Current Component Index Algorithm for Voltage Sag Source Localization

Transcription

1 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. Current Component Index Algorithm or Voltage Sag Source Localization N. Hamzah, Member, IAENG, IEEE, A. Mohamed, Senior Member IEEE, A. Hussain, IEEE Abstract Voltage sag can cause hours o downtime, 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 algorithm to locate the source o voltage sag in 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. The proposed method has been veriied by simulations and real data. V Index Terms Voltage sag, Double source, Current I. INTRODUCTION OLTAGE sag is a temporary decrease in the RMS voltage magnitude between..9 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 [], 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 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. Manuscript received November 8,. N. Hamzah is with the Universiti Teknologi MARA, 445 Shah Alam, MALAYSIA. (phone: ; ax: ; noralizah@salam.uitm.edu.my. Mohamed, is with Universiti Kebangsaan Malaysia, 436 Bangi, MALAYSIA. ( azah@vlsi.eng.ukm.my. A. Hussain is with Universiti Kebangsaan Malaysia, 436 Bangi, MALAYSIA. ( aini@vlsi.eng.ukm.my. ISBN: ISSN: (Print; ISSN: (Online Locating the source o voltage sag is important beore any voltage sag mitigation algorithm 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 troubleshooting, 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 algorithm 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 threephase-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 the ault on the distribution power system. The development o the new algorithm based on a single source system was published in [9]. The new algorithm proposed in this paper is or a double source system. The proposed algorithm utilizes the phase angle dierence between current and voltage or power actor angle is used to determine the voltage sag source. In the method, magnitude o currents and phase angles o voltages and currents are measured at the measuring point. The current magnitude is then multiplied with the cosine o the power actor angle and the product is then plotted against WCE

2 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. 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 also on real data. The data are processed via MATLAB codes. E φ δ I I X δ I E φ δ II. VOLTAGE SAG SOURCE LOCATION FOR DOUBLE SOURCE SYSTEM ANALYSIS N In this section, development o voltage sag source indicator is elaborated based on double source system. Most o power system network has more than one source, hence, double sources network are very commonly used worldwide. Figure shows a single line diagram o a double source system. There are two sources in the system, namely source and source Source E φ δ Source E φ Figure Double sources system During Fault A. Development o Current Component Index (CCI In this research steps taken to develop the Current Component Index (CCI algorithm is based on the single line diagram in Fig. 3. In the igure, short circuit ault and the monitoring point is assumed to occur at point X and at M A respectively. The current beore and ater ault occurs will be considered and the current is assumed to low rom source E to source E. N E φ X M A E φ Figure Double Source System, beore ault occurs V From Figure, beore ault occurs, current lows rom E to E and is given by, E φ E φ δ In which, δ is the impedance between the sources, E φ and E φ is the source rom and respectively. Beore ault occurs, current lows in a loop rom source to source, assuming that E > E. When ault occurs at point X, automatically ault impedance will be created as shown by δ in Figure. In the igure, two loops will be created as well. The voltage at X is approaching zero and current I, I and I will be developed. Current I lows rom source E φ, current I lows rom source E φ and I is the current through the ault impedance to the ground. The direction o current I is similar to the direction o current beore since the currents low rom the same source E towards point X. I, impedance is much higher than the ault impedance, thereore current I and current rom source E will low towards akan. Otherwise, current I will be seen as lowing rom source E towards. The concept o these directions o currents as either lowing rom source E or E during ault will be employed to develop an indicator to locate the source o voltage sag in this paper. ( Figure 3 Double Source System and Monitoring Point at M A Beore short circuit ault occurs at point X, employing Kircho Current Laws, current at M A is given by, From (, E φ E φ I α ( ( T * I is denoted as ollows, E ( φ E ( φ E ( φ + E ( φ + I (3 T ( T Multiplying both sides o (3 by the voltage at the monitoring and by considering the real part will yield, V VE VI cos( cos( φ VE cos( φ T By dividing both sides o (4 with V, the current magnitude and its direction can be obtained as, E I cos( cos( φ E cos( φ T (4 (5 ISBN: ISSN: (Print; ISSN: (Online WCE

