Claims:1. A current sensor device comprising:
a plurality of planar insulating substrates having plurality of coiling section, wherein said coiling section comprising an arrangement of a forward direction coil and a reverse direction coil, wherein said forward direction coil formed by connecting plurality of series connection of first conductor loop and second conductor loop in an odd sequence, while said reverse direction coil formed by series connection of first conductor loop and second conductor loop in an even sequence;
wherein, said substrates further comprising at least one electronic section to filter and integrate alternating current (AC) output signal from said coil section for phase compensation and thereby perform direct current (DC) offset compensation.

2. The current sensor device as claimed in claim 1, wherein said substrate comprises a flexible and/or foldable configuration.

3. The current sensor device as claimed in claim 1, wherein said reverse direction coil arranged to guard forward direction coil to achieve complete external field rejection with matched impedances.

4. The current sensor device as claimed in claim 1, wherein said forward direction coil comprises plurality of winding arranged on top and bottom layer of said substrate for sensing, and similarly said reverse direction coil comprises plurality of winding arranged on top and bottom layer of said substrate for electromagnetic shielding.

5. The current sensor device as claimed in claim 4, wherein each of said top and bottom layer of said substrates for said forward direction coil and said reverse direction coil are inter-connected through holes in said substrate.

6. The current sensor device as claimed in claim 5, wherein said inter-connection at said reverse direction coils and said forward direction coils are created as to provide cancellation turn in said reverse direction coil made of coiled traces which is magnetically additive with said forward direction coil for the X and Y component of a magnetic flux and rejecting Z component of said magnetic flux.

7. The current sensor device as claimed in claim 1, wherein said electronic section comprises: instrumentation amplifier, RC integrator, DC-offset compensator and buffer.
, Description:FIELD OF THE INVENTION

[001] This instant application, in general, pertains to a current sensing device, and more particularly to, a current sensor having a unique arrangement of coiling such that the current sensor device is more reliable in sensing, control and monitoring of current signal in electrical power system and measuring of current.

BACKGROUND AND PRIOR ART

[002] A current sensor is a device that detects electric current (AC or DC) in a wire, in general, and generates a signal proportional to it. The generated signal could be an analog voltage or current or even digital output. It can be then be utilized to display the measured current or can be stored for further analysis in a data acquisition system or can be utilized for control purpose.

[003] With the advent of microprocessor-based protection and measurement equipments, it has become necessary to sense, control and monitor the current signals in electrical power systems and measure current in a wire. Conventionally, rogowski coils are also suitable for measuring current in a variety of other applications, including, for example, measuring the current distribution in parallel fuses or in parallel bus bars.

[004] Rogowski coil is an electrical device for measuring alternating current (AC) or high speed current pulses. It consists of a helical coil of wire with the lead from one end returning through the centre of the coil to the other end, so that both terminals are at the same end of the coil. The whole assembly is then wrapped around the straight conductor whose current is to be measured.

[005] In prior art, inductive measuring procedures employing the Rogowski principle is comprises of several turns of the conductive coil disposed evenly on a non-conductive bobbin surrounding the primary conductor through which the current is to be measured. The former on which the winding is disposed can be a flexible plastic core or a printed circuit board on which the coil is implemented by metal deposits on each of the two phases of the plate. These embodiments talk of either a single Rogowski coil or a plurality of Rogowski coils connected in a cascaded fashion on a base plate.

[006] Conventionally, inductive measuring procedures according to the Rogowski principle are known in the area of current measuring technology. In the known models, the current-carrying conductor is routed through a coil. The sensor coil can vary in design. Reference is made to some to the prior art published documents, US2006113987A1, US2009115399A1, WO2011018530A1, WO2011018533A1, US5414400, US6271655, US6366076, US7227442, which all discuss the formation of Rogowski coil with discrete PCBs which are independently manufactured and assembled onto a base PCB to form a toroidal shaped coil. The manufacturing process is at the least multistep which includes manufacturing of individual PCBs and assembling into a coil, and at worst can introduce assembly variations causing errors in the sensitivity of the coil which is already very poor and hence intolerant to variations.

[007] Reference is made to US6965225B2, wherein discloses that the surface coils etched on both sides of a flexible PCB such as to not require separate assembly process for coil formation. While they have clearly presented one of the means to achieve efficient coil geometry, the shield from the effect of external magnetic field is achieved with one single return copper trace laid down for the purpose. This can lead to mismatch of impedance in the forward coil and the reverse trace causing asymmetric noise linkage in them. Hence it is desirable to replace the return trace with a coil in reverse direction laid out such as to not cancel the induced EMF of the measured current in the primary coil.

