FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
DISTRIBUTED CURRENT SENSING SYSTEM FOR AC
AND DC SYSTEMS
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No, 278,
Mumbai, 400 001, Maharashtra,
INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001] The present invention generally relates to the field of semi-
conductor devices and particularly to current sensors. The present invention more particularly relates to a current sensor having a current carrying conductor and a plurality of Hall sensors arranged in the vicinity of the conductor.
B) BACKGROUND OF THE INVENTION
[0002] One of the general methods of measuring control current for
regulating a control equipment or the like is a method of indirectly measuring control current by detecting the gradient of a current magnetic field generated by the control current. A variety of current measurement devices are known in the art, including current transformers, Rogowski coil transformers, resistive shunts in series or in parallel with a current-carrying conductor, magnetic field point sensors, magnetic field line integral sensors, line integral optical current sensors and the like.
[0003] A conventionally used current transformer has a major
disadvantage of being bulky and gets saturated quite early due to the use of laminated iron cores. In contrast, current sensors are used to measure the amount of current flowing through a conductor. Hall Effect current sensor is one such sensor that measures current flowing through a conductor and provides an output signal proportional to the level of current. Hall Effect

current sensors offer several advantages over traditional current transformers such as a more compact size, higher current levels for a given size and a larger frequency bandwidth.
[0004] However, a significant limitation to conventional Hall sensors
is that the contacts used to bias the sensor can "shunt" the Hall voltage, if the length of the sensor is much less than the width of the sensor. However, as the length-to-width ratio of the Hall sensor becomes smaller, the ability to sense a Hall voltage is reduced. This places a fundamental limit to the sensitivity of the conventional Hall sensors. Thus, the geometry of the Hall sensor and the placement of the contacts on the sensor are important considerations for effective current sensing
[0005] Another significant limitation to conventional Hall sensors is
that the sensors are not capable of sensing weak magnetic fields at a much greater sensitivity level. The sensors also fail to reduce the shunting effect of the external power supply contacts. Also conventional current sensors produces generates a high temperature during operation, which can lead to system damage.
[0006] Hence there is a need to provide an improved current sensor for
dynamic sensing of the current flow in a single phase or three phase electrical circuit system.

[0007] The above mentioned shortcomings, disadvantages and
problems are addressed herein and which will be understood by reading and studying the following specification.
C) OBJECT OF THE INVENTION
[0008] The primary object of the present invention is to develop an
improved current sensing system for dynamic sensing of current flow in a single phase electrical circuit system using multiple hall sensors arranged in a predefined manner.
[0009] Another object of the present invention is to develop an
improved current sensing system for dynamic sensing of current flow in a three phase electrical circuit system using multiple hall sensors arranged in a predefined manner.
[0010] Another object of the present invention is to develop an
improved current sensing system for measuring sensing current flow in the electrical conductor by measuring the magnetic field strength around the conductor.
[0011] Another object of the present invention is to develop an
improved current sensing technique for measuring both AC and DC currents.

[0012] Yet another object of the present invention is to develop an
improved current sensing technique to provide for complete electrical isolation of the sensor from the live conductor.
[0013] Yet another object of the present invention is to develop an
improved current sensing method which has a high linearity over a wide current sensing range.
[0014] These and other objects and advantages of the present invention
will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
C) SUMMARY OF THE INVENTION
[0015] The above mentioned shortcomings, disadvantages and
problems are addressed herein and which will be understood by reading and studying the following specification.
[0016] The various embodiments of the present invention provide a
current sensor assembly comprising a conductor and a plurality of Hall Effect sensors arranged radially away from the conductor. The plurality of Hall Effect sensors produces output signals representative of the strength of the magnetic field passing through the conductor. Further a signal processing system processes the output signals of the Hall Effect sensors to measure the current flowing through the conductor.

[0017] The signal processing system measures a weighted average of
the output from the plurality of Hall Effect sensors to measure the magnitude of current flowing through the conductor. The plurality of Hall Effect sensors are arranged at incremental orthogonal distance from a conductor core. According to an embodiment herein, the current sensor assembly is employed for measuring current in both AC systems and DC systems. The conductor is at least one of a single phase current carrying conductor and a three-phase current carrying conductor. The cross section of a .current carrying conductor is usually circular or rectangular.
[0018] For a single phase conductor, two or more Hall Effect sensors
are placed at incremental orthogonal distances from any chosen surface of the conductor with circular or rectangular cross-section) When current is passed through the conductor, the magnetic field generated across conductor line is sensed by them and a weighted average of the multiple Hall Effect sensor outputs hold a direct correlation to magnitude of current flowing in the conductor.
[0019] In the case of a three phase system, such sets of Hall Effect
sensors are placed adjoining each phase conductor. When current passes through the three phase conductor system, the magnetic field generated across each conductor line is sensed and a weighted average of the multiple Hall Effect sensor outputs hold a direct correlation to magnitude of current

