FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
SELF POWERED NOISE REDUCED COMPACT CURRENT SENSOR;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA
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 circuit breakers, and more particularly to current sensing in circuit breakers. BACKGROUND OF THE INVENTION
Circuit breakers are switches that automatically interrupt the flow of electrical current when the rated current exceeds due to an electrical overload or fault. Typically, a circuit breaker comprises housing, contacts enclosed within the housing, an operating mechanism to operate the contacts, and an arc chute.
The operating mechanism of a circuit breaker primarily consists of two springs, a main spring (or a closing spring) and an opening spring (or a return spring). The main spring is used for closing operation wherein the spring is held in a charged condition by a closing latch. On releasing the closing latch, the spring releases energy, and this turns ON the circuit breaker. The closing spring generates required driving force to close the circuit breaker and charge the opening spring, and energy needed for the vital opening operation is stored in the opening spring when the circuit breaker is in closed position.
A current sensor is a device that detects electrical current (AC or DC) in a wire, and generates a signal proportional to it. The generated signal could be analog voltage, current or even digital output. It can be then utilized to display the measured current in an ammeter or can be stored for further analysis in a data acquisition system or can be utilized for control purpose.
Figs. 1a-c show different Self Powered Current Sensors as disclosed in US Patent No: 7078888 B2, US Patent No. 7078888 B2 and US Patent No. 6018239.

US Patent 7078888 B2 discloses a current sensor wherein construction of the sensing coil is based on a closed construction consisting of three or more pieces. Due to this, there will be lot of external interference in the output signal of the sensing coil. This is because there will be joints between each pieces. This is given priority as the signal from the coil has to be processed in a micro controller and necessary filtration of the noise has to be done to isolate the sensing signal. Hence, lesser the noise in the input signal, better the sensing signal.
In US Patent 6018239, because of the co-axial construction, the window area (i.e. the space in the middle of the sensor unit left open so that the bus bar of which the current has to be sensed passes through) obtained is very low in the given volume, which restricts the sensor to be put around relatively large bus bars.
Thus, the current sensors used in Circuit breakers especially MCCB are not capable of sensing very large values current. The ones that are able to sense are prone to noise, so conditioning of signals is required.
in view of the above, there is a need of a current sensor that can overcome the drawbacks of the existing sensors known in the prior art.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a self powered parallel bus bar current sensor for sensing current from a current source. The bus bar current sensor comprises a power unit including a power up coil and a plurality of magnetic core stack stacks, a sensing unit having a sensing coil for sensing current through a magnetic field of the bus bar, the sensing coil having a window opening at center of the coil; and a front cover and a back cover enclosing the power unit and the sensing unit wherein the front cover and the back cover are configured to ensure the window opening is at center of the sensing coil for avoiding distortion when sensing current from the bus bar.

BRIEF DESCRIPTION OF THE DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Fig. 1a, 1b, 1c shows prior art current sensors in accordance with an embodiment of the present invention.
Fig. 2a shows an exploded view of a current sensor with a front cover, a back cover, power unit and sensing unit in accordance with an embodiment of the present invention.
Fig. 2b shows a 3 phase arrangement of current sensors with bus bars in accordance with an embodiment of the present invention.
Fig. 2c shows a single enclosed current sensor in accordance with an embodiment of the present invention.
Fig. 3 shows a power up unit with a magnetic core stack and a sensing unit with an air core in accordance with an embodiment of the present invention.
Fig. 4a shows stacking of magnetic lamination in accordance with an embodiment of the present invention.
Fig. 4b shows interlocking of magnetic laminations in accordance with an embodiment of the present invention.
Fig. 4c shows securing of stacks with sleeves in accordance with an embodiment of the present invention.
DESCRIPTION OF THE INVENTION
Various embodiments of the present invention provide a self powered parallel bus bar
current sensor for sensing current from a current source. The bus bar current sensor

