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 CALIBRATION SYSTEM FOR CIRCUIT BREAKERS USING A SPECIALIZED SCREW

2. Applicant(s)
(a) NAME :
(b) NATIONALITY:
(c) ADDRESS:

LARSEN & TOUBRO LIMITED
An Indian Company.
L & T House, Ballard Estate, P.O. .Box: 278 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:

TECHNICAL FIELD
[001] The present subject matter described herein, in general, relates to circuit
breakers, and more particularly to circuit breakers having an improved calibration screw.
BACKGROUND
[002] In Circuit breaker(s) is/are used to protect the device from overload and
short circuit current. Circuit breakers like molded case circuit breaker (MCCB) can be functionally divided into 3 sub-systems namely, mechanism, contact system, and release.
[003] Release part in MCCB is responsible to give the circuit break command
to the MCCB. There are 2 kinds of releases available in market, theyare, Thermo magnetic (TM) release and Electronic release.
[004] Both the release has to do the basic function of giving the circuit break
command during overload and short circuit condition. TM release is to provide performance equivalent to microprocessor release at a much lower cost. TM release can be further sub divided into 2 sub parts, namely thermal part and magnetic part.
[005] An overload condition, in MCCB, in simple terms can be explained as
high current (though not as high as short circuit current) that can hamper the well-being of the equipment in use. The equipment will be designed to carry a particular rated current for a period of time based on its duty cycle. If higher current (overload current) flows in the system for longer periods, then the system will not be able to dissipate the excess heat generated because of the overload and ultimately the system will break down. The thermal part of the TM release usually consists of a heater, a bimetal, a

calibration screw, and a shaft. Deflection of bimetal with change in temperature is the phenomenon used in TM release to protect the circuit from overload current.
[006] A heater (1) element is used, which will carry current and will provide
the necessary heat to bimetal (2) either by passing current through the bimetal (direct heating) or by thermally conducting the heat to the bimetal (Indirect heating).
[007] In indirect heating method, current injected flows via. Heater. The
current heats the bimetal and it gets deflected. A calibration screw may be placed at the top of the bimetal which will serve for 2 purposes: a point contact and calibration.
[008] As the screw will have a narrow end than the surface of a bimetal, it can
hit the shaft more precisely.
[009] Due to varied reasons like improper mechanical joints, assembly and
component level tolerance, the gap between the bimetal (2) and the shaft (4) varies. In order to adjust this gap, the calibration screw is adjusted to its correct distance either by screwing or unscrewing it. This gap is called trip gap (6) 'X'.
[0010] With the bimetal, the calibration screw moves and hits the shaft which in
turn produces the trip (circuit break) command.
[0011] Calibration is actually a tedious and a cumbersome process. Much
iteration is to be done to achieve the perfect operation. The iterations are intercepted with a cooling period during which the bimetal cools and comes back to the original condition and gets ready for the next iteration.
[0012] In the conventional calibration method, bimetal has to move a distance
4X' mm to touch the overload shaft. To trip the MCCB, it has to move a distance 4X' plus a certain distance or angle to rotate the overload shaft and trip the TM release (TMR).

[0013] The operator may pass current to breaker and the heater and bimetal
heats up to deflect the bimetal by 'X - Ax' mm. The breaker does not trip within the
given time limit. The operator may allow the breaker to cool it for a period of time to reach the ambient. The operator may calibrate i.e., reduces the gap between the calibration screw and shaft so that the circuit breaks open within the desired time limit, and puts it into test. The bimetal deflects 4X - Ay' mm. (where y
[0021] In one implementation, the present invention provides ease of offline
calibration of MCCBs, with the appropriate degree of rotation
[0022] In one implementation, the present invention provides ease of automation
with servo and special tools.
[0023] In one implementation, the present invention provides elimination of
error in bimetal deflection as well as shear force during rotation of screw towards trip plate.
[0024] In one implementation, the present invention provides accessibility from
the front side of MCCB with two different varieties of tools.
[0025] In one implementation, the present invention at breaker level, online
calibration / hot calibration may be done with finer adjustment.
[0026] In one implementation, the present invention discloses a gear-head
calibration screw, as shown in figure 5, suitable for mechanical pre-calibration. The screw has two ends, front and rear= The front end is a convex tip surface while the rear end is gear-headed with Allen slot. The Gear head can be driven by a screw driver/driving gear while the Allen slot is driven by Allen key/hex key. The orientation for accessing gear teeth is perpendicular to the body of the screw while Allen key will access in line to the Allen slot, thus able to provide two types of accessibility in different orientations. The calibration may be done both at sub assembly level and also in integrated condition; also fine adjustment may be possible with motor driven tool. The method of calibration is automation friendly and may not be possible in prior-art or existing method as well as in reference patent ('759) cited above.
[0027] In one implementation, the Gear head is proposed to locate at rear end.
But, it can also be positioned at the front end next to the convex tip as shown in figure
6. . .

