Description:
TECHNICAL FIELD
The present disclosure relates to current transformer, circuit breaker, compact current transformer, switchgear and the like. More particularly, the preset invention relates to a co-centric current transformer assembly with optimized compact design and improved accuracy by virtue of concentric placement of Rogowski coil and Iron CT to achieve better metering linearity.
BACKGROUND
Circuit breakers are designed to protect our electrical circuits from danger caused by an electrical hazard such as circuit overload, fluctuated currents etc. They are designed with a rating that conveys how much electrical current a breaker can carry or interrupt safely. There are many kinds of breakers, but most of the breakers have some main components in common. The frame protects what’s inside, a terminal where wires are connected, a lever to flip the breaker on or off (and to show when a breaker has tripped), contacts that move to open or close the circuit, actuator mechanisms, and trip units. The trip unit is the part of the circuit breaker that determines when the contacts will open automatically. In a thermal-magnetic circuit breaker, the trip unit includes elements designed to sense the heat resulting from an overload condition and the high current resulting from a short circuit. All pieces work together, and when the amount of electrical charge exceeds safe amounts, they interrupt the current. The apparatus used for controlling, regulating, and switching on or off the electrical circuit in the electrical power system is known as Switchgear. Further, the circuit breaker as discussed earlier are commonly known as interrupters that opens and closes the contacts to stop and start the flow of electrical current to the circuit. Circuit breakers are required to have a current transformer connected to trip unit to sense faults and issue trip instructions. The Trip unit is also required to display the current flowing through the contact system. Current transformer (CT) assembly comprises of iron core current transformer which is vital to match the trip unit power requirement and Rogowski coil for sensing the current through circuit breaker. Traditionally, the iron core current transformer and Rogowski coil are placed adjacent to each other with an electromagnetic shield between them. However, with circuit breakers becoming compact over the years, the current transformers also need to be concise in design to improve metering linearity.
References of some of the prior arts listed below provided:
US2002/0145416A1: This invention relates generally to current transformers for providing secondary power and current sensors for monitoring electrical current, and, more particularly, to magnetic cores used in such devices having a mixture of magnetic materials that provide a low-cost design in a compact configuration. Regarding limiting CT size, a single iron core current transformer has been used to both sense the circuit current along with providing operational power to the electronic trip unit in higher ampere-rated circuit breakers.
CN201417674Y: This invention relates to a compact current transformer, including an iron core, a secondary coil and a primary coil which are wound on the iron core, wherein the outer surface of the iron core, the primary coil and the secondary coil are covered with an insulated layer; and the primary coil is wound to be a ring and locked on the iron core. The utility model is characterized in that two sets of iron cores are arranged in parallel and the ring body part of the ring form primary coil respectively penetrates through two sets of iron cores, the iron core, the primary coil and the secondary coil are installed on the base, a secondary coil binding post is arranged on the side edge of the base, the secondary coil binding post is electrically connected with the secondary coil, two sets of iron cores stand on the base and the axes of the iron cores are vertical, and the binding post of the primary coil is lead out from the top of the insulated layer. The compact current transformer has compact structure, high magnetic flux utilization ratio of the primary coil and less insulating material utilization.
CN215578167U: The utility model discloses a metering transformer device for measuring an intelligent circuit breaker, which comprises a seat body and an upper cover which are matched with each other, a plurality of groups of coaxial measuring current transformers and rapid saturation current transformers are arranged between the seat body and the upper cover, the measuring current transformers are of annular structures, and the rapid saturation current transformers comprise frame-shaped iron cores. A plurality of through holes which are arranged at equal intervals are formed between the seat body and the upper cover, and the through holes are communicated with a current transformer for measurement and a fast saturation current transformer which are coaxially arranged. The utility model has the advantages of compact and stable structure and convenience and rapidness in installation.
CN215578168U: A combined current transformer relates to the technical field of transformers and comprises a metering transformer and a zero sequence transformer coaxially connected with the metering transformer through a U-shaped conductor, the zero sequence transformer comprises a shell, a coil arranged in the shell, an output pin and a self-checking pin, and the output pin and the self-checking pin are arranged on the shell. The self-checking pin is of a U-shaped structure, the self-checking pin is inserted and fixed on the shell, the bending part of the self-checking pin of the U-shaped structure is a fillet, one end of the self-checking pin of the U-shaped structure, which is opposite to the opening, is a flat edge, and the structure adopts the U-shaped self-checking pin, so that the production and assembly efficiency is improved, and the defective rate is reduced.
