DESC:TECHNICAL FIELD
[0001] The present disclosure relates generally to a current transformer.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Most circuit breakers include a current transformer, along with other electrical components, to make up the breaker system. Current transformer (CT) is a type of instrument transformer designed to provide current in its secondary winding proportional to the alternating current flowing in its primary. The current transformer safely isolates measurement and control circuits from the high voltages typically present on the circuit being measured and can also be used to power electronic trip units as elaborated hereunder.
[0004] A current transformer consists of only one or very few turns as its primary winding. This primary winding can be of either a single flat turn, a coil of heavy duty wire wrapped around the core or just a conductor or bus bar placed through a central hole as shown. Due to this type of arrangement, the current transformer is often referred to as a “series transformer” as the primary winding, which never has more than a very few turns, is in series with the current carrying conductor.
[0005] The secondary winding may have a large number of coil turns wound on a laminated core of low-loss magnetic material which has a large cross-sectional area so that the magnetic flux density is low using much smaller cross-sectional area wire, depending upon how much the current must be stepped down.
[0006] There are three basic types of current transformers: “wound”, “toroidal” and “bar”. In wound current transformers, the transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit. The magnitude of the secondary current is dependent on the turns ratio of the transformer. Toroidal current transformers do not contain a primary winding. Instead, the line that carries the current flowing in the network is threaded through a window or hole in the toroidal transformer. Some current transformers have a “split core” which allows it to be opened, installed, and closed, without disconnecting the circuit to which they are attached. Bar-type current transformers use the actual cable or bus-bar of the main circuit as the primary winding, which is equivalent to a single turn. They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device.
[0007] Conventional circuit breaker devices with electronic trip units typically include a current transformer disposed around a line conductor of a distribution system providing electrical power to a load. The current transformer has a multi-turn secondary winding electrically connected to the circuit breaker's electronic trip unit. The secondary winding is used to sense a current overload or imbalance in the aforesaid line conductors and, in response thereto, provide an output signal proportional to the current overload or imbalance to the trip unit. Upon receipt of such a signal the trip unit initiates an interruption of the current supplied to the load through the line conductors. The secondary winding may also be used to provide operating power to the electronic components within the circuit breaker's electronic trip unit.
[0008] Existing current transformers (CTs) comprise of ferrite core laminations that are arranged in the form of a stack through bobbin. The bobbin is wound with secondary turns. CT assembly has a provision for inserting a primary conductor through a gap between the laminations and bobbin (for a toroidal or bar type current transformer), or has a provision for winding the primary turns (for a wound type current transformer) over the secondary turns via insulation. The ferrite laminations used are generally Cold Rolled Non Grain Oriented Steels (CRNGO).
[0009] Increasingly more sophisticated electronic circuits are being employed in circuit breakers to provide protection to various electric systems. These circuits incorporate application specific integrated circuits (ASICs), or processors, typically microprocessors. Such ASICs and processors offer a significant benefit in being capable of analyzing system situation and judiciously opening or closing power circuits based upon the analysis of prevalent system condition.
[0010] Such advanced microcontroller based protection circuitry, however, requires sufficient power for its operation over larger current range; for example from starting condition to running to locked rotor condition for a motor control system and that too without loading primary source of power. Smaller sizes of overload relays may not be able to provide sufficient power for operation of microprocessor-based control circuitry.
[0011] Some power supply circuits for such purposes use a dual mode power supply circuit- one mode for measurement and another for power supply requirements to drive the microcontroller based protection circuits. This leads to more current requirements leading in turn to more expensive components for the associated circuitry with in efficient power .management of power supply and over design of electronic circuit with increased part count.
[0012] It makes good design and manufacturing sense to power this circuitry from power that may be extracted from current transformers already being provided for in the circuit breaker.
[0013] Presently, however, this is not feasible since designing a CT for more current draw will make it more bulkier and expensive, all the more so as CTs are made of cold rolled non grain oriented steel (CRNGO) generally due cost considerations. Space is always at a premium in circuit breaker design as that has a direct effect on its overall cost.
[0014] Hence there is a need in the art for a method to make Current Transformers compact and to optimize their design for an increased current output with lesser material, cost and space requirements.
[0015] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0016] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0017] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0018] It is an object of the present disclosure to provide a current transformer that is not bulky and costly.
[0019] It is an object of the present disclosure to provide a current transformer that reduces error in output current.
[0020] It is an object of the present disclosure to provide a current transformer that can provide sufficient power for advanced micro-processor based protection and control circuits.
[0021] It is an object of the present disclosure to provide a current transformer that reduces error in output current.
[0022] It is an object of the present disclosure to provide a current transformer that increases saturation performance of its core without introducing an air gap for the same.
[0023] It is an object of the present disclosure to provide a current transformer that can allow for secondary winding with same number of turns to be used for primary conductors of different current ratings.

SUMMARY
[0024] The present disclosure relates to the field of current transformers. More particularly it relates to a method for optimizing the design and manufacture of a current transformer (CT) with its consequent benefits.
