1. HARDWARE IMPLEMENTATION, REAL TIME TESTING AND DATA TRACKING USING GSM TECHNOLOGY OF PMU S. Suresh1, V. Gomathi2 Power Systems Engineering Division, College Of Engineering, Anna University 1 ssallthebest@gmail.com 2 gomesvg@annauniv.eduAbstract-Phasor Measurement Unit (PMU) plays a vital role for base and calculating the corresponding phasor [3], thismeasuring the Synchronized voltage and current phasor for real time produces an image of the electric system behaviour at asystem. In this work, the hardware implementation of the Phasor particular point in time, delivers information in real time andMeasurement Unit is carried out and is tested in the LabVIEW provides data to be processed by analyzing the irregularitiesenvironment. The main objective of this paper is to measure voltage of the power electric system [7].(current) magnitude and angle in real time with time tag and toinvestigate the performance of PMU with help of Total Vector Error(TVE). To measure phasor information and track the phasor values of A phasor is a mathematical representation of avoltage and current synchronously on a power system in real time sinusoidal waveform. The phase angle at a given frequency isPhasor Measurement Unit (PMU) is used. Hardware for PMU using determined with respect to a time reference. SynchrophasorsDSP microcontroller, GPS receiver and associated supporting are phasor values that represent power system sinusoidalcomponents has been developed. Three phase voltage and current waveforms referenced to the nominal power system frequencysignals analog data are converted into digital word and transferred and coordinated universal (UTC) time. The phase angle of ato the computer through RS232 communication link. The outputs synchrophasor is governed by the waveform, the systemsignals obtained from the hardware is send via SMS through GSM frequency, and the instant of measurement [4]. Thus, with amodem. universal precise time reference, power system phase angles can be accurately measured throughout a power system.Index Terms— Phasor Measurement Unit, DSPMicrocontroller, DFT Algorithm, LabVIEW, Total Vector The global positioning system (GPS) technologyError, GSM modem. provides an economic option for the same. An important advantage of the GPS technology is that its receiver can I. INTRODUCTION automatically detect accurate synchronization. The device Power systems are large interconnected nonlinear which provides synchronized phasor measurements is called a systems where system wide instabilities or collapses can Phasor Measurement Unit (PMU). A number of widely occur when the system is subjected to unusually high stress. distributed PMUs in the power system may be utilized for the Such system-wide blackouts lead to considerable economic following purpose [8]: costs as well as adverse impacts on the society. Therefore, the operational reliability of the electric power system is of • Real time monitoring and control fundamental importance to power system operation and • State estimation planning. Operator actions together with automatic control • Protection and control for distributed generation actions are designed to prevent or minimize the damage • Network congestion management caused by such outages. • Angular and voltage stability monitoring The recently developed WAMS (Wide-Area Measurement System) technology offers a great potential to implement dynamic supervision and control of wide-area II. SYNCHRONIZED PHASOR MEASUREMENT power system. It helps in monitoring and assessing the stability, for various preventive and emergency controls and to increase the transmission capability of the existing assets. Phasor Measurement Units (PMUs) are electronic As a basic component of WAMS, PMU (Phasor devices that use state-of-the-art digital signal processors that Measurement Unit) uses highly accurate PPS (one-pulse- can measure 50Hz AC waveforms typically at a rate of 30 per-second) signal of GPS to achieve precise and samples per cycle (1500 samples per second). The analog synchronous measurement. It has the ability to measure signals are sampled and processed by a recursive phasor voltage (current) magnitude and angle, frequency and other algorithm to generate voltage and current phasors [5]. parameters, which are transferred to the data control center. Different components of a PMU are shown by a block diagram These synchronously measured data can then be used for in Figure 1. It measures standardized frequency and rate of system stability assessment and control. change node voltage and current magnitudes, node voltage and Synchrophasor technology is currently a widely current phase angles, branch flow magnitudes and angles accepted technique of measurement in power electric (MW, MVAR, MVA and Current). systems due to its unique ability to show data, from analog voltage and current, that is synchronized using the same time
