Claims:1. A DC current sensor adapted to detect pulsed DC or AC current, said sensor comprising:
a split core;
wherein the split core is substantially rectangular in shape;
a cylindrical magnet holder;
wherein the magnet holder is situated between two ends of the split core;
wherein axis of the magnet holder is substantially perpendicular to the axis of the split core;
a cylindrical permanent magnet with two or more number of poles;
wherein the magnet is placed within the magnet holder;
a winding;
wherein the winding is on an arm substantially parallel to the magnet holder;
wherein the split core and the magnet holder forms a closed path;
wherein the magnet is connected to a prime mover; and
wherein the winding feeds a wave to an electronic processor module.

2. A DC current sensor to detect smooth DC current, said sensor comprising:
an excitation coil;
wherein the excitation coil produces wave shapes;
a split core;
wherein the split core is substantially rectangular in shape;
wherein the excitation coil is situated between two ends of the split core;
a pole piece;
wherein the pole piece is situated between two ends of the excitation coil;
a winding;
wherein the winding is on an arm substantially parallel to the magnet holder;
wherein the split core and the excitation coil forms a closed path; and
wherein the excitation coil is energized by a pulse width modulation module.

3. The sensor as claimed in claims 1 or 2, wherein the split core is a core balance current transformer with a split in its core.

4. The sensor as claimed in claim 1, wherein the magnet holder is situated on a substantially longer arm of the split core.

5. The sensor as claimed in claims 1 or 2, wherein the winding is situated below the magnet holder.

6. The sensor as claimed in claim 1, wherein the prime mover is preferably a brushless DC motor.

7. The sensor as claimed in claims 1 or 2, wherein the winding captures the wave in closed loop.

8. The sensor as claimed in claim 1, wherein the split core and the cylindrical magnet generate a rotating magnetic field.

9. The sensor as claimed in claim 2, wherein the split core and the excitation coil generate a rotating magnetic field.

10. The sensor as claimed in claim 1, wherein the cylindrical magnet comprises pole faces on its sides.

11. The sensor as claimed in claim 10, wherein the pole faces are a non-circular surface.

12. The sensor as claimed in claims 1 or 2, wherein the winding is preferably a copper winding.

13. The sensor as claimed in claim 6, wherein the DC motor is operatively controlled by a pulse width modulation module.

14. The sensor as claimed in claim 2, wherein saturation point of the pole piece just below saturation point of the split core.

15. A core balance current transformer for detecting AC or pulsated DC current or smooth DC current, said transformer comprising:
a high permeability core;
wherein the core is substantially rectangular in shape;
a sensing winding;
wherein the sensing winding is on a substantially longer arm of the core;
a first winding;
wherein the first winding is situated below the sensing winding;
a second winding;
wherein the second winding is substantially perpendicular to the first winding and sensing winding;
wherein the sensing winding is on an arm substantially parallel to the first winding;
wherein the second winding feeds a wave to an electronic processor module; and
wherein the second winding detects DC currents.

16. The transformer as claimed in claim 15, wherein the electronic processor module passes the wave.

17. The transformer as claimed in claim 16, wherein the wave is a square or a triangular or saw tooth or rectified AC or the like.

18. The transformer as claimed in claim 16, wherein the wave is an input signal for generating Lissajous curves.

19. The transformer as claimed in claim 15, wherein the second winding is controlled by the electronic processor.

20. The transformer as claimed in claim 18, wherein the curve generation occurs inside the electronic processor.

21. The transformer as claimed in claim 15, wherein energy of the curve is calculated based on type of fault current.
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to protection of load side devices, and more particularly, pertains to DC current sensing in closed loop electromagnetic systems.

BACKGROUND OF INVENTION

[002] Leakage current is the current that flows through the protective ground conductor to ground. In the absence of a grounding connection, it is the current that could flow from any conductive part or the surface of non-conductive parts to ground if a conductive path was available (such as a human body). There are always extraneous currents flowing in the safety ground conductor.

[003] There are two types of leakage current: ac leakage and dc leakage. Dc leakage current usually applies only to end-product equipment, not to power supplies. Ac leakage current is caused by a parallel combination of capacitance and dc resistance between a voltage source (ac line) and the grounded conductive parts of the equipment. The leakage caused by the dc resistance usually is insignificant compared to the ac impedance of various parallel capacitances. The capacitance may be intentional (such as in EMI filter capacitors) or unintentional. Some examples of unintentional capacitances are spacing’s on printed wiring boards, insulations between semiconductors and grounded heatsinks, and the primary-to-secondary capacitance of isolating transformers within the power supply.

