Claims:1. A method for error compensation in metering devices using Rogowski coils in a circuit breaker, wherein said method comprising:
(i) storing, by using at least one barcode, values corresponding to amplitude and phase angle of said Rogowski coils for different phases, to enable calibration of said rogowski coil;
(ii) scanning, by using scanner means, said barcode and/or said said Rogowski coils having said barcode, for each phase to obtain calibration data, during assembly of said circuit breaker;
(iii) communicating said calibration data from said scanner means to an electronic system, wherein said electronic system is adapted to communicate said calibration data to said metering devices;
(iv) storing, by said metering devices, said calibration data, wherein during normal operation of said circuit breaker said metering devices adapted to enable, by means of a metering module, accurate metering using said stored calibration data.

2. The method as claimed in claim 1, wherein said metering devices includes electronic trip units.

3. The method as claimed in claim 1, wherein said barcode is selected from matrix barcode or two-dimensional barcode.

4. The method as claimed in claim 1, wherein said electronic system is selected from human-machine interface (HMI) based systems.

5. The method as claimed in claim 1, wherein said calibration data is stored by using a non-volatile memory module in said metering devices.
, Description:TECHNICAL FIELD OF THE INVENTION

[001] The present subject matter described herein, in general, relates to a calibration of metering devices which provide current or power metering by using Rogowski coils, and more particularly relates to a method of calibrating Rogowski coil to compensate for Rogowski errors like non-linearity, amplitude error and phase angle error to provide metering with high accuracy.

BACKGROUND OF THE INVENTION

[002] Protection devices like circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload, short circuit or instantaneous condition. This functionality is basically achieved using the trip unit in these protection devices. Trip units are broadly classified as thermo-magnetic and electronic trip unit. The thermo-magnetic trip unit includes a bimetal, which heats and bends in response to a persistent overcurrent condition and in turn , unlatches a spring powered operating mechanism, to open the contacts of circuit breaker and break the flow of current

[003] Electronic trip units (ETU) typically make use of microprocessor to achieve the protection functionality. Electronic trip units design is illustrated in U.S. Pat No 4,428,022 and 5,525,985 which include microprocessors, to provide improved performance and flexibility. These digital systems sample the current waveforms periodically to generate a digital representation of the current wherein the microprocessor uses the samples to execute algorithms to provide protection functionality. Since electronic trip units works on the principle of sampling, it computes Root Mean Square (RMS) in the firmware which are used by protection modules to provide various protections like overload, short circuit and so on. This RMS value is used by the metering module to provide metering on display. This principle is also applicable for metering devices.

[004] In conventional electronic trip unit, current transformer was used to step down the current and provide signal to signal conditioning module of microprocessor. Due to the use of iron core, the output gets saturated after certain value. Rogowski coils have air core and hence, the saturation point is much higher than the current transformers, therefore Rogowski coils are used in protection devices.

[005] Rogowski is connected on the current line and step down voltage at the output of Rogowski is given to electronic trip unit. This output is passed through signal conditioning and then given to microcontroller for sampling which is used for computation of RMS values for mattering.

[006] Though Rogowski coil provides linear output over a wide range of current, certain non-linearity is introduced due to design limitations. Also, Rogwoski output for a certain value of current can deviate from the expected output. In the microcontroller unit of the metering devices, Rogowski output will considered ideal and the computation will done. Hence, error may be introduced in metering devices. Therefore, Rogowski calibration is essential to ensure highest accuracy.

[007] In addition to current metering, electronic trip unit as well as other metering devices provide power metering. Secondary output corresponding to current passed is taken from Rogowski output. For voltage signal, a voltage module is used. Generally voltage module consists of resistor divider network to step down the line voltage to a value which can be given to microcontroller for sensing. Using the step down value of voltage and current, power computation is done. Rogowski output error in amplitude will introduce error in power parameters measurement. In addition to amplitude error, Rogowski output also has error in phase angle. In case of Rogowski coil, the current passed will lag output ideally by 90 degrees. But this angle varies depending on Rogowski design. Hence an error in angle is introduced for output of Rogowski signal. But the voltage module output does not have error in phase angle as it is purely resistive network. This Rogwoski output signal with phase angle error and voltage module output signal is used for computation of power parameters. Hence, error is introduced in the measurement of power parameters due to phase angle error.