3 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. By employing (5, the current beore ault at monitoring point M A can be written as, E cos( α φ E cos( α φ b (6 T Subsequently, by considering the impedance during ault as, then at the monitoring point M A, the current component index is given as, E cos( φ (7 Equation (7 is the current component during ault. By dividing (7 and (6 the ollowing equation is obtained, I cos( I cos( b E cos( φ E cos( E cos( α φ α φ T These angles φ, φ are the double source angles whereas and α is the voltage and current angle at the monitoring point respectively. Assuming that R<<X these values are very small. It is commonly practiced that the source voltage angle is used as reerence and approaching zero. Thus, the right hand side o (8 can be written and simpliied as, E E (9 T b E E E E T Since normally the value o T > then T >, and also E that E >E will yield >, thus (9 can be written E E as, b > T (8 ( Quotation Icos(- and Icos(- b is the current component index during ault (CCI and beore ault (CCI b respectively. Thereore ( can be written as. CCI > ( CCI b From (, it can be concluded that at the beginning o voltage sag, i the current is higher than the current beore ault, i.e. CCI >CCI b, the source o voltage sag is located in ront o the monitoring point. The ollowing derivation is or the source o voltage sag behind the monitoring point. Figure 4 shows the ault at point X and the monitoring point is at M B. E φ X E φ M B Double Source System For Voltage Sag analysis and Monitoring Point at M B In the case o the source o ault is behind the monitoring point, M B, current beore the occurrence o the ault is rom E to E and is given in (7. During the occurrence o the ault at point X, in which the value o << the current will low to the ground through ault impedance, and thus current at the monitoring point M B is actually rom the source E to the monitoring point X. Hence, the value o current rom E to point X, is given as, E φ I α ( ( α * From (, I can be quoted as, ( φ E ( φ + E I (3 ( Multiplying both sides o (3 with the voltage at the monitoring V, and only consider the real part will yield, VE cos( φ + V (4 By dividing both sides o (4 with V, the current component at the monitoring point M B is given as, E cos( α φ I cos( α (5 Equation (5 shows the current component at monitoring point M B generated rom the source E, in which obviously the value is negative hence lowing rom E to X as compared to the positive value o current component beore ault as shown in (6, which lows rom E to E. Quotation Icos(- and Icos(- b is the current component index during ault (CCI and beore ault (CCI b occurs respectively. Thereore at monitoring point M B, at the beginning o voltage sag it can be shown that CCI <CCI b. The conclusion can be made or the double source system is that, i at the beginning o the voltage sag, the current component index during sagging is lower than the current component beore sagging, i.e,, the location o the source o voltage sag is in ront o the monitoring point. By reerring, the monitoring point is at M B. On the other hand, i at the beginning o the sagging, it is observed that, the location o the source o voltage sag is to be in ront o the monitoring point, which is M A in this case. To demonstrate the application o the CCI, the Icos(- is plotted against time. Figure 5a shows the ISBN: ISSN: (Print; ISSN: (Online WCE

4 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. plot when the location o voltage sag source is in ront o the monitoring point. On the hand, Figure 5b represents the plot when the location o voltage sag source is in behind the monitoring point. The beginning and end o the voltage sag is denoted by t and t respectively. PCC FC MB I cos ( -α I cos ( - CCI s>cci bs I cos ( -α I cos ( - CCI s <CCI bs MA MA FB FA MB t t a Masa Figure 7 Current Component Index For Double Source System ain ront o monitoring point b Behind the monitoring B. The Implementation O The Current Component Index 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 measuring meter at pre-ault and during ault times. (iiicalculate the values o Icos(-α or a ew cycles o pre-ault and during ault durations. (ivgraphically plot coordinates o Icos(-α against time o a ew cycles o pre-ault and during ault durations. Check the polarity o Icos(- bs and Icos(- s 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, the source o voltage sag is in ront o the monitoring point. III. 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 and 3 kv, 7.5MVA at 5 Hz requency. By reerring to Fig. 6, three ault locations have been considered, which are FA, FB and FC, whereas the monitoring points are PCC, MA, MA, MB and MB. Two types o aults have been simulated namely balanced and unbalanced aults. The three phase balanced aults have been simulated or about.3 seconds. On the other hand the unbalanced aults simulated are the single line ault (SLF and double line ault (DLF. t b t Masa Figure 8 Double source 3 bus system A. Balanced Faults 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 DOUBLE SOURCE SYSTEM Fault Monitoring points Location In ront o ault location Behind ault location FA PCC, MA MA, MB, MB FB PCC, MB MA, MA, MB FC - PCC, MA, MA, MB, MB Fig. 9 shows the plots o CCI against currents or monitoring points at MA, MA and MB or balanced aults at point FA. In Fig. 9a, it can be seen at the beginning o voltage sag, the value o CCI beore sag is higher than the value o CCI during sag, i.e,. This result indicates that the source o voltage sag is in ront o the monitoring point. The results or the monitoring at points MA and MB are plotted in Fig. 7b and c show that at the beginning o voltage sag,. Both results show that the source o voltage sag is behind the monitoring points MA and MB. These results are in a good agreement with the observation in Table I. Hence, it has been proven that the CCI can be used to locate the source o voltage sag. Time(s a Time(s b Figure 7 Results o CCI or Balanced a Fault at FA with monitoring points at a MA b MA and c MB. I cos (-α (ka 3 Time(s c ISBN: ISSN: (Print; ISSN: (Online WCE

