|Title of Invention||
SAFETY INTERLOCKING DEVICE FOR CIRCUIT BREAKERS
|Abstract||This invention relates to a novel door interlocking assembly for drawout circuit breakers such that it prevents any unauthorized access to a circuit breaker when the same is in live condition; said mechanism comprising a set of components positioned on panel door and another set of co-ordinated components mounted on circuit breaker, such that the assemblies lock effortlessly when panel door is closed and remains interlocked when circuit breaker is in SERVICE or TEST condition; while it needs a designed skill to defeat or undo the interlock; the invention having a specific ease of mounting the door part of the assembly. Deepak Mehra Agent for Applicant Dated 28th day of May, 2003.|
THE PATENTS ACT 1970
Complete Specification (Section 10)
SAFETY INTERLOCKING DEVICE FOR CIRCUIT BREAKERS
LARSEN and TOUBRO LIMTED
L & T House, Ballard Estate,
Maharashtra State, India
An Indian Company duly registered and incorporated under the Companies Act, 1956.
The following specification particularly describes and ascertains the nature of the invention and the manner under which it is to be performed:
This invention relates to
"SAFETY INTERLOCKING DEVICE FOR CIRCUIT BREAKERS"
and is aimed at achieving the prevention of accidental / unauthorized access to the the Circuit Breaker when it is in live condition i.e the main current path is completed.
Prior and Present Art
Circuit Breakers for low voltage generally find application in the current range of below and upto 6400A. These circuit Breakers are available in Fixed and Drawout versions. For a Drawout Circuit Breaker, additionally a chamber like unit, henceforth called Cradle, is generally required. Through cradle, current carrying parts of the circuit breaker get connected to the current carrying parts of the panel, also called panel. Panel is a large chamber, where these complete assemblies are mounted and whereby it gets connected to main power supply through cables, links or any other means. In any Circuit Breaker a control circuit is also provided for power supply to it's various accessories viz. Closing release, Shunt release, Electrical charging device etc.
Drawout circuit breaker can assume 3 different positions inside a Cradle:
1. "Service" position; where Power as well as control circuit is completed. This is the position when circuit breaker is in operation.
2. Test" position; where Power circuit is disconnected but control circuit is connected. In this position, the circuit breaker can be tested for proper functioning without switching / carrying power.
3. "Isolated" position; when control circuit is also disconnected.
It is imperative that the panel door remain closed when the circuit breaker is in service / test condition, as human access to circuit breaker can be fatal. It can cause damage to operator and installation. However for inspection purpose, the panel door may required to be opened by concerned knowledgable person, under supervision. Opening of the panel door by any of the conventional / obvious methods, like pushing / turning the key part of door locking arrangement/s should not be possible. Also, when the circuit breaker is in Service / test condition and if the panel door is in open condition, it should be possible to close the same without any additional skill/ intelligence, for safety purposes. Such arrangement/s when provided is known as Interlocking.
Interlocking of the panel door with the Circuit Breaker necessarily requires the co¬ordination of one set of components on circuit Breaker with the other set of components on panel door. While the arrangement for fixing the components on cradle can be provided by the concerned manufacturer/s, the arrangement for fixing components on panel door is to be necessarily provided by the panel builder. Hence, it is necessary that the mounting arrangement required to be done on panel door should be very simple, and ought not to require special skill / tool, and should be less time consuming.
This mounting arrangement design on panel door should take care of locating, trapping & anti-rotation of an assembly. To take care of all of these requirements
many times a non-obvious cut-out is required to be done on panel door which could be of rectangular, square, triangular or any other irregular shape.
Hence mounting arrangement provision on panel door of most manufacturers either necessitates a complex cutout, i.e. one that requires special tools / hardware or a simple cutout which requires fixing of components on the panel door with irreversible processes like riveting / welding. In some of the variants, the set of components are adapted in such a way that they can be mounted either on the left or the right side of the circuit breaker alone. This can cause great inconvenience to a user whose panel is then required to be aligned to the positioning of said components. Also in most existing arrangements if breaker is in Service / test condition and if the door is in open condition, the door cannot be closed by the simple action of pushing the panel door towards the circuit breaker. On the other hand in these arrangements the defeating of interlock / opening of door is extremely easy and requires no or minimum intelligence. Hence, an ordinary and any / unauthorized person can easily open the door with the live circuit breaker inside it. Thus the safety element in these arrangements is low.