[008] Error in Rogowski output may be non-linearity over the range, amplitude error and phase angle error introduces error in measurement of power parameters that may include but not limited to active power, reactive power, apparent power, maximum demand active power, maximum demand reactive power, maximum demand apparent power, power factor and the kike.

[009] Reference is made to US 20150028852 disclose an arrangement for measuring a current with a Rogowski type current transducer and transducer electronics. The current transducer has a primary conductor winding for carrying the rated current to be measured, and a secondary conductor winding. The secondary conductor winding adapted to induce a voltage signal VS' between a pair of second terminals. The current transducer having a third conductor winding adapted to receive a calibration current signal. The voltage signal VS' contains a coil sensitivity S and is a superposition of a rated current voltage signal and an additional calibration signal. The transducer electronics being adapted to amplify both the current voltage signal and the calibration signal in the same amplifier and divide the amplified current voltage signal by that part of the amplified calibration signal that contains the coil sensitivity and the gain.

[0010] Reference is made to US 20150028850 relates to a method for calibrating a current transducer of the Rogowski type including a Rogowski coil sensor and an electronic device which is performed by determining and correcting the sensitivity of the current transducer of the Rogowski type through the measurement of the self-inductance LRCCT of the coil using the electronic device.

[0011] Reference is also made to US 6735535 B1, wherein a power meter is provided having an auto-calibration feature and a data acquisition node for measuring the power usage and power quality of electrical power in an electrical power distribution network. The auto-calibration feature calibrates the power meter at predetermined time increments and as a function of temperature changes.

[0012] Reference is also made to US 5539304 which is related to calibration of power meters. An apparatus and a method is provided wherein power pulses are supplied from a standard meter to a supplementary data accumulating means associated with a meter under test. Data accumulation means in the supplementary data accumulating means and in the meter under test is set to a known value and both meters are subjected to similar voltage and current values. A stop signal is generated when the supplementary data accumulating means reaches a predetermined value N and the value in the meter data accumulating means is latched. The stop signal causes arithmetical division of the latched value by N to form a quotient value and is entered into a reference value memory in the meter under test, the reference value memory value determining the number of pulses per unit power pulse generated by the meter.

[0013] In US 5495167, an electrical energy metering system is disclosed which includes a solid-state electrical energy meter with non-volatile factory calibration memory and non-volatile field calibration memory therein. The system also includes a programming unit, such as a hand-held computer, for programming the factory calibration memory with factory calibration parameters and for programming the field calibration memory with field calibration parameters obtained from field testing of the meter. The calibration parameters include parameters relating to meter measurement accuracy such as full-load, light-load and lag calibration parameters. These parameters can be generated during periodic field tests and stored in the meter for retrieval at a later date, such as during a subsequent test of the meter. Because the meter is capable of retaining a plurality of calibration parameters from each field test, a chronological history of data relevant to meter accuracy can be stored in the meter and a paperless transfer of this data to a utility database can be achieved

[0014] Further, reference is also made to US201500228852 and US201500228850 which relate to different methods of calibrating Rogowski coil. The patent applications US6735535 discloses a power meter having an auto-calibration feature and a data acquisition node for measuring the power usage and power quality of electrical power in an electrical power distribution network. The auto-calibration feature calibrates the power meter at predetermined time increments and as a function of temperature changes.