[0028] Additional objects, advantages and novel features of the invention will
be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
[0029] „ Figure 1 illustrates an isometric view of Modular TM Release, in accordance with an embodiment of the present subject matter.
[0030] figure 2 illustrates the functional components of the Thermal release, in
accordance with an embodiment of the present subject matter.
[0031] Figure 3illustrates a trip gap between calibration screw and shaft, in
accordance with an embodiment of the present subject matter.
[0032] Figure 4 illustrates an alignment of gear head calibration screw with
Allen slot with bimetal, in accordance with an embodiment of the present subject matter.
[0033] Figure 5 illustrates a top view and Isometric view of the gear head
calibration screw with Allen slot with bimetal, in accordance with an embodiment of the present subject matter.

•

[0039] It is to be understood that the singular forms "a," "an," and "the" include
plural referents unless the context clearly dictates otherwise.
[0040] By the term "substantially" it is meant that the recited characteristic,
parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
[0041] Features that are described and/or illustrated with respect to one
embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
[0042] It should be emphasized that the term "comprises/comprising" when
used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
[0043] This present invention generally relates to low voltage switchgear
applications and specifically to MCCB using bimetal for overload protection. This invention also relates to any overload protection device, which has adjustable thermal settings, in the switchgear industry.
[0044] Unlike in conventional calibration method, the calibration screw in the
present invention is customized with gear head along with Allen slot that supports dual method of calibration process to form a specialized screw (3). Gear teeth can be accessed using a screw driver/ special tool while an Allen key can also be used for accessibility. The degree of rotation can be defined in the circular pitch of the gear teeth that avoids ambiguity in calibration. This Gear head calibration screw (3) is easy to rotate from front side of MCCB which is not feasible in the conventional method.

[0045] Depending on the bimetal deflection, the calibration varies for each pole
and also for every sample of TMR. In this method, the first phase of calibration will start at TMR unit alone that exists in all MCCB manufacturing process. Next phase will be for MCCB, for refinement to trip the system to arrive at the trip characteristics curve. This way many drawbacks in conventional method like loading of bimetal during calibration by the operator, tolerance variations, etc., may be accounted.
[0046] After passing the test current to the circuit breaker, the operator waits for
a given time and if the breaker does not trip, the gear head calibration screw is adjusted to trip the breaker. Similarly all the three poles calibrated independently and separately using three calibration screws. Hence number of iterations is reduced compared to conventional method.
[0047] In one implementation, the present invention discloses the development
of gear head calibration screw for offline mechanical pre-calibration of TMR. In this method, a modular thermal release is used to issue the trip command to the mechanism of the breaker. The thermal release consists of a heater (1), bimetal (2), gear head calibration screw (3), shaft (4), temperature compensation bimetal (8), latch (5) and tripper (7). During overload condition, as discussed earlier, settings are adjusted using adjuster (9) and bimetal (2) gets deflected by indirect heating. Adjuster (9) is used as an interface between the user and internal components of TMR. Adjuster is connected to trip plate. When user selects a particular setting by tuning the adjuster, the trip plate moves in X - axis. This deflection rotates the shaft (4) which in turn gives signal to temperature compensation bimetal (8). The compensation bimetal then de-latches the latching system so that the tripper issues the trip command to the mechanism.
[0048] In one implementation, the required degree of rotation for calibration is
defined in the circular pitch of the gear, which is may be an added advantage in case of iterations. Accordingly, number of gear teeth can also be decided. This gear head calibration screw can be designed for multiple teeth with equal space definition. A tool

