DESC:FIELD OF THE INVENTION

[001] This instant application, in general, pertains to current sensors, and more particularly to, a current sensor for use in sensing, control and monitoring of current signal in both AC and DC electrical power system and measuring of current in a wire.

BACKGROUND AND PRIOR ART

[002] A current sensor is a device that detects electric current (AC or DC) in a wire, and generates a signal proportional to it. The generated signal could be analog voltage or current or even digital output. It can be then 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 measuring current in a wire. 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] A 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. Various embodiments designate a conductor winding coiled on a toroidal former made of non-ferromagnetic material, thereby conferring characteristics of excellent linearity on the coil because of the absence of saturation. However, by the virtue of the principle of operation, these current sensors are naturally suited for AC signal applications. Thus, there is a need to overcome this limitation by developing a universal sensor which is compatible to both AC and DC measurements.

[006] Reference is made to US 20040156155 A1, wherein the double grounded neutral fault detection circuit comprises a second current transformer CT2 which has a multiple turn winding W2 and an oscillator circuit OSC which induces a signal into the winding W2. In the event of a ground fault at the load neutral, the neutral and earth return paths will form a single loop, and the signal induced into W2 will in turn be induced into this loop. The oscillator signal will be seen by CT1 as a residual current, causing the RCD to trip.

[007] However, the prior art teaches about the detection of residual current in the range of mA which normally uses a high initial permeability and low saturation flux density as its magnetic core. These cores go into saturation and are used for residual current (here in the prior art, the residual current is the bypass current between the Line-Earth terminal) detection in the form of offset added into the original output.

[008] Thus, in view the hitherto measuring procedures, there exists a dire need to provide an improved current sensing assembly that enhances the signal strength of the sensor output, thereby bypassing the need of associated costly and complex signal processing and strengthening circuits. Further, there is also a need to provide a hybrid sensor output which facilitates a provision of both DC and AC measurements.

SUMMARY OF THE INVENTION

[009] 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.

[0010] An object of the present invention is to provide a system for measuring an alternating current and direct current in a conductor.

[0011] Another object of the present invention is to provide a hybrid sensing device for DC measurement by means of a high frequency (in kHz) oscillator circuit, which superimposes small signal DC into the hybrid sensor output.

[0012] Accordingly, in one aspect, a system for measuring a current in a conductor is provided. The system comprises a hybrid sensor module, at least one oscillator circuit module as modulator, and at least one demodulator circuit module.

[0013] The sensor includes at least one inner coil, at least one outer coil, and one or more planar insulating substrates. The inner coil further includes at least one first printed conductor loop and at least one second printed conductor loop. The at least one first printed conductor loop wound with a substantially constant winding density in a first direction on top layer on a first metallic substrate. The at least one second printed conductor loop wound with a substantially constant winding density in a first direction on bottom layer on the metallic substrate. The at least one second printed conductor loop is connected in series with the at least one first printed conductor loop, via a hole pierced through the first metallic substrate, forming a first section (A). The outer coil further includes at least one first printed conductor loop and at least one second printed conductor loop. The at least one first printed conductor loop wound with a substantially constant winding density in a second direction on top layer on a second metallic substrate. The at least one second printed conductor loop wound with a substantially constant winding density in a second direction on bottom layer on the metallic substrate. The at least one second printed conductor loop is connected in series with the at least one first printed conductor loop, via a hole pierced through the second metallic substrate, forming a second section (B). The one or more planar insulating substrates formed by connecting the first section (A) continuously in odd sequence in forward direction and the second section (B) in even sequence in reverse direction.

[0014] The at least one oscillator circuit, coupled to the sensor, devised to superimpose a small signal DC in to a resultant signal output of the sensor to provision DC and AC measurements. The at least one demodulator circuit adapted to receive the resultant signal output of the sensor and communicate the resultant signal output to at least a controller unit.