flowing in the conductor. However, as the magnetic field due to adjoining conductor would directly alter the readings of a standalone conductor measurement, a processing unit carries out a compensation based on the spacing of the conductors to nullify their effects. This correction ensures that current measured across each conductor is not influenced by magnetic effect of adjoining current carrying conductor.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The other objects, features and advantages will occur to those
skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0021] FIG.l illustrates the structure of a Hall Effect current sensor
assembly for a single phase conductor according to one embodiment of the present invention.
[0022] FIG.2 illustrates the cross-sectional view of a single phase
circular current carrying conductor and a single phase rectangular current carrying conductor according to one embodiment of the present invention.
[0023] FIG. 3 illustrates the arrangement of Hall Effect sensors for a
three phase conductor system according to one embodiment of the present invention.

[0024] FIG.4 illustrates the magnetic field derivation across a
rectangular conductor in a current sensing system according to one embodiment of the present invention.
[0025] FIG.5 illustrates an arrangement to derive field correction
derivation for a plurality of circular single phase conductors according to one embodiment of the present invention.
[0026] FIG. 6 illustrates the block diagram explaining the functionality
of the current sensing assembly according to one embodiment of the present invention.
[0027] Although specific features of the present invention are shown in
some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0028] In the following detailed description, reference is made to the
accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the

scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0029] The various embodiments of the present invention provide a
current sensing method for dynamic sensing of the current flow in a single phase or a three phase electrical circuit system. The current sensing system uses a plurality of hall elements such as Hall Effect sensors strategically distributed in the space to measure the current flow. For a single phase conductor, a plurality of Hall Effect sensors is placed at incremental orthogonal distances from a selected surface of the conductor with a circular or rectangular cross-section. When current is passed through the conductor, it senses the magnetic field generated across the conductor line. The weighted average of the plurality of Hall Effect sensors output gives a direct correlation to magnitude of current flowing in the conductor.
[0030] In the case of a three phase system, the plurality of Hall Effect
sensors are placed adjoining each phase conductor. When current passes through the three phase conductor system, the magnetic field generated across each conductor line is sensed and a weighted average of the multiple Hall Effect sensor outputs hold a direct correlation to magnitude of current flowing in the conductor. Further a processing unit carries out a compensation based on the spacing of the conductors to nullify the effect of magnetic field due to adjoining conductor in the readings of a standalone conductor measurement. This correction ensures that the current measured

across each conductor is not influenced by magnetic effect of adjoining current carrying conductor.
[0031] FIG.l illustrates the structure of the Hall Effect current sensor
assembly for a single phase conductor according to one embodiment of the present invention. A plurality of Hall Effect sensors 5, for instance three Hall Effect Sensors (H1, H2 and H3) are placed in a PCB assembly 6. The PCB assembly 6 in turn is mounted on the current carrying conductor 1 with the assembly clamps 4 as shown in FIG. 1. For instance, the current carrying conductor 1 has a rectangular cross-section.
[0032] The Hall Effect sensors 5 are provided with an input supply 2.
When the current is passed through the conductor with a rectangular cross-section 1, the magnetic field generated across conductor line is sensed by the Hall sensors. Further, a weighted average of the multiple Hall Effect sensor outputs 3 is taken to obtain a direct correlation to magnitude of current flowing in the conductor 1.
[0033] FIG. 2 illustrates across-sectional view of a single phase current
carrying conductor with a circular cross-section and a rectangular cross section according to one embodiment of the present invention. A plurality of Hall Effect sensors H1, H2 and H3 are placed at incremental orthogonal distances from any chosen surface of the conductor with a circular surface 7 or conductor with a rectangular surface 1.