Our novel safety interlocking device, effectively, innovatively and economically solves the above stated shortcomings in present day door interlocking mechanisms by ensuring that the skill / intelligence required at the time of closing the door, to ensure safety, is at minimum. Also a higher level of intelligence / skill is required to open the door, so that persons acquainted with the operation of circuit breakers / supervisors alone are able to access the circuit breaker in the live or test condition. Thus there is increased level of safety both at the time of closing and opening the switchboard door.
The Different levels of intelligence- at the time of opening and closing of the switchboard door ensure safety.
Disclosure of the invention
In our invention, unique co-ordination between panel door components and Circuit Breaker components leads to the aim of auto-latching and intelligent defeat of a panel door. This in turn helps in achieving higher level of safety for operator and desired convenience for a circuit breaker user.
For the purpose of description, the set of components positioned on panel door is termed as "Door latch assembly". "Door latch assembly" comprises of bracket, cam, nut, key, follower pin, defeater and key return spring.
Likewise, the set of components positioned on Circuit Breaker, is termed as "Engaging Mechanism". This "Engaging Mechanism" comprises of Latch, stopper, actuator, latch return spring, actuator spring and latch hinge.
The "Engaging Mechanism" is made in a way whereby it can be mounted either on the left or the right side of the Circuit Breaker. This option is given so as to enable the panel builder to choose any arrangement depending on the hinging arrangement of his panel door. Thus the panel layout is never a hindrance for the user in opting for this accessory. If a door is left hinged then the interlock is to be fitted on right hand side and vice versa.
In order to mount the "Door latch assembly" on a panel door, cutout suitable to "Door latch assembly" is required to made on the panel door. This cutout takes care of locating, trapping and anti-rotation of "Door latch assembly". In our unique arrangement, the cutout "D" required on door can be made / achieved with the help of an ordinary drilling operation. No special punch / tool is required for it. For fixing of "Door latch assembly", required cutout "D" is actually a smaller size hole merging with a larger size hole. Cam is trapped on door with the help of this cutout between door and nut. The Bracket is trapped
between nut and switchboard door. One of the major advantage about trapping of Cam and Bracket is that it doesn't require any additional hardware / tool.
In "Engaging Mechanism" the latch is hinged on cradle. Provision for mounting of "Engaging Mechanism" is kept on both left and right side of circuit breaker. Latch actuator is mounted on latch hinge with two springs; actuator spring and latch return spring respectively. When Circuit Breaker is in 'Isolated' position, one arm of actuator spring is trapped against the actuator and the other arm is trapped against first fixed referenced part of cradle so as to get desired spring action. Second referenced part mounted ahead of first reference part in cradle acts as a stopper for an actuator to achieve initial position of actuator. The projection kept on Latch stops against actuator's surface thereby defining the initial position of latch i.e. unlatched position of latch.
As the circuit breaker starts moving towards test position and just before reaching the test position circuit breaker housing starts pushing the actuator. Since the latch is hinged with the help of Latch hinge and It is loaded with Latch return spring, as circuit breaker starts pushing the actuator, the Latch starts rotating about it's hinge and stops against Second reference part of cradle and decides final position of Latch. When Latch completes its travel, the tip of the latch gets trapped in the groove of the bracket. This results in locking effect of a door. Latch remains in the same orientation till the circuit breaker reaches the service position.
"Engaging Mechanism" mounted on Circuit Breaker has to co-ordinate with "Door latch assembly" mounted in a Panel. Manufacturing variations can be of the order of 4-5 mm in X, Y & Z planes for a panel, panel door & Circuit Breaker mounting in panel. Bracket in our arrangement is adapted in such a way that it takes care of manufacturing variations in X & Y planes intelligently. Also stopper provided on "Engaging Mechanism" takes care of manufacturing variations within Z plane.
To operate / defeat this locking mechanism on the key part, which is mounted on the panel door, a Follower Pin is press fitted in the key part has to follow the profile provided in cam for defeating: of lock. The Profile provided on cam which the follower pin follows is designed in such a way that this Interlock cannot be operated by pushing I rotating \he key atone OT by any other obvious \way o1 operating oi look. To operate / defeat this Interlock one needs to push it partially, rotate it and again push it to it's final position. Lock defeater is mounted at the end portion of key part. It is fitted with click fit mechanism. While the key part is getting pressed, the chamfer shaped profile on Latch starts riding on chamfer shaped profile on defeater. When key is pressed to it's final position, it lifts the latch to delatch it from the bracket.