[004] Generally, to accurately detect weak control current flowing through a circuit in control equipment, a method of connecting resistors in series in the circuit and measuring a voltage drop in the resistors is used. In this case, however, a load different from that of a control system is applied and there is the possibility that an adverse influence is exerted on the control system. Consequently, a method of performing indirect measurement by detecting the gradient of a current magnetic field generated by the control current is used. As a concrete example, there is a method of winding a line to be measured around a toroidal core, supplying control current to the line to be measured, and detecting a magnetic flux generated in the center portion of the toroidal core by a hall element.

[005] Residual Current Circuit Breakers (RCCBs) are widely used all around the world for protection from the residual current flowing in any circuit. It is a different class of circuit breakers. An RCCB is essentially a current sensing device used to protect a low voltage circuit in case of a fault. It contains a switch device that switches off whenever a fault occurs in the connected circuit. It offers protection to humans from unexpected electrical shock inducing severe burns to fatal conditions, infrastructure from unexpected fire accidents created by the flow of residual currents through unintentional paths and devices from allowing excess leakage current flow making the life cycle of the device to lower. RCCBs are designed in such way that they continuously sense and compare for difference (residual current value) in current values between the live and neutral wires. Any small change in the current value on account of such event would trigger the RCCB to trip off the circuit.

[006] These devices use mutual induction principles used in transformers as an operation. In particular, it uses Core Balanced Current Transformers (CBCTs). CBCT’s are employed for providing earth leakage protection in a power system. They are different from normal protective and metering current transformers due to their performance requirement. They are manufactured with one core and one secondary winding. The number of secondary turns does not need to be related to the cable/feeder rated current because no secondary current would flow under normal balanced conditions. This allows the number of secondary turns to be chosen such as to optimize the effective primary pick up current. CBCTsums the total current flowing through the core. i.e., when both phase and neutral passes through the circuit, the net output of the CBCT is zero. Any imbalance in the phase and neutral gives rise to output of CBCTs which in turn means that a portion of current is going out of the loop.This difference in current captured by CBCT is fed into an electronic circuit for logically checking the value of missing current. Once this value is greater than the threshold value, the electronic circuit issues trip command to the circuit breaker and hence clears the threat ahead.

[007] Such devices are employed in all kind of electrical infrastructures. Majority of them are alternating types and for DC currents, very limited devices are available.The DC current sensing is used in the solar, UPS and any circuit where DC current is the operating current.

[008] Reference is made to US 5923514 A, wherein an electronic trip circuit breaker with Giant Magnetic Resistive (GMR) current sensor is disclosed. The current sensor has a closed loop magnetic hoop with a gap and a central aperture for receiving a conductor. An IC chip incorporating a GMR sensor is positioned in the gap to provide a measure of the current in the conductor. A relatively small current transformer provides the necessary information about the direction of the current to an electronic trip unit for a circuit breaker as well as power supply for the IC chip and the trip unit. The trip unit operates in the presence of AC and DC faults. In a three phase power system, a single GMR chip in the proximity of three closely spaced phase conductors, together with a current measurement from the neutral line, enables trip units to operate on the occurrence of AC and DC faults. This document details the use of a closed loop magnetic hoop along with an IC chip incorporating a GMR sensor positioned in the gap to provide a measure of the current. It does not employ split cores, cylindrical magnets, sensing winding etc. for sensing small imbalanced current.

[009] Reference is also made to US 2006/0291106 A1, wherein a magnetic sensor and current sensor are disclosed. The current sensor is capable of detecting a current magnetic field generated by a current to be detected with high precision and stability while realizing a compact configuration. The current sensor has: first and second magneto-resistive elements each including a pinned layer having a magnetization direction pinned in a predetermined direction, a free layer whose magnetization direction changes according to applied magnetic fields, and an intermediate layer sandwiched between the pinned layer and the free layer; and first and second permanent magnets for applying bias magnetic fields to the first and second magneto-resistive elements. The bias magnetic field has a parallel component parallel to a magnetization direction under no magnetic field and an orthogonal component orthogonal to the parallel component. Consequently, uniaxial anisotropy of the free layer can be enhanced without using shape anisotropy. Therefore, the current magnetic field to be detected can be detected with high precision and stability irrespective of the shapes of the magneto-resistive elements, and the invention is favourable for miniaturization. This document details the use of magneto-resistive elements, permanent magnets and some other components for detecting the unbalanced current. It does not employ split cores, cylindrical magnets, sensing winding etc. for sensing small imbalanced current.