[0025] An exemplary embodiment of the present disclosure provides for a current transformer having a core, wherein the core comprises a plurality of Cold-Rolled Grain-Oriented (CRGO) laminations that are each provided with a V-notch, and wherein the CRGO laminations are stacked in an anti-parallel arrangement and aligned using the V-notches to be in proper magnetic orientation with one another, in order to make the core.
[0026] Another exemplary embodiment of the present disclosure provides for a CT, wherein turns of the secondary winding of the current transformer remain unchanged irrespective of the current being carried by the primary conductor using the current transformer.
[0027] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. In the Figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
[0029] FIG. 1A, 1B and 1C illustrate stampings of the present disclosure and how they can be assembled to form a transformer core with low magnetic resistance, as per an embodiment of the present disclosure.
[0030] FIG. 2 illustrates how the stampings can be arranged in alternate anti parallel arrangement to form a core of a current transformer, as per an embodiment of the present disclosure.
[0031] FIG. 3 illustrates one exemplary implementation of electronic protection relay wherein current transformers configured therein in accordance with an embodiment of the present disclosure are used.

DETAILED DESCRIPTION
[0032] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0033] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0034] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0035] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0036] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0037] An exemplary embodiment of the present disclosure provides for a CT having a core, wherein the core comprises a plurality of CRGO laminations that are each provided with a V-notch, and wherein the CRGO laminations are stacked in an anti-parallel arrangement and aligned using the V-notches to be in proper magnetic orientation with one another, in order to make the core.
[0038] Another exemplary embodiment of the present disclosure provides for a CT, wherein turns of the secondary winding of the current transformer remain unchanged irrespective of the current being carried by the primary conductor using the CT.
[0039] In an aspect, the proposed CT, as per an embodiment of the present disclosure, can include a core and a winding, wherein the core of the CT can be manufactured with stampings made out of CRGO (cold rolled grain oriented) steel.
[0040] CRGO steel is manufactured in such a way that the optimal magnetic properties are developed in the rolling direction, due to a tight control of the crystal orientation relative to the sheet. The magnetic flux density is increased by upto 30% in the coil rolling direction.
[0041] Hence, when using CRGO stampings, it is very important that they be assembled in proper magnetic orientation with each other so that the magnetic circuit formed has the least resistance and allow for maximum magnetic flux to be formed with its consequent advantages.
[0042] The present disclosure provides for the CRGO stampings of such a CT to be notched in such a way so as to provide a visual indication to enable the core assembler to put them together in proper magnetic orientation with each other.
[0043] In an exemplary embodiment, such visual indications can be provided by means of appropriate notches on the stampings. The notches can be provided in such a fashion that when stampings with such notches are stacked in an anti-parallel arrangement, the stack so formed has stampings in proper magnetic orientation with each other as explained hereunder.
[0044] FIGs. 1A, 1B and 1C illustrate how the notches can be provided in an exemplary embodiment of the present disclosure.
[0045] As illustrated in FIG. 1A, stamping1 can have a V shaped notch on its one leg illustrated as 1-1, and a surface shown as 12 (back of the surface not indicated).Likewise, stamping 2 can have another V shaped notch on its other leg, illustrated as 2-1 leg, and a surface with same magnetic orientation surface as 12 illustrated as 14 (back of the surface not indicated) as shown in FIG. 1B. To make a stack, the two stampings can be put together in such a fashion that they form a closed rectangle as illustrated in FIG. 1C (Top View). At the same time the magnetic orientation of surface 12 of stamping 1 has to be aligned properly with that of surface 14 of stamping 2. In an aspect, this can be done by positioning the notches 1-1 and 2-1 on stampings 1 and 2 respectively during their manufacturing in such a fashion that when the stampings 1 and 2 are assembled keeping the notches on opposite sides and forming a rectangle with the stampings, the surfaces of the stampings are properly aligned magnetically with each other. In this fashion, the magnetic flux that can pass through the core is increased that in turn provides for a more compact design with lesser material costs for same current measurement and current provisioning requirements.
[0046] It is to be understood that the V notch illustrated above is as an exemplary embodiment and any suitable marking that serves a similar purpose can be employed. A V-notch, however, can be easily attained during the stamping process itself of making the stampings and hence can be ideal.
[0047] FIG. 1C illustrates an exemplary stack of five stampings disclosed above forming a core of an exemplary current transformer.
[0048] As illustrated, each stamping can have a notch illustrated as 1-1, 2-1, 3-1, 4-1 and 5-1 for stampings 1, 2, 3, 4 and 5 respectively. The stampings can be arranged in an alternate anti-parallel arrangement thereby forming a stack of magnetic stampings that can make the core of the current transformer of the present disclosure. The notch in each stamping can be used to keep all the stampings in proper magnetic orientation with each other.
[0049] As can be seen in the top view, notch 1-1 on stamping 1 is indicated. However notch configured on stamping 2 cannot be seen in this view, as it is on the other leg and in the top view is below stamping 1.
[0050] The left side view shows edges of all the five stampings. However, side view of notch 2-1 and notch 4-1 of stampings 2 and 4 can only be seen since those on the other stampings are on the opposite side as elaborated above.