[0034] When current is passed through the conductors 1 and 7, the
magnetic field generated across the conductor line is sensed by the Hall sensors H1, H2 and H3 and the weighted average of the multiple Hall Effect sensor outputs the magnitude of the current carrying conductors 1 and 7. In the rectangular conductor 1 of FIG. 2b, the sensors are placed orthogonal to the length or the breadth of the conductor 1 depending on the space constraints in the final application area. For optimal distributed magnetic field sensing, three Hall Effect sensors H1, H2 and H3 have been placed radially away from the conductor core.
[0035] In the case of single phase circular cross section conductor of
FIG. 2a, the magnetic field sensed is a function of current flowing in the conductor and the distance from the centre axis of the conductor. Thus, we have

Where,
Bi = Magnetic field at location i (T)
I = Current through the conductor (A)
ri = distance (m) from the centre of the conductor at locations 1, 2, 3.
The hall elements H1, H2 and H3 measures the magnetic field, B as a function
of output voltage (VH1, VH2, VH3) developed across the Hall sensors H1, H2
and H3. Although from the above equation (1), the current through the
conductor can be found out from one hall element itself. However, a

weighted average of the elemental readings is taken to arrive at value of current, I. This partially offsets the adverse effects of stray magnetic fields, thereby providing an accurate reading for the current magnitude to be measured. So, if the magnetic field measured from each element is B], B2, B3, then true reading is taken as Blav (i.e. referenced at locationl) such that

The current corresponding to B]av can then be found out by considering the magnetic field Bl. B2, B3 measured from each sensor as the true reading at location 1. In case, any Hall Effect sensor saturates due to close proximity to the conductor's magnetic field, then the reading of that sensor can be bypassed and weighted average can be calculated based upon the remaining Hall sensor readings. This approach also offsets any issue of saturation with use of Hall elements. Such saturation limits are usually observed when the maximum current flow limit or the magnetic field strength exposure is exceeded.
[0036] In the case of a single phase rectangular cross-sectional
conductor of FIG. 2b and FIG. 2c, a detailed derivation based upon the length and breadth of the conductor cross-section provides the following formulation.

A resultant of Bx_net and By --net provides the absolute value and the direction of the resultant magnetic field. Now, to carry out an averaging as done in equation (2) for circular conductors, the appropriate constants for any given design of H/W ratio would have to be evaluated. For any such design, such constants are theoretically evaluated as k1, k2, k3. Thus, in this case, the new B1 av would be

Here, each proportionality ratio, k1 denotes the ratio of (Bl / B2) for fixed conductor geometry. Average B at location 1 is then found out by using the equation (4).

[0037] FIG. 3 illustrates the arrangement of Hall Effect sensors for a
three phase conductor system according to one embodiment of the present invention. Three Hall Effect sensors H1, H2 and H3 are placed adjoining to each phase conductor 1. When current passes through the three phase conductor system, the magnetic field generated across each conductor line is sensed and a weighted average of the multiple Hall Effect sensors output hold a direct correlation to magnitude of current flowing in the conductor 1. However, as the magnetic field due to adjoining conductor 1 would directly alter the readings of a standalone conductor measurement, a processing unit carries out a compensation based on the spacing of the conductors to nullify their effects. This correction ensures that current measured across each conductor is not influenced by magnetic effect of the adjoining current carrying conductor.
[0038] FIG.4 illustrates the magnetic field derivation across a
conductor with a rectangular cross section in a current sensing system according to one embodiment of the present invention. FIG. 4 illustrates the magnetic field derivation across a rectangular conductor at any point (X, Y). In this case, the concept of averaging has to be extrapolated to the magnetic field correction based on proximity effect i.e. Magnetic field for conductor 1 (three phase) at (X1,Y1) =
[Magnetic field for conductor 1 (Isolated) - Magnetic field for
conductor 2 (three phase) - Magnetic field for conductor 3 (three phase)] at
(X1,Y1). ...(5)

[0039] Magnetic field correction as proposed in equation (5) is
vectorial in nature and that correct magnetic field calculation is based upon resolving the individual X and Y components and their vector summation as per their instantaneous directionality. The current through the conductors of each phase can then be accurately detected based on the distributed magnetic field sensing technique discussed herein.
[0040] FIG.5 illustrates an arrangement to derive field correction
derivation for a plurality of circular single phase conductors according to one
embodiment of the present invention. According to FIG.5, only Hall Effect
sensor for each phase is taken into consideration. The notations described in
the FIG. 5 are as follows:
BRT - True magnetic field reading of isolated R-phase
BRM - Measured magnetic field reading at R-phase
BYT - True magnetic field reading of isolated Y-phase
BYM - Measured magnetic field reading at Y-phase
BBT - True magnetic field reading of isolated B-phase
BBM - Measured magnetic field reading at B-phase
HR - Hall sensor for R-phase
HY - Hall sensor for Y-phase
HB - Hall sensor for B-phase
R - Radius of the conductor (same for each phase)
r - Distance of hall sensor from centre of phase conductor

