FORM 2
THE PATENT ACT, 1970 (39 OF 1970)
AND THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; Rule 13)
CURRENT TRANSFORMER CIRCUIT WITH SENSOR
MODULE
SELEC CONTROLS PVT.LTD.
an Indian Company of Plot No. EL -27/1, Electronic Zone, TTC Industrial Area,
MIDC, Mahape, Navi Mumbai 400710,
Maharashtra, India
Inventor: KAJISAMIR
The following specification particularly describes the invention and the manner in which it is to
be performed.

TECHNICAL FIELD OF INVENTION
The present invention relates to electric measurement devices.
The present invention particularly relates to a current transformer circuit which
minimizes device errors and enhances measurement accuracy, and a method
thereof.
BACKGROUND OF THE INVENTION
A current transformer is commonly used for measurement of electric current in AC circuits. A typical current transformer comprises a primary winding, a magnetic core, and a secondary winding. The magnetic core comprises a magnetic body having a defined relationship with one or more conductive windings. When an alternating current is passed through the primary winding,. an alternating magnetic field is produced in the magnetic core, which induces an alternating current in the secondary winding. Depending on the application, the wire used in the secondary winding is connected to a meter that detects the current from the secondary winding and responsively provides an output indication which may be a measurement of current, voltage, and the like. In most electrical installations typically these measurements are converted into various derived outputs such as power, power factor, energy, and the like. The current transformers can be of different types such as an air-core (Rogowski coil) or a Hall-effect sensing.
In the state of art, the common errors encountered in the current transformer devices and the derived measurement thereof, include:
a. phase angle error - in which the currents flowing through the primary
winding and the secondary winding are not in phase with each other
such that to induce an error, thereby producing errors in the derived
measurements such as power, energy, and the like;
b. magnetizing current error - in which saturation and non-linearity, the
non-linear response curve of the magnetic core, determines the

magnitude of error, in proportion to the ratio of turns of the primary winding to the secondary winding;
c. load regulation error - in which the current transformer output varies
based on the load conditions;
d. installation error - in which incorrect connection of the secondary
winding wire or direction of the primary conduction passing through the
core induces errors in the derived measurements; and
*
e. environmental error - in which environmental factors, particularly
temperature, affect the winding or core performance, based on
characteristics of the material used, which in turn induces an error in the
current transformer output or the derived measurements.
A current transformer can be situated within a measuring device such as in a static electricity meter or can be remotely placed outside an electrical/electronic measuring, controlling, or tripping device such as a meter, a regulator or a protection relay device. When the current transformer is remotely placed the characteristics of the current transformer add to the errors in the connected electronic device and thereby produce inaccuracy in measurements. Often, when the current transformer is located within the electronic device the errors of the current transformer may be factored in and compensated for by the hardware/software in the electronic device and hence such errors can be mitigated.
However, for remote or externally connected current transformer systems, the sum of the individual accuracies of each, the current transformer and the device connected to it, will have to be within the total system accuracy requirement. Hence, for a 1.0 % accurate system, the total of the accuracy of the current transformer and the device must be equal 1.0 %; say, for example, 0.5% each. The combination accuracy therefore necessitates that the current transformer as well as the electronic device have better individual accuracies. This comes at an increased cost.

There is therefore felt a need to overcome the afore-mentioned drawbacks of the typical current transformer circuits and thereby provide an improved current transformer circuit which minimizes device errors and enhances measurement accuracy at a reduced cost.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to overcome the afore-said drawbacks of the typical current transformer circuits.
Accordingly, an object of the present invention is to provide a current transformer circuit which eliminates phase-angle error and magnetizing current error in the current transformer. It is also an object of the present invention to provide a current transformer circuit which minimizes load regulation, installation and environmental errors in the current transformer. An intended object of the present invention is to provide a method for enhancing the measurement accuracy of a current transformer circuit.
It is a further object of the present invention to provide a current transformer circuit which is simple, efficient, and cost-effective. Additionally, the modification of the present invention can be configured in a conventional current transformer circuit, thereby providing savings.
These objects and other advantages of the present invention will be more apparent from the following description of the preferred embodiments of the present invention.
In accordance with the present invention, there is provided a current transformer circuit comprising: at least one current transformer coupled to a primary current input and adapted to generate a secondary current output in relation to the primary current input, where said secondary current output is

