Automatic calibration of a substation device The present invention relates to a method and system for automatic calibration of a power substation device and more particularly, to a method and system for automatic calibra ^¬ tion of a merging unit installed in an electrical substation. An electrical substation is an important part of electrical power generation, transmission and distribution system.

Transformation of voltage from low to high or high to low are mainly performed at the substation. The substation has transformers along with switching, protection and control devices. Another important task performed at the substation is to mo ^¬ nitor and control the flow of power of the electrical power generation, transmission and distribution system along with the protection of machines and devices installed in the sub ^¬ station. Few decades back, the monitor, control and protec- tion actions performed at the substation needed lot of manual effort for data collection, analysis, maintenance and so on. However in present time, by using power system automation techniques, the manual effort for controlling the substation has been significantly reduced.

The power system automation is an act of automatically controlling a power system by using instrumentation and power devices. In case of substation automation i.e. automatically controlling a substation, a remote user monitors and controls the functionality of the substation with the help of data re ^¬ ceived from various sensors and/or intelligent electronic de ^¬ vices (IED) installed within the substation. Tasks performed under substation automation can be broadly categorized in three categories namely, data acquisition, monitor and con- trol. In data acquisition, data like analog current and/or voltage values are measured and collected from various sen ^¬ sors and/or IEDs installed at various sections of the substa ^¬ tion. The acquired data can be used by the device collecting it, can be sent to another IED or a processing terminal or a database for further analysis. The analysis of the data can be done either by using some predefined algorithms i.e. auto ^¬ matically or manually.

In monitoring task, the data acquired from various devices is analyzed by a computer process or by a supervisor like an en ^¬ gineer or an operator, for checking the status and conditions of various devices, machines and processes associated with the substation. The control task refers to sending command messages to various devices installed within the substation. The command messages are based on the analysis of the ac ^¬ quired data and are created automatically or by the engineer or operator who is monitoring the acquired data. Other tasks performed under the substation automation are sending and receiving data and the command messages. For a reliable opera ^¬ tion of the substation, it is necessary that all the tasks performed under the substation automation i.e. data acquisi ^¬ tion, monitoring and control are mutually synchronized along with the communication of the data and the command messages.

The devices installed within the substation for substation automation includes measuring devices like electronic current transformers, electronic voltage transformers, or other in- strumentation transformers, data collection and routing devices like merging units, data transmitting mediums like ca ^¬ bles, and processing units like laptops, computers, etc.

A merging unit is used for receiving and combining different measure types and then to produce a homogeneously defined digital data stream created from the received measured data. Merging units used in some modern substation automation systems can be synchronized with a GPS signal. The merging unit received analog data from various measuring devices like cur- rent transformers and voltage transformers. The merging unit output digital data stream is defined according to IEC61850 standard and is send to various protection devices, power quality devices and other devices that are supporting the substation automation system.

To ensure the reliable functionality of the substation auto- mation, various tests are performed for all the devices in ^¬ stalled within the substation. Based on the test results the devices are calibrated to achieve a best performance of the system. Testing of the functionality of the merging unit is done by sending multiple analog test patterns from a signal generator and then analysing digital data outputs of the merging unit for the multiple analog test patterns. In pre ^¬ sent scenario the output digital data also known as sampled measured values (SMV) are analyzed in a laboratory or by us ^¬ ing an analyzer. In general, the analyzer can be a software tool that is capable of verify, view and analyze SMV for testing the merging unit by comparing the received SMV with predefined ideal sampled values. The analyzer is also capable of displaying waveforms of the received SMV in an oscillo- scopic view along with electrical units. The analyzer can also display RMS values and phase angles calculated from the received SMV with the help of a phasor diagrams and measure ^¬ ment tables. On the bases of values and information displayed by the analyzer, an engineer or operator verifies the functionality of the merging unit and in case of any discrepancy in the received SMV and predefined sampled values, the engi ^¬ neer calibrates the merging unit. The calibration of the mer ^¬ ging unit is done by setting the filter coefficients of the merging unit. From the foregoing it is clearly evident that the testing, verification and calibration, when required, are essential tasks that need to be performed for ensuring a reliable func ^¬ tioning of the merging unit which leads to an ensured reli ^¬ able functioning of the substation automation system. But the method and system utilised for testing and verification of the merging unit, as explained above, are time consuming, needs additional system module like analyzer and also needs manual efforts. From the above mentioned problems associated with the testing and calibration of a merging unit, it is clearly evident that there is a strong need of an automatic system and method for testing and calibration of the merging unit without using an additional analyzer or without performing an analysis in a laboratory .