Similarly, when key is released, it returns back because of key return spring along with the defeater mounted on it. Hence the latch moves downwards and gets trapped in the bracket. When the circuit breaker starts moving from service position towards test position, the actuator moves along with the circuit breaker housing. As the circuit breaker reaches the test position and further moves towards isolated position, actuator's surface comes in contact with Latch's surface. Hence, actuator starts pushing Latch in upward direction till second reference part obstructs the movement of the actuator. When the actuator stops against the second reference part, it delatches the latch completely from the bracket.
When the circuit breaker is in service / test position, it is hazardous to work around the same if the panel door is open. Hence, it is necessary to close the door in such situation without any additional efforts / intelligence, i.e. any person (whether or not familiar with the working of circuit breakers) should be able to shut and lock the panel in one simple action, preferably a simple pushing action. In our design, while
closing the door the chamfer shaped profile on Latch comes in contact with bracket's rear surface. Since the Latch is loaded with Latch return spring it gets lifted. Once the door is completely closed the bracket clears the latch and Because of the latch return spring the latch returns and the front tip of the latch gets trapped inside the groove in the" bracket.
Brief description of the drawings
Figure 1a shows door cutout details. 1
Figure 1b is an exploded view of the set of components to be fixed on the panel door.
Figure 2a shows details of cam.
Figure 2b shows assembly of key with follower pin,
Figure 2c shows details of the pusher.
Figure 3 shows isometric view of assembly of set of components sitting on door.
Figure 4a shows details of an actuator. Figure 4b shows details of Latch.
Figure 5 shows isometric view of assembly of components to be fixed on the cradle of the circuit breaker.
Figure 6 shows sectional side view for two different positions of Latch and Actuator corresponding to Isolated and Test positions of circuit breaker.
Figure 7 is a sectional side view showing riding of Latch on Pusher at the time of Operation / defeat
Figure 8 shows sectional side view during functioning of Auto-Latching feature.
Detailed Description of the preferred embodiment
The invention will now be described with the help of above referred drawings, which are non-restrictive examples. They are duly marked with appropriate numerals for convenient reference.
We shall first describe in detail the assembly by referring to the drawings of the components positioned on panel door of the components positioned on the cradle of the circuit breaker.
Cutout (1) as shown in figure 1 is required to be made on the panel door (2) This cutout is a combination of a smaller size hole (1a) merging with a larger size hole (1b). As a variation, it can be formed by combination of two simple cutouts so as to be able to mount the assembly in non-rotating way.
Cam (3) has external threading on it and is mounted on the panel door with nut (4), which has corresponding internal threading. Bracket (5) has same opening as cutout
(1) as is required on the panel door (2). Bracket (5) is trapped between panel door
(2) and nut (4) with a suggested orientation as shown in figure 3. While assembling the cam (3) on the panel door, the operator need to take care that half round
projection (3a), provided on cam (3), fits in the smaller size hole (1a), made in the panel door (2) and bracket (5), so that assembly will be secured for non-rotation.
Key-follower pin assembly (Figure. 2b) comprising key (6) and a follower pin (7) is assembled in the groove (3b) provided in cam (3). Key return spring (8) is also assembled in the same groove (3b), which helps for auto returning of key-follower assembly (Figure. 2b).
Latch (10) is hinged with the help of Latch Hinge (11) on non-moving part of the cradle called side plate (12). Actuator (13) is mounted on the same Latch Hinge (11). Two springs, actuator spring (14) and Latch return spring (15) are assembled on the actuator (13). A Stopper (16) is trapped in groove (10a) on Latch (10).
When the circuit breaker (19) is in Isolated position (201), shown in dash-dotted lines in Figure.6, (one arm of actuator spring (14a) is trapped against First reference part of cradle (17) and the other arm of the same (14b) rests against the actuator (13). Due to the spring action of actuator spring (14), actuator (13) rests against Second reference part (18) of cradle. Projection (10b) on Latch (10) stops against surface (13a) of actuator (13), which decides initial position of Latch (10). In this condition Latch (10) doesn't come in contact with bracket (5), hence it is known as "delatched" position of the latch (10) / panel door (2). As the circuit breaker starts moving towards test position (20T), and just before it reaches the test position (20T), the projection (19a) on the breaker housing (19) comes in contact with the tip (13b) of an actuator (13). As breaker reaches the test position (20T), the tip (10c) of the latch (10) gets trapped in the cavity (5a) of bracket (5). This is known as Latched position of Latch (10) / panel door (2).