with gear head engaging with calibration screw or a customized special tool can be used for gear teeth accessibility. Dual accessibility feature is available in the same customized Gear head-Allen slot calibration screw.
[0049] In one implementation, the mechanical pre-calibration process may be
done in two phases as before and after integration of TMR with MCCB, Iterations are reduced comparatively leading to appropriate trip gap to arrive at trip characteristics curve. This concept requires minimum effort for calibration that saves time and avoids manual error.
[0050] In one implementation, it may be understood by the person skilled in that
art that, for the conventional calibration screw, Allen key is used for accessibility. Due to this, calibration is feasible only from the top of MCCB that gives an approximate idea on degree of rotation leading to several iterations. But in this present invention, front side accessibility is feasible that makes calibration simple and easy. This method of calibration avoids shear stress on bimetal that can be expected. in the conventional method. Rotation of screw can also be automated with servo and other special tools and can also support online calibration with refinement.
[0051] Accordingly, in one implementation, a calibration system for use in
circuit breakers with a heater (1), bimetal (2), a shaft (4), temperature compensation bimetal (8), a latch (5) and tripper (7), that includes one or more gear hea.d calibration screw (3) configured to rotate from a front side of the circuit breaker and comprises of a degree of rotation defined in a circular pitch of one or more gear teeth is disclosed.
[0052] In one implementation, a calibration screw is customized with a gear
head along with an Allen slot and configured to support a dual method of calibration process.

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[0053] In one implementation, the gear teeth of the gear head calibration screw
(3) are configured to provide access to a screw driver and/or a special tool comprising gear head engaging capability.
[0054] In one implementation, the Allen slot is configured to provide access to a
screw driver and/or a special tool.
[0055] In one implementation, the gear head calibration screw (3) is configured
to provide an offline mechanical pre-calibration.
[0056] In one implementation, the gear teeth are designed with equal space
definition.
[0057] In one implementation, the calibration process by using the gear head
calibration screws (3) avoids shear stress on the bimetal.
[0058] In one implementation, the degree of rotation is automated by use of a
servo and one or more special tools that enable to support online calibration process, f
[0059] In one implementation, the present invention is used in a thermo-
magnetic release of the circuit breakers.
[0060] In one implementation, the present invention comprises of an adjuster (9)
configured to provide an interface between the user and the circuit breaker, wherein, the adjuster is connected to trip plate.
[0061] Referring now to figure 1, illustrates an isometric view of Modular TM
Release, in accordance with an embodiment of the present subject matter.
[0062] Referring now to figure 2, illustrates the functional components of the
Thermal release, in accordance with an embodiment of the present subject matter.

h
[0063] Referring now to figure 3, illustrates a trip gap between calibration screw
and shaft, in accordance with an embodiment of the present subject matter.
[0064] Referring now to figure 4, illustrates an alignment of gear head
calibration screw with Allen slot with bimetal, in accordance with an embodiment of the present subject matter. Allen slot is a locator to engage hex key/Allen key. Allen slot is provided at the core of the gear head. The slot radius takes the midpoint of the cylindrical body with an average depth of about 2 mm for hex key engagement.
[0065] Referring now to figure 5, illustrates a top view and an isometric view of
the gear head calibration screw with Allen slot, in accordance with an embodiment of the present subject matter.
[0066] Referring now to figure 6, illustrates a front view and isometric view of
the gear head located at front end of the calibration screw with Allen slot at rear end, in accordance with an embodiment of the present subject matter.
[0067] In one implementation, the present invention provides the direction of
screw access is at front side of MCCE. that makes calibration easy and the degree of rotation is traceable during iterations.
[0068] In one implementation, the present invention provides precise degree of
rotation is known to the operator.
[0069] In one implementation, the present invention provides elimination of
error in bimetal deflection as well as shear force during rotation of screw towards trip plate.
[0070] In one implementation, the present invention provides an ease of
automation with servo and special tools.

*>
[0071] In one implementation, the present invention provides possibilities to
access from the front side of MCCB that makes calibration simple.
[0072] In one implementation, the present invention enables to reduce the
number of iterations during calibration process.
[0073] In one implementation, the present invention provides a gear head
calibration screw with circular pitch defining the degree of rotation.
[0074] In one implementation, using the present invention a calibration is
possible using two different tools in two different orientations unlike existing method of calibration.
[0075] In one implementation, the gear head calibration screw (3) include
cylindrical body portion having at least one threading, and wherein a diameter of the cylindrical body portion enables threaded engagement of the screw with a bimetal. The gear teeth and the circular pitch are designed based on the required degree of rotation for calibration.
[0076] In one implementation, the gear head calibration screw (3) is made of
steel or any metal existing. The person skilled in the art may understand that any existing material for the manufacturing of the screw may be used.
[0077] In one implementation, the gear head calibration screw (3) comprises of
a gear head having a radius preferably within the range from 2 mm to 6 mm. The preferable radius of the head with gears of the screw is 2mm (min).
[0078] In one implementation, the preferable length of the screw is 6mm (min).
Possible range is within 6-20mm. .

