Development of New Algorithm for Voltage Sag Source Location

Transcription

1 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong Development o New Algorithm or Voltage Sag Source Location N. Hamzah, IEEE, A. Mohamed, Senior Member IEEE, A. Hussain, IEEE Abstract Voltage sag is among the major power quality disturbances that can cause substantial loss o product and also can attribute to malunctions, instabilities and shorter lietime o the load. Accurate voltage sag source location can help to minimize the loss and problems caused by voltage sag in a power distribution system. This paper presents a development o a current component index (CCI) algorithm to locate the source o voltage sag in a power distribution system. The product o the RMS current and the power actor angle at the monitoring point is employed or the sag source location. A graph o this product against time is plotted. The voltage sag source location is determined by examining the magnitude o the current component index at the beginning o the sag. I the magnitude o the CCI during sag is higher than the magnitude o CCI beore sag, it indicates that the voltage sag source is in ront o the monitoring point. On the other hand i the magnitude o the CCI during sag is lower than the magnitude o CCI beore sag, it indicates that the voltage sag source is in behind the monitoring point. The proposed method has been veriied by simulations on a radial distribution system. Comparative studies with other method namely, the slope o the line itting parameters o current and voltage method were also conducted in order to highlight the strength o the proposed method V Index Terms Voltage sag, Single source, current. I. INTRODUCTION oltage sag is a temporary decrease in the RMS voltage magnitude between p.u and with duration o mostly less than second. Its requency o occurrence is between a ew tens and several hundreds times per year []. It is the most important power quality problem acing many industrial customers since equipment used in modern industrial plants such as process controllers and adjustable speed drives is becoming more sensitive to voltage sag. The causes o voltage sags are ault conditions, motor starting, transormer energizing and other sudden load changes. Voltage sags are typically caused by ault conditions [2], in which short-circuit aults and earth aults are ound to cause severe voltage sags [3]. In industrial and commercial power systems, aults on one-eeder tend to cause voltage drops on all other eeders in the plant [4]. During short circuit aults, voltage sags occur whenever ault current lows through ault impedance. Voltage returns to normal as soon as a Manuscript received October 3, N. Hamzah is with the Universiti Teknologi MARA, Shah Alam, MALAYSIA. (phone: ; ax: ; noralizah@salam.uitm.edu.my ). A. Mohamed, is with Universiti Kebangsaan Malaysia, Bangi, MALAYSIA. ( azah@vlsi.eng.ukm.my). A. Hussain is with Universiti Kebangsaan Malaysia, Bangi, MALAYSIA. ( aini@vlsi.eng.ukm.my). ault-clearing device interrupts the low o current. These aults may be ar rom the interrupted process, but close enough to cause problems throughout the system. Even when voltage returns to normal, many sensitive loads experience a production outage i the voltage sag magnitude and duration are outside the load ride-through capabilities. Locating the source o voltage sag is important beore any voltage sag mitigation technique is done to eliminate the sag. A wrong mitigation solution can aggravate the voltage sag problem because only ater inormation about a voltage sag source location is available, can power-quality trouble-shooting, diagnosis and mitigation be carried out. The advantage o locating the source o voltage sag is that any disputes among the major responsibility party can be resolved airly [5]. To date only our reerences cite the methods to locate the sources o voltage sags rom the literature. A method using the disturbance power and disturbance energy to determine which side o a recording device the voltage sag originates is based on the concept that active power tends to low away rom a nonlinear load [6]. This concept is translated in terms o disturbance power and disturbance energy to determine on