[0010] Reference is also made to US 7164263 B2, wherein a current sensor is disclosed. The current sensor employs a plurality of magnetic field sensors positioned around a current carrying conductor. The sensor can be hinged to allow clamping to a conductor. The current sensor provides high measurement accuracy for both DC and AC currents, and is substantially immune to the effects of temperature, conductor position, nearby current carrying conductors and aging. This document details the use of a plurality of magnetic field sensors positioned around a current carrying conductor for detecting the unbalanced current. It does not employ split cores, cylindrical magnets, sensing winding etc. for sensing small imbalanced current.

[0011] The state of art DC sensing current sensing circuitry that resolve leakage of current by the phenomena of DC sensing employ some exotic sensors such as Hall sensors, Flux gates, AMRs, GMRs, etc. These sensors require calibration and each sensor will have their own error ratio. These solutions are also expensive as they involve use exotic sensing elements to sense DC currents, require complex electronics and embedded designs, and current values detected by said devices are limited owing to limited capabilities of the sensing elements.

[0012] Therefore, there arises a need for a simple, efficient, effective, calibration less, and economic technique for sensing leakage currents of different values and shapes (i.e., smooth and pulsated DC) that does away with manufacturing level issues faced by conventional sensors.To overcome the drawbacks in existing Dc current sensing techniques, the present invention discloses DC current sensing using induced electrodynamic forces and current-voltage interactions in closed loop electromagnetic systems.

SUMMARY OF THEINVENTION

[0013] 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.

[0014] An object of the present invention is to provide protection of load side devices from DC fault currents appearing in the circuit either through leakage in the device itself or through external faulty systems in contact with the device under protection.

[0015] Another object of the present invention is to provide DC current sensing in closed loop electromagnetic systems.

[0016] Another object of the present invention is to provide sensing of DC current using the electrodynamic forces induced in common core balance current transformer like circuits.

[0017] Yet another object of the present invention is to provide detection of DC current using electrodynamic forces through magnet or electromagnet in stationary or moving or rotating producing its own magnetic field or externally induced magnetic field either through PWM module controlling the prime mover attached to the magnet or pulsating coils wound over an electromagnet.

[0018] Yet another object of the present invention is to provide core balanced current transformer with split core(s) closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the core balanced current transformers core.

[0019] Yet another object of the present invention is to provide common core balanced current transformers measuring both AC current and DC current.

[0020] Yet another object of the present invention is to provide core balance current transformer detecting the DC currents using Lissajous curves.

[0021] Yet another object of the present invention is to provide core balance current transformer detecting the DC currents using input and output voltage-current interactions.

[0022] Yet another object of the present invention is to provide earth leakage modules and circuit breakers using the core balance current transformer with split cores closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the core balance current transformer core.

[0023] Yet another object of the present invention is to provide earth leakage modules and circuit breakers using the common core balance current transformer measuring both AC and DC currents.

[0024] Yet another object of the present invention is to provide earth leakage modules and circuit breakers using the core balance current transformer detecting the DC currents using Lissajous curves.

[0025] Yet another object of the present invention is to provide earth leakage modules and circuit breakers using the core balance current transformer detecting the DC currents using input and output voltage-current interactions.

[0026] Briefly, the present invention pertains to protection of load side devices from DC fault currents appearing in the circuit either through leakage in the device itself or through external faulty systems in contact with the device under protection. It involves sensing of DC current using the electrodynamic forces induced in a common core balance current transformer like circuits.

[0027] A DC current sensor to detect pulsed DC or AC current is disclosed. It comprises of a split core; wherein the split core is substantially rectangular in shape; a cylindrical magnet holder; wherein the magnet holder is situated between two ends of the split core; wherein axis of the magnet holder is substantially perpendicular to the axis of the split core; a cylindrical magnet; wherein the magnet is placed within the magnet holder; a winding; wherein the winding is on an arm substantially parallel to the magnet holder; wherein the split core and the magnet holder forms a closed path; wherein the magnet is connected to a prime mover; and wherein the winding feeds a wave to an electronic processor module. The cylindrical magnet comprises two or more number of poles.