[0079] In one implementation, the preferable length of the gear teeth is 1.5mm
(min). Possible range is 1.5-5mrri.
[0080] In one implementation, a person skilled in the may understand that the
Allen slot is a slot for Allen key (i.e., key with hexagonal socket for driving bolt/screw). Further, gear is a standard profile whereas in the present invention, the design modifications lie on the circular pitch and gear teeth arrangement based on engagement with the driving tools.
[0081] The present invention provides the calibration screw has Gear teeth at the
rear end with an Allen slot. However, it is to be noted that the gear teeth of the present invention may also be placed at the front end near the convex tip, with Allen slot remaining at the rear end.
[0082] The illustrations of arrangements described herein are intended to
provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other arrangements will be apparent to those of skill in the art upon reviewing the above description. Other arrangements may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Figures are also merely representational and may not be drawn to scale. Certain proportions thereof may be exaggerated, while others may be minimized. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
[0083] Thus, although specific arrangements have been illustrated and described
herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific arrangement shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments and arrangements of the invention. Combinations of the above arrangements, and other

tl
arrangements not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

WE CLAIM:
1. A calibration system for use in circuit breakers with a heater (1), bimetal (2), a shaft (4), temperature compensation bimetal (8), a latch (5) and tripper (7), CHARACTERIZED BY HAVING one or more gear head calibration screw (3) configured to rotate and comprises of a degree of rotation defined in a circular pitch of one or more gear teeth.
2. The calibration system as claimed in claim 1, wherein the gear head calibration screw (3) include cylindrical body portion having at least one threading, and wherein a diameter of the cylindrical body portion enables threaded engagement of the screw with a bimetal.
3. The calibration system as claimed in claim 1, wherein the gear head calibration screw (3) comprises of a front end and a back end, wherein the front end comprises of a convex surface, and the back end is gear-headed with an Allen slot.
4. The calibration system as claimed in claim 1, wherein the Gear teeth and the circular pitch are designed based on the required degree of rotation for calibration.
5. The calibration system as claimed in claim 1, wherein the gear head calibration screw (3) comprises of a gear head having a radius preferably within the range from 2 mm to 6 mm.
6. The calibration system as claimed in claim 3, wherein the Allen slot having a depth within the range from 2 mm to 4 mm.
7. The calibration system as claimed in any of the preceding claims is of a length
within the range from 6-20 mm.

8. The calibration system as claimed in any of the preceding claims, wherein the
gear teeth are a length within the range from 1.5-5mm.
9. The calibration system as claimed in claim 1, wherein a calibration screw is customized with a gear head along with an Allen slot and configured to support a dual method of calibration process.
10. The calibration system as claimed in any of the preceding claims, wherein the gear teeth of the gear head calibration screw (3) are configured to provide access to a screw driver and/or a special tool comprising gear head engaging capability.
11. The calibration system as claimed in any of the preceding claims, wherein the Allen slot is configured to provide access to a screw driver and/or a special tool.
12. The calibration system as claimed in any of the preceding claims, wherein the gear head calibration screw (3) is configured to provide an offline mechanical pre-calibration.
13. The calibration system as claimed in any of the preceding claims, wherein the gear teeth are designed with equal space definition.
14. The calibration system as claimed in any of the preceding claims, wherein calibration process by using the gear head calibration screws (3) avoids shear stress on the bimetal.
15. The calibration system as claimed in any of the preceding claims, wherein the degree of rotation is automated by use of a servo and one or more special tools that enable to support online calibration process.

16. The calibration system as claimed in any of the preceding claims is used in a thermo-magnetic release of the circuit breakers.
17. The calibration system as claimed in any of the preceding claims comprises of an adjuster (9) configured to provide an interface between the user and the circuit breaker, wherein, the adjuster is connected to trip plate.

18. The calibration system as claimed in any of the preceding claims, wherein said gear head is located at front end of the calibration screw with Allen slot at rear end.
19. The calibration system as claimed in any of the preceding claims, wherein said gearhead is locatedwith Allen slot at rear end of the calibration screw.