[0051] Similarly, the right side view shows edges of all the five stampings. The right side in turn shows side view of notch 1-1, 3-1 and 5-1 of stampings 1, 3 and 5. As can be seen, stampings 2 and 4 cannot be seen since they are on the opposite side as elaborated above.
[0052] In this fashion, the notches made on each stamping provide visual identification on how the stampings have to be aligned against each other so that stack (core) finally formed has low magnetic resistance due to proper magnetic orientation of the stampings with each other.
[0053] FIG. 2 illustrates a transformer core manufactured using the stampings, notches therein and their alignment as explained above, wherein the stamping can be arranged in an alternate anti-parallel arrangement, thereby forming a stack (or core) (20) of CRGO magnetic stamping. For core (20) to perform optimally, orientation of surface of each stamping (one of surface being illustrated as (12)) with respect to that of other (as explained in FIG. 1 above) is important as output of the current transformer is dependent on this surface.
[0054] In order to improve output, and to avoid wrong assembly, the stampings can be configured in anti-parallel configuration using V notch in each as elaborated above so that all the stampings are in correct magnetic alignment with each other. When aligned so, V notch of a stamping shall be visible in alternate stampings of the stack (core) when viewed from the side as explained above. This is illustrated at 26, while the V-notch of a stamping at one end of the core 20 is shown at 24.
[0055] In an aspect, the stampings can be arranged in a coil former (23), wherein, on the coil former (23), secondary winding can be accomplished in such a way that winding is constrained in upper and lower surface of the coil former (23). In the exemplary embodiment of the current transformer illustrated, primary conductor at one end is depicted as 22, while its second end is depicted as 25.
[0056] In an aspect, secondary-winding leads can be connected to connector (27) for connection with electronic circuit (not shown in FIG 3). In an exemplary embodiment secondary current can be about 7mA for any maximum current as defined in design. The saturation limit for a design made in this fashion can be upto 11 times that of the maximum current, without introduction of any air gap in the core.
[0057] Hence, in an aspect, configuring the core in such a fashion increases the saturation performance of the core so that it can handle larger input currents without deterioration in accuracy of the secondary current. Hence ratio error of the transformer can be reduced.
[0058] The present disclosure therefore provides a current transformer having at least two or more stampings each of which is provided with a V-notch, wherein the stampings are stacked in an anti-parallel arrangement with the V-notch in each stamping providing a visual indication to the core assembler as to how to position the stampings to achieve their proper magnetic orientation.
[0059] FIG.3 illustrates one exemplary implementation of electronic protection relay wherein current transformers configured therein in accordance with an embodiment of the present disclosure are used.
[0060] In an aspect invention disclosed allows for a compact design of current transformers.
[0061] In another aspect, invention disclosed can allow for a secondary winding of same turns on a stack (core) of same width but wherein the primary winding can be allowed to be varied for same current outputs to be taken from the secondary winding of the current transformer, the current flowing through the primary conductor being different. It is easier to vary the number of turns on the primary side as the primary side winding wire is thicker and number of turns much lesser than that of the secondary side which is thinner with much higher number of turns.
[0062] In an exemplary embodiment, the secondary side microcontroller based protection circuit can require a current of 2 mA to 6mA. Then for a primary conductor of current rating of 30A to 60A the primary winding of the current transformer can be designed to be of a certain number that can easily be reduced to another for a second primary conductor of current rating of 10 A to 30 A.
[0063] One of such implementation is explained with electronic protection relay where these current transformers (CTs) are arranged in housing (30) with 3 CTs (one of which is illustrated as 31) arranged.
[0064] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE PRESENT INVENTION
[0065] The present disclosure provides for a current transformer that is not bulky and costly.
[0066] The present disclosure provides for a current transformer that reduces error in output current.
[0067] The present disclosure provides for a current transformer that can provide sufficient power for advanced micro-processor based protection and control circuits.
[0068] The present disclosure provides for a current transformer that reduces error in output current.
[0069] The present disclosure provides for a current transformer that increases saturation performance of its core without introducing an air gap for the same.
[0070] The present disclosure provides for a current transformer that can allow for secondary winding with same number of turns to be used irrespective of the current being carried by the primary conductor using the current transformer.
,CLAIMS:1. A current transformer (CT) comprising a core comprising a plurality of laminations, wherein each lamination is configured with a V-notch, and wherein the plurality of laminations are stacked in an anti-parallel arrangement and aligned based on respective V-notches to enable desired magnetic orientation with each other.
2. The current transformer of claim 1, wherein the CT further comprises a secondary winding and a primary winding, wherein turns of the secondary winding remain unchanged irrespective of the current being carried by the primary winding.
3. The current transformer of claim 1, wherein each lamination is manufactured with stamping made out of CRGO steel.
4. The current transformer of claim 1, wherein a first V-notch configured on a first leg of a first lamination is engaged with a second V-notch configured on a second leg of the second lamination.
5. The current transformer of claim 1, wherein the first lamination is coupled with the second lamination such that they form a closed rectangle and such that their magnetic orientation is aligned.
6. The current transformer of claim 1, wherein the plurality of laminations are arranged in a coil former, wherein secondary winding is configured such that it is constrained in upper and lower surface of the coil former.