TRANSMISSION PROTECTION SCHEMES FOR TRANSMISSION SYSTEMS USING DWT 1 T.Jayanth, 2 Srikanth Rajasekar, 3 G.MadhusudhanaRao,

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1 TRNSMISSION PROTETION SHEMES FOR TRNSMISSION SYSTEMS USING DWT 1 T.Jayanth, 2 Srianth Rajasear, 3 G.MadhusudhanaRao, 1 sst.engineer, PGENO, 2 KIT-KKD, 3 Prof of EEE MR Group of Institutions gurralamadhu@gmail.com, jayanthr@gmail.com, srianth.chowdary999@gmail.com, bstract: novel approach to protection of TEED transmission lines using Wavelet transforms with multi resolution analysis has been presented in this paper. Faults on the transmission line should be detected and classified rapidly and accurately to maintain system reliability. Wavelet analysis is used for signal processing. Synchronized sampling of the three phase voltage and current signals at the three ends of the TEED transmission line over a moving window length of half cycle is carried out using GPS cloc. Fault Indices are calculated based on the sum of local and remote end detail coefficients, and compared with threshold values for different locations and different types of faults to detect and classify the faults. For estimation of approximate fault location, the ratios of absolute maximum and minimum detail D1 coefficients at all the three ends are compared. The algorithm has been tested for different fault locations and the results are found to be satisfactory in terms of reliability. Key Words: Wavelet Transformers, Transmission Lines, TEED circuits, Fault detection, Sampling Waveforms I. INTRODUTION TO PROTETION SYSTEMS: The increased growth of power systems both in size and complexity has brought about the need for fast and reliable relays to protect major equipment and to maintain system stability.the conventional protective relays are either of electromagnetic or static type. The electromagnetic relays have several drawbacs such as high burden on instrument transformers, high operating time, contact problems etc. protective system protects the power system from deleterious effects of a sustained fault, which occurs as a random event. If some faulted power system component (line, bus, transformer, etc.) is not isolated from the system quicly, it may lead to power system instability or brea up of the system through the action of other automatic protective devices. protection system must therefore remove the faulted element from the rest of power system as quicly as possible. lthough a protection system is mainly relays, it consists of many other subsystems, which contribute to the fault removal process. The circuit breaer actually isolates the faulted circuit by interrupting the current at or near current zero. modern extra high voltage (EHV) circuit breaer can interrupt fault currents of the order of 1, amperes at system voltages of up to 8 V. The transducers (current and voltage transformers, or T s and VT s) contribute another major component of the protective system. They are necessary because the high magnitude currents and voltages of the power system must be reduced to more manageable levels in order to drive low energy devices such as relays. Last and the most important component of protection system is the relay. This is a device which responds to the condition of its inputs (Voltages, currents) in such a manner that it provides appropriate output signals to trip circuit breaers when input conditions correspond to faults for which the relay is designed to operate. Relays are the logic elements in the entire protection system. II. PROTETION OF TRNSMISSION LINES: Usually the power stations are situated far away from the load centers, resulting in hundreds of ilometer length of overhead lines being exposed to atmospheric conditions. The chances of faults occurring due to storms, falling of external objects on the lines, flashover resulting from dirt deposits on insulators, etc., are greater for overhead lines than for other parts of the power system. bout 5 % of total faults occur on overhead lines. The time needed to determine the fault point along the line will affect the quality of power delivery. Therefore, an accurate fault location on the line and classification is an important requirement for a permanent fault. If the minimum fault current possible within the zone of protection is greater than the maximum possible load current, then the operating principle of the relay is defined as follows: I >= I p fault in zone, trip. < I p no fault in zone, do not trip. Where I is the current in the relay I p is the setting. Wavelets are a recently developed mathematical tool for signal processing. ompared to Fourier analysis, which relies on a single basis function, a number of basic functions of a rather wide functional form are available in wavelet analysis. The basic difference is that, in contrast to the short time Fourier transform which uses a single analysis window; the WT uses short windows at high frequencies and long ISSN:

