FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - IMPROVED CURRENT TRANSFORMERS FOR CIRCUIT BREAKERS
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:

TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a current transformer. More particularly, the invention relates to an improved current transformer for circuit breakers used in measurement and powering.
BACKGROUND AND THE PRIOR ART
Conventional Current sensors like Rogowski coils and Hall Effect transducers have gained large dominance as a current measurement technique owing to low cost, high reliability, high accuracy and wide measuring range. The conventional technique of current measurement includes use of use of iron core curren transfarmers which can be rather bulky and saturate quite early due to use of laminated iron cores. Air core Rogowski coils offer multiple advantages over the existing techniques. However, such coils are incapable of delivering adequate Power output for signal processing, annunciation or operating tripping devices. Also, other electronic sensors like Hall Effect sensors require auxiliary power. To overcame this disadvantage, Power CTs are used in conjunction with such sensors.
US 5,726,846 disclose a trip device comprises at least one current transformer for supplying power to electronic circuits. The current transformer comprises a magnetic circuit, surrounding a primary conductor, a secondary winding wound onto a part of the magnetic circuit forming a core, and a magnetic shunt branch connected on the magnetic core. The magnetic shunt comprises an air-gap When the current flowing in the primary conductor is of low value, the magnetic flux stopped by the air-gap flows essentially via the core of the secondary winding. At high current levels the induction is greater and a large part of the magnetic flux parses through the shunt via the air-gap. The current transformer has a non-linear current response which limits excess

power supplied to the electronic circuits and dissipated in the transformer. The trip device is useful, for example, in a circuit breaker.
US 6,459,349 disclose a circuit breaker assembly having an electronic trip unit used to detect an overcurrent condition in a protected Electrical circuit. The electronic trip unit being electrically connected to a current transformer used to sense electrical current and provide operating power to the electronic trip unit. The current transformer comprising a metal core having a top surface and a bottom surface where the difference between top and bottom surfaces defines height of the core. The core having a concentrical opening extending through the height so that the distance between an outside point on the concentrical opening and the closest outside point of the core defines thickness of the core at the point. Passing through Che care opening
is a primary winding and encircling the thickness of me core is a secondary winding. To optimize usage of the current transformer, a partial air gap is added to the metal core so that the range of operation is maximized while at the same time minimizing the remanence attenuation.
WO 2007045985 (Al) discloses a current transformer (10) comprises a coil (14) , a core (12) and a shunt member (16). The core forms a magnetic circuit and has a first permeability. At least a portion of the core is encircled by the coil. The shunt member is coupled to the core and has a second permeability The shunt member is continuous and forms a magnetically parallel path with the at least a portion of the core encircled by the coil. The current transformer may be incorporated in to a trip device.
However, none of the cited documents has known about incorporation of an external component for flux bypass in the magnetic circuit. Thus, there is a need to overcome the problems of the prior art.

Therefore, the present inventors have developed an improved current transformer for use in circuit breakers having high permeability shunt. It would be used in measurement and powering purposes and for offering relatively flat VA output characteristics so as to satisfy the purpose of supplying power for metering, signal processing, annunciation and operating actuating devices in limited space constraint.
OBJECTS OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.
Another object of the present invention is to provide an improved current transformer for circuit breakers used in measurement and powering.
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying
drawings.
SUMMARY OF THE INVENTION
There is provided a current transformer for use in circuit breakers.
According to one embodiment of the present invention, there is provided improved current transformer for circuit breakers used in measurement and powering, said current transformer comprising a shunt branch of substantially high magnetic permeability, a rod of substantially low permeability placed to bypass magnetic flux at higher current levels; a core (4) of substantially low permeability; and a secondary coil (5) wound on a substantially high magnetic material (1) and a main conductor (3) forming a bypass path (2).