It is therefore an object of the present invention to provide an automatic system and method for testing and calibration of the merging unit with no need of an additional analysis mod ^¬ ule or laboratory based analysis.

The object is achieved by providing a method for calibrating one or more merging units by using one or more substation de ^¬ vices according to claim 1, and a merging unit calibration system for calibrating the one or more merging units according to claim 11. Further embodiments of the present inven ^¬ tion are addressed in the dependent claims.

In a first aspect of the present invention, a method for calibrating one or more merging units by using one or more substation devices is disclosed. A first step of the method disclosed in the first aspect of the present invention is, receiving one or more sampled measured values at the one or more substation devices from the one or more merging units along with one or more test patterns from one or more testing devices. At next step, the one or more sampled measured val ^¬ ues are compared with the one or more test patterns at the one or more substation devices and a difference between the one or more sampled measured values and the one or more test patterns is identified. At a final step of the method dis ^¬ closed in the first aspect of the present invention, one or more coefficients are applied on one or more filters wherein the one or more coefficients are computed on the basis of the comparison between on the comparison of the one or more sampled measured values and the one or more test patterns. Further in accordance with the first aspect of the present invention, the one or more test patterns are received at the one or more merging units from the one or more testing de ^¬ vices before the one or more sampled measured values are re- ceived at the one or more substation devices.

Furthermore, in accordance with the first aspect of the pre ^¬ sent invention, the one or more sampled measured values are generated by the one or more merging units from the one or more test patterns received from the one or more testing de ^¬ vices.

Also, in accordance with the first aspect of the present in ^¬ vention, the one or more sampled measured values are con- verted in a set of analog signals by the one or more substa ^¬ tion devices before the one or more sampled measured values are compared with the one or more test patterns by the one or more substation devices. In addition to this, the method disclosed in accordance with the first aspect of the present invention also includes, the one or more test patterns are converted in a set of sampled values by the one or more substation devices before the one or more sampled measured values are compared with the one or more test patterns by the one or more substation devices.

Further in accordance with the first aspect of the present invention, at least one substation device from the one or more substation devices is a protection device.

Furthermore, in accordance with the first aspect of the pre ^¬ sent invention, at least one testing device from the one or more testing devices is a signal generator. Furthermore, in accordance with the first aspect of the pre ^¬ sent invention, the one or more test patterns are one or more analog voltage and/or current signals. In accordance to a second aspect of the present invention, a merging unit calibration system is disclosed. The system includes one or more testing devices for generating one or more test patterns and one or more merging units for generating one or more sampled measured values from the one or more test patterns. The system also includes one or more substation de ^¬ vices for generating one or more coefficients for one or more filters wherein the one or more coefficients are generated from a comparison of the one or more sampled measured values with the one or more test patterns.

Further, in accordance with the second aspect of the present invention, the system comprises at least one connection for sending the one or more test patterns from the one or more testing devices to the one or more merging units.

Furthermore, in accordance with the second aspect of the pre ^¬ sent invention, the system comprises at least one connection for sending the one or more test patterns from the one or more testing devices to the one or more substation devices.

Also in accordance with the second aspect of the present in ^¬ vention, the one or more merging units comprises at least one analog processing module, at least one analog to digital con- verter and at least one digital processing module.

In addition to this, the system disclosed as the second as ^¬ pect of the present invention, also comprises at least con ^¬ nection for sending the one or more sampled measured values from the one or merging units to the one or more substation devices .

Accordingly, the present invention provides a method for calibrating one or more merging units (104) by using one or more substation devices and a merging unit calibration system. The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompany ^¬ ing drawings, in which: FIG 1 illustrates a block diagram of a merging unit calibration system in accordance with an embodiment of the present invention.

Various embodiments are described with reference to the draw- ings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details.

