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 THERMO MAGNETIC RELEASE
ASSEMBLY FOR USE IN MOULDED CASE CIRCUIT BREAKER
2. Applicant(s):
(a) NAME: LARSEN & TOUBRO LIMITED
(b) NATIONALITY: An Indian Company
(c) ADDRESS: L & T House, Ballard Estate, 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:

FIELD OF THE INVENTION
The present invention relates to an improved thermo magnetic release assembly for use in Moulded Case Circuit Breaker. More particularly, the invention relates to a thermo magnetic release assembly comprising a uniquely designed latch mechanism for ameliorating the de-latching force, adjusting for minimum settings in overload and short circuit mechanism, positive latching without opening the circuit breaker and/or automatic temperature compensation.
BACKGROUND OF THE INVENTION
US 5444423 discloses a latch mechanism for a circuit breaker comprises a pair of longitudinal legs, a lateral section bridging the pair of longitudinal legs, and a longitudinal section extending from the lateral section in an opposite direction relative to the pair of legs. The lateral section includes a lower bearing surface for releasably engaging a cradle of the circuit breaker. The lower bearing surface includes a coined radius for facilitating engagement and disengagement of the cradle. The longitudinal section includes a protrusion for supporting a latch spring. The latch mechanism is manufactured in a single stamping operation, during which the protrusion is formed by cold extrusion. But, this document did not address the problems of early saturation of the electromagnetic system at low current, trip de-latching force requirement and large size design of the circuit breaker.
US 6,956,452 discloses an apparatus and method for circuit breaker trip unit adjustment In which an air gap is disposed between the stationary pole face and the movable pole face; and wherein the dimension of the air gap is responsive to movement of the tripping member. Further, the trip system having means for adjusting the trip force in the absence of adjustment to the air gap and means for adjusting the air gap in the absence of adjustment to the trip force.
US 4,951,015 discloses a circuit breaker with moving magnetic core for low current magnetic trip. The invention relates to circuit breakers having a magnetic trip assembly in which the magnetic field induced by an abnormal current unlatches a latchable operating mechanism to trip the breaker, and more particularly to such a magnetic trip assembly which includes a supplemental magnetic core which allows the magnetic trip assembly to trip the breaker at relatively low levels of over current.
US 5,608,367 discloses a molded case circuit breaker with interchangeable trip unit having bimetal assembly which registers with permanent heater transformer airgap. It is an

improved circuit breaker in which the thermal trip characteristic can be easily and reliably adjusted. The improved circuit breaker, in which, the thermal trip characteristic can be adjusted by changing the gap in the magnetic core of heater transformer. In which different trip units may be interchangeably inserted and withdrawn with each providing a different gap in the magnetic circuit to provide a range of current ratings for the circuit breaker.
US 3165609 discloses temperature compensation for ambient temperature variations in the circuit breakers. It is having a tripping mechanism that is compensated for ambient temperature variations while at the same time preserving a constant magnetic air gap in a tripping mechanism having both magnetic and thermal tripping arrangements.
US 5,225,800 discloses a molded case thermal-magnetic circuit breaker having improved low current magnetic trip response pivotally arranges the magnet within the circuit breaker thermal-magnetic trip system for controllably moving toward the latching armature assembly. The movement of the magnet decreases the magnetic separation distance between the magnet and the latching armature to optimize the magnetic trip forces and thereby enhance low current magnetic trip response.
In the prior art, the air gap was kept constant and only the spring force was adjusted which leads to earlier saturation of the electromagnet and thermo magnetic release the adjustment for different settings were made by varying the spring force. The problem faced by auto temperature compensation bimetal initial stress is due to latch plate in the prior art.
Thus there is a need to provide an improved thermo magnetic release assembly for use in Moulded Case Circuit Breaker which would overcome the problems prevailing in the prior art. The present inventors have found that a latch mechanism designed in a unique manner when introduced in a magnetic release assembly for use in circuit breakers provides reduced de-latching force, adjustment for minimum settings in overload and short circuit mechanism, positive latching without opening the circuit breaker and/or automatic temperature compensation.
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 thermo magnetic release assembly for use in Moulded Case Circuit Breaker.