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the appended drawings:
Fig 1 illustrates an improved current transformer in an embodiment of the invention.
Fig 2 illustrates an improved current transformer in another working position.
Fig 3 illustrates a graph depicting conventional CT vs. power CT used in present invention.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Reference is first invited to Fig 1 where an improved current transformer in an embodiment of the invention is shown.
Fig. 2 shows an improved current transformer in another working position.
Fig 3 shows a graph depicting conventional CT vs. power CT used in present invention.

The invented system is thus an improved current transformer for circuit breakers used in measurement and powering.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly in the present invention there is provided an improved current transformer for use in circuit breakers having high permeability shunt. It is an improvement in existing technology for drawing power from current flow in an electrical conductor by using an iron core current transformer with high permeability material in shunt. As there exists an upper limit to the power requirement for the various operations, schemes are necessary to limit the power output by either restricting the flux through the iron core or bypassing it away from the secondary winding.
The present invention has current transformer (CT) which can be used in tripping device. CT has shunt branch of high magnetic permeability material. This shunt path delivers almost constant secondary power at higher current levels. Hence the size of CT and processing circuit is much smaller compared to regular iron core CT. This can be used in many products which require current sensing with large current range and small power.
Constructional components
High permeability material (1) Flux bypass path (2) Conductor (3) Iron core (4) Secondary coil (5)

The invention provides an improved current transformer for use in circuit breakers having high permeability shunt. As shown in figure 1, high permeability material (1) is placed externally in the main magnetic circuit, below which the low permeability materials like iron rod (4) is placed to bypass the magnetic flux at higher current levels. C shaped low permeability core and high permeability material (1) form a main magnetic circuit. The low permeability rod could be of same material as that of core or it could be different. Note that both externally added rods, higher permeability as well as lower permeability like iron, must have good surface finish. The bypass path (2) is in between the secondary winding (5) which is on the high permeability material (1) and the main conductor. For the lower currents, maximum magnetic flux flows through high permeability material (1) and hence power generated at the secondary is linearly increasing. Above such currents, magnetic flux of the conductor (3) is bypassed through the iron, lower permeability material. Hence output VA of the secondary winding is limited and gives almost flat characteristics. Due to this arrangement, overall size of current transformer gets reduced. Apart from this, the ratings of electronic components used for processing the power output of current transformer can be reduced.
As shown in figure 2, bypass path (2) is shifted upwards and the secondary coil (5) wound on the high permeability material (1) is placed in between the conductor (3) and bypass path (2). This embodiment as shown in figure 2 is advantageous over the other as shown in figure 1 due to smaller magnetic path hence lesser magnetizing power in the same configuration. However, secondary VA would be slightly higher as the leakage flux linking with secondary winding after saturation will increase. Figure 3 shows a graph depicting conventional CT vs. power CT.
Both the embodiments provide flexibility in terms of cross sectional areas as well as overall shape of the high permeability material and the low permeability material.

The present invention gives an advantage that both arrangements can be added externally in existing current transformer configurations as well.
ADVANTAGES:
1. Compact
2. Reliable and consistent power output applicable for AC systems
3. Complete electrical isolation of the sensor from the live conductor.
4. No temperature rise issues.
5. Ease of manufacturability and assembly
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM:
1. An improved current transformer for circuit breakers used in measurement and
powering, said current transformer comprising:
a shunt branch of substantially high magnetic permeability,
a rod of substantially low permeability placed to bypass magnetic flux at
higher current levels;
core (4) of substantially low permeability; and
a secondary coil (5) wound on a substantially high magnetic material (1) and a
main conductor (3) forming a bypass path (2).
2. Current transformer as claimed in claim 1 wherein said shunt branch delivering constant secondary power.
3. Current transformer as claimed in claim 1 wherein said core is substantially c shaped.
4. Current transformer as claimed in claim 1 wherein said secondary coil (5) is of substantially high permeability.
5. Current transformer as claimed in claim 1 wherein said rod has substantially good surface finish.

6. An improved current transformer for circuit breakers used in measurement and powering as herein described and illustrated with reference to accompanying drawings-