A State-of-the-Art PMU and MATLAB Based GUI Development towards Power System State Estimation on Real Time Basis

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1 I J E E E International Journal of Electrical, Electronics ISSN No. (Online) : and oputer Engineering (): 40-45(0) Special Edition for Best Papers of Michael Faraday IET India Suit-0, MFIIS- State-of-the-rt and MTLB Based GUI evelopent towards Power Syste State Estiation on Real Tie Basis yindrila Roy*, Jitendranath Bera** and Gauta Sarkar** *Techno India ollege of Technology, New Town, Rajarhat, Kolkata,, (WB) **epartent of pplied Physics, University ollege of Science and Technology, 9.P.. Road, Kolkata, (WB) (Received 5 October, 0 ccepted 0 eceber, 0) BSTRT: The ain ai of this paper is to onitor the phasors of voltage and current wavefors and to calculate the real and reactive power consuption at the different bus ends of a transission syste using state-of-the-art icrocontroller based Phasor Measureent Unit (). Each is designed and developed to acquire the saples of voltage and current signals of the line ends in a synchronized tie reference frae. Each of the coputes the peak values of each signal and the real and reactive power consuption at each of the ends utilizing these saples only along with their direction of flow. The individual voltage and current phasors at each of the ends are also detected fro the zero crossing instants of the respective signals with respect to the synchronization pulses. The data packet containing the inforation regarding phase angles, peak values, active and reactive power fro the s are collected and stored in a P using a centralized Intelligent Electronic evice (IE). MTLB based front end graphical user interface (GUI) is developed to acquire these data using the P s serial port. The IE coordinates all the tie synchronization pulses to each in ulticast ode and aintains a sequential routing for the data collection fro the in a unicast ode of networking. The overall functioning of the s, IE and the GUI is tested in a laboratory odel of the power syste and satisfactory perforance is obtained. Index Ters, IE, GUI, Tie synchronized pulses, ctive Power, Reactive Power. I. INTROUTION is usually achieved by the sae-tie sapling of voltage and current wavefors using tiing signals fro the Global The conventional electric power industry is essentially a Positioning Syste (GPS) satellite [3]. detailed insight regulated industry with bulk generation, econoic shows that a runs of its own sapling tie which can be transission over long distances and efficient distribution for synchronized by the coon tie reference frae with the doestic and industrial applications. The necessary control utilization of a PLL syste. Synchronized phasor and protection devices are also provided to aintain its reliability, stability and efficiency. However, the latest Electricity ct, as well as, the use of odern technologies for control, counication and protection purposes, have opened up huge opportunities to both the suppliers and consuers easureents elevate the standards of power syste onitoring, control, and protection to a new level [3]. The Phasor Measureent Unit () technology provides phasor inforation (both agnitude and phase angle) in real tie [4]. The advantage of referring phase angle to a global reference regarding generation, distribution, iport and export of tie is helpful in capturing the wide area snap shot of the electricity and sharing of the power transission syste. s a result, the power industry has started its restructuring. This has not only encouraged copetition in the electric industry to tackle onopoly but has also assured the consuer of good quality power supply, on deand basis, at a copetitive price. ong all the state-of-the-art technologies in building a odern power grid, the phasor easureent unit () is an iportant and proising one []. Phasor easureent units (s) are high speed power syste devices that provide synchronized easureents of real-tie phasors of voltages and currents [, 3]. They can be further used to calculate voltage and current agnitudes, phase angles, real and reactive power flows etc. The synchronization power syste [4]. Effective utilization of this technology is very useful in itigating blackouts and learning the real tie behavior of the power syste [4]. Since the bus voltage angle of a power syste is very closely linked with the behavior of a network, its real tie easureent is a powerful tool for operating a network [5, 6, 7]. In this work, the authors have tried to develop a onitoring syste with the help of a icrocontroller based and a MTLB based GUI. The acquires the saples of voltage and current signals at the line ends in a synchronized tie reference frae and coputes the active and reactive power consuption at the respective ends. The individual voltage and current phasors at each of the ends are detected

