 illustrates a top view of two circuit breakers 900A and 900B placed adjacent to each other with the interlocking module mounted in between the two circuit breakers. As seen from the Figure 9, interlocking assembly is placed in between two


circuit breakers 900A and 900B. Both circuit breakers 900A and 900B are placed adjacent to each other. The design is suitable for two breakers mounted adjacent to each other and may also be customized for a few millimeter gap between the breakers. Since the interlock module designed is a separate, single 'integrated part', the user can install it on MCCBs whenever required without any difficulty. The entire assembly is mounted on the MCCBs using mounting screws 1002A, 1002B, 1002C and 1002D (as shown in FIGURE 10) on either side. FIGURE 9 illustrates the complete view of the interlocking module after installing it on the MCCBs. It also shows the window 208 provided for access to thermal adjustment and push to trip button according to one embodiment of the invention.
[0049] The complete understanding of the embodiments and working of the interlock assembly with the different operating positions of the switches can be seen from FIGURE 10. The assembly includes two plates: moving plate 200 and base plate 400. Moving plate 200 and base plate 400 as shown in the figure are riveted to each other. Moving plate 200 has position interlock 204 and space 208 provided for access to the thermal adjustment and pushes to trip button. It includes locking holes 206A and 206B for double locking arrangement with the base plate holes 410A and 410B. Base plate 400 or the fixed plate acts as a bridging plate between the breakers with the two fixing points on both the breaker. The assembly includes a sliding component with slots according to one embodiment of the invention. The sliding component includes three slots to decide the required position for interlock.


[0050] Base plate 400 contains rectangular slots 408A and 408B on the two vertical sections for the slider action. The protruding part 204 of moving plate 200 interlocks with slider 100. At this position the interlock is locked. The three required position are decided by slots 102A, 102B, and 102C on the slider. It avoids the paralleling of the two supply sources. It ensures that both breakers can only be locked in "OFF" positions. If the position interlock 204 in the moving plate 200 interlocks with the middle slot 102B on the slider then the both the circuit breaker will be in "OFF" position. In the same way the interlock may be adjusted with respect to the other two slots 102A and 102C to control the circuit breakers independently in either "ON" or "OFF" positions. It ensures that both the breakers 900A and 900B should not be switch "ON" simultaneously hence avoids the paralleling of the two supply sources. Accordingly the entire assembly forms an integrated part so that the user may directly install it on the molded case circuit breakers when ever required without any difficulty. According to another embodiment of the invention the interlocking is done independent of the distance between the two switching device. The two locking positions on the slider are directly decided by the punch protrusions.
[0051] FIGURE 11 illustrates a side view of the circuit breaker and interlocking assembly showing a hinge point, provision for locking and the mounting screws. A hinge point shown in the figure ensures the flexible movement of moving plate 200 with respect to base plate 400. The double locking holes are shown from the side view. The mounting screws will be hidden once the moving plate is closed as shown in the figure. With the


double locking arrangement the entire interlock assembly will be resistant to theft or tamper.
[0052] The entire assembly is very compact with good mechanical strength hence cannot be tampered easily. The entire assembly forms a novel interlock device to prevent the simultaneous switching "ON" of the two MCCBs placed adjacent to each other. The main advantage of the invention is that the whole design forms an integrated part which is compact in size and can be installed on the circuit breakers whenever required. Also it is easy to manufacture with the lesser critical dimension to be maintained. The manufacturing cost of the interlock device is also low. The novel mechanical interlock is aesthetically good. It is more durable with very less design cost.


CLAIMS:
WHAT IS CLAIMED IS:
1. A mechanical interlock assembly between two switching devices, wherein at a
time only one device can be switched on and hence avoiding the paralleling of
two supply sources, wherein both the devices can also be switched off
simultaneously at the same time and hence insuring the safety of human beings
while maintenance of equipments. The assembly comprising of:
a base plate, wherein base plate is fixed on two circuit breakers and acts as a bridging plate between said switching devices with one fixing points on each device;
a moving plate, wherein said moving plate has two protruding position interlocks, wherein said protruding part interlocks with position slot of slider; and
a slider with three position slots for three locking positions, wherein the protruding part of said moving plate gets inside the position slot of said slider and interlocks the said assembly.
2. The assembly of claim 1, wherein said switching devices can be circuit breakers.


3. The assembly of claim 1, wherein said switching devices can have ON-OFF, OFF-ON, OFF-OFF operating positions.
4. The assembly of claim 1, wherein said two switching devices are mounted adjacent to each other.
5. The assembly of claim 1, wherein said slider has punches on both ends to help said slider locking within said assembly.
6. The assembly of claim 1, wherein locking positions are decided by said punch position.
7. The assembly of claim 1, wherein said moving plate has a window to have an access to thermal adjustment and push to trip button of said switching devices.
8. The assembly of claim 1, wherein holes are provided on the front ends of said base plate and said moving plate for locking said assembly.
9. The assembly of claim 1, wherein said moving plate and said base plate are operatively fixed at a common hinge point.
10. The assembly of claim 1, wherein said slider is fixed in-between the rectangular holes of said base plate.
11. The assembly of claim 1, wherein said moving plate is closed with respect to the base plate, once interlock position is decided and adjusted by said slider.


12. The assembly of claim 1, wherein said moving plate is closed with respect to the base plate, once interlock position is decided and adjusted by said slider.





ABSTRACT:
The present invention provides an interlocking device with slider for adjacent placed circuit breakers. It prevents the simultaneous switching "ON" of the two MCCBs placed adjacent to each other. It is particularly designed to provide a tamper proof interlock for molded case circuit breakers. The interlock assembly ensures that only one of the two circuit breakers is switched "ON" at any point of time or both the circuit breakers could be switched "OFF" at the same time. The interlocking module includes two plates: a moving plate and a base plate. The moving plate is fixed to a hinge so that it can be moved flexibly to cover the base plate. The interlock assembly includes a slider with slots wherein a protruding part of the moving plate comes and interlocks. At this position the interlock is locked. The three required positions are decided by the slots on the slider.
11 Claims, 11 Drawing Sheets