[0028] A DC current sensor to detect smooth DC current is also disclosed. It comprises of an excitation coil; wherein the excitation coil produces wave shapes; a split core; wherein the split core is substantially rectangular in shape; wherein the excitation coil is situated between two ends of the split core; a pole piece; wherein the pole piece is situated between two ends of the excitation coil; a winding; wherein the winding is on an arm substantially parallel to the magnet holder; wherein the split core and the excitation coil forms a closed path; and wherein the excitation coil is energized by a pulse width modulation module.

[0029] A core balance current transformer for detecting AC or pulsated DC current or smooth DC current is disclosed. It comprises of a high permeability core; wherein the core is substantially rectangular in shape; a sensing winding; wherein the sensing winding is on a substantially longer arm of the core; a first winding; wherein the first winding is situated below the sensing winding; a second winding; wherein the second winding is substantially perpendicular to the first winding and sensing winding; wherein the sensing winding is on an arm substantially parallel to the first winding; wherein the second winding feeds a wave to an electronic processor module; and wherein the second winding detects DC currents.

[0030] 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

[0031] 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:

[0032] Figure 1a illustrates a DC sensor for detecting AC or pulsed DC current according to one implementation of the present invention.

[0033] Figure 1b illustrates the flux path of the DC sensor for detecting AC or pulsed DC current according to one implementation of the present invention.

[0034] Figure 2 illustrates the sweep of a varying frequency wave generated by the PWM controlled permanent magnet rotated at various speedsaccording to one implementation of the present invention.

[0035] Figure 3 illustrates the block diagram of the electronic processor according to one implementation of the present invention.

[0036] Figure 4 illustrates the core balance current transformers output’s with and without the DC componentaccording to one implementation of the present invention.

[0037] Figure 5a illustrates a DC sensor for detecting smooth DC current according to another implementation of the present invention.

[0038] Figure 5b illustrates the section view of the DC sensor for detecting smooth DC current according to another implementation of the present invention.

[0039] Figure 6 illustrates the induced electrodynamic pulses from the electronic processor according to one implementation of the present invention.

[0040] Figure 7 illustrates the Lissajous plot indicating waves with difference in phase anglesaccording to one implementation of the present invention.

[0041] Figure 8 illustrates a core balance current transformer sensor according to one implementation of the present invention.

[0042] Figure 9 illustrates the Lissajous curves with and without the DC componentsaccording to another implementation of the present invention.

[0043] Figure 10 illustrates the complete flow of processes in the DC current sensoraccording to one implementation of the present invention.

[0044] 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

[0045] 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.

[0046] 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.

[0047] 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.

[0048] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0049] 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.

[0050] 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.

[0051] 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 component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0052] The subject invention lies in providing a DC current sensor using electrodynamic forces induced in transformers.

[0053] The present invention pertains to protection of load side devices from DC fault currents appearing in the circuit either through leakage in the device itself or through external faulty systems in contact with the device under protection. It involves sensing of DC current using the electrodynamic forces induced in a common core balance current transformer like circuits. The sensor comprises of a split core, a cylindrical magnet holder, a cylindrical magnet and sensing winding. The split core forms a part of the closed path and the remaining gets closed by the cylindrical magnet. The magnet is connected to the prime mover, typically a brushless DC motor by the cylindrical magnet holder. The sensing winding captures the wave in the closed loop and feeds it to the electronic processor module.

[0054] In one implementation, protection of load side devices from DC fault currents appearing in the circuit either through leakage in the device itself or through external faulty systems in contact with the device under protection is provided for.

[0055] In one implementation, DC current sensing in closed loop electromagnetic systems is provided for.

[0056] In one implementation, sensing of DC current using the electrodynamic forces induced in common core balance current transformer like circuits is provided for.

[0057] In one implementation, detection of DC current using electrodynamic forces through magnet or electromagnet in stationary or moving or rotating producing its own magnetic field or externally induced magnetic field either through PWM module controlling the prime mover attached to the magnet or pulsating coils wound over an electromagnet is provided for.