[008] Reference is made to US2014167740A1, which discloses a Rogowski coil disposed on a flexible PCB with the main conductor passing through it. This small opening of the conductor on the PCB restricts the range of the conductor sizes that are suitable with this sensor.

[009] Thus, in view of the existing current sensor device, there is a need to provide a current sensor device with foldable/flexible printed circuit board containing both sensor coil and signal processing means which aids to retro-fitting and compactness into switchgear apparatus. Besides, there is also a need for a unique coiling layout for better electromagnetic interference/ electromagnetic compatibility (EMI/EMC) immunity and total external electromagnetic field cancellation for enhancing accuracy in sensor output.

SUMMARY OF THE INVENTION

[0010] The following 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.

[0011] An object of the present invention is to provide a current sensor device with foldable/flexible printed circuit board containing both sensor coil and signal processing means which aids to retro-fitting and compactness into switchgear apparatus.

[0012] Another object of the present invention is to provide a unique coiling layout for better electromagnetic interference/ electromagnetic compatibility (EMI/EMC) immunity and total external electromagnetic field cancellation for enhancing accuracy in sensor output.

[0013] Accordingly, in one aspect, the present invention provides a current sensor device comprising: a plurality of planar insulating substrates having plurality of coiling section, wherein said coiling section comprising an arrangement of a forward direction coil and a reverse direction coil, wherein said forward direction coil formed by connecting plurality of series connection of first conductor loop and second conductor loop in an odd sequence, while said reverse direction coil formed by series connection of first conductor loop and second conductor loop in an even sequence; wherein, said substrates comprising at least one electronic section to filter and integrate alternating current (AC) output signal from said coil section for phase compensation and thereby perform direct current (DC) offset compensation.

[0014] 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 certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0015] Figure 1 illustrates the Perspective view of the current sensor in accordance with an embodiment of the present invention.

[0016] Figure 2 illustrates the Tear down view, in accordance with an embodiment of the present invention.

[0017] Figure 3(a) and figure 3(b) illustrates the 24 flexible coil and 12 flexible coil, in accordance with an embodiment of the present invention.

[0018] Figure 4 illustrates the curled view of star-shaped view of the flexible sensor coil, in accordance with an embodiment of the present invention.

[0019] Figure 6 illustrates a flexible coil strip in accordance with an embodiment of the present invention.

[0020] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not 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 OF THE PRESENT INVENTION

[0021] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0022] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0023] 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 invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0024] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0025] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0026] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0027] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0028] Reference is made to figure 1 which illustrates the Perspective view of the current sensor in accordance with an embodiment of the present invention.

[0029] Reference is made to figure 2 which illustrates the Tear down view (for sake of clarity, not all coils are shown, however, it is understood that same pattern repeats itself), in accordance with an embodiment of the present invention.

[0030] Figure 3(a) and figure 3(b) illustrates the 24 flexible coil and 12 flexible coil, in accordance with an exemplary embodiment of the present invention.

[0031] In one embodiment, as shown in figures 1 and 2, the layout of the current sensor device for measuring alternating current in a conductor comprises plurality of conductor coils formed by:
• a first printed conductor loop wound with a substantially constant winding density in a first direction on top layer on a metallic substrate;
• a second printed conductor loop wound with a substantially constant winding density in a first direction on bottom layer on a metallic substrate;
• the second loop connected in series with the first loop through a through hole pierced through a metallic substrate forms section A;
• a first printed conductor loop wound with a substantially constant winding density in a second direction on top layer on a metallic substrate;
• a second printed conductor loop wound with a substantially constant winding density in a second direction on bottom layer on a metallic substrate;
• the second loop connected in series with the first loop through a through hole pierced through a metallic substrate forms section B.

[0032] In one embodiment, a plurality of planar insulating substrate will be formed by connecting section a continuously in odd sequence in forward direction and the section B in even sequence in reverse direction.

[0033] In one embodiment, the whole arrangement can be placed around a current conductor that has a substantially constant cross section.

[0034] In one embodiment, a complete coil to coil guard copper trace can be laid down to achieve complete external field rejection with matched impedances. The interconnection of the coils will be created so as to provide the cancellation turn made of coiled traces which is magnetically additive with the first coil for the X and Y component of the flux but rejects the Z component of the flux and any noise due to high frequency components in the primary circuit.

