International conference

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 [email protected]@annauniv.edu

Abstract-Phasor Measurement Unit (PMU) plays a vital role for measuring the Synchronized voltage and current phasor for real time system. In this work, the hardware implementation of the Phasor Measurement Unit is carried out and is tested in the LabVIEW environment. The main objective of this paper is to measure voltage (current) magnitude and angle in real time with time tag and to investigate the performance of PMU with help of Total Vector Error (TVE). To measure phasor information and track the phasor values of voltage and current synchronously on a power system in real time Phasor Measurement Unit (PMU) is used. Hardware for PMU using DSP microcontroller, GPS receiver and associated supporting components has been developed. Three phase voltage and current signals analog data are converted into digital word and transferred to the computer through RS232 communication link. The outputs signals obtained from the hardware is send via SMS through GSM modem.

Index Terms— Phasor Measurement Unit, DSP Microcontroller, DFT Algorithm, LabVIEW, Total Vector Error, GSM modem.

I. INTRODUCTION

Power systems are large interconnected nonlinear systems where system wide instabilities or collapses can occur when the system is subjected to unusually high stress. Such system-wide blackouts lead to considerable economic costs as well as adverse impacts on the society. Therefore, the operational reliability of the electric power system is of fundamental importance to power system operation and planning. Operator actions together with automatic control actions are designed to prevent or minimize the damage caused by such outages.

The recently developed WAMS (Wide-Area Measurement System) technology offers a great potential to implement dynamic supervision and control of wide-area 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. As a basic component of WAMS, PMU (Phasor Measurement Unit) uses highly accurate PPS (one-pulse-per-second) signal of GPS to achieve precise and synchronous measurement. It has the ability to measure voltage (current) magnitude and angle, frequency and other parameters, which are transferred to the data control center. These synchronously measured data can then be used for system stability assessment and control.

Synchrophasor technology is currently a widely accepted technique of measurement in power electric systems due to its unique ability to show data, from analog voltage and current, that is synchronized using the same time

base and calculating the corresponding phasor [3], this produces an image of the electric system behaviour at a particular point in time, delivers information in real time and provides data to be processed by analyzing the irregularities of the power electric system [7].

A phasor is a mathematical representation of a sinusoidal waveform. The phase angle at a given frequency is determined with respect to a time reference. Synchrophasors are phasor values that represent power system sinusoidal waveforms referenced to the nominal power system frequency and coordinated universal (UTC) time. The phase angle of a synchrophasor is governed by the waveform, the system frequency, and the instant of measurement [4]. Thus, with a universal precise time reference, power system phase angles can be accurately measured throughout a power system.

The global positioning system (GPS) technology provides an economic option for the same. An important advantage of the GPS technology is that its receiver can automatically detect accurate synchronization. The device which provides synchronized phasor measurements is called a Phasor Measurement Unit (PMU). A number of widely distributed PMUs in the power system may be utilized for the following purpose [8]:

Real time monitoring and control State estimation Protection and control for distributed generation Network congestion management Angular and voltage stability monitoring

II. SYNCHRONIZED PHASOR MEASUREMENT

Phasor Measurement Units (PMUs) are electronic devices that use state-of-the-art digital signal processors that can measure 50Hz AC waveforms typically at a rate of 30 samples per cycle (1500 samples per second). The analog signals are sampled and processed by a recursive phasor algorithm to generate voltage and current phasors [5]. Different components of a PMU are shown by a block diagram in Figure 1. It measures standardized frequency and rate of change node voltage and current magnitudes, node voltage and current phase angles, branch flow magnitudes and angles (MW, MVAR, MVA and Current).

Figure 1: Block Diagram of PMU The first commercial PMU was the Macrodyne 1690

introduced in 1991 that performed only the data recording function. By the year 1997 PMUs capable of real time measurement were developed. At present the PMUs provide data at the rate of about 6-60 samples per second. The lower end of the range can represent the inter area power system dynamics while the higher range can cover local oscillations, generator shafts, and controller actions in [2].

Algorithms to compute phasors from measured signals use a recursive moving window of data samples to estimate the phasor parameters. Simple algorithms assume a fixed nominal frequency value and compute only the magnitude and the angle of the phasor. Discrete Fourier Transform is one of the most widely used phasor estimation technique.

III. MEASUREMENT TECHNIQUES

The basic definition of the phasor representation of a sinusoid is illustrated in Figure 2. Assume a single frequency constant sinusoid of frequency ω is observed starting at time t=0.The sinusoid can be represented by a complex number called ‘Phasor’ which has a magnitude equal to the root-mean-square (rms) value of the sinusoid, and whose angle is equal to the angle between the peak of the sinusoid and the t=0 axis.

Figure 2: Definition of a Phasor, a complex number representation of a constant pure sinusoid.

If the sinusoid is not a pure sine wave, the phasor is assumed to represent its fundamental frequency component calculated over the data window is illustrated in Figure 3.

Figure 3: Estimation of phasors from sampled data using Discrete Fourier Transform.