2. Figure 1: Block Diagram of PMU Figure 3: Estimation of phasors from sampled data using The first commercial PMU was the Macrodyne 1690 Discrete Fourier Transform.introduced in 1991 that performed only the data recordingfunction. By the year 1997 PMUs capable of real time The most commonly used method of calculatingmeasurement were developed. At present the PMUs provide phasors from sampled data is that of Discrete Fourierdata at the rate of about 6-60 samples per second. The lower Transform (DFT). The sampling clocks are usually kept at aend of the range can represent the inter area power system constant frequency even though the input signal frequencydynamics while the higher range can cover local oscillations, may vary by a small amount around its nominal value. Othergenerator shafts, and controller actions in [2]. options and secondary corrections when the signal frequency deviates from its nominal value are described in [3]. A more Algorithms to compute phasors from measured signals computationally efficient method is to compute the estimateduse a recursive moving window of data samples to estimate the phasor recursively by adding the contribution made by the newphasor parameters. Simple algorithms assume a fixed nominal sample, and subtracting the contribution made by the oldestfrequency value and compute only the magnitude and the sample.angle of the phasor. Discrete Fourier Transform is one of themost widely used phasor estimation technique. IV. PMU HARDWARE IMPLEMENTATION AND TECHNICAL REQUIREMENTS III. MEASUREMENT TECHNIQUES The IEEE C37.118 standard has been utilized for standardizing the Phasor Measurements and for defining the The basic definition of the phasor representation of a performance requirements [7]. The block diagram of PMUsinusoid is illustrated in Figure 2. Assume a single frequency with LabVIEW is shown in the Figure 4. Three phase voltageconstant sinusoid of frequency ω is observed starting at time and currents signal from PTs and CTs are connected to the antit=0.The sinusoid can be represented by a complex number aliasing filter which is nothing but a low pass filter. Anti-called ‘Phasor’ which has a magnitude equal to the root-mean- aliasing filter cutoff frequency is 2 KHz. This filter output issquare (rms) value of the sinusoid, and whose angle is equal to given to the DSP micro controller analog input channels whichthe angle between the peak of the sinusoid and the t=0 axis. is converted into digital word using ADC converter. Phasor Measurement Unit technical requirement as follow: • Input signal range –5v to +5v • Data resolution not less than 12 bit • Reporting rate 10-25 reports per second • Reporting time xx.000000 seconds with time reference • It should estimate frequency as well as rate of change of frequency • Measurement accuracy Figure 2: Definition of a Phasor, a complex number • Total Vector Error (TVE) should be less than 1% representation of a constant pure sinusoid. • Communication protocol If the sinusoid is not a pure sine wave, the phasor isassumed to represent its fundamental frequency componentcalculated over the data window is illustrated in Figure 3.
3. Block diagram with LabVIEW Three major blocks in the LabVIEW 1. Data reading blocks GPS 2. Calculating recursive Discrete Fourier Transform 3. Displaying the captured data IPPS Data read block contain a VISA port configuration PLL and VISA read, here we can be set serial port PT1 configurations, while loop configurations, bytes read Antialiasing PT2 and also error detection. dsPIC30 PT3 filter F4013 CT1 CT2 Captured data is continues string, this format is CT3 transferred to substring of single set of six channel Serial to USB data. In this way all sampled channel information is converter connected to waveform chart after bundling. LabVIEW From the captured data magnitude and phasor values Data read Channel separation Wave form chart are calculated for all the three phase voltage and currents using recursive moving window DFT using LabVIEW. This calculation is updated for every 5ms. Figure 4: Block Diagram of the PMU VI. LABVIEW FRONT PANEL VIEW FOR ALL SIX CHANNELS Using GPS 1PPS signal is generated into 9600 PPS Three phase output was monitored with the help of 50signal using phase locked loop. Using this 9600 PPS signal all KVA uninterrupted power supply (UPS).To see an inputsix channels are samples sequentially. GPS generated time waveform of three phase voltage and current as shown in theinformation with resolution of 1µs as well as sample data are Figure 6.transmitted to LabVIEW through USB port. Magnitude andphasor information are calculated using recursive DFTalgorithm in LabVIEW. This magnitude and phasor and UTCinformation is transported into the central computer throughEthernet. V. TESTING THE PMU HARDWARE IN LABVIEW ENVIRONMENTLABVIEW DATA CAPTURING LOOP BLOCK DIAGRAM The PMU hardware has been integrated with LabVIEWusing the port RS 232. The data is being read and processed in Figure 6: Input waveform of three phase Voltage and CurrentLabVIEW. The data capturing loop of LabVIEW blockdiagram is shown in Figure 5. FRONT PANEL THREE PHASE WAVEFORM DISPLAY IN LAB VIEW Loads are almost balanced and THD was less than 5%. PMU output waveform is illustrated in Figure 7. Figure 5: LabVIEW block diagarm This front panel block diagram shows the typical datacapturing using USB port and displaying the six channels in Figure 7: Output waveform of three phase Voltage andwaveform chart. Current