2 Roy, Bera and Sarkar 4 fro the zero crossing instants of the respective signals with respect to the synchronization pulses. The data packet containing the inforation regarding phasor angles, peak values, active and reactive power fro the s are collected and stored in a P using a centralized Intelligent Electronic evice (IE). MTLB based front end graphical user interface (GUI) is developed to acquire these data us ing the P s serial port and a dedicated counication channel. The IE coordinates all the tie synchronization pulses to each in ulticast ode and aintains a sequential routing for the data collection fro the in a unicast ode of networking. II. MTERILS N METHOS. Fundaentals of pure sinusoidal signal represented as x( t) = X cos( ω t) + ϕ () The phasor representation of this sinusoid is given by X j X x ( t ) = e = (cos + j sin ) () It can be therefore, concluded fro equation () that the signal frequency,, is not explicitly stated in the phasor representation. The agnitude of the phasor is the rs value of X the sinusoid and its phase angle is φ [7]. The concept of technology provides real tie phasor inforation of voltage and current signals by acquiring their saples in a tie synchronized reference frae. It helps in easuring, as well as, onitoring the agnitudes and phase angles of the voltage and current signals of different buses over a distributed transission network. The inforation regarding the aount of power flow and the current injected at different nodes of a transission network can also be obtained. This will help the syste operators to aintain the healthiness of the network. Thus, deands the easureents to be ade at coon sapling instants so that a coparison of the signal agnitudes and angles between the at different buses can be ade. The synchronization is achieved by sae-tie sapling of voltage and current wavefors using tiing signals fro different coon tie reference frae, such as the Global Positioning Syste (GPS) Satellite or any other reference tiing signal generator. B. Saple Shifting Technique The inforation about the active and reactive power, consued at the sending and receiving ends of the transission line, is obtained by utilizing the voltage and current saples using the Saple Shifting technique. One iportant advantage of this ethod is that it does not require the coputation of power factor angle between the voltage and the current signals [8]. alculation of ctive Power (P) If the voltage and current signals are sinusoidal in nature with the current lagging the voltage signal by an angle, then the two signals can be expressed as follows: v () t = s in t i () t = I s in( t- ) In such a case the expression for the instantaneous power becoes ( ) = v ( t ) i ( t ) p t = I sin() sin() t t - Since the average value of the instantaneous power is called as the active power, its equation can be expressed as: P = Pa v g = p ()() t d t 0 = I c o s (4) Thus, it can be concluded fro equation (4) that the active power, P, is basically the average of the products of instantaneous voltage and current saples over a coplete cycle. In other words, equation (4) can be odified as, N Pa v g = P = I c o s = v n in (5) N n = where, vn and i n are the saples of the instantaneous values of the voltage and current signals at the nth instant respectively and N is the total nuber of saples over a full cycle. The active power is thus easured using equation (5) following the ethods as described in [8]. alculation of Reactive Power (Q) The reactive power, Q, can also be calculated if the saples of voltage and current are known. The product of voltage and current saples at an instant, shifted by 90 degrees, gives the reactive power at that instant. Q = I s i n where, = I c o s( 9 0) N = v n i N 9 0 n = vn and i 9 0 o n o n (3) are the saple values of voltage and 90 o shifted current signals and N is the total nuber of saples over a full cycle. Using the above equation reactive power (Q) is easured fro the saples only as described in [8].. Sensing of irection of Power Flow With deregulated power syste, electric energy is now being iport or export as the situation deands. The identification of export or iport of power is done with the sensing of direction of power flow. Sensing of direction of power flow is done fro the saple values of the voltage and current signals only. The following logic is ipleented to detect the power flow direction without eploying any kind of direction sensing hardware eleent. The direction of power flow can best be understood fro the fig. in which the phasors of voltage and current signal are shown.