[0035] In prior art, the shield from the effect of external magnetic field is achieved with one single return copper trace laid down for the purpose. This can lead to mismatch of impedance in the forward direction coil and the reverse direction coil (return trace), causing asymmetric noise linkage in them. Hence it is desirable to replace this with a coil in reverse direction laid out such as to cancel the induced EMF of the measured current in primary coil.

[0036] In one embodiment, a complete coil to coil guard (guard can be visualized with PCB in folded fashion) copper trace can be laid down to achieve complete external field rejection with matched impedances. This would enable reverse direction coil to guard the forward direction sensing coil from external field noise. The interconnection of the coils will be created so as to provide the cancellation turn (reverse direction coil) made of coiled traces which is magnetically additive with the first coil (forward direction coil) for the X and Y component of the flux but rejects the Z component of the flux and any noise due to high frequency components in the primary circuit.

[0037] By the term “Copper trace” as mentioned above, it means the main coil which can be the sensing coil senses the primary current, laid down in forward direction and is completely guarded by EMI shield coil that is the reverse direction coil, from the EMI stray fields.

[0038] In one embodiment, as shown in figure 4, the coil can be formed by curling the flexible substrate of desired length over the conductor thus making it suitable for variety of conductor sizes with the same manufacturing setup.

[0039] In one embodiment, the current sensing device is manufactured by chemically cleaning the PCB substrate Panel prior to application of circuit forming film, to ensure proper film adhesion. Panel is overlaid with circuit pattern, exposed with UV light to transfer circuit image to the substrate panel. Circuit pattern is chemically etched on ultra-thin material core. The circuit hole pattern is created in the substrate panel using high precision drilling process. Then electrolytic copper plating can be done. After that cover-lay lamination process under heat, pressure and temperature to ensure proper adhesion. Then, electrical test by netlist check and testing of circuits for continuity and isolation. Finally, individual part is die cut from substrate panel using high precision punch and die sets.

[0040] In one exemplary embodiment, the current sensing device may comprises the following parameters but not limited to it:
Length of the flexible substrate = 179 mm;
Height of the flexible substrate = 6.5 mm;
Thickness of the flexible substrate = 120 microns;
Material of the PCB substrates: Polyamide
Interconnection means: VIA hole
Spacing between coils: Coil to coil gap = 1.5 mm and Centre to Centre coil distance = 4.47 mm.
[0041] In one implementation, as shown in figure 5, the electronic section (analog integrator module) are also incorporated in the said PCB substrate which will give an added advantage of sheer compactness.
[0042] In one embodiment, the analog integrator module consist of four sub-sections which includes: instrumentation amplifier, RC integrator, DC-offset compensator and buffer. Working of the analog integrator module includes: Output AC signal from the disclosed coil section etched on the flexible substrate which may contain noise along with the desired signal, will be fetched into instrumentation amplifier. The instrumentation amplifier adapted to remove common mode noise and adjusts the gain of the input signal as per the requirement. This input signal will be connected to the inverting pin of the op-amp based main RC integrator (integration needed as the coil signal is 90 degree out of phase of the actual signal to be sensed). This signal will be again fed to an RC integrator but with larger time constant, due to which the AC component of the signal will be suppressed and only the low frequency DC component will be retained and integrated. After this, an RC filter will be provided to ground the left over AC signal. This signal will be inverted through an inverting op-amp and will be fed-back to the inverting pin of the main RC integrator. This DC signal subtracts the DC imperfections that may include but not limited to DC bias voltage, DC offset voltage and the like, present at the input before. Buffer is used to project the processed signal further to the microcontroller or an intelligent unit with unity gain.

[0043] Some of the important features of the present invention, considered to be noteworthy are mentioned below:

1. The integration of the sensor coil and the integrator electronics in the same flexible PCB substrate thus reducing the sensor footprint significantly. The incorporation of the sensor coil and the integrator electronics in the same PCB substrate is a unique combination for best possible compact design.
2. The progression of the printed conductor loop (section A) in forward direction and the printed conductor loop (section B) in reverse direction.
3. The present invention provides a cost effective solution by using the existing hardware interface.
4. By the virtue of the said coiling pattern of the current sensor device, output voltage is unaffected by the external fields produced by nearby currents which do not flow through the inside of the core. The said invention can be extended for multi-layered configuration for even better performances.
5. Also, the ground plane of the integrated electronics in the same PCB substrate acts as a RF noise shield for the discrete electronic component arrangement.

[0044] Although a current sensing device have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the current sensing device.