metered to an electronic device; and a control means configured to be remotely connected to said current transformer and electrically coupled to a communication interface; wherein said control means comprise an in-built memory adapted to store data relevant to the characteristics of said current transformer and in operation communicate said data via said communication interface to said electronic device to make dynamic compensation for the errors in the current transformer characteristics and thereby manipulate the operation of said electronic device in accordance with said communicated data.
Typically, said circuit is configured on a printed circuit board with at least one connector terminal for connecting to said electronic device.
In accordance to said invention, said data consists of at least one characteristic selected from turns ratio, phase angle characteristic, linearity curve data, VA rating, VA accuracy class, temperature characteristics and serial number.
Preferably, said in-built memory is selected from a non-volatile memory and a static memory, with battery back-up.
Additionally, a resistor can be provided for converting said secondary current output to a voltage signal.
Alternatively, protection means are provided to prevent overvoltage condition across said current transformer.
Typically, said current transformer, said control means, and said communication interface are placed in a housing.

Alternatively, said control means and said communication interface are remotely positioned from said current transformer.
Preferably, said control means further comprise a temperature sensor.
In accordance with the present invention, there is provided a method for. configuring a current transformer circuit, said method comprising: providing a primary current input across a current transformer to generate a secondary current output; and communicating by means of a control means a characteristic data to an electronic device to facilitate dynamic compensation for the errors in the current transformer characteristics to thereby manipulate the operation of said electronic device in accordance with said communicated data.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will be described here below with reference to the. following drawings, in which,
FIG. 1 illustrates a block diagram showing the current transformer circuit in accordance with the present invention; and
FIG. 2A illustrates a circuit diagram showing a series of current transformer circuits in communication with control means, in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in detail with reference to the preferred embodiments illustrated in the accompanying drawings, which are illustrated in use as a current transformer circuit for measuring electric current. Reference to the embodiments and the use thereof does not limit the scope of

the invention in any way and is to be considered as illustrative with the only purpose of exemplifying the invention.
The present invention envisages a current transformer circuit with a sensor module. FIGURE 1 of the accompanying drawings illustrates a block diagram showing the current transformer circuit in accordance with the present invention. The current transformer circuit, generally referenced by numeral 100 in FIGURE 1, comprises at least one current transformer 102 remotely connected to a control means 104. The control means 104 may be a microcontroller or a storage memory. The current transformer 102 is coupled to a primary current input 110 and adapted to generate a secondary current output 112 in relation to the primary current input 110. The secondary current output 112 is metered to an electronic device (not shown). The secondary current output 112 can be attenuated or amplified. Further, a resistor may be provided for converting current output to a voltage signal. Optionally, a mathematical function such as an integral or derivative of the output signal can be derived. A protection means may be provided to prevent overvoltage condition across the current transformer 102. The current transformer output can be protected by overvoltage conditions by use of diodes, diode chain, Zener diodes, metal oxide varistors or any other clamping mechanism, that limits the output voltage across the current transformer secondary output.
The control means 104 are electrically coupled to a communication interface 106 as shown by 114. The communication interface 106 is typically a transceiver. The control means 104 comprise an in-built memory (not shown) adapted to store the data relevant to the characteristics of the current transformer 102. The data consists of at least one characteristic selected from turns ratio, phase angle characteristic, linearity curve data, VA rating, VA accuracy class, temperature characteristics and serial number. The control means 104 may further comprise a temperature sensor for monitoring real¬time ambient temperature and then compensate the current transformer

output as per the temperature characteristics. The current transformer characteristics may be determined during testing and stored in the in-built memory of the control means 104. Alternatively, the characteristics can be downloaded in the control means 104 or updated during operation.
In operation, the control means 104 communicate the data (shown by arrow 116) via the communication interface 106 to the electronic device to make dynamic compensation for the errors in the current transformer 102 characteristics and thereby manipulate the operation of the electronic device in accordance with the communicated data.
The circuit 100 is configured on a printed circuit board with at least one connector terminal for connecting to the electronic device. The in-built memory is selected from a non-volatile memory and a static memory, with battery back-up. The control means 104 and the communication interface 106 may receive the power supply 108 at 118 & 120, respectively, from the electronic device (shown by arrow 122) or the current transformer 102 or may alternatively comprise a battery. The current transformer 102, the control means 104 and the communication interface 106 may be positioned within a housing. Alternatively, the control means 104 and the communication interface 135 may be remotely located, plugged on to or placed outside the current transformer housing.
In accordance with the present invention, the Communication Link and the bus interface could be on any physical communication layer such as i2cr SPI, UART, wireless, etc. or any other protocol designed for such interface. The present invention may include a read/write command mechanism that is initiated by the device host to either read the stored current transformer
a
characteristic parameters or to write new characteristic values into the memory.