CN215770827U: The utility model relates to the technical field of current transformers, and discloses a protection and metering integrated current transformer which comprises an iron core piece, grooves are formed in the upper portion and the lower portion of the iron core piece, a first winding is wound on the iron core above an upper end notch, a second winding is wound on one side face of the iron core piece along the groove edge of a lower end notch, and the first winding and the second winding are wound around the iron core. The second winding is an annular winding, and the second winding is pasted on one side face of the iron chip through a non-ferromagnetic circuit board. Compared with the prior art, a traditional current transformer with an iron core is combined with the Rogowski coil to form the current transformer integrating protection and metering, the current transformer with the closed iron core is used for supplying power to a self-generated power source, the Rogowski coil is used for high-precision current sampling, the problem of magnetic saturation existing in the traditional current transformer is solved, and the current transformer has the advantages of being simple in structure and convenient to use. Errors are small during large current measurement, and the protection precision is greatly improved.
However, the cited prior arts fail to disclose and/or claim any specific assembly/geometric placement of Rogowski coil and iron current transformers (CT) in a novel design where iron core current transformer being encircled by the Rogowski coil was developed with the major challenge being maintaining Rogowski coil metering linearity since iron CT winding was encompassed in the toroidal plane. FEM simulation using JMAG helped in optimizing the placement of the shield between the iron core current transformer and Rogowski coil so that the net flux due to iron CT winding cutting the plane of Rogowski coil is negligible.
Therefore, there is a need for an optimized compact design of co-centric current transformers for having improved metering linearity. The present invention based on co-centric current transformer along with the Rogowski coil having optimized design and/or claims the improved accuracy based on co-centric placement of iron CT.
SUMMARY OF THE INVENTION
The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
An object of the present invention is to address and remove all the above limitations.
Another object of the present invention is to provide a co-centric current transformer assembly for optimized design to achieve improved metering linearity.
Yet another object of the present invention is to provide an improved protection of circuit breaker in relation to the chances of decreased trip unit failure.
Yet another object of the present invention is to provide a compact co-centric current transformer design involving Rogowski coil and thus improving its accuracy by reducing linearity error.
Yet still another object of the present invention is to provide a co-centric optimized design for current transformers and improved accuracy by involving primary material of main core made up of CRGO material for powering up the circuit and/or secondary core made up of CRNGO material to have minimum secondary current.
First aspect of the present invention is to provide a co-centric current transformer (CT) assembly for optimized compact design, the assembly comprises at least one main iron core CT wherein a main winding performed on the iron core CT, at least one secondary core wherein a secondary winding performed on the secondary core, at least one Rogowski coil encircled the iron core CT wherein the iron CT winding encompassed in the toroidal plane and at least one shield wherein the shield placement is optimized between the iron core CT and the Rogowski coil using simulation techniques wherein the placement of the iron core CT is in a co-centric orientation with respect to the Rogowski coil to improve metering linearity.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:
Figure 1 illustrates a diagrammatic representation of an iron core current transformer (CT) displaying embodiments working as a system in accordance with the present invention.
Figure 2 illustrates a secondary core between the main core of the co-centric current transformer (CT) in accordance with the present invention.
Figure 3 illustrates a prototyping of a co-centric placement of iron current transformer (CT) with respect to Rogowski coil in accordance with the present invention.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to “a component surface” includes a reference to one or more of such surfaces.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure. The embodiments/components terms used is case insensitive and does not differ from its definitions as is construed within the context of the specifications.
The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein it is understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.
The present invention will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.
Embodiments discloses a co-centric iron current transformer (CT) assembly (100) and Rogowski coil (F) with optimized compact design to achieve improved metering linearity. In a non-limiting embodiment, the present invention CT assembly (100) comprises of iron core current transformer (CT), Rogowski coil (F) for sensing the current through the circuit, primary and secondary core with winding to protect the shield (E) from saturating such that Rogowski Coil (F) output is affected minimally.