[0015] Further, reference is made to US5539304 that disclose apparatus and method is provided wherein power pulses are supplied from a standard meter to a supplementary data accumulating means associated with a meter under test. Data accumulation means in the supplementary data accumulating means and in the meter under test are set to a known value and both meters are subjected to similar voltage and current values. A stop signal is generated when the supplementary data accumulating means reaches a predetermined value N and the value in the meter data accumulating means is latched. The stop signal causes arithmetical division of the latched value by N to form a quotient value and is entered into a reference value memory in the meter under test, the reference value memory value determining the number of pulses per unit power pulse generated by the meter.

[0016] Reference is also made to US 5495167 relates to calibration using non-volatile memory. An electrical energy metering system includes a solid-state electrical energy meter with non-volatile factory calibration memory and non-volatile field calibration memory therein. The system also includes a programming unit, such as a hand-held computer, for programming the factory calibration memory with factory calibration parameters and for programming the field calibration memory with field calibration parameters obtained from field testing of the meter. The calibration parameters includes parameters relating to meter measurement accuracy such as full-load, light-load and lag calibration parameters. These parameters can be generated during periodic field tests and stored in the meter for retrieval at a later date, such as during a subsequent test of the meter. Because the meter is capable of retaining a plurality of calibration parameters from each field test, a chronological history of data relevant to meter accuracy can be stored in the meter and a paperless transfer of this data to a utility database can be achieved.

[0017] Although, there existed method of calibrating metering devices, however the present inventors have felt a need to provide an improved method of calibration that can effectively use barcode scanning to achieve metering accuracy in electronic trip unit as well as in other electronic metering devices so as to reduce cost of production and production time by eliminating the need for making tedious setup for calibration.

SUMMARY OF THE INVENTION

[0018] 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.

[0019] An object of the present invention is to provide a method for compensation of the Rogowski error to provide metering with high accuracy in electronic trip unit as well as electronic metering devices.

[0020] Another object of the present invention is to provide a method of calibration that eliminate the usage of current and voltage sources to achieve Rogowski calibration after assembly.

[0021] Yet another object of the present invention is to reduce production cost and time during breaker assembly by eliminating the current and voltage source to be used for Rogowski calibration.

[0022] Still another object of the present invention is to reduce production time by eliminating the need for making tedious setup for calibration.

[0023] Accordingly to one aspect, the present invention provides a method for error compensation in metering devices using Rogowski coils in a circuit breaker, wherein said method comprising:
(i) storing, by using at least one barcode, values corresponding to amplitude and phase angle of said Rogowski coils for different phases, to enable calibration of said rogowski coil;
(ii) scanning, by using scanner means, said barcode and/or said said Rogowski coils having said barcode, for each phase to obtain calibration data, during assembly of said circuit breaker;
(iii) communicating said calibration data from said scanner means to an electronic system, wherein said electronic system is adapted to communicate said calibration data to said metering devices;
(iv) storing, by said metering devices, said calibration data, wherein during normal operation of said circuit breaker said metering devices adapted to enable, by means of a metering module, accurate metering using said stored calibration data.

[0024] 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

[0025] 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:

[0026] Figure 1 illustrates the block diagram of the electronic trip unit, according to one embodiment of the present invention.

[0027] Figure 2 illustrates ideal and erroneous Rogowski output signal, according to one embodiment of the present invention.

[0028] Figure 3 illustrates a QR Code Scanning Process according to one embodiment of the present invention.

[0029] 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

[0030] 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.

[0031] 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.

[0032] 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.

[0033] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Typically, Rogowski coil exhibit various errors. There can be non-linearity error for the entire range of metering. There can be amplitude error and phase angle error. The ideal Rogowski output will main a constant ratio of Rogowski output and current passed throughout the range. Also, ideally Rogowski output lags current by 90 degrees. Due to design limitations, Rogowski output can have error in amplitude and phase angle.

[0038] In one implementation, there is provided a method for error compensation in Rogowski based devices that may include electronic trip units of circuit breakers, and which eliminates the use of current and voltage sources to achieve Rogowski calibration after assembly thereby reducing cost of production and production time. The method effectively uses barcode code scanning to achieve metering accuracy in electronic trip unit as well as electronic metering devices. The method compensates various errors of Rogowski that may include but not limited to non-linearity, amplitude error and phase angle error.