FIG 1 illustrates a block diagram of the merging unit cali ^¬ bration system 100 in accordance with an embodiment of the present invention. The merging unit calibration system 100 is a part of a substation automation system. For simplicity and understanding purposes, only the merging unit calibration system 100 is shown in FIG 1.

The merging unit calibration system 100 includes a signal generator 102, a merging unit 104 and a protection device 106. The signal generator 102 is a testing module which is capable of generating different types of test patterns for testing various devices installed in the substation automa ^¬ tion system. For testing the merging unit 104, the signal generator 102 generates multiple analog current and voltage signals as test patterns. In a preferred embodiment of the present invention, the signal generator 102 is capable of generating the analog current and voltage signals for testing the merging unit 104 and the analog current and voltage sig- nals are scaled according to the outputs of current trans ^¬ formers and voltage transformers of the substation automation system connected with the merging unit 104. An analog processing module 110 of the merging unit 104 re ^¬ ceives the analog current and voltage signals from the signal generator 102 via connection 108, as shown in FIG 1. The analog processing module 110 may include filters, amplifiers, and/or other analog components for processing the received analog current and voltage signals from the signal generator 102. The analog processing module 110 transmits the processed analog signals to an analog to digital converter 112 which converts the processed analog signals into digital signal. The analog to digital converter 112 sends the converted digi ^¬ tal signals to a digital processing module 114. The digital processing module 114 processes the digital signals received from the analog to digital converter 112 and generate sampled measured values (SMV) . The digital processing module 114 fur- ther transmits the SMV to the protection device 106 via con ^¬ nection 118, as illustrated in FIG 1. Internal architecture of the merging unit 114 shown in FIG 1 is for exemplary purpose. In a preferred embodiment of the present invention, the internal architecture of the merging unit 104 may differ from the architecture shown in FIG 1. In an embodiment of the pre ^¬ sent invention, the internal architecture of the merging unit 104 can be any architecture of a merging unit known in the state of the art. The protection device 106 receives SMV from the digital proc ^¬ essing module 114 of the merging unit 104 through the connection 118. In addition to this, the protection device 106 also receives the analog current and voltage signals from the sig ^¬ nal generator 102 via connection 116, as shown in FIG 1. The analog current and voltage signals received by the protection device 106 from the signal generator 102 via connection 116 are the same analog current and voltage signals received by the analog processing module 110 of the merging unit 104 from the signal generator 102 through the connection 108, as il- lustrated in FIG 1. The protection device 106 process the analog current and voltage signals received from the signal generator 102 and generate sampled values from the analog current and voltage signals. Then the protection device 106 compares the sampled values with SMV received from the digi ^¬ tal processing module 114 of the merging unit 104. The pro ^¬ tection device 106 determines the difference between the sam ^¬ pled values and SMV from the comparison. If the difference determined by the protection device 106 is more than a prede ^¬ fined difference then the protection device 106 computes and applies filter coefficients automatically in order to cancel out the effects of the difference in SMV introduced by the merging unit 104. The predefined difference is an allowable limit of difference between the sampled values and SMV de ^¬ fined for a substation automation system.

In an embodiment of the present invention, the protection de ^¬ vice 106 converts SMV received from the merging unit 102 into analog signals and compares the analog signals with the ana ^¬ log current and voltage signals received from the signal gen ^¬ erator 102 to determine the difference introduced by the mer ^¬ ging unit 104. Based on the difference, the protection device 106 computes and applies filter coefficients automatically in order to cancel out the effects of the difference in SMV in ^¬ troduced by the merging unit 104. In another embodiment of the present invention, the protection device 106 can be re ^¬ placed by a control device, a monitoring device or any other device used in the substation automation system.

It is evident from the foregoing description of the present invention that the invention provides an automatic system and method for testing and calibrating a merging unit by cancelling out values introduced by the merging unit in SMV without using an additional analyzer or without performing an analysis in a laboratory.

In addition to this, the present invention demonstrate a me ^¬ thod and system for testing and calibrating a merging unit which is cost effective as additional analysis modules are not required, fast as done by calibration is performed by the devices of the substation automation system and does not need any manual efforts. While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those embodi- ments. In view of the present disclosure, many modifications and variations would present themselves, to those of skill in the art without departing from the scope of various embodi ^¬ ments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.