FIGURE 2 of the accompanying drawings illustrates a series of current transformer circuits in communication with the control means, the combination network referenced by the numeral 200. A plurality of current transformers 202A, 202B & 202C are connected in a three-phase system adapted to receive primary current inputs 210A, 21 OB & 210C and generate secondary current outputs 212A, 212B, 212C, 212D, 212E & 212F at the connector terminal 216. The control means 204 and the communication interface 206 are electrically connected to the connector terminal 216. The power supply is shown by numeral 222.
The device of the present invention enhances the measurement accuracy of the combination system as shown in FIGURE 2. The phase angle errors and the magnetizing current error are completely eliminated. With the system described above, the current transformer accuracy is not a factor in the total accuracy of the system; and the connected device used could be less stringent and need only match the overall accuracy requirements. For example, a 1 % accurate current transformer with a 1 % accurate connected device would still give an overall accuracy of 1 %. Thus, the present invention provides a current transformer circuit which lowers cost and gives higher accuracy.
Embodiment of the present invention is applicable over a wide number of uses and other embodiments may be developed beyond the embodiment discussed heretofore. Only the most preferred embodiments and their uses have been d3scribed herein for purpose of example, illustrating the advantages over the prior art obtained through the present invention; the invention is not limited to. these specific embodiments or their specified uses. Thus, the forms of the invention described herein are to be taken as illustrative only and other embodiments may be selected without departing from the scope of the present invention. It should also be understood that additional changes and modifications, within the scope of the invention, will be apparent to one skilled

in the art and that various modifications to the construction described herein may fall within the scope of the invention.

WE CLAIM
1. A current transformer circuit (100) comprising: at least one current transformer (102) coupled to a primary current input (110) and adapted to generate a secondary current output (112) in relation to the primary current input (110), where said secondary current output (112) is metered to an electronic device; and a control means (104) configured to be remotely connected to said current transformer (102) and electrically coupled to a communication interface (106); wherein said control means (104) comprise an in-built memory adapted to store data relevant to the characteristics of said current transformer (102) and in operation communicate said data via said communication interface (106) to said electronic device to make dynamic compensation for the errors in the current transformer (102) characteristics and thereby manipulate the operation of said electronic device in accordance with said communicated data.
2. The current transformer circuit as claimed in claim 1, wherein said circuit (100) is configured on a printed circuit board with at least one connector terminal for connecting to said electronic device.
3. The current transformer circuit as claimed in claim 1, wherein said data consists of at least one characteristic selected from turns ratio, phase angle characteristic, linearity curve data, VA rating, VA accuracy class," temperature characteristics and serial number.
4. The current transformer circuit as claimed in claim 1, wherein said in-built memory is selected from a non-volatile memory and a static memory, with battery back-up.

5. The current transformer circuit as claimed in claim 1, wherein a resistor is provided for converting said secondary current output (112) to a voltage signal.
6. The current transformer circuit as claimed in claim 1, wherein protection means are provided to prevent overvoltage condition across said current transformer (102).
7. The current transformer circuit as claimed in claim 1, wherein said current transformer (102), said control means (1(H), and said communication interface (106) are placed in a housing.
8. The current transformer circuit as claimed in claim 1, wherein said control means (104) and said communication interface (106) are remotely positioned from said current transformer (102).
9. The current transformer circuit as claimed in claim 1, wherein said control means (104) further comprise a temperature %ensor.
10. A method for configuring a current transformer circuit, said method comprising: providing a primary current input across a current transformer to generate a secondary current output; and communicating by means of a control means a characteristic data to an electronic device to facilitate dynamic compensation for the errors in the current transformer characteristics to thereby manipulate the operation of said electronic device in accordance with said communicated data.