[0058] In one implementation, a core balanced current transformer with split core(s) closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the core balanced current transformers core is provided for.

[0059] In one implementation, a common core balanced current transformer measuring both AC and DC currents is provided for.

[0060] In one implementation, a core balance current transformer detecting the DC currents using Lissajous curves.

[0061] In one implementation, a core balance current transformer detecting the DC currents using input and output voltage-current interactions is provided for.

[0062] In one implementation, earth leakage modules and circuit breakers using the core balance current transformer with split cores closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the core balance current transformer core is provided for.

[0063] In one implementation, earth leakage modules and circuit breakers using the common core balance current transformer measuring both AC and DC currents is provided for.

[0064] In one implementation, earth leakage modules and circuit breakers using the core balance current transformer detecting the DC currents using Lissajous curves is provided for.

[0065] In one implementation, earth leakage modules and circuit breakers using the core balance current transformer detecting the DC currents using input and output voltage-current interactions is provided for.

[0066] Figure 1 illustrates the DC current sensor that uses electrodynamic forces induced in a common core balance current transformer like circuit. It comprises of four major components, viz., a split core (1), a cylindrical magnet holder (2), a cylindrical magnet (3) and sensing winding (4). The split core (1) forms a part of the closed path and the remaining gets closed by the cylindrical magnet (3).

[0067] The sensor of Figure 1 is to detect an AC current or pulsated DC current. Here the magnet is connected to the prime mover, typically a brushless DC motor, by the cylindrical magnet holder (2). The sensing winding (4) captures the wave in the closed loop and feeds it to the electronic processor module, as illustrated in Figure 3.

[0068] Significantly, a split is made in the common core balance current transformer core in-order to create a rotating magnetic field. This rotating magnetic field is created using a cylindrical magnet having its pole faces on its sides, i.e., a non-circular surface, marked N and S, in Figure 1a. The flux path is illustrated in Figure 1b. When the magnet rotates, the poles rotate as in a permanent magnet based generators. Thus, it creates a rotating magnetic field in the core balance current transformer circuit. After a copper winding is wound around the core balance current transformer core like a secondary winding in the transformer, the output observed is the output of the rotating magnetic field created by the permanent magnet rotation. The waveform thus generated through the rotation of permanent magnet at various speed is illustrated in Figure 2.

[0069] The conductor that is passing through the core balance current transformer is the primary conductor. Now if the primary conductor is carrying a current of 1A Sine wave, this will be getting overlapped or disturbed by the permanent magnet flux created due to rotation. Now in order to completely offset or disturb the wave, we need an equally timed waveform. This is achieved by the rotating permanent magnet which is controlled by the DC motor which in turn is controlled by an electronic circuit via pulse width modulation module. The pulse width modulation module decides the frequency of the wave it generates through the circuit. For example, to create a sine wave of 50Hz frequency, we need to run the motor at 3000 RPM based on the formula:
f=NP/120

[0070] Where, N is speed of the motor; f is frequency of the input wave, and P is number of poles of the motor.

[0071] Therefore, the motor controller can sweep about multiple frequencies of the wave and sample multiple currents passing through the core balance current transformer. Thus, the core balance current transformer senses an AC current or pulsated DC.

[0072] Another sensor to detect a smooth DC current is illustrated in Figure 5a. If smooth DC is the fault current in the circuit, then the manner in which smooth DC current is detected is the saturated electrodynamic mode. Here, the core or the magnet is selected in such a manner that it is working just below the saturation point of the core. Now, when an additional fault current flows through the core balance current transformer, this will make the core balance current transformer’s core to saturate and hence change in the wave shape output. This offset/change in wave is the input to the electronic processor.

[0073] The block diagram of the electronic processor is illustrated in Figure 3. The main purposes of the electronic processor are: to control the sweep of the permanent magnet rotation (PWM module); sample the incoming wave periodically at higher frequency than the core balance current transformer output frequency (sensing/sampling module); compare the wave with a reference or threshold value; and monitor and test the circuit through user interface. The output waveforms of the core balance current transformer with and without DC current flowing through has been illustrated in Figure 4.