3 Roy, Bera and Sarkar 4 onsidering the voltage phasor as a reference phasor i.e. <0, the current phasor ay be at any angle within -90 < θ <90 for a particular direction of power flow. This flow ay be tered as forward direction of power flow i.e. fro power grid to the load with either lagging or leading load angle. For backward direction of power flow, the current phasor will be in the opposite direction to that of the forward direction i.e. the phasor angle will be within 90 < θ <-90 w.r.t. the sae voltage phasor. It is also illustrated in Table-I. Fro the respective voltage and current wavefors, as shown in fig., the load angle θ can be evaluated fro their zero crossing instants. The lagging or leading states will be coputed fro the slope of the wavefors. s it is shown in the fig., for lagging load angle within -90 <θ<0 the zero crossing instant of current wavefor falls within 0 <θ<90 fro that of voltage wavefor considering their positive slope only. Siilarly, for leading load angle within 0 < θ <90 the zero crossing instant of current wavefor falls within 70 < θ <360 for the sae easuring condition. This is true for forward power flow. On the other hand, for reverse power flow, for lagging load angle within -90 <θ<80 the zero crossing instant of current wavefor falls within 80 <θ<70 and for leading load angle within -80 < θ <-90 the zero crossing instant of current wavefor falls within 90 < θ <80 for the sae easuring condition. Table. Table showing the power direction for different load angles. Power irecti on Forwar d Forwar d Revers e Revers e 0 I(lead) Load ngle range Positive slope zero crossing angles Quadra nt 0 <θ<-90 (lag) 0 <θ<90 First 0 <θ<90 (lead) 70 < θ <360 Fourth 90 <θ<80 (lag) 80 <θ<70 Third -80 < θ <-90 (lead) 90 < θ <80 Second I(lag) 0 I(lag) I(lead) (a) (b) (c) (d) Fig.. oltage and current phasors for positive power flow in (a) & (b) and negative power flow in (c) & (d) for lead and lag power angle respectively.. Phasor and Power Measureent details in a Figure 3 shows the scheatic diagra of the block. The voltage and current signals at the ends of the transission line are stepped down using potential and current transforers respectively before they are sapled by the s of the s. For a three phase transission line, six nubers of s are eployed three of the saple the respective phase voltages and the reaining three s saple the respective phase currents. The IE transits a synchronizing coand data 0 fps in tie synchronization with the GPS in ulticast ode to all the s. The icrocontroller in the generates a reference clock pulse on receipt of the synchronizing coand. s shown in figure 4, T ref denotes the period between the successive synchronizing coands. This reference clock pulse of 0Hz is fed to a PLL in order to get the sapling frequency of the s at khz, the period of which is shown by T.The sapling instant of all the s will then be the sae and in phase with the synchronizing coand. The icrocontroller coputes and stores the peak values, phase angles, active and reactive power for one coplete cycle of the input signal wavefor. 3 I 4 I 5 6 LK I PLL REF ONTROL PIN u T T (a) Fig.. oltage and current wavefors for (a) positive (b) negative power flow in lag or lead power angle condition. (b) PT T 3 PHSE SUPPLY Fig.3. Scheatic diagra of the Block. RS4/485 ONERTE TO OMMUNITION HNNEL

4 Roy, Bera and Sarkar 43 T Fig.4. Showing reference clock pulses and the pulses generated fro the PLL. While the axiu value of the signal can be obtained by coparing the sapled values with one another, the phase angle difference between any two signals is deterined fro the zero crossing instants of the two signals on either the rising or the falling edges. The active and reactive power is calculated using the Saple Shifting technique. These data are sent to the IE for their storage and display in the P using RS4/ 485 protocol, only when the data request coand is sent to the. Provision has also been ade in the IE for acquisition of all the saples of the voltage and current signals if continuous onitoring of voltage and current signals is required if soe abnoral conditions prevail in the network. E. Organization of the at different Transission Lines Figure 5 shows the arrangeent of s at different transission lines in a power syste. ll the s counicate with the IE through the sae counication channel. The IE sends the synchronizing 0 fps to all the s of one zone continuously in a ulticast ode. The s saple the signals for one coplete cycle of the signal and wait for the next synchronizing coand. The s wait for the data request coand along with the I nuber for transferring the data to the IE for its storage. Only the whose I nuber atches with that of the IE sends its data to the IE for its storage. In this way, only one counicates with the IE at a tie. Fig.5. T ref BUS RS4/ 485 RS4/485 BUS RS4 /485 3 IE BUS3 RS4 / rrangeent of s in a Power Syste. tie BUS4 5 F. IE and Synchronization The basic purpose of the IE is to establish coordination aong the different s installed at different locations and the P. The coordination aong the s is done with the help of wired network counication using RS4/485 protocol. Using RS485 protocol the axiu distance between the IE and the can be up to k. The icrocontroller in the IE counicates with the P using RS3 protocol, the scheatic diagra of which is shown in figure 4. IE sends a synchronizing coand