[0015] The present invention provides a system for measuring of alternating current and direct current in a conductor. The alternating current is measured by inclusion of a magnetic strip into a current sensor device which improves signal to noise ratio which leads to better metering and protection accuracy. For DC current measurement, a high frequency (in kHz) oscillator circuit is employed in communication with the sensor output, which superimposes small signal DC into the hybrid sensor output and thus facilitates the provision of both DC and AC measurements. The said signal can further be demodulated through a demodulator circuit and then be sent to a controller unit for subsequent computations.

[0016] In one implementation, the applicability of the present invention is for metering applications for the whole range of current which can measure AC and/or DC. The suitability of the scheme is for cores with high permeability and high saturation that may include air-cored sensor, CT or any combination thereof, which can detect whole range of current in line. The resultant signal is the superimposition of the true AC signal from the core and the high frequency oscillator output in case of AC measurement. This technique assists in strengthening the signal which is feeble in case of sensors used such as Rogowski and the like. Further, the DC offset superimposition can be performed on the high frequency oscillator output in case of DC measurements. Thus the current sensor of the present invention is suitable for both AC/DC measurements.

[0017] 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:

[0018] Figure 1 illustrates a perspective view of the current sensor in accordance with an embodiment of the present invention.

[0019] Figure 2 illustrates an exploded view of the current sensor in accordance with an embodiment of the present invention.

[0020] Figure 3 illustrates a pictorial view of hybrid current sensor with metallic strip, in accordance with an embodiment of the present invention.

[0021] Figure 4 illustrates the schematic block diagram of the system for AC/DC measurement, in accordance with an embodiment of the present invention.

[0022] Figure 5 illustrates the schematic of flowchart to show the flow of the AC/DC measurement in the system, in accordance with an embodiment of the present invention.

[0023] Figure 6 illustrates the output waveforms that shows the modulated secondary current due to DC primary current.

[0024] 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

[0025] 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.

[0026] 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.

[0027] 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.

[0028] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, 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.

[0030] 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.

[0031] 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.

[0032] The present invention achieves the objective for measuring both AC and DC current by integrating at least one oscillator circuit high frequency (in kHz) oscillator circuit with hybrid current sensor device, such that the oscillator circuit superimposes small signal DC into the hybrid sensor output and thus facilitates the provision of both DC and AC measurements. Thus DC measurement can be added into the sensor.

[0033] This application derives information from a co-pending Indian Patent Application having application number 201621011228 filed on March 30, 2016 with respect to the unique coiling layout of the current sensor employed in the invention.

[0034] In one implementation, the layout of the current sensor coil as shown in figures 1 and 2, includes:
i. 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.
ii. 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 hole pierced through a metallic substrate forms section B.

[0035] In one implementation, a plurality of planar insulating substrate formed by connecting section A continuously in odd sequence in forward direction and the section B in even sequence in reverse direction.

[0036] In one implementation, the whole arrangement can be placed around a current conductor that has a substantially constant cross section.

[0037] In one implementation, analog integrator electronics are also incorporated in the said PCB substrate which gives an added advantage of sheer compactness.

[0038] In one implementation, a circular metallic strip (Sheet Steel / Iron Steel metal) as shown in figure 3, passes through the cutout on the printed circuit board. By the virtue of the said metallic strip’s magnetic characteristics, it assists in the induced magnetic field production which ultimately strengthens the resultant signal output from the said sensor. As shown in figure 4, a high frequency (in kHz) oscillator circuit is electrically coupled with the hybrid sensor device, which superimposes small signal DC into the hybrid sensor output and thus facilitates the provision of both DC and AC measurements. This signal can further be demodulated through a demodulator circuit and then can be sending to a controller unit for further computations.

[0039] In one implementation, figure 5 illustrates the flowchart of the system during measuring of the DC current by modulating the secondary output from the saturated MS ring 1 with a HF oscillator 2. This acts as a modulator. Demodulator 3 is used to obtain the demodulated signal i.e. IDC output. This signal goes into the ADC of the micro-controller. In one exemplary implementation, the output of current and voltage may be measured as follows:
Output:
Current (A) 4 40 400
Voltage (V) 0.02 0.2 2

[0040] In the exemplary implementation, reference is made to figure 6 that shows the output waveforms of the modulated secondary current due to DC primary current. DC offset turns out to be the measurable quantity to detect the DC current (At time t1, sensor circuit is closed). The measurement of AC is done by the Rogowski coil which gives the induced EMF as an output and is feed into the ADC of the micro-controller.