comprising a power unit including a power up coil and a plurality of magnetic core stacks, a sensing unit having a sensing coil for sensing current through a magnetic field of the bus bar, the sensing coil having a window opening at center of the coil; and a front cover and a back cover enclosing the power unit and the sensing unit wherein the front cover and the back cover are configured to ensure the window opening is at center of the sensing coil for avoiding distortion when sensing current from the bus bar.
Fig. 2a, 2b, 2c shows a current sensor 100 in accordance with an embodiment of the present invention. Current sensor 100 includes a front cover 110, a back cover 130, and a sensor unit 120. Sensor unit 120 includes a PCB 122, a sensing unit 124, and a power unit 127.
Power unit 127 includes a power up coil 128 and a plurality of magnetic core stacks 126. Sensing unit 124 includes a sensing coil 124a and a window opening 124b for accommodating a bus bar (not shown). Power up unit 127 is inserted in back cover 130.
Magnetic core stack 126 is made by stacking individual laminations. Power up coil 128 is inserted and a second magnetic core stack 126a is interlocked. The magnetic core comprising of two magnetic core stack 126b is sleeved.
In an embodiment, sensing coil 124a is connected to power unit 127 by two substantially parallel bars (140a, 140b) as shown in Fig. 3.
In an embodiment, sensing coil 124a is a closed race-track constructed sensing coil with toroidal compensated winding for noise reduction and quality replication of the signal as shown in Fig. 3.
In an embodiment, sensing coil 124a is air cored enabling to sense large range of current.
In an embodiment, sensing coil 124a is placed above power up coil 128.
In an embodiment, back cover 130 and front cover 110 are configured to ensure window 124b comes in center of sensing coil 124a. It is important because the sensing coils

can pick up and replicate the same signal of the bus bar with lesser amplitude and when the bus bar is offset from the center of the sensing coil, it will lead to distortion and will affect the repeatability of the signal from coil to coil. Hence, the window which carries the bus bar is centered with respect to sensing coil. Front cover 110 has an opening 132 in accordance vith window 124b of sensing coil 124a for enabling bus bar entry as shown in Fig. 2c.
In an embodiment, sensing coil 124a as shown in Fig. 3, with race track profile is vound with a compensation winding on a plastic former (not shown). A race track profile is jsed because the bus bars are usually rectangular shaped and hence the magnetic field around the bus bar tends to take a rectangular shape with rounded edges (race track shaped). The race track profile of sensing coil 124a will help picking up the signal very effectively)
In an embodiment, power up coil 128 is linearly wound coil with electrically conducting material like copper over a bobbin 128a of dielectric material.
In an embodiment, power up coil 128 is soldered to a PCB 122 which is arrested in bobbin 128a.
In an embodiment, magnetic core stacks 126 are interlocked and connected to power up coil 128.
In an embodiment, lamination of magnetic core stacks 126 for interlocking utilizes a two L shaped stacks using method of welding or sleeving.
In an alternate embodiment, lamination of the magnetic core stacks 126 for interlocking utilizes C and I shaped stacks joined using the method of welding or sleeving.
The power up unit which consists of a magnetic core stack and powering up coil provides the power to a card for the entire functioning of the card and also the device which gives the mechanical signal from the release namely the FSD. (The construction of this and the relevance of each component are mentioned later). The signal given by the power up

coil is rectified and linearly regulated by the electronic card to various voltage levels required for different functions in the card.
The powering coil is put around magnetic core stacks. This is done for higher residual current and hence higher wattage for powering the processing electronic unit and the tripping device, (generally a Flux Shift device in MCCB). Again the magnetic core stack is not made of a single piece but instead as a stack of lamination to avoid eddy current and hysteresis losses and thereby decreasing the heating of the stack and increasing the efficiency of the stack. In order to hold these laminations together methods like welding, indie stacking etc. are used. The proposed method uses a slightly elastic plastic loop which secures all the lamination together. This is very cheap and very consistent. The complexity involved in securing the laminations is nothing when compared to the aforementioned methods. The sleeving method is shown in fig. 4c in accordance with an embodiment of the present invention.
The lamination of the magnetic core stack is ideally expected to be as a single piece for very good magnetic continuity. But for the ease for winding the coil put around it either 2 'L' shaped stacks are joined or a 'C and a T shaped stack is joined using the method like welding, or in the latest case sleeving (the method mentioned above). The small air gap which comes in between both the stacks is undesirable. So an interlock (as shown in figure 4a) is created and both the stacks are joined (as shown in fig. 4b). This increases the magnetic property of the stack to a large extend compared to welding of the stacks.
Signal from the sensing coil is integrated and then amplified in the card using operational amplifiers. And this signal is used by the micro controller(in the card) to issue trip commands, monitor the line current and to maintain the fault history when various faults due to short circuit, over current, earth leakage, single phasing etc. occurs.
The Co-Axial Self Powered Sensors have very small window area, so large conductors cannot be passed.