4. Using this sampled data window with DFT algorithmthe magnitude and phasor values are calculated along withGPS data of 1µs (xx.000000s) accuracy also transmitted toPDC (phasor data concentrator) typical one frame data valuesare given here. The measurement shows that 49.999265Hz inTable 1. TABLE 1 THREE PHASE OUTPUT (VOLTAGE AND CURRENT) Phases Voltage Current U phase 441.464524V,10.23432° 68.962153A,26.56465° V phase 439.178783V,130.47435° 64.176323A,142.17682° W phase 438.786862V, 254.34252° 71.345982A,266.46534° Figure 9: PMU setup with GSM Modem From the Figure 9 it can be inferred that the output values Phasor values of three phase Voltage and Current are obtained from the hardware can be sent via SMS using GSMsynchronously measured with help of the hardware of Phasor modem.Measurement unit. VII. DATA RECEIVING USING BHYPER IX. CONCLUSION TERMINAL PMU hardware is build with six analog channels. The The data available in data read block of LabVIEW is six channels are scanned synchronously using PLL generatedread continuously and can be received using hyper terminal. 9600 Hz signal using one second pulse. The PMU hardwareThe received output measurements are shown in the Figure 8. has been integrated and its voltage and current are captured and it has been realized in Labview. The six channel data is transferred to LabVIEW. In LabVIEW all six channel waveforms is observed on waveform chart. The vector from of voltage and current can be sent as a SMS through GSM modem. REFERENCES [1] Baldwin, T.L., Mili, L., “Power system observability with minimal phasor measurement placement” IEEE Trans. Power Syst., 1993, 8(2):707–715.[doi:10.1109/59.26 0810]. [2] Chunchuan Xu, Xiaoguang Qi, “Recent Developments in Power System Diagnostics and Protection: Synchronized Sampling and Phasor Measurement”, Recent Patents on Figure 8: Received voltage and current Outputs using Engineering 2009, 3, 13-17.hyper terminal [3] IEEE Standard 1344-1995: “IEEE Standard for VIII. APPLYING GSM MODEM FOR OBTAINING Synchrophasors for Power Systems”, 2001. OUTPUT VALUES VIA SMS [4] IEEE Standard C37.118-2005: “IEEE Standard for The synchronous measurement of PMU outputs are Synchrophasors for Power Systems”, 2006.received with the help of hyper terminal and these values aresent to any of the control center through SMS using GSMmodem. [5] Kenneth E Martin, James Ritchie Carrol, “Phasing in the Technology”, IEEE Power & Energy Magazine, Vol. 6 No. 5 Sep/Oct 2008, pp.24-33. [6] Komarncki .P, Dzienis .C, Styczynski Z.A, Blumschein .J, Centeno .V, “Practical Experience with PMU System Testing and Calibration Requirements”, IEEE Power and
5. Energy Society General Meeting Conversion and Delivery of Electrical Energy in the 21st Century, 20-24, July 2008.[7] Martin K.E and others (2005), “Exploring the IEEE Standard C37.118–2005 Synchrophasors for Power Systems”, IEEE transactions on power delivery, vol. 23, no. 4, October 2008.[8] NASPI: “PMU System Testing and Calibration Guide”, Technical Report for the North American Synchrophasor Initative, Performance and standard Task, team leader Meliopoulos .S, December 2007.[9] Phadke .G, Thorp .J.S and Karimi .K, “State estimation with phasor measurements”, IEEE Trans. Power Syst., Vol. PWRD-1, no. 1, pp. 233–241, Feb- 1986.[10] Ray Klump, Ph.D., Robert E Wilson, Ph.D. Kenneth E Martin, “Visualizing Real-Time Security Threats Using Hybrid SCADA / PMU Measurement Displays”, Proceedings of the 38th Hawaii International Conference on System Sciences, 2005.[11] Zhenyu Huang, Senior Member and others “Performance Evaluation of Phasor Measurement Systems”, IEEE Power Engineering Society General Meeting 2008, Pittsburgh, PA. BIOGRAPHIESSuresh Sampath received his Bachelors degree fromGovernment College of Engineering, Salem in 2010. He ispursuing his Masters in Power Systems Engineering, Collegeof Engineering Guindy, Anna University, Chennai. His fieldsof interest includes Transmission and distribution, PowerSystem Analysis and Power System Protection. Gomathi Venugopal received the Bachelors degree from University of Madras, in 2002. Received the Masters degree from College of Engineering, AnnaUniversity Chennai in 2004. She received her Ph.D in the year2012. She is presently working as an Assistant Professor inCollege of Engineering, Anna University, Chennai. Her fieldsof interest includes Power System Control and Operation,Service Oriented Architecture and Web Services.
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