d - Equal spacing between the three phase conductors.
[0041] Now, for a given conductor dimensioning and spacing, there
exists a fixed relationship given by;
BRM = BRT - resolved magnitude of (BYT & BBT) along BRT ... (6)
BYM = BYT - resolved magnitude of (BRT & BBT) along BYT -. ■ (7)
BBM = BBT - resolved magnitude of (BRT & BYT) along BBT • • ■ (8)
[0042] Here BRM, BYM and BBM are measured by HR, HY and HB hall
sensors respectively. The solution to the above set of equations are unique and need to be derived only once for a given installation. They can then be coded into the signal processing system appropriately for the chosen system. Thus, based on the three measured readings, the three isolated magnetic fields due to individual phase currents can be deduced.
[0043] Once the isolated/individual magnetic field data is available, it
is well known that phase current, IR is



The value of B is thus calculated from the hall output which is in form of voltage.

where KH is a proportionality constant for a given hall sensor. So, the value of B can be derived easily from (10) which when put into equations (6) to (8), provides for deducing the individual isolated readings of each phase. The instantaneous current of each phase can be then measured using equation (9).
[0044] The instantaneous Hall output is only a function of the
dimensions of the Hall plate and the instantaneous magnetic field orthogonally incident on the plate. By a high frequency sampling of the Hall output, the static and time varying magnetic fields can be measured. Thus the physical construction of system remains common for AC as well as DC systems. However, an additional signal processing algorithm for measuring the RMS current is required in case of AC systems depending on the type of application. For multiple sensors, the procedure adopted will have to be same as discussed for the single sensor system.
[0045] FIG. 6 illustrates the block diagram explaining the functionality
of the current sensing system according to one embodiment of the present invention. When current passes through a single phase conductor system or a three phase conductor system, the magnetic field generated across each conductor line is sensed by the Hall sensors H1, H2 and H3 601. When the output voltage of the sensor is nearly equals to the input supply voltage, the sensor is no longer capable of registering any further readings. The positioning of the sensors would thereby have to be decided based on

maximum saturation limit and the maximum field to be measured. The maximum field and the maximum saturation limit are determined based on the highest value of current to be sensed. Ideally, it would be desirable to ensure that none of the sensors arrive at saturation. Generally the Hall Effect sensor kept close to the conductor is likely to saturate whereas for the other sensors, it is desired that they be placed in a way such that they are within their operable region. Therefore, only the readings 602 of Hall sensors which are in the operating range are considered for sensing the current flow. Then adjacent field correction is done based on current sensor system dimensions 603. A weighted average of the multiple Hall Effect sensor outputs 604 provides a direct correlation to magnitude of current flowing in the conductor. The current in each conductor is measured as a function of magnetic field 605.
G) ADVANTAGES OF THE INVENTION
[0046] The distributed current sensing technique of the present
invention offers a robust, reliable and consistent method for sensing current. The current sensing technique of the present invention is employed to measure both AC and DC currents. The present invention provides complete electrical isolation for the sensors from the live conductor. The present invention solves the problem of temperature rise issues during current flow through the conductor. The current sensors of the present invention can be used for metering and protection in electrical power line systems. The

current sensing method of the present invention has high linearity over wide current sensing range based on proper positioning of the sensors. The current sensing technique of the present invention enhances the current measurement limitations.
[0047] Although the invention is described with various specific
embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0048] It is also to be understood that the following claims are
intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
What is claimed is:
1. A current sensor assembly comprising
a conductor;
a plurality of Hall Effect sensors arranged radially away from the conductor;
and
Wherein the plurality of Hall Effect sensors produce output signals
representative of the strength of the magnetic field passing through the
conductor.
2. The current sensor assembly according to claim 1, further comprising a signal processing system to processes the output signals of the Hall effect sensors to measure the current flowing through the conductor.
3. The current sensor assembly according to claim 2, wherein the signal processing system measures a weighted average of the output from the plurality of Hall Effect sensors to measure the magnitude of current flowing through the conductor.

4. The current sensor assembly according to claim 1, wherein the plurality of Hall Effect sensors are arranged at incremental orthogonal distance from a conductor core.
5. The current sensor assembly according to claim 1, wherein the current sensing is performed for at least one of an AC system and a DC system.
6. The current sensor assembly according to claim 1, wherein the conductor is at least one of a single phase current carrying conductor and a three-phase current carrying conductor.

7. The current sensor assembly according to claim 1, wherein the conductor has at least one of a circular cross-section and a rectangular cross-section.
8. The current sensor assembly according to claim 1, further comprising a support structure to electrically isolate the plurality of the sensors from the conductor.