According to embodiments of the present invention, the current sensor comprises a single piece race track profile for the closed loop winding. And while winding, the incremental pitch advancement of the helical winding sums over the perimeter of the race track to creates an undesirable one-turn loop normal to the axis of the coil. Any magnetic flux normal to this loop induces an error voltage into the coil's output. Sources of normal flux can originate from the bus bar geometry, nearby return conductors, other current-carrying conductors, leakage flux from transformers, or warped fields due to the presence of ferromagnetic materials. To compensate for this undesired one-turn loop, another one-turn loop can be placed inside the helical winding in the opposite direction to that of the pitch-advancement turn. It is located in a plane parallel to that of the pitch advancement turn. It is connected electrically in series with the coil's output. For fields having no gradient, a compensation voltage is induced in this loop that is equal and of the opposite polarity to that voltage induced in the pitch-advancement turn. This again gives a very minimal noise in output in our sensing coil making the filtration easy.
As per the present invention, the sensor has larger window area because of the arrangement of the sensing and powering coils in different planes side by side, because of this, much smaller and compact sensors may be used for measuring current carried by same bus bar compared to the one used in the prior art.
The present invention is advantageous in providing a Wireless termination for noise reduction. Further, it provides a closed Race-track constructed sensing coil with toroidal compensated winding for noise reduction and quality replication of the signal. The coil is Air cored enabling it to sense large range of Current. The present invention provides routing using PCB tracks for noise reduction.
In an embodiment, advantageously, the present invention provides the alternated Lamination arrangement method for making stacks of magnetic core stack (for the powering up unit) which are interlockable. Same lamination types are used for arranging alternatively.

In an advantageous aspect, method for arranging the stack is inexpensive compared to the known methods like die stacking and different welding techniques.
Further, the use of sleeves for the magnetic core stack provides extra rigidity to the powering up unit.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since, modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims.

We Claim:
1. A self powered parallel bus bar current sensor for sensing current from a current source,
the bus bar current sensor comprising:
a power unit including a power up coil and a plurality of magnetic core stacks;
a sensing unit having a sensing coil for sensing current through a magnetic field of the bus bar, the sensing coil having a window opening at center of the coil; and
a front cover and a back cover enclosing the power unit and the sensing unit wherein the front cover and the back cover are configured to ensure the window opening is at center of the sensing coil for avoiding distortion when sensing current from the bus bar.
2. The self powered current sensor as claimed in claim 1 wherein the sensing coil is connected to the power unit by two substantially parallel bars.
3. The sensor as claimed in claim 1, wherein the sensing coil is a closed race-track constructed sensing coil with toroidal compensated winding for noise reduction and quality replication of the signal.
4. The sensor as claimed in claim 1, wherein the sensing coil is air cored enabling to sense large range of current.
5. The sensor as claimed in claim 1, wherein the magnetic core stacks are interlocked and connected to the power up coil.
6. The sensor as claimed in claim 5, wherein lamination of the magnetic core stacks for interlocking utilizes a two L shaped stacks using method of welding or sleeving.

7. The sensor as claimed in claim 5, wherein lamination of the magnetic core stacks for interlocking utilizes C and I shaped stacks joined using the method of welding or sleeving.
8. The sensor as claimed in claim 1, wherein the power up coil is linearly wound coil with electrically conducting material like copper over a bobbin of dielectric material.
9. The sensor as claimed in claim 8, wherein the power up coil is soldered to a PCB which is arrested in the bobbin.
10. The sensor as claimed in claim 1, wherein the sensing coil is placed above the power up coil.
11. The sensor as claimed in claim 1, wherein the sensing coil with race track profile is wound with a compensation winding on a plastic former.