The most commonly used method of calculating phasors from sampled data is that of Discrete Fourier Transform (DFT). The sampling clocks are usually kept at a constant frequency even though the input signal frequency may vary by a small amount around its nominal value. Other options and secondary corrections when the signal frequency deviates from its nominal value are described in [3]. A more computationally efficient method is to compute the estimated phasor recursively by adding the contribution made by the new sample, and subtracting the contribution made by the oldest sample.

IV. PMU HARDWARE IMPLEMENTATION AND TECHNICAL REQUIREMENTS

The IEEE C37.118 standard has been utilized for standardizing the Phasor Measurements and for defining the performance requirements [7]. The block diagram of PMU with LabVIEW is shown in the Figure 4. Three phase voltage and currents signal from PTs and CTs are connected to the anti aliasing filter which is nothing but a low pass filter. Anti-aliasing filter cutoff frequency is 2 KHz. This filter output is given to the DSP micro controller analog input channels which 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 Total Vector Error (TVE) should be less than 1% Communication protocol

Block diagram with LabVIEW

Serial to USB converter

PT1

PT2

PT3

CT1

CT2

CT3

GPS

IPPS

PLL

dsPIC30F4013

Antialiasingfilter

Wave form chartChannel separation

Data read

LabVIEW

Figure 4: Block Diagram of the PMU

Using GPS 1PPS signal is generated into 9600 PPS signal using phase locked loop. Using this 9600 PPS signal all six channels are samples sequentially. GPS generated time information with resolution of 1µs as well as sample data are transmitted to LabVIEW through USB port. Magnitude and phasor information are calculated using recursive DFT algorithm in LabVIEW. This magnitude and phasor and UTC information is transported into the central computer through Ethernet.

V. TESTING THE PMU HARDWARE IN LABVIEW ENVIRONMENT

LABVIEW DATA CAPTURING LOOP BLOCK DIAGRAMThe PMU hardware has been integrated with LabVIEW

using the port RS 232. The data is being read and processed in LabVIEW. The data capturing loop of LabVIEW block diagram is shown in Figure 5.

Figure 5: LabVIEW block diagarm

This front panel block diagram shows the typical data capturing using USB port and displaying the six channels in waveform chart.

Three major blocks in the LabVIEW

1. Data reading blocks 2. Calculating recursive Discrete Fourier Transform 3. Displaying the captured data

Data read block contain a VISA port configuration and VISA read, here we can be set serial port configurations, while loop configurations, bytes read and also error detection.

Captured data is continues string, this format is transferred to substring of single set of six channel data. In this way all sampled channel information is connected to waveform chart after bundling.

From the captured data magnitude and phasor values are calculated for all the three phase voltage and currents using recursive moving window DFT using LabVIEW. This calculation is updated for every 5ms.

VI. LABVIEW FRONT PANEL VIEW FOR ALL SIX CHANNELS

Three phase output was monitored with the help of 50 KVA uninterrupted power supply (UPS).To see an input waveform of three phase voltage and current as shown in the Figure 6.

Figure 6: Input waveform of three phase Voltage and Current

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 7: Output waveform of three phase Voltage and Current

Using this sampled data window with DFT algorithm the magnitude and phasor values are calculated along with GPS data of 1µs (xx.000000s) accuracy also transmitted to PDC (phasor data concentrator) typical one frame data values are given here. The measurement shows that 49.999265Hz in Table 1.

TABLE 1THREE 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°

Phasor values of three phase Voltage and Current are synchronously measured with help of the hardware of Phasor Measurement unit.

VII. DATA RECEIVING USING BHYPER TERMINAL

The data available in data read block of LabVIEW is read continuously and can be received using hyper terminal. The received output measurements are shown in the Figure 8.

Figure 8: Received voltage and current Outputs using hyper terminal

VIII. APPLYING GSM MODEM FOR OBTAINING OUTPUT VALUES VIA SMS

The synchronous measurement of PMU outputs are received with the help of hyper terminal and these values are sent to any of the control center through SMS using GSM modem.

Figure 9: PMU setup with GSM ModemFrom the Figure 9 it can be inferred that the output values

obtained from the hardware can be sent via SMS using GSM modem.

IX. CONCLUSION

PMU hardware is build with six analog channels. The six channels are scanned synchronously using PLL generated 9600 Hz signal using one second pulse. The PMU hardware 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 Engineering 2009, 3, 13-17.

[3] IEEE Standard 1344-1995: “IEEE Standard for Synchrophasors for Power Systems”, 2001.

[4] IEEE Standard C37.118-2005: “IEEE Standard for Synchrophasors for Power Systems”, 2006.

[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 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.

BIOGRAPHIES

Suresh Sampath received his Bachelors degree from Government College of Engineering, Salem in 2010. He is

pursuing his Masters in Power Systems Engineering, College of Engineering Guindy, Anna University, Chennai. His fields of interest includes Transmission and distribution, Power System 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, Anna University Chennai in 2004. She received her Ph.D in the year 2012. She is presently working as an Assistant Professor in College of Engineering, Anna University, Chennai. Her fields of interest includes Power System Control and Operation, Service Oriented Architecture and Web Services.