Another object of the present invention is to provide a mechanism for adjustable overload settings.
Another object of the present invention is to provide a mechanism for adjustable short circuit settings.
Another object of the present invention is to provide a trip latch mechanism for thermo-magnetic release assembly.
Further object of the present invention is to provide an auto temperature compensation arrangement.
Further object of the present invention is to provide slide to trip arrangement.
Yet, another object of the present invention is to provide a trip position indication.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided an improved thermo
magnetic release assembly for use in multi pole moulded case circuit breaker, said
assembly comprising:
a housing;
overload shaft means mounted on said housing;
trip actuator means;
plurality of spring means;
plurality of knob means;
trip latch mechanism;
an electromagnetic system;
an auto temperature compensation arrangement;
wherein said auto temperature compensation arrangement comprising:
auto temperature compensation bimetal means hinged on said housing so as to rotate about
its axis to deflect freely with respect to ambient temperature variations;
main bimetal means;
plurality of fastener means;
wherein said auto temperature compensation bimetal being substantially horizontally located
with respect to said main bimetal which is arranged so as to establish a substantially vertical
relation with the said housing base providing ambient temperature compensation; and
wherein said auto temperature compensation bimetal during overload condition being

operatively actuated by said main bimetal means being adapted to actuate said trip actuator
means ;
wherein said electromagnetic system comprising:
moving magnet means;
fixed magnet means;
magnetic slider means being located in the said housing;
wherein said moving magnet means being hinged on said fixed magnet means so as to
rotate about a hinge point; wherein said moving magnet means being connected to one end
of one of said plurality of spring means and said magnetic slider means being connected to
the other end of the said spring means;
wherein said magnetic slider means having tapered profile adapted to adjust an air gap
between said moving magnet means and said fixed magnet means and simultaneously to
adjust said spring force while said magnetic slider means is driven by said knob means; and
wherein said auto temperature compensation bimetal during short circuit condition being
operatively actuated by said moving magnet means being adapted to actuate said trip
actuator means;
wherein said trip latch mechanism comprising:
trip plate means;
trip plate holder means;
pin means;
wherein said trip plate means being hinged on said trip plate holder means by using said pin
means
wherein said trip plate holder means and said trip plate means having another spring means
being operatively engaged to the said holder means and the said plate means thereby
producing de-latch force on trip actuator means to trip said circuit breaker when there is a
fault.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates a rear view of entire release assembly having all components.
Fig 2 illustrates a left side cross sectional view of release latch mechanism at latched position clearly indicated inside the circle.
Fig 3 illustrates a left side cross sectional view of release latch mechanism at de-latched position clearly indicated inside the circle
Fig 4 illustrates a right side cross sectional view of torsion spring arrangement provided for reset overload shaft and trip actuator is at reset position

Fig 5 illustrates a left side cross sectional view of an assembly of electromagnet in open position and the tension spring that holds the moving core
Fig 6 illustrates a left side cross sectional view of an assembly of electromagnet in closed position which actuates the overload shaft to de-latch the release mechanism indicated inside the circle
Fig 7 illustrates a top cross sectional view of an assembly of electromagnet at maximum air gap position indicated inside the circle (i.e. at maximum SC setting)
Fig 8 illustrates a top cross sectional view of an assembly of electromagnet at minimum air gap position indicated inside the circle (i.e. at minimum SC setting)
Fig 9 illustrates a rear view of an assembly of electromagnet at minimum air gap and minimum spring force position indicated inside the circle (i.e. at minimum SC setting)
Fig 10 illustrates a rear view of an assembly of electromagnet at maximum air gap and maximum spring force position indicated inside the circle (i.e. at maximum SC setting)
Fig 11 illustrates a top cross sectional view of an assembly of electromagnet at trip position indicated inside the circle.
Fig 12 illustrates a top side cross sectional view of an assembly of bimetal at normal position indicated inside the circle.
Fig 13 illustrates a left side cross sectional view of an assembly of short circuit setting knob with O-ring in the housing with lock mechanism to arrest its motion in y axis after assembly of magnetic slider.
Fig 14 illustrates a bottom cross sectional view of lock arrangement in knob to arrest z axis motion
Figures 15 and 16 illustrate an isometric view of entire release module assembly with trip indication
Fig 17 illustrates an isometric view of entire release module assembly in general view
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
According to the invention there is provided a thermo magnetic release assembly used in moulded case circuit breaker. The entire assembly described in the present embodiment is designed for 3 pole operation. However, this should not be considered as any limitation of