The present invention discloses a co-centric compact design current transformer (CT) assembly (100) comprising iron core CT, shield (E) and the Rogowski coil (F) performed over an elliptical former with its axis co-centric to the iron core CT assembly (100). The iron core Current Transformer comprises of two cores with winding on both. Main core which is primarily responsible for power up is made of CRGO material. Also, as rate of rise of secondary current should be as minimum as possible after powering up, forced saturation was required to be employed. Hence a secondary core made of CRNGO material is employed which is placed adjoining the main core with small air gap between them. The main core winding & secondary core winding are connected such that net secondary current is difference of induced currents in former & latter. The secondary core will have negligible contribution during power up, hence rate of rise of secondary current would be high. However, as the flux gets shunted through secondary core as primary current through contacts increase, the rate of rise of secondary current decreases.
Further, Current transformer (CT) assembly (100) comprising of iron core current transformer which is required to match the trip unit power requirement and Rogowski coil (F) for sensing the current through circuit breaker. Rogowski coil (F) was developed with the major challenge being maintaining Rogowski coil (F) metering linearity. FEM simulation using JMAG helped in optimizing the placement of the shield between the iron core current transformer and Rogowski coil (F). The concentric placement of Iron core CT within Rogowski coil combined with shield placement such that the net flux due to iron CT (100) winding cutting the plane of Rogowski coil (F) is negligible.
Due to reduction in secondary current at rated primary current, the assembly (100) able to reduce the wire gauge and hence save copper cost by at least 78%. Also, due to reduced cross-section of iron core, at least 40% cost of iron is saved. Additionally, it also contributed to less electromagnetic interference from iron CT winding due to which shield did not saturate and was able to route stray flux through itself, hence improving the Rogowski coil (F) metering linearity.
In an exemplary embodiment, the stages of development of the co-centric CT assembly (100) is provided for reference purpose and is not limiting the present inevntion:
1. Theoretical analysis and calculations to adjust CT characteristics.
2. Designing CT models and JMAG analysis to evaluate CT performance against theoretical analysis.
3. Prototyping & testing of the CT models to validate our soft simulation results.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly for optimized compact design, the assembly comprises at least one main iron core (A) CT wherein a main winding (C) performed on the iron core CT, at least one secondary core (B) wherein a secondary winding performed on the secondary core (B) , at least one Rogowski coil (F) encircled the iron core CT wherein the iron CT winding encompassed in the toroidal plane and at least one shield wherein the shield placement is optimized between the iron core CT and the Rogowski coil (F) using simulation techniques wherein the placement of the iron core CT is in a co-centric orientation with respect to the Rogowski coil (F) to improve metering linearity.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the main core responsible for a power up mode and made up of (Cold Rolled Grain Oriented) CRGO material.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the main core winding (C) connected in a way that net secondary current is difference of induced currents in the main core (C) and the secondary core (B).
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the secondary core (B) made up of (Cold Rolled Non Grain Oriented) CRNGO material placed adjoining the main core (A) with small air gap between them.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design involving secondary core placed adjacent to the main core (A) with small air gap wherein the presence of air gap in the secondary core (B) path is of high reluctance comparing with the main core (A) path to avoid a flux getting shunted/propelled to the secondary core (B) in a power up mode.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the secondary core (B) does not participate in the power up mode resulting into a high rate of rise of the secondary core (B).
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the rate of rise of secondary current decreases by the propelled flux of the secondary core (B) when the primary current through contacts increases resulting into reduction of a wire gauge to save copper cost by at least 78%.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein reduction of cross-section of iron core (A) resulting from the reduction of the wire gauge save the iron cost by at least 40%.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design an electromagnetic interference from the iron CT winding protects the shield (E) from saturating and/or able to route the stray flux through itself to improve the Rogowski coil (F) metering linearity.
In a non-limiting embodiment, the present invention provides a co-centric current transformer (CT) assembly (100) with optimized compact design wherein the flux generated by the winding of the iron CT less effective on the Rogowski coil (F) resulting into reduced linearity error using (finite element method) FEM simulation like techniques. The FEM simulation using JMAG helped in optimizing the placement of the shield between the iron core current transformer and Rogowski coil (F) so that the net flux due to iron CT winding cutting the plane of Rogowski Coil (F) is negligible.
