FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

ASSIST MECHANISM FOR ELECTRICAL PROTECTION DEVICES;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAl - 400 001, MAHARASHTRA, INDIA
THE FOLLOWING SPECIFICATION
PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

BACKGROUND OF THE INVENTION
Field of the invention
This invention relates generally to switching and protection devices such as
circuit breakers, relay, and the like and more particularly to actuating mechanism
in such devices.
Prior Art
Isolation of electrical circuits is necessary to protect downstream equipments or apparatus against high currents/voltage arising during short circuit, overload current or in other words abnormal situations. Devices used to accomplish electrical isolation during fault have evolved from early fuse elements with obvious need of replacement of fuse to reenergize the circuit. Advent of electrical protection devices such as circuit breakers and relays overcame this problem. Generally for tripping arrangement main spring is used and other associated biasing springs act against it so as to achieve desired function of carrying current. During abnormal condition in current repulsion based system these biasing springs force acts against main spring force by given degree of freedom and undergoes for clipping action before main spring acts there by achieving protection against fault.
Above arrangement is normally used for circuit breaker but in case of thermal overload relays during abnormal condition thermal actuating means pushes actuator which in turn brings changes in spring position and force balance is altered where new position is stable spring position accompanied by indicating contacts.
In other protection devices where biasing springs doesn't have degree of freedom the main mechanism spring acts in such a manner so as to alter force

balance in such a way that it establish new force balance condition along with
biasing springs and achieve fault protection.
Chinese patent 101562100 to Gen Electric describes a spring discharge
mechanism for circuit breaker which includes two linkages for crashing or
discharging the circuit breaker springs to allow the circuit breaker to be used in
either fixed breaker installation or in an installation having a drawout mechanism.
Similarly Chinese patent publication no. 201210469 to Zhejang Chint Electric
Appliance Co., Ltd. describes an assistant tripping mechanism for circuit breaker
and 201270221 to Guizhou Space Appliance Co., Ltd. descirbes acceleration
relay overload sensitive mechanism mass block.
The systems referred above have at least one of the following disadvantages.
There is a need to minimize the response time of these protection devices to
abnormal situations. Further, since operation of these devices is initiated by
actuating means and assisted by mechanism, need arises to have faster
mechanism with low response time from mechanism without loading actuating
means.
The quickness and reliability should not be achieved at the cost of intricate
complex structure which may further entangle troubleshooting.
SUMMARY OF THE INVENTION
An objective of the invention is to provide a simple and compact assist mechanism for electrical protection devices which has a low response time. Accordingly, the present invention provides an assist mechanism for electrical protection devices comprising a housing to house the assist mechanism, a pair of normally opened and a pair of normally closed contacts, a slider attached to the pairs of normally opened and closed contacts, a holding means for providing a positive force to the slider, an actuator connecting the assist mechanism to a thermal assembly, and a trip lever connected to the actuator having a protrusion for initiating the motion of the slider, the trip lever being initiated by the actuator.

As a result, the assist mechanism provided is simple and compact as the biasing spring has been done away with and the response time is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features of the present invention
can be understood in detail, a more particular description of the invention, briefly
summarized above, may be had by reference to various embodiments, some of
which are illustrated in the appended drawings. It is to be noted, however, that
the appended drawings illustrate only typical embodiments of this invention and
are therefore not to be considered limiting of its scope, for the invention may
admit to other equally effective embodiments.
Fig. 1 shows a thermal over load relay using an assist mechanism, in accordance
with an embodiment of the invention.
Fig. 2 shows an isometric view of a slider of the assist mechanism, in accordance with an embodiment of the invention.
Fig. 3 shows an isometric view of a thermal overload relay using the assist
mechanism, in accordance with an embodiment of the invention.
Fig. 4 shows an isometric view of a trip level of the assist mechanism, in
accordance with an embodiment of the invention.
Fig. 5 shows the thermal overload relay in auto condition, in accordance with an
embodiment of the invention.
Fig. 6 shows the thermal overload relay in trip condition, in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION OF INVENTION
Various embodiments of the invention provide a simple and compact assist
mechanism for electrical protection devices which has a low response time.
in various embodiments the electrical protection device may be a circuit breaker,
a thermal over load relay and the like.
Figure 1 shows a thermal over load relay 100 using the assist mechanism, in
accordance with an embodiment of the invention.