which side o a recording device the voltage sags originate. The directions o the disturbance energy as well as the disturbance o real power low are used to locate the voltage sag source. The method will rely on the degree o conidence o both the disturbance power and disturbance energy. Thus, the degree o conidence will be reduced i results rom disturbance energy and disturbance power do not match. Another most recent technique to locate the origin o voltage sag is by employing the slope o the line itting parameters o current and voltage during voltage sag [5]. The method plots the product o voltage magnitude and power actor against current magnitude at a particular measurement point. A line itting o the measured points are perormed and the sign o the slope indicates the direction o voltage sag source. A positive slope shows that the sag is rom upstream and a negative slope shows that it is rom downstream. The method has only been veriied using three-phase-to-ground aults. Reerence [7] applies the concept o instantaneous energy direction or voltage sag source detection which is claimed to be able to locate the voltage sag source. The other method is by applying the state estimation theory to estimate the location o voltage sag [8]. Faults in distribution system have been well known as a major cause o voltage sag. Hence this paper ocuses on the development o new algorithm which is based on ault in a distribution power system. The proposed algorithm utilizes the phase angle dierence between current and voltage or ISBN: IMECS 2009

2 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong power actor angle to determine the voltage sag source. In the method, magnitude o currents and phase angles o voltages and currents are measured at the monitoring point. The rms current is then multiplied with the cosine o the power actor angle and the product is then plotted against time. The product polarity is used to indicate the direction o voltage sag source either it is rom behind the monitoring point or in ront o the monitoring point. The proposed method is veriied on a test distribution system modeled using an electromagnetic transient program EMTDC/PSCAD and the data are processed via MATLAB codes. II. VOLTAGE SAG SOURCE LOCATION FOR SINGLE SOURCE SYSTEM ANALYSIS The index developed to determine the direction o the voltage sag source rom the monitoring is based on the single source system in Fig.. In the igure, the direction o current is as shown. Source E φ δ E φ δ I I N Fig. 2 Single source system during ault A. Development o Current Component Index The derivation o the proposed Current Component Index (CCI) to locate the source o voltage sag is based on the single line diagram as shown in Fig. 3(a). In the igure, assuming that the ault occurs at point and the monitoring points are at M A and M B. The direction o current beore and ater aults will be considered. The positive direction o the current is rom E to the monitoring. δ 2 δ 2 I 2 E φ M A M B 2 Fig. Single source system beore ault From Fig. the current lows beore sag occurs is as seen rom E and given by, E φ () δ in which, δ is the line impedance and E φ is the voltage source. Beore sag occurs, there is only one loop and the current that lows is. Assume there is ault at point in which the impedance is given by δ as in Fig. 2, two loops are created. The voltage at point will be very small or approaching zero [9], and the current namely as I, I 2 and I will be created. Current I lows rom source E φ, I 2 lows rom the ault point and I lows through the ault impedance to ground. From Fig. 2, the direction o I is similar with the direction o current beore ault occurs, since it is rom the same source, E and the current lows towards. I the impedance 2 is higher than the ault impedance, current I 2 0 and the current rom the source E will low towards. Otherwise, the current I 2 will low rom but the value is smaller than the value o current beore ault occurs. The current direction either it is rom the source o voltage sag or towards the source o voltage sag will be used to develop the new indicator or determining the location o source o voltage sag. N Fig. 3 (a) Single source system or voltage sag analysis beore aults occur