[0041] The present invention makes the current sensor universal for AC as well as DC measurements. The present invention overcomes the limitations of a current sensor which operates on the principle of Faraday’s law of electromagnetic induction by superimposing a high frequency signal on the regular sensor output. Thus the sensor is compatible for both AC and DC measurements.

[0042] Some of the important features of the present invention, considered to be noteworthy are as mentioned below:
i. The present invention strengthens the signal output from the sensor.
ii. The present invention is a means of easy interface with simple connections.
iii. The present invention facilitates the provision of both DC and AC measurements.
iv. The present invention provides a cost effective solution by using the existing hardware interface.

[0043] It may be clearly understood by a person skilled in the art that for the purpose of convenient and brief description, for a detailed working process of the foregoing system, devices, and unit, reference may be made to a corresponding process in the foregoing device/apparatus embodiments, and details are not described herein again.

[0044] In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and device may be implemented in other manners. For example, a plurality of units or components or mechanisms may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

[0045] The various mechanisms described as separate parts may or may not be physically separate, and the parts displayed as mechanisms may or may not be physical units, may be located in one position, or may be distributed at various location of the device. Some or all of the units may be selected to achieve the objective of the solution of the embodiment according to actual needs.

[0046] In addition, the mechanisms in the embodiments of the present invention may be integrated into one processing unit, or each of the mechanisms may exist alone physically, or two or more mechanisms may be integrated into one mechanism.

[0047] Although a system for ac and dc measurement and a method thereof disclosed, 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 system for ac and dc measurement and a method thereof.
,CLAIMS:1. A system for measuring a current in a conductor, the system comprising:
at least one hybrid current sensor module adapted to receive resultant signal output proportional to the current in the conductor;
at least one oscillator circuit module, coupled to the hybrid current sensor module, devised to superimpose a small signal DC in to a resultant signal output of the sensor to provision DC and AC measurements; and
at least one demodulator module adapted to receive the resultant signal output of the sensor and communicate the resultant signal output to at least a controller unit.

2. The system as claimed in claim 1, wherein the hybrid current sensor module comprises:
at least one inner coil having:
at least one first printed conductor loop wound with a substantially constant winding density in a first direction on top layer on a first metallic substrate;
at least one second printed conductor loop wound with a substantially constant winding density in a first direction on bottom layer on the metallic substrate, wherein the at least one second printed conductor loop is connected in series with the at least one first printed conductor loop, via a hole pierced through the first metallic substrate, forming a first section (A);
at least one outer coil having:
at least one first printed conductor loop wound with a substantially constant winding density in a second direction on top layer on a second metallic substrate;
at least one second printed conductor loop wound with a substantially constant winding density in a second direction on bottom layer on the metallic substrate, wherein the at least one second printed conductor loop is connected in series with the at least one first printed conductor loop, via a hole pierced through the second metallic substrate, forming a second section (B);
one or more planar insulating substrates formed by connecting the first section (A) continuously in odd sequence in forward direction and the second section (B) in even sequence in reverse direction;

3. The system as claimed in claim 2, wherein the sensor further comprises a current conductor with a substantially constant cross section adapted to enclose the at least one inner coil, the at least one outer coil, and the one or more planar insulating substrates.

4. The system as claimed in claim 2, wherein the sensor further comprises one or more analog integrator electronics incorporated in the first metallic substrate and the second metallic substrate.

5. The system as claimed in claim 2, wherein the one or more planar insulating substrates is at least one circular metallic strip, preferably made of a sheet steel or an iron steel metal, passing through a cutout provided on the first metallic substrate and the second metallic substrate, and thereby adapted to induce magnetic field production whilst generating a resultant signal output of the sensor.

6. The system as claimed in claim 1 is characterized in that the system is compatible for both AC and DC measurements.