[0074] The sensor for detecting a smooth DC current is a stationary device unlike the previous motor based method where motor controlled magnet. Instead, stationary cores with coil wound on the poles are used thereby making them act as an electromagnetic pole faces. The coil energizing is done using electronic processor. Unlike PWM module controlling the speed of the motor, here the electronic processor changes the voltage on the coil in a manner that the stationary core simulates the changing magnetic field on the earlier mode. This manner of is more stable as there are no moving parts. The sweep achieved in the circuit by changing the speed of the motor, is achievable directly in the poles as PWM is removed and instead be energized at changing voltages, thereby improving the response time of the sensing circuit.

[0075] The DC sensor for detecting smooth DC current is illustrated in Figure 5a. It comprises of an excitation coil (5), a split core (6), pole piece (7) and sensing winding (8). The excitation coil (5) gives the necessary wave shapes required to sense the current flowing through the closed loop. The pole piece (7) completes the closed path and helps to propagate the wave through the closed loop. The cross section of the closed loop is illustrated in Figure 5b.

[0076] The induced electrodynamic pulses are given from electronic processor as illustrated in Figure 6. The PWM signals are tweaked as and when there is a requirement of different wave shape.

[0077] A core balance current transformer that detects conventional AC and pulsed DC and smooth DC current is also disclosed that considers the voltage-current interactions happening in the sensing system. Plotting the output signal as a function of input as suggested by Lissajous curve plotting, a single plot is obtained. The plot shape depends on the magnitude and phase lag of the curves. The time domain that is used to plot voltage and current has been removed and the voltage-current relationship is plotted. The plots of various phase differences are illustrated in Figure 7.

[0078] The construction of the core balance current transformer that uses the voltage-current interactions of the core balance current transformer is illustrated in Figure 8. The construction is similar to the conventional core balance current transformer with the following components, viz., High permeability core (11), Sensing winding (9) and Test winding (10). In addition, there is an added winding (12) in the core balance current transformer that is connected to the electronic processor for additional function of sensing DC currents. Through this winding (12), electronic processor passes a wave of known frequency and magnitude. This wave is the input signal that used for generating the Lissajous curves as a replacement for the conventional time function.

[0079] In conventional core balance current transformers, the input signal is generally the load current passing through the circuit breaker. It will be complex and impractical to use that signal as a function for Lissajous patterns and DC current flowing will not give any appreciable output in Lissajous curves. In order to maintain harmony across the various input fault current patterns, the input function is self-generated through the electronic processor. In this case, testing of the core balance current transformers with conventional sinusoidal waves has been performed. However, this method can produce Lissajous using waves such as square, triangular, saw tooth, rectified AC, etc. The output waves of such CBCTs are measured and illustrated in Figure 9, with and without DC current.

[0080] The curve generation occurs inside the electronic processor and the energy of the curve is calculated based on the type of the fault current. Therefore, this core balance current transformer has the dual capability of detecting the conventional AC and pulsated DC current as well as the capability to sense the smooth DC current flowing through the circuit using additional winding controlled by the electronic processor.

[0081] In the curves illustrated in Figure 9, it may be observed that the sharp flat regions at both top and bottom indicate that the core is operating at saturation. Figure 10 illustrates the complete flow of processes of the DC current sensing mechanism disclosed in the present invention.

[0082] Some of the important advantages of the present invention, considered to be noteworthy are indicated hereinbelow:

a) Detection of DC current using electrodynamic forces through magnet or electromagnet in stationary or moving or rotating producing its own magnetic field or externally induced magnetic field either through PWM module controlling the prime mover attached to the magnet or pulsating coils wound over an electromagnet;
b) CBCT with split core(s) closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the CBCT core;
c) Common CBCT measuring both AC and DC currents;
d) CBCT detecting the DC currents using Lissajous curves;
e) CBCT detecting the DC currents using input and output voltage-current interactions;
f) Earth leakage modules and circuit breakers using the CBCT with split cores closed with a magnetic or electromagnetic component free to rotate or mounted fixed to the CBCT core;
g) Earth leakage modules and circuit breakers using the common CBCT measuring both AC and DC currents;
h) Earth leakage modules and circuit breakers using the CBCT detecting the DC currents using Lissajous curves; and
i) Earth leakage modules and circuit breakers using the CBCT detecting the DC currents using input and output voltage-current interactions.

[0083] Although a simple, economic and reliable manner of DC current sensing using induced electrodynamic forces and current-voltage interactions in closed loop electromagnetic systems has been described in language specific to structural features/methods indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations of an DC current sensor.