the present invention as the present design construction of the assembly can also be extended for multi-pole operation. This assembly consists of heater (2) (current carrying part), set of electromagnets (core and plate), torsion spring (7) all in three sets. This assembly also consists of a pair of adjustment knobs, an electromagnet adjustment component, a bimetal adjustment component, auto temperature compensation bimetal (15) and separate trip latch mechanism which gives the output from the release.
According to one embodiment of the invention, the trip latch mechanism consist of trip plate (10) hinged on trip plate holder (11) by a pin (18) and the compression spring (8) provided between trip plate holder (11) and trip plate (10) give de-latch force to trip main MCCB's mechanism using its stored energy. The clockwise torque produced by compression spring (8) on trip plate (10) hinged on trip plate holder (11) through pin (18) and anti clockwise torque produced by torsion spring (7) on trip actuator (9) hinge on housing (1) create a latch point (19) when two of them exactly at perpendicular to each other shown in figure 2. At latched position both the component dose not experience any torque mutually with respect to each other. While de-latching due to fault the trip actuator (9) experience minimum torque produced by trip plate (10) due to compression spring (8). In other it produces minimum opposing torque on overload and short circuit actuators. The de-latching force produced by either magnet due to short circuit or bimetal due to overload through auto temperature compensation bimetal (15) as shown in figure 3. The torsion spring (7) provided for reset the overload shaft (12) and trip actuator (9) after fault has been cleared is mounted on housing (1) through pin and its first arm reset the trip actuator (9) and the second arm reset overload shaft (12) shown in figure 4. Slide to trip arrangement provide in the trip actuator (9) can does the function of tripping and trip position indication in the release.
According to another embodiment of the invention, auto temperature compensation bimetal (15) is hinged on housing (1) as shown in figure 1 consists of two calibration screws (25). Mounting of auto temperature compensation bimetal (15) on the housing (1) can make it perfect to rotate with respect to it axis. Arrangement this bimetal here is such a way it doesn't experience any force under normal operation. The need of stress less ambient compensation bimetal is to deflect freely with respect to ambient temperature variations. Rotation of auto temperature compensation bimetal with respect to hinge point (26) is shown in figure 1. Ambient temperature variation can be solved by auto temperature compensation U shape bimetal in horizontal position. The horizontal arrangement of this component can ensure the constant offset distance between main bimetal (16) and overload shaft (12) even when the ambient temperature changes. The advantage of this compensation is no need to de-rate or upgrade the breaker due to ambient temperature variation. Auto temperature

compensation bimetal (15) arrangement also provides better mechanical advantage to fault actuators due longer length shown in figure 1. Overload shaft (12) mounted in the housing (1) can act as an interface between fault actuator (i.e. magnet and bimetal) and provide adjustable overload setting with its slope shown in figure 12.
According to a further embodiment of the invention, the electromagnetic system consists of a core and a movable part. Horizontally mounted electromagnet with its actuation in vertical direction provides more space for wound coil (3) on fixed core (4) for low current MCCBs. The movable part is hinged as shown in the figure 2 and figure 5 so it can be rotated about hinged point. The arrangement of the spring is such that it always opposes the electromagnetic force and holds the electromagnetic part (movable part) in its open position as shown in figure 5. The hinge point of tension spring (6) that holds moving magnet (5), its one end is fixed to magnetic slider (17) and another end at moving magnet (5) shown in figure 5. Magnetic slider (17) placed on housing (1) with tapered profile helps to adjust spring force while it was driven by knob shown in figure 9 and figure 10. Air gap (20) between moving magnet core (5) and fixed magnet core (4) can also be adjusted by the same magnetic slider (17) as shown in figure 7 and figure 8. Both air gap (20) and spring force adjusted by short circuit setting knob shown in figure 1. Actuating mechanism of moving magnet (5) on overload shaft (12) is shown in figure 6. Electromagnet is instantaneous tripping device.
+Short trip is achieved by first the magnet actuate the overload shaft (12) (i.e. in figure 6) which in turn actuate the auto temperature compensation bimetal (15) (i.e. in figure 6) future it actuate trip actuator (9) (i.e. in figure 3) to de-latch the mechanism. Overload tripping is delayed here because the bimetal deflect leads to actuation only after the temperature rise across it which is usually not an instantaneous process .overload trip is achieved by first the bimetal actuate the overload shaft (12) which in turn actuate the auto temperature compensation bimetal (15) which again actuates trip actuator (9) that trips the mechanism.
The adjusting knobs namely overload setting knob (13) and short circuit setting knob (14 ) provided in the housing (1) for overload setting and short circuit setting respectively . Individual knobs degree of ration is restricted to less than 180 degree after the assembly of overload shaft (12) and magnetic slider. O-ring (21) provided in the knob provides enough friction to hold the knob in corresponding setting position shown in figure 13. The lock is provided in such a way that with slot (22) provided in housing (1) and the degree of rotation constrained by overload shaft (12) assembly shown in figure 10 and figure 14. The purpose of the lock is to hold the knob in the hinged position i.e. the knob can rotate with respect to y axis but will not translate in y axis until unless overload shaft (12) and magnetic slider (17)