Referring to the brief description of the drawings stated above all Figures. The Figure 1 illustrates an iron core CT where (A) is the main core, (B) is the secondary core, (C) is the main winding, (D) is the secondary winding, (E) is the shield and F is the Rogowski Coil. The present invention provides improved accuracy and compactness based on the co-centric placement of iron CT and the Rogowski coil in the assembly (100). The iron current transformer being encircled by the Rogowski coil was developed with the major challenge being maintaining the Rogowski metering linearity since iron CT winding was encompassed in the toroidal plane. Further, the FEM simulation performed using JMAG analysis to optimized the placement of shield between the iron core CT and the Rogowski coil for cutting the plane of Rogowski coil to negligible amount by the net flux generated due to iron CT winding. In the present invention, the main core (A) is made of CRGO steel & the secondary core (B) of CRNGO steel to exhibits the optimized compact design for CT assembly (100) along with the Rogowski coil (F) involvement.
Figure 2 illustrates the secondary core (B) position which is in between the main core with small air gap. The primary current flows through the contact system which passes through center of the main core (A). The primary current sets up magnetic field in the region around it. The magnetic flux density is the measure of concentrating magnetic field lines per unit area at a particular value of magnetic field strength. At low magnetic field strength (Power Up Region), the permeability of CRGO material very large as compared to CRNGO material. Also, due to presence of air gap, the secondary core (B) path is of high reluctance whereas the main core (A) path is of low reluctance. Hence the flux does not get shunted to secondary core (B) during power up. However, at high magnetic field strength, as saturation sets in both the materials, the permeability of both materials drop and their reluctances become comparable hence flux now gets shunted through both the cores (A, B) and the net opposing current flows through the secondary winding. Hence, the assembly (100) get a much-reduced secondary current at rated primary current.
Figure 3 illustrates a prototyping and testing of the CT model on a stable current source and referencing the primary current from 0.2 s class meter. The test results were aligning to the simulation results, hence concluded an improvement in metering linearity. By the virtue of concentric placement of iron CT with respect to Rogowski coil (F) the flux generated by the winding of iron CT has less effect on the Rogowski coil (F) thus improving its accuracy by reducing linearity error. The present invention provides an improved metering linearity and accuracy achieved by virtue of Rogowski coil (F) co-centric placement with iron CT.
As used herein, Rogowski coil (F) refer to an electrical device for measuring alternating current (AC) or high-speed current pulses. Rogowski coils offer improved measurement capabilities compared to traditional current transformers (CT)s. The Rogowski coil is an inductor with closed ferrite core in form of toroidal to catch the induced magnetic field of the electric current flow. Then the induced magnetic field will provide voltage after passing through a passive RC integrator.
As used herein, metering linearity with regard to Rogowski coil (F) refers to the linearity and accuracy, when measuring current, demonstrates exceptional results. Given the right measuring equipment, it is possible to gauge linearity to practically zero amps on the low end. It is also possible to measure above 25,000 amps on the high end with low linearity error. The flowmeter's ability to remain within its defined limits over the entire specified flow range is its linearity.
As used herein, CRGO steel refers to the Cold Rolled Grain Oriented Steel available in various grades (generally called M3, M4, M5 & M6, Major international standards such as Japanese (JIS), American (ASTM), German (DIN) and British Standards which specify CRGO grade). CRGO laminations in a transformer are used to minimize both eddy current and hysteresis losses. CRGO is cold rolled grain oriented steel and as the name suggests, its grains (crystals) are aligned in the direction of rolling.
As used herein, trip unit refers to the part of the circuit breaker that determines when the contacts will open automatically. A trip unit, specifically, is the “brain” of the circuit breaker as its function is to measure physical parameters such as electrical current and decide when to “trip” or rapidly open the mechanical contacts of the circuit breaker. At the bare minimum, a trip unit needs to offer overload and short circuit protection.
As used herein, FEM refers to finite element method shows how a component or material reacts to certain influences. With this numerical calculation method, a component or an entire assembly is divided into a finite number of elements (sub-areas). The three canonical stages in the finite-element (FEM) process involve: pre-processing (the division into a number of simpler problems), then solving, and finally post-processing to obtain the overall result. In sophisticated software tools such as JMAG the post-processing includes further manipulation of the basic solution to provide graphic images of the solution and engineering parameters. 