As the circuit breaker further moves towards service position, actuator (10) further moves inside, Since Latch (10) is stopped against bracket (5), it disengages from the actuator and hence doesn't move further. Stopper (16) provided on Latch (10) takes care of manufacturing variations in the panel design in 'Z' plane. If assembly on the panel door shifts downwards then stopper (16) will decide the final position of a Latch (10) in it's latched condition. Width (5W) & depth (5D) of Bracket (5) takes care of corresponding manufacturing variations in circuit breaker mounting in panel in 'X' & Y planes.
If the operator needs to open the door when the circuit breaker (19) is in test / service position, it requires additional skill / intelligence to operate / defeat the door (2) in such situation. This is possible because of a unique profile (3b) provided in the cam (3). Due to which operating / defeating will be possible only after pushing the key (6) by some distance, then rotating it by few degree and then again pushing it till the end of the profile. Because of this operation of key (6), tip (10c) rides on end tip (9a) of pusher (9), hence Latch (10) disengages from the bracket (5), which in turn allows opening of door (2). This is shown in Figure. 7
If the circuit breaker (19) is in test / service position and the door (2) is in open condition. In our invention of door interlocking mechanism, only a simple act of pushing the panel door towards the circuit breaker can lock the said door and no additional skill is required to close the door, which will now be described in detail as shown in Figure. 8. If the circuit breaker is in test / service position, the Latch (10) will be in it's lowered position. When the door is closed, tip (10c) of Latch (10) rides over the end surface (5c) of bracket (5), which allows further movement of panel door (2), after which Latch (10) gets trapped inside the cavity (5a) of bracket (5) and thus the panel door (2) gets locked / latched.
1) A safety interlocking device for drawout circuit breakers comprising of two co-ordinated assemblies: "Door Latch assembly" mountable on panel door and mountable on an engaging mechanism; Said "Door Latch Assembly" comprising: -
a cam circular in shape, having diameter equivalent to that of bigger size of hole (1) of door cutout & a half round projection (3a) at it's one end having diameter equivalent to that of smaller size of hole (la) of door cutout, hence gets trapped in panel door (2) cutout with a collar of bigger diameter than that of bigger size of hole in panel door, hence sits on panel door with resting against the outer side of the panel door in the desired orientation;
& having external threads with a hollow cavity to adapt key (6) part with key slots at front end, a follower pin (7) press fitted inside it & a pusher (9) fitted at it's rear end with a chamfer (9a) shaped profile which comes in contact with Latch tip (10c) of "Engaging Mechanism" at the time of operation; to follow the cam profile (3b) provided in cam which first moves inside, then rotates & then again moves inside at the time of operation of key part;
a 'G' shape bracket (5) having a cutout same as panel door cutout (1) at it's front end & a Latching cavity (5a) at it's rear end trapped on the cam (3) between the panel door (2) & a nut (4) with internal threads to match with corresponding external threads on cam; and
Said "Engaging Mechanism", mountable on either left or right side of the cradle on cradle side plate (12) of draw out circuit breaker comprising: -
a Latch (10) with having Latching Tip (10c) at front end, a surface with two rectangular grooves (10a) in between, half-round projection (10b) residing next to it & 2 bends forming 'IF shape at rear end with a co-axial bearing holes with the help of which it sits on the Latch hinge (11) & fixed to the cradle side plate (12);
an actuator (13) having bearing holes in it which sits on Latch hinge (11) having rotary motion around same Latch hinge (11) at the time of drawing in & out the circuit breaker inside cradle & trapped in between two bends of Latch (10), with one arm (14a) of actuator spring (14) resting against First reference part (17) of cradle & other arm (14b) resting against an actuator (13) having a tip (13b) at it's one end & a flat surface (13a) against which Latch projection (10b) rests; having Latch spring with one arm trapped in a hole in an actuator (13) & the other arm is trapped in a hole in a Latch (10); and
a stopper (16), trapped with the help of one groove (10a) when the assembly is mounted on left hand side 8c with the help of another groove (10a) when it is mounted on right hand side; provided on Latch (10) which rests against Second reference part (18) fixed on cradle side plate (12).
2) A Safety Interlocking Device for Circuit Breakers as Claimed in Claim 1 substantially as herein described with reference to the accompanying specification and drawings.
Dated 28th day of May, 2003.
Deepak Mehra Agent for Applicant
|Indian Patent Application Number||620/MUM/2003|
|PG Journal Number||30/2007|
|Date of Filing||13-Jun-2003|
|Name of Patentee||LARSEN & TOUBRO LIMITED|
|Applicant Address||BALLARD ESTATE, MUMBAI,|
|PCT International Classification Number||H01H 009/26|
|PCT International Application Number||N/A|
|PCT International Filing date|