has been removed from the assembly. Snap fit is provided in the release housing assembly for reducing screws in the assembly.
ADVANTAGES OF THE INVENTION
Providing wide adjustable short circuit, overload setting and ambient temperature compensation for specifically lower current MCCB's.
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 trip actuator, bimetal, knobs, trip plate, trip plate holder, pins, springs, and magnetic core as stated do not limit the scope of the present invention. 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 stiff be comprised within its true spirit.
housing -1 heater 2 coil -3
fixed magnetic core 4 moving magnet core 5 tension spring 6 torsion spring 7 compression spring 8 trip actuator 9 trip plate 10 trip plate holder 11 overload shaft 12 overload setting knob 13 short circuit setting knob 14 auto temperature compensation bimetal 15 main bimetal 16' magnetic slider 17
hinged position of auto temperature compensation bimetal -- 26 (hinge point) holding pin 18 trip latch point 19 air gap 20

O-ring arrangement 21
calibration screw 25
slot —22
snap fit 23
slide to trip arrangement 24

We Claim
1. An improved thermo magnetic release assembly for use in multi pole moulded case circuit breaker, said assembly comprising: a housing;
overload shaft means mounted on said housing; trip actuator means; plurality of spring means; plurality of knob means; trip latch mechanism; an electromagnetic system; an auto temperature compensation arrangement;
wherein said auto temperature compensation arrangement comprising:
auto temperature compensation bimetal means hinged on said housing so as to
rotate about its axis to deflect freely with respect to ambient temperature variations;
main bimetal means;
plurality of fastener means;
wherein said auto temperature compensation bimetal being substantially horizontally
located with respect to said main bimetal which is arranged so as to establish a
substantially vertical relation with the said housing base providing ambient
temperature compensation; and wherein said auto temperature compensation
bimetal during overload condition being operatively actuated by said main bimetal
means being adapted to actuate said trip actuator means ;
wherein said electromagnetic system comprising:
moving magnet means;
fixed magnet means;
magnetic slider means being located in the said housing;
wherein said moving magnet means being hinged on said fixed magnet means so as
to rotate about a hinge point; wherein said moving magnet means being connected
to one end of one of said plurality of spring means and said magnetic slider means
being connected to the other end of the said spring means;
wherein said magnetic slider means having tapered profile adapted to adjust an air gap between said moving magnet means and said fixed magnet means and simultaneously to adjust said spring force while said magnetic slider means is driven by said knob means; and wherein said auto temperature compensation bimetal

during short circuit condition being operatively actuated by said moving magnet means being adapted to actuate said trip actuator means ;
wherein said trip latch mechanism comprising:
trip plate means;
trip plate holder means;
pin means;
wherein said trip plate means being hinged on said trip plate holder means by using
said pin means
wherein said trip plate holder means and said trip plate means having another spring
means being operatively engaged to the said holder means and the said plate means
thereby producing de-latch force on trip actuator means to trip said circuit breaker
when there is a fault.
2. Assembly as claimed in claim 1, wherein said auto temperature compensation bimetal is substantially U shaped.
3. Assembly as claimed in claim 1 wherein said spring means selectively comprising torsion spring, tension spring, compression spring and the like.
4. Assembly as claimed in claim 3 wherein said torsion spring is adapted for resetting the overload shaft.
5. Assembly as claimed in claim 3 wherein said torsion spring is further adapted for resetting the trip actuator means.
6. Assembly as claimed in claim 1, wherein said knob means is adapted to be rotated upto about 180 degree.
7. Assembly as claimed in any one of the preceding claims further comprising a substantially O-shaped ring.
8. Assembly as claimed in any one of the preceding claims further comprising slide-to-trip arrangement.
9. Assembly as claimed in any one of the preceding claims being optionally snap fitted.
10. A latch mechanism for thermo magnetic release assembly used in moulded case circuit breaker as herein substantially described and illustrated with the accompanying drawings.