Henceforth, the present invention proposes an optimized compact design co-centric current transformer (CT) assembly along with the Rogowski coil to achieve improved accuracy and reduced metering linearity. The present invention provides a solution to reduce the temperature rise of CT winding due to decreased CT secondary current at rated primary current. Designing CT models and JMAG analysis to evaluate CT performance against theoretical analysis to provide an improvised CT assembly in a compact design. The present invention also helps the circuit breaker to power up the trip unit which is ultimately responsible for issuing trip command to it in case of a fault.
The present invention offers multiple technical advantages out of which few have been enumerated below for ease of understanding:
• The present invention provides a co-centric current transformer assembly with optimized design to achieve improved metering linearity.
• The present invention provides reduction in secondary current at rated primary current and reduce wire gauge to save the copper cost by 78 % and iron cost saved at 40% due to reduced cross section.
• The present invention provides an electromagnetic interference from iron CT winding and able to stray flux through the assembly hence improving the Rogowski metering linearity.
• The present invention provides an improved power up of trip unit to ensures current detection and display available at lower value of primary current.
• The present invention provides an improved protection of circuit breaker due to decreased chances of trip unit failure due to reduced secondary current at short circuit fault.
• The present invention provides a reduction in copper cost due to increased SWG (Standard Wire Gauge) of copper wire because of decreased CT secondary current at rated primary current.
• The present invention provides a temperature rise of CT winding reduced due to decreased CT secondary current at rated primary current.
• The present invention provides a compact co-centric current transformer design that is an avenue in air circuit breaker current path reduction.
• The present invention provides an improved metering linearity by optimizing shield placement such that Rogowski Coil output is affected minimally.
• The present invention provides an air Gap introduced between both cores to offer a high reluctance path for the current transformer assembly.
The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or forms disclosed, and other modifications and variations may be possible in light of the above teachings wherein those of skill in the art will recognize certain modifications, permutations, additions and sub combinations thereof.
, Claims:
1. A co-centric current transformer (CT) assembly (100) with optimized compact design, the assembly (100) comprising:
- at least one iron core CT ,including a main core(A), a main core winding (C) performed on the iron core CT(A), at least one secondary core (B), wherein a secondary core winding (D) performed on the secondary core (B).
- at least one Rogowski coil (F) encircled the iron core CT, wherein the iron CT winding encompassed in the toroidal plane; and
- at least one shield (E), wherein the shield placement is optimized between the iron core CT and the Rogowski coil (F) using simulation techniques,
wherein the placement of the iron core CT is in a co-centric orientation with respect to the Rogowski coil (F) to improve metering linearity.

2. The assembly (100) as claimed in claim 1, wherein the iron core CT is responsible for a power up mode.

3. The assembly (100) as claimed in claim 1, wherein the main core is made up of (Cold Rolled Grain Oriented) CRGO material.

4. The assembly (100) as claimed in claim 1, wherein the main core winding (C) and the secondary core winding operatively connected in a way that net secondary current is the vector sum of induced currents in the main core winding (C) and the secondary core winding (D).

5. The assembly (100) as claimed in claim 1, wherein the secondary core (B) made up of (Cold Rolled Non Grain Oriented) CRNGO material placed adjoining the main core (A) with small air gap between them.

6. The assembly (100) as claimed in claim 5, wherein by virtue of material property of CRNGO material and the presence of air gap in the secondary core (B) path is of high reluctance comparing with the main core (A) path to avoid a flux getting shunted/propelled to the secondary core (B) in the power up mode.

7. The assembly (100) as claimed in claim 5, wherein the rate of rise of secondary current decreases by the propelled flux of the secondary core (B) when the primary current through contacts increases.

8. The assembly (100) as claimed in claim 1, wherein the shield(E) protects the Rogowski coil from the EMI due to the iron CT.

9. The assembly (100) as claimed in claim 1, wherein the net flux generated by the winding of the iron CT is less effective on the Rogowski coil (F) resulting into reduced linearity error.