[0039] In one implementation, referring to figure 1, which illustrates a basic block diagram of electronic trip unit. When current is passed through the circuit breaker, the current output will be available at the secondary of the current transformer (1) and voltage output is available at the output of Rogowski coil (2). The current transformer output can be given to power supply module (4) and the Rogowski output can be given to signal conditioning module (3). The power supply signal can be passed through regulator (7) and used for powering the microcontroller (8). The power supply can be also made available to flux shift device (FSD) 6 through trip circuit (5). The voltage line may be sensed using voltage module and the output of voltage module (11) may be given to signal conditioning stage. The output of signal conditioning can be given to ADC input of a microcontroller. This secondary signal corresponding to current line and voltage line can be used for metering computation.

[0040] In one exemplary implementation, after the manufacturing of Rogwoski coils, they are tested for quality approval at the manufacturing end. For the purpose of testing, the Rogowski coil output is checked at various points and the error at these points are observed and recorded. Also, the phase angle deviation at these points are checked if necessary and recorded. After the quality checks are done, required details can be put on Rogowski coil that may include but not limited to serial number using printed label or QR code or some other type of labelling. Then these Rogowski coils are used at assembly of the product involving electronic unit, mechanical assembly and outer body. Generally at this stage Rogowski calibration is done. A setup is made which involves current and voltage source used for multi-point calibration. During this process, the electronic trip unit or the metering module can store the amplitude data and phase angle data at various points in a non-volatile memory module. During the normal operation, these values can be retrieved from non-volatile memory and used in the metering computation to compensate Rogowski coil error.

[0041] In one implementation, referring to figure 2, which illustrates ideal Rogowski output as well as erroneous Rogowski output for the current passed. As shown the ideal Rogowski output will maintain a constant ratio of Rogowski output and current passed throughout the range.

[0042] In one implementation, when the Rogowski coil are tested for quality approval after manufacturing, the data will be usually saved for reference purpose. As shown in figure 3, the amplitude and phase angle data of Rogowski will be stored for various points on the barcode that may be selected from matrix barcode or two-dimensional barcode, such QR code, which will be attached with the Rogowski and the data is saved at various points to compensate for non-linearity error. During the assembly, the QR code on Rogowski will be scanned for each phase .The entire process can be controlled using an electronic system that may be selected from PC-HMI. A QR code scanner will communicate the calibration data to PC-HMI which in turn will communicate it to electronic unit or metering device. This data will be stored in the nonvolatile memory module of the microcontroller as illustrated in figure 3.

[0043] Some of the noteworthy features of the present invention, are as follows:
• In the present invention, the method compensates various error of Rogowski that may include non-linearity, amplitude error and phase angle error.
• In the present invention, the quality check process after Rogowski manufacturing is utilized to capture the required data for Rogowski calibration and saved in the QR code.
• In the present invention, during assembly of breaker, calibration data is read using barcode code scanner and communicated to electronic trip unit which saves data in a non-volatile memory module.
• In the present invention, during normal operation, electronic trip unit accesses non-volatile memory for calibration data and it is used in metering module for accurate metering.

[0044] Some of the advantages of the present invention, are as follows:
• The method of the present invention, reduces production cost during breaker assembly as the current and voltage source for Rogowski calibration is eliminated.
• The quality check process after Rogowski manufacturing is utilized to capture required data for Rogowski calibration and it is saved in a barcode
• The production time is also reduced as the time for making tedious setup for calibration is eliminated.
• The method of implementation of calibration of the present invention effectively uses barcode scanning to achieve metering accuracy in electronic trip unit as well as electronic metering devices.
• The present invention provides a method which will be applicable for all devices which use Rogowski coil for current and power metering.

[0045] Although a method for error compensation in rogowski coil based metering devices in a circuit breaker have been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations of the method for error compensation in rogowski coil based metering devices in a circuit breaker.