Beore short circuit ault occurs at point, and by applying the Kircho Current Law, the current at point M A or M B, is given by, T E φ θ α In which, θ : voltage angle at monitoring point α: current angle at monitoring point The phase dierence (θ-α) is a power actor angle and * T + 2. From (2), I is given by, E φ E φ I α (3) T θ α T By multiplying the voltage at the monitoring point, V θ, with the let and right hand side o (3), the ollowing equation is obtained, V θe φ V θ I α T By considering only the real power, equation (4) will provide the ollowing, EV cos( α φ ) VI cos( θ α) (5) T For a practical case, the angle (θ-α) are only between zero and 90 o, i.e, the irst quadrant o current lagging voltage case and (2) (4) ISBN: IMECS 2009

3 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong in the third quadrant o current leading voltage case. In order to obtain the current value, both sides o equation (5) will be divided with V, hence the current component lowing rom E will produce, E cos( α ) I cos( θ α ) (6) φ T Thus rom equation (6), the current beore ault, Icos(-) b rom E to the monitoring point is given as, E cos( α φ) I cos( θ α) b (7) T Equation (7) is thus the current component index beore ault occurs and can be written as CCI bs Icos(θ-α) b. Fig. 3(b) shows the equivalent circuit when ault occurs at point. By reerring to M A as the monitoring point, the source o ault is in ront o the point M A. In the igure, and I, is the ault impedance and current respectively. During ault, the voltage at is very small, i.e, almost zero. Thus, current lows rom E to the monitoring point is given by, E φ I α (8) θ α * From equation (8), I is given by, E φ E φ I α (9) θ α The power equation can be obtained by multiplying both right and let hand side o equation (9) with the voltage at the monitoring point, V θ, as ollows, V E φ MA V Fig. 3(b) Single source system or voltage sag analysis during ault and monitoring point at M A V θ E φ θ I α (0) By considering the real power component, the ollowing equation can be given as ollows, I 2 E cos( α φ ) I cos( θ α) (2) Thereore, the current component during ault, i.e, Icos(-) rom E to the monitoring point, is given by, E cos( α φ) I cos( θ α ) (3) Equation (3) is the current component index during ault and can be written as CCI s I cos(θ-α). By dividing equation (3) with equation (7), we can obtain, E cos( α φ) I cos( ) θ α T (4) I cos( θ α) b E cos( α φ) T Since the value o T > and T >, hence equation (4) can be written as ollows, I cos( θ α ) I cos( θ α) b > (5) Equation Icos(-) b and Icos(-) is the current component index beore and during ault respectively. Thereore equation (5) re-written as, CCI > (6) s CCI bs Where CCI s and CCI bs is the current component index during and beore ault respectively. From equation (6), it can be concluded that, at the beginning o voltage sag, i the current component index during ault is higher than current component index beore ault, i.e, CCI s > CCI bs, the source o voltage sag is in ront o the monitoring point, M A. Next, it is to consider i the ault occurs at point, which is behind the monitoring point M B, in which beore ault occurs, the current component index is similar as in equation (7). Fig. 4 shows the current when ault occurs at point and the monitoring point is at point M B. E φ M B 2 I θ E V cos( α φ) VI cos( θ α) () To obtain the current values, the let and right hand side o equation () is divided with voltage, V, hence the current component that lows rom E is given as ollows, Fig. 4 Voltage sag a equivalent circuit system or single source during ault and the monitoring point is at M B By reerring to Fig. 3(a) and Fig. 4, during short circuit ault at point, by applying Current Kircho Law, the current component at point M B is as ollows, ISBN: IMECS 2009