In accordance with an embodiment of the invention, thermal over load relay (relay) 100 includes a housing 102 to house the assist mechanism, a pair of normally opened (NO) contacts 104 and a pair of a normally closed (NC) contacts 106, a slider 108, holding means, an actuator 110, and a trip lever 112. Figure 1 also shows terminals 114a-e.
Slider 108 is functionally and physically attached to pairs of NO 104 and NC 106 contacts. Figure 2 provides a detailed isometric view of slider 108 identifying slots 108a-d.
Holding means provide a continuous positive force to slider 108. In accordance with an embodiment of the invention, holding means is an interlace spring 116. Interlace spring 116 is better seen in the exploded view of relay 100 in figure 3. Interlace spring 116 always maintains a stable positive force on slider 108 during travel of slider 108. In tripped condition, interlace spring 116 holds on to slider 108 thereby reducing chances of resetting back of the assist mechanism. Since interlace spring 116 always act on slider 108 and maintains positive force on slider 108, during normal operation any shock and vibration will not alter slider 108 stable condition. During faulted and tripped condition interlace spring 116 is in connection with slider 108 and always maintains positive force on slider 108. Trip lever 112 is connected to actuator 110 and is responsible for movement of slider 108. Figure 4 provides a detailed isometric view of trip lever 112 identifying elements 112a-c. Trip lever 112 has a protrusion 112a for initiating motion of slider 108.
Actuator 110 connects the assist mechanism to a thermal assembly. Thermal assembly is a bimetal assembly reacting to a change in current passing through relay 100. In case of an abnormal condition, when enough heat is generated, thermal assembly deflects to initiate trip lever 112 action. When trip lever 112 action is initiated through actuator 110, there will not be any motion of slider 108. As shown in figure 1, in an embodiment relay 100 also includes a trip indicator 118 for indicating the status of relay 100 - healthy or tripped. Trip indicator 118 is connected to trip lever 112 through an indicator biasing spring 120 which is secured in trip indicator 118 and trip lever 112.

As shown in figure 1, in an embodiment relay 100 also includes an auto/manual
selector 122 for automatic resetting of relay 100. Auto/manual selector 122 has
one degree of freedom of rotation and enables automatic resetting of assist
mechanism when condition changes from abnormal to normal.
In an embodiment, relay 100 also includes a pivot assembly 124 (shown in figure
1). Actuator 110 is housed in the housing through pivot assembly 124.
During normal operation, interlace spring 116 rests on slider 108 at slot 108a.
Force is acting on slider 108 so that slider 108 does not respond to any shock
and vibration and chance of nuisance tripping is eliminated.
During isolation, actuator 110 starts moving slider 108 to a predetermined point.
As a result of which, contact force reduces but there is no change in force
direction.
In faulted condition, trip lever protrusion 112a (shown in figure 4) touches slider
108 and initiates slider motion. As slider 108 moves, it starts motion of NO 104
and NC 106 contacts. After a predefined travel, NC 106 will open up and trip
indicator 118 will flip as indicator biasing spring 120 changes force direction
resulting in trip condition of the assist mechanism. Trip indicator 118 has one
degree of freedom-rotation about 112b.
Therefore, during tripping operation or during normal operation holding means
force is always higher such that chances of nuisance tripping and nuisance
resetting are avoided. Holding means force is not exorbitantly high to cause
permanent damage to thermal structure. When actuator starts moving it does not
alter any force direction but because of indicating contacts loading, absolute
value of force can reduce.
While the foregoing is directed to embodiments of the present invention, other
and further embodiments of the invention may be devised without departing from
the basic scope thereof, and the scope thereof is determined by the claims that
follow.

We Claim:
1. An assist mechanism for electrical protection devices comprising:
a. a housing to house the assist mechanism;
b. a pair of normally opened and a pair of a normally closed contacts;
c. a slider, the slider being attached to the pairs of normally opened
and normally closed contacts;
d. a holding means for providing a positive force to the slider, the
holding means being housed in the housing mechanism;
e. an actuator, the actuator connecting the assist mechanism to a
thermal assembly; and
f. a trip lever, the trip lever being connected to the actuator, the trip
lever having a protrusion for initiating the motion of the slider, the
trip lever being initiated by the actuator.
2. The assist mechanism according to claim 1 further comprising a pivot assembly, the actuator being housed in the housing through the pivot assembly.
3. The assist mechanism according to claim 1 further comprising an auto-manual selector for automatic resetting of the electrical protection device.
4. The assist mechanism according to claim 1 further comprising a trip indicator for indicating the status of the electrical protection device, the trip indicator being connected to the trip lever through an indicator biasing spring.
5. The assist mechanism according to claim 1, wherein the thermal assembly is a bimetal assembly reacting to a change in current passing through the electrical protection device.

6. The assist mechanism according to claim 1, wherein the holding means is an interlace spring.