data packet to all the s for tie synchronized sapling of the signals by the respective s. It also sends a data request packet to the, by entioning the I nuber within the packet, in order to acquire the data. The responds to this request only when its own I nuber is atched, by transitting the data packet consisting of phasor angles, peak values, active and reactive power to the P for its storage and analysis. The next data will be acquired in a siilar technique by changing the I nuber in the data request packet, only when the previous one will be copleted. In this way the P collects the data packet of all the s within the tie interval between the successive synchronizing coands. s shown in the figure 6, the icrocontroller within the IE receives a GPS reference signal and generates a synchronizing coand 0fps for the required synchronized data acquisition by the s. The icrocontroller also receives the GPS real tie clock and sends the tie to the P. The P stores the data fro all the s as well as this tie inforation in a server such that the power syste paraeters fro different zones can be onitored with respect to the real tie clock. GPS Fig.6. RS4/485 ONERTER u MX 3 Scheatic diagra of the Intelligent Electronic evice (IE). G. ounication Bandwidth The sapled values of the signal (voltage / current) are transitted to the IE via the counication channel by eans of serial counication. The sapling rate of the is selected at KHz. This gives 0 saples of a 50 Hz signal (voltage / current) in one coplete cycle of the wavefor. Thus, every counication channel carries 0 bytes of a signal in 0 illisecond duration. If the sapling rate is increased to 0 KHz, 00 bytes / cycle will be transitted serially through every channel. In other words, the nuber of transitted bytes is directly proportional to the sapling frequency (f). P

5 Roy, Bera and Sarkar 44 If the technology is ipleented in a single phase syste to easure the voltage and current signals, the data rate will be 0 Kbps. For a three phase syste, six nubers of s will be required to transit the voltage and current signals. Hence, the data rate will be 60 Kbps for such a syste. So, the nuber of transitted data bytes increases if the nuber of signals (s) or the nuber of phases (n) of the syste is increased. In a power syste, the s ay be located at different points. The IE ay be designed in such a way that it acts as a centralized data collection syste to collect the data fro different s. Thus, the counication speed of the serial channel is the ain constraint. The counication speed ust be sufficiently high enough to collect all the data fro the s without any data loss. Matheatically, the nuber of transitted data bytes (B) can be represented as: B = f n s The state of a transission line or a bus at its sending or receiving ends can be deterined using the peak values of voltage and current, active power, reactive power and power factor at its respective ends. Hence, only six bytes of data need to be transitted fro each to the IE. In this way, the IE is able to collect data fro ore nuber of s without stressing the counication speed. The inforation collected fro the different s can be stored and displayed in the P using a MTLB based GUI. III. EXPERIMENT RESULTS Figure 7 shows the experiental set up of the hardware that has been used in the laboratory to ipleent a. For testing the perforance of the s, two of the have been stationed at two different plug ends in the laboratory and the corresponding voltage data were acquired and displayed in the P as shown in figure 8. IE Fig.8. Front End of MTLB based GUI displaying the voltage wavefors of the s. The wavefors of the voltages as well as the phase angle between the two wavefors at the two different plug ends are displayed in the GUI. Provision has also been ade in the GUI for the corresponding phasor representation of the two signals. Table I shows the experiental data obtained for one coplete cycle of the voltage wavefors that have been easured by the respective s. I. ISUSSION The uniqueness of the proposed syste is that a state-of-theart icrocontroller based and IE are developed and tested in the laboratory with satisfactory results. The IE generates the tie synchronization fps with respect to the GPS and transits it to all the for their synchronization. The runs of its own clock (@ khz) with tie synchronized pulses fro IE. The phase angle is calculated fro the voltage or current saples of both the ends by coparing the zero crossing instants of the respective signal saples. rough estiation of the angle can be evaluated in this way since the saples do not always fall on the zero line. For exact easureent an interpolation technique can be adopted to know the exact zero crossing points. The GPS syste in each is avoided here by sending the tie synchronized pulses with respect to the GPS fro the IE only. This reduces the cost of using GPS receiver with each. Fig.7. Experiental setup of the hardware along with the results obtained. KNOWLEGMENT The authors acknowledge PRI Bangalore MOP GOI for providing the infrastructural facilities procured fro their sponsored project. REFERENES [] Jin Ma, Pu Zhang, Hong-jun Fu, Bo Bo, and Zhao-yang ong, pplication of Phasor Measureent Unit on Locating isturbance Source for Low-Frequency Oscillation, IEEE Transactions On Sart Grid, ol., No. 3, eceber 00, pp

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