4 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong I cos( θ α) I cos( θ α) I cos( θ α ) (7) b In which, phrases Icos(-) and Icos(-) b is the current during ault and current beore ault at point M B respectively. The phrase Icos( - ) is the current equation which lows through ault impedance,, in which, : voltage angle at ault location : current angle at ault location. From equation (7), it can be seen that the current during ault, which is Icos(-) is less than the current component beore ault, Icos(-) b. Thus, by replacing the terms Icos(-) and Icos(-) b with the terms CCI s and CCI bs, it can be seen that at monitoring point M B, at the beginning o voltage sag, i CCI s < CCI bs then, the location o the source o voltage sag is behind the monitoring point. The proposed Current Component Index (CCI), i.e, Icos(θ-α), is the product o r.m.s current and power actor. This index is plotted against time as shown in Fig. 5. Fig. 5(a) shows the plot when the location o the voltage sag source is in ront o the monitoring point. On the other hand, the plot when the source o voltage sag is behind the monitoring point is plotted in Fig. 5(b). In the igures t and t 2 is the beginning and end o the voltage sag duration respectively. (iv)graphically plot coordinates o Icos(θ-α) against time o a ew cycles o pre-ault and during ault durations. Check the polarity o Icos(-) b and Icos(-) at the beginning o ault. I then, the location o the source o voltage sag is behind the monitoring point. On the other hand i CCI s > CCI bs, the source o voltage sag is in ront o the monitoring point. IV. TEST SYSTEM AND RESULTS The test system used in this study is as shown in Fig. 6. The system is ed by a voltage source o 33kV, 5MVA at 50 Hz requency. By reerring to Fig. 6, our ault locations have been considered, which are F, F2, F3 and F4, whereas the monitoring points are PCC, M, M2 and. Two types o aults have been simulated namely balanced and unbalanced aults. The three phase balanced aults have been simulated or about 0.3 seconds. On the other hand the unbalanced aults simulated are the single line ault (SLF) and double line ault (DLF). PCC 33 kv 33/ kv, 5 MVA F4 2 0 F3 M F2 F 2 I cos ( θ-α) 0 CCI s>cci bs t t2 a) III. IMPLEMENTATION OF THE CURRENT COMPONENT INDE The proposed method to locate the source o voltage sags is veriied on a test distribution system modeled using an electromagnetic transient program PSCAD/EMTDC. The procedure implemented is as ollows: (i) Detect the beginning o the voltage sag. (ii) Obtain the magnitude and phase o voltage and current rom the monitoring point at pre-ault and during ault times. (iii)calculate the values o Icos(θ-α) or a ew cycles o pre-ault and during ault durations. I cos ( θ-α) Fig. 5 Index or Voltage Location or Single Source System (a) In Front o Monitoring Point (b) Behind the Monitoring Point 0 t CCI s <CCI bs Time(s) b) t A. Balanced Faults Fig. 6 Test System For Voltage Sag Results o voltage sag which is caused by balanced aults are tabulated in Table I. By reerring to Fig. 6, details o results rom observation or the monitoring points and their respective ault location can be obtained. Table I presents the details o ault location and monitoring points simulated or the test system in Fig. 6. TABLE I DETAILS OF BALANCED FAULTS FOR A SINGLE SOURCE SYSTEM Fault Monitoring points Location Sag source in ront Sag source behind F M, PCC M2, F2, PCC M, M2 F3 PCC M, M2, F4 M, M2, PCC M2 ISBN: IMECS 2009

5 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong Fig. 7 shows the plots o CCI against currents or monitoring points at M, M2 dan or balanced aults at point F. In Fig. 7a), it can be seen at the beginning o voltage sag, at t 0.42 s, the value o CCI during sag is higher than the value o CCI beore sag occurs, i.e, CCI s > CCI bs. This result indicates that the source o voltage sag is in ront o the monitoring point. The results or the monitoring at points M2 and plotted in Fig. 7b) and c) show that at the beginning o voltage sag, the value o CCI during sag is lower than the values o CCI beore sag, i.e,. Both results show that the source o voltage sag is behind the monitoring points. These results prove that the CCI index can be used to locate the source o voltage sag and the results are in a good agreement with the observation in Table I. CCI s > CCI bs (a) B. Unbalanced Faults In this paper, results rom unbalanced ault are also presented or various points o monitoring points o Fig. 6. Two types o unbalanced aults are considered namely, single line to ground ault (SLF) and double line to ground aults (DLF). Table II presents the details o an unbalanced aults at