5 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. The credibility o CCI algorithm has also been veriied by applying a balanced ault at FB with monitoring points are at MB, MB and MA. Figure 8a shows. This result indicates that the source o voltage sag at FB is in ront o the monitoring point, i.e. at MB. On the hand, Figures 8b and 8c show that which indicate the source o voltage sag is behind the monitoring points. These results are also in good agreement with the observation in Table I, thus prove the credibility o the CCI in determining the source o voltage sag. a b c a B. Unbalanced Faults b c Figure 8 Results o CCI or Balanced Fault at FB with monitoring points at a MB b MB and c MA. In this paper, results rom unbalanced ault are also presented or various monitoring points o Fig. 6 to urther veriy the CCI algorithm. Table II presents the details o ault location and monitoring points simulated or the test system in 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 unbalanced aults at FA, FB and FC. This inormation is then used to justiy the accuracy o the simulation results using the CCI. TABLE II DETAILS OF UNBALANCED FAULTS FOR A DOUBLE SOURCE SYSTEM Fault Monitoring points Location In ront o ault location Behind ault location FA PCC, MA MA, MB, MB FB PCC, MB MA, MA, MB FC - PCC, MA, MA, MB, MB The results o unbalanced aults created at FA are presented and analyzed. In Fig. 9a, it can be seen at the beginning o voltage sag, the value o CCI beore sag is higher than the value o CCI during sag, i.e,. This result indicates that the source o voltage sag is in ront o the monitoring point. On the other hand results plotted or the monitoring points at MA and MB are shown in Fig. 9b and c respectively. Both results show. These results imply that the source o voltage sag is behind the monitoring points MA and MB. By comparing the details observation in Table II, these results are correct. Figure 9 Results o CCI or Unbalanced Fault at FA with monitoring points at a MA b MA and c MB. C. Real data The CCI algorithm has also been veriied using real data obtained rom a utility. Figure a and b depict the voltage sag waveorm and its respective CCI plot. In Fig. a at the beginning o the sag, t.7s it is observed that in which it indicates that the source o voltage sag is behind the monitoring point. This result is in aggreement with the inormation rom the utility that the source o voltage sag is behind the monitoring point. Another sample o real data depicted in Figure also shows that in which it indicates that the source o voltage sag is behind the monitoring point. This result also aggrees with the inormation obtained that the source o voltage sag is behind the monitoring point. Thus both real data have veriied the validity o the CCI in determining as whether it is behind the monitoring point or vice versa. Voltage (kv a Voltan (kv Voltage (kv I cos (-α b Masa (s.. -. Beginning o voltage sag a Masa (s b Figure a Original Voltage sag waveorm b CCI plot ISBN: ISSN: (Print; ISSN: (Online WCE

6 Proceedings o the World Congress on Engineering Vol II WCE, July 6-8,, London, U.K. Voltage (kv Voltage (kv I cos (-α Voltan (kv a b Masa (s Beginning o voltage sag a Masa (s a Figure a Original Voltage sag waveorm b CCI plot IV. CONCLUSION This paper has presented a new algorithm to locate the source o voltage as seen at the monitoring points by examining the value o the current component index (CCI at the beginning o the voltage sag. From the results, it has been proven that the CCI satisy % o the voltage sag source location or balanced and unbalanced aults or the double source system. The CCI algorithm also been veriied using real data. 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 double source distribution system. ACKNOWLEDGMENT The authors would like to express heartiest appreciations to Universiti Teknologi MARA and its Research Management Institute or the support during the research. The authors also grateully acknowledge Universiti Kebangsaan Malaysia (IRPA code --4-EA88 or inancial support on the project. [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, pp [7] W. Khong, X. Dong and. Chen, Voltage Sag Source Location Based on Instantaneous Energy Detection, Proc. O The 8 th Int. Power Engineering Conerence 7, 3-6 Dec 7, 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 st Century, -4 July 8, pp. -4. [9] N. hamzah. A. Mohamed, A. Hussain, Development o New Algorithm or Voltage Sag Source Location, Proc. Int. MultiConerence o Engineers and Computer Scientists 9, 8- March 9, pp 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 (Electrical and Electronics rom the Universiti Kebangsaan Malaysia in 6. She is an associate proessor at the aculty o Electrical Engineering, University Teknologi MARA, Malaysia. She is actively publishing technical papers in the national and international conerences and journals and also serves as reeree internationally journal. 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 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. REFERENCES [] M. H. J. Bollen, Voltage Sags in Three-Phase Systems, IEEE Power Engineering Review, September, pp.8-5, 7. [] M. H. J. Bollen, Understanding Power Quality Problems, IEEE Press,, pp [3] M. F. McGranaghan and D. R. Mueller, Voltage Sags in Industrial systems, IEEE Trans. On Industry Applications, Vol. 9, No., March/April 993, pp [4] IEEE Std : Recommended Practice or Monitoring Electric Power Quality, ISBN [5] C. Li, T. Tayjasanant, W. Xu and X. Li, Method or voltage sag source detection by investigating slope o the system trajectory, IEE Proc. Gener. Transm. Distrib., Vol. 5, No. 3, May 3, pp ISBN: ISSN: (Print; ISSN: (Online WCE