F2 and the results obtained at monitoring points M, M2, and PCC. This inormation is then used to justiy the accuracy o the simulation results using the CCI. TABLE II DETAILS OF UNBALANCED FAULTS FOR A SINGLE SOURCE SYSTEM Fault Location F2 Monitoring Points Single Line to Ground Fault (Phase A) Double Line to Ground Faults, (Phase A) Double Line to Ground Faults, (Phase B) CCI s< CCI bs (b) Sag source in ront PCC, PCC, PCC, Sag source behind M, M2 M, M2 M, M2 The results o unbalanced aults (SLF) created at F2 are presented and analyzed. Fig.8 a), b) and c) show the graph o current component index against time or ault at F2 and the monitoring points at M, M2 and respectively. In Fig. 8a) and b), it can be seen that at the beginning o voltage sag, CCI s < CCI bs. These results indicate that the source o voltage sag is behind the monitoring points M and M2. On the other hand the result o the monitoring point at shows that at the beginning o ault, CCI s > CCI bs (Fig. 8c). This result indicates that the source o voltage sag is in ront o the Fig. 7 Balanced Faults at F or monitoring points a) M b) M2 and c). (c) monitoring point,. Thus, in the case o unbalanced ault, the CCI is able to accurately locate the source o voltage sag relative to its monitoring points as compared to the details in Table II. CCIs <CCI bs Fig. 8 Results o CCI or unbalanced aults (SLF) at F2 or monitoring points, phase A, a) M b) M2 and c). The results o unbalanced aults (DLF) created at F2 are also presented and analyzed. Fig. 9 shows the result o CCI plotted against time obtained at monitoring points M, M2 and. Fig. 9a) and 9b) show that at the beginning o aults the value o CCI s < CCI s, which indicate that the source o voltage sag is behind the monitoring points. On the other hand, Fig. 9c) shows that CCI s > CCI bs indicating that the source o voltage sag is in ront o the monitoring point. From these results, the CCI thereore is accurate in indicating that the source o voltage sag is in ront o the monitoring point as compared to the details in Table II. C. Comparative Studies With Other Method CCI s > CCI bs This section presents the comparison analysis between the CCI and Slope O The Line Fitting Parameters O Current and Voltage [5] method. Table III tabulates the comparison results or the balanced ault. The ault location is at F as shown in Fig. 6. The results in Table III are or monitoring points o PCC, M, M2 and. From the table it can be seen that at monitoring points PCC and M, both methods indicate the source o voltage sag is in ront o the monitoring point. On the other hand, at monitoring points M2 and, both methods indicate that the source o voltage sag is behind the monitoring points. CCI s > CCI bs Fig. 9 Results o CCI or unbalanced aults (DLF) at F2 or monitoring points, phase A, a) M b) M2 and c). ISBN: IMECS 2009

6 Proceedings o the International MultiConerence o Engineers and Computer Scientists 2009 Vol II IMECS 2009, March 8-20, 2009, Hong Kong TABLE III COMPARISON OF VOLTAGE SAG SOURCE FOR BALANCED FAULTS FOR A SINGLE SOURCE SYSTEM, FAULT LOCATION AT F Monitoring Points Slope o the Line Fitting Parameters o Current and Voltage Current Component Index PCC, M In Front o Voltage In Front o Voltage Sag Source M2, Behind o Voltage Behind o Voltage Table IV tabulates the comparison results or the unbalanced ault (DLG) or a test system in Fig. 6. Results or phase A and Phase B or monitoring points PCC, M, M2 and are tabulated or comparison between Slope o the Line Fitting Parameters o Current and Voltage and CCI methods. From the table it can be seen that or phase A, at monitoring points PCC and, both methods indicate that the source o voltage sag is in ront o the monitoring point. On the other hand, at monitoring points M and M2, both methods indicate that the source o voltage sag is behind the monitoring points. Similarly or phase B, both methods are in a good agreement in indicating that the source o voltage sag is in ront and behind the monitoring points. TABLE IV COMPARISON OF VOLTAGE SAG SOURCE FOR UNBALANCED FAULTS (DLG) FOR A SINGLE SOURCE SYSTEM, FAULT LOCATION AT F2 Phase A PCC, Slope o the Line Fitting Parameters o Current and Voltage In Front o Voltage M, M2 Behind o Voltage Phase B PCC, Slope o the Line Fitting Parameters o Current and Voltage In Front o Voltage M, M2 Behind o Voltage Current Component Index In Front o Voltage Sag Source Behind o Voltage Current Component Index In Front o Voltage Sag Source Behind o Voltage However, the implementation o the CCI is simpler than the Slope O The Line Fitting Parameters O Current and Voltage because the CCI only requires the voltage and current data. On the other hand the Slope O The Line Fitting Parameters O Current and Voltage method requires a line itting technique on the top o current and voltage data to locate the source o voltage sag. V. CONCLUSION This paper has presented a new algorithm development to locate the source o voltage as seen at the monitoring points by examining the value o the current component index at the beginning o the voltage sag. From the results, it has been proven that the CCI satisy 00% o the voltage sag source location or balanced and unbalanced aults or the one source system. The advantage o the CCI can be listed as ollows: It only requires three parameters or calculations, namely the magnitude or current and the phase angles o voltage and current at the monitoring points. It has been proven to work well with both balanced and unbalanced aults in a single source distribution system or radial system. The method also can be used or a two-source system which will be published in our next paper. VI. REFERENCES [] M. H. J. Bollen, Voltage Sags in Three-Phase Systems, IEEE Power Engineering Review, September 200, pp.8-5, 7. [2] M. H. J. Bollen, Understanding Power Quality Problems, IEEE Press, 2000, pp [3] M. F. McGranaghan and D. R. Mueller, Voltage Sags in Industrial systems, IEEE Trans. On Industry Applications, Vol. 29, No. 2, March/April 993, pp [4] IEEE Std : Recommended Practice or Monitoring Electric Power Quality, ISBN [5] C. Li, T. Tayjasanant, W. u and. Li, Method or voltage sag source detection by investigating slope o the system trajectory, IEE Proc. Gener. Transm. Distrib., Vol. 50, No. 3, May 2003, pp [6] A. C. Parsons, W. M. Grady, E. J. Powers and J. C. Soward, A Direction Finder For Power Quality Disturbances Based Upon Disturbance Power and Energy, IEEE Transactions On Power Delivery, Vol. 5, No. 3, July 2000, pp [7] W. Khong,. Dong and. Chen, Voltage Location Based on Instantaneous Energy Detection, Proc. O The 8 th Int. Power Engineering Conerence 2007, 3-6 Dec 2007, pp [8] H. Liao, Voltage sag Source Location in High-Voltage Power Transmission Networks, Proc. IEEE Power and Energy Soceity General Meeting- Conversion and Delivery o Electrical Energy in the 2 st Century, July 2008, pp. -4. [9] McGranaghan, M. F, Mueler, D. R. & Samotyj,. Voltage Sags in Industrial Systems. IEEE Transaction Industry Application. M. J. 993, 29 (2), pp VII. BIOGRAPHIES N. Hamzah received her B.Eng. (Hon) and M.Sc. (Power System), rom University o Wales Institute o Science and Technology, UK in 988 and University o Malaya, Malaysia in 993 respectively. She obtained a PhD in Electrical Engineering (Power Quality) rom the Universiti Kebangsaan Malaysia in She is an associate proessor and head o program at the aculty o Electrical Engineering, University Teknologi MARA, Malaysia. She has published more than 50 technical papers in national and international conerences and journals. Her research interests include power quality studies, application o advanced signal processing in power system and artiicial neural network studies. A. Mohamed received her B.Sc.Eng. rom King s College, University o London in 978 and M.Sc. and PhD (Power System), rom University o Malaya, Malaysia in 988 and 995, respectively. She is currently a proessor at Universiti Kebangsaan Malaysia (UKM), Malaysia. Her current research interests are in power quality and other power system studies. A. Hussain received her BSc. in Elect. Eng. Louisiana State University, USA, Sc in System and Control, UMIST, UK and PhD, Universiti Kebangsaan Malaysia (UKM) in 985, 989 and 997, respectively. She is currently a proessor at Universiti Kebangsaan Malaysia, Malaysia. Her research interests are signal processing, neural networks and their applications, which include power quality. ISBN: IMECS 2009