2 windows at low frequencies. Prediction of line impedance from the phasor components of the distorted voltage and current signals estimated using WT with multi resolution analysis (MR) approach is more applicable for real time signal processing as the chosen mother wavelet can be employed as a pair of complementary finite-impulse response (FIR) filters. Wavelet Transform (WT) has the ability to decompose signals into different frequency bands using multi resolution analysis (MR). It can be utilized in detecting faults and to estimate the phasors of the voltage and current signals, which are essential for transmission line distance protection. III. TEED ircuits Electrical supply line protection apparatus used with Teed circuit supply lines having three terminals, comprising: a unit at one terminal and the other two are at each of the other terminals. road band communication lins between the three units and separate from the supply lines. Three terminal lines, or Teed circuits, often offer considerable economic, technical and environmental advantage over 2-terminal lines. Systems 1, 2 and 3 represent the three external equivalents and L I, L II and L III are the three line sections of the three-terminal line shown in Fig.2.1. Fig 2. urrent In feed The system shown in Fig2 has an out feed current at terminal rather than an in feed current. In this case, the apparent impedance seen by the relay at terminal for a fault at terminal is 1.5 ohms, which is less than the actual impedance to the fault. n additional problem is also introduced by the current out feed at terminal ; since the current flows out of the line at, a forward looing distance relay will not see this internal fault, in fact, if there is a blocing unit at, it may see the internal fault as an external fault and thus prevent tripping. Fig1: Three-terminal lines with the external systems a) Problems in Protection of Teed ircuits The protection of multi-terminal lines is not as simple as that of two-terminal lines. They usually experience additional problems caused by the intermediate in feed from the third terminal, an out feed, different line lengths to the tee point, etc. The relay first zone reach may not even extend beyond the tee point in some under reach cases. onsider the system shown in Fig2. Due to the in feed current at terminal, the distance relay at terminal will see an apparent impedance of 3 ohms, which is greater than the actual impedance to the fault. Fig3 urrent Out feed IV. WVELET NLYSIS Wavelet analysis represents the next logical step: a windowing technique with variable-sized regions. Wavelet analysis allows the use of long time intervals where we want more precise low-frequency information, and shorter regions where we want highfrequency information. Wavelet analysis does not use a time-frequency region, but rather a time-scale region. ISSN:

3 The DWT is considerably easier to implement when compared to the WT. the basic concepts of the DWT will be introduced in this section along with its properties and the algorithms used to compute it. nd the discrete wavelet transform is given by Fig 4: Wavelet nalysis ) Definition of Wavelet wavelet is a waveform of effectively limited duration that has an average value of zero. ompared to sine waves, the basis of Fourier analysis, which do not have limited duration (they extend from minus to plus infinity) and are smooth and predictable, wavelets tend to be irregular and asymmetric. Fig 5: Sine Wave and a Wavelet wave Fourier analysis consists of breaing up a signal into sine waves of various frequencies. Similarly, wavelet analysis is the breaing up of a signal into shifted and scaled versions of the original (or mother) wavelet. V) THE DISRETE WVELET TRNSFORM (DWT) Need for Discrete Wavelet Transform lthough the discretized continuous wavelets transform enables the computation of the continuous wavelet transforms by computers, it is not a true discrete transform. s a matter of fact, the wavelet series is simply a sampled version of the WT, and the information it provides is highly redundant as far as the reconstruction of the signal is concerned. This redundancy, on the other hand, requires a significant amount of computation time and resources. The Discrete Wavelet Transform or Dyadic Wavelet Transform (DWT), on the other hand, provides sufficient information both for analysis and synthesis of the original signal, with a significant reduction in the computation time. The DWT is considerably easier to implement when compared to the WT. DWT ( m, n) x[ ] ( na b m a a m / 2 m --- (1) y comparing the eq (1) with general equation for impulse response (FIR) digital filter y ( n) x[ ] h[ n ] / c (2) zt can be seen that Ψ () is the impulse response of Low pass digital filter with transfer function Ψ (ω). For a = 2, each dilation of Ψ () effectively halves the bandwidth of Ψ (ω). Multilevel DWT filter bans implement the DWT eqn (1) in the forward transform stage and the IDWT in the reverse transform stage. ) Multi-Resolution nalysis In MR, wavelet functions and scaling functions are used as building blocs to decompose and construct the signal at different resolution levels. The wavelet function will generate the detail version of the decomposed signal and the scaling function will generate the approximated version of the decomposed signal. That is wavelet function constitutes the high pass digital filter and the scaling function constitutes low pass digital filter. Let c (n) be a discrete time signal recorded from a physical measuring device. This signal is to be decomposed into a detailed and smoothed representation. From the MR technique, the decomposed signals at scale 1 are c 1 (n) and d 1 (n),where c 1 (n) is the smoothed version of the original signal (or approximation), and d 1 (n) is the detailed representation of the original signal c (n) in the form of wavelet transform coefficients. They are defined as c1( n) h( 2n) c( ) d1( n) g( 2n) c( ) (3) (4) Where h (n) and g (n) are the associated filter coefficients that decompose c (n) in to c 1 (n) and d 1 (n) respectively. That means in first stage decomposition the original signal is divided into two halves of frequency bandwidth. The next higher scale ISSN:

4 onn1 onn3 onn5 onn2 onn4 onn6 onn1 onn4 onn2 onn5 onn3 onn6 onn2 onn4 onn6 onn1 onn3 onn5 decomposition is now based on the signal c 1 (n). The decomposed signal at scale 2 is given by c2( n) h( 2n) c1( ) (5) d 2( n) g( 2n) c1( ) (6) Higher scale decompositions are performed in the same way as described above. Thus the procedure is repeated until the signal is decomposed to a pre-defined certain level. The set of signals thus attained represent the same original signal, but all corresponding to different frequency bands. source to TEE junction. The system is simulated using MTL. Source 1 Source 2 Fault TEE point Source 3 Fig 7: Simulated Power System VIII.SIMULTION RESULTS ) Modeling of transmission line typical 5 KV transmission system used in the simulation studies presented herein. It consists of three transmission line sections of 15 m each, fed from 5KV sources from three ends. The nominal power frequency is 6Hz. The single line diagram of the considered power system is already shown in section (7). The transmission line is modeled as five Π sections, each of 3Km length from each source to TEE point, connected in tandem. The system is simulated for different fault conditions using Matlab software pacage. 3-Phase source2 3-Phase Source1 Measurements 15 m Transmission line 15 Km Transmission line 15 Km Transmission Line Measurements1 Measurements2 3-Phase Source3 Fig6: Multi Resolution nalysis VI. Fault Detection Technique ) Transmission system design The single line diagram of the system along with the various blocs of the proposed scheme considered is shown in Fig6. The transmission line to be protected in the system connects three systems represented by equivalent voltage source behind constant impedance. The transmission line is modeled as T shape and is represented in three sections each of five pi-sections connected in cascade form voltage Fig 8: Transmission Line Model ) Detection of Fault Figures (9-11) illustrates the variations in three phase currents of three terminals in the event of ground fault on phase- at 4% of the line on phase-. ISSN:

5 Fig9: Three Phase currents at Source-1 of G fault at 4% of the line Fig1: Three Phase currents at Source-2 of G fault at 4% of the line Fig11: Three Phase currents at Source-3 of G fault at 4% of the line ) lassification of Fault However double line to ground (LLG) faults cannot be distinguished from line to line (LL) faults just by nowing the number of faulty phases. To discriminate the LLG faults from LL faults, another fault index called ground fault index I f2 is calculated, with the help of all three phase current indexes which is given by equation (8). This fault index I f2 is nothing but fault index of the zero sequence current. If double line fault involves ground the transients would appear in neutral current or the zero sequence and hence the fault index I f2 will have large value. If ground is not involved in double line fault there will not be any path for zero sequence current and hence the fault index will have very low value. This concept is made use to discriminate the LL faults from LLG faults. Hence the fault index I f2 is compared discriminate LL faults from LLG faults. I f2 for LLG faults is greater than I f2 for LL faults. This is illustrated in Figure 12. Fig12: Discrimination between LL and LLG faults VII. Testing of proposed lgorithm The proposed algorithm has been tested for all types of faults at different locations by simulating LG, LL, LLG and LLLG faults at different locations of transmission line. The testing has been done for the distances from Sources 1 to 2 and for the distances for Source 1 to 3. The variation of Fault Index I f1 with the location for all types of faults for distances from 1 to 2 is illustrated in the Figures (13-16). The variation of Fault Index I f1 with the location for all types of faults for distances from 1 to 3 is illustrated in the Figures (17-2). The fault index I f1 of all faulty phases varies with the type of fault. However its value remains greater than Threshold T h1. The fault Index of healthy phases remains less than the threshold value G-Fault Ic Ib Ia Thre Distance in Km (S1-S2) Fig13: Variations in Fault Indexes of three phase currents for G Fault ISSN:

6 Fault Diatance in Km(S1-S2) Fig14: Variations in Fault Indexes of three phase currents for Fault G-Fault Ic Ib Ia Thre Distance in Km(S1-S3) Fig17: Variations in Fault Indexes of three phase currents for G Fault -Fault G-Fault Ic Ib Ia thre Distance in Km(S1-S2) Diatance in Km(S1-S3) Fig18: Variations in Fault Indexes of three phase currents for Fault Fig15: Variations in Fault Indexes of three phase currents for G Fault G-Fault Distance in Km(S1-S2) Fig16: Variations in Fault Indexes of three phase currents for G Fault G-Fault Ic Ib Ia thre Distance in Km(S1-S3) Fig19: Variations in Fault Indexes of three phase currents for G Fault ISSN:

7 1 1 8 G-Fault Distance in Km(S1-S3) Fig2: Variations in Fault Indexes of three phase currents for G Fault IX. ONLUSIONS In this Paper, a TEED transmission line fed from the three sources is simulated in Matlab environment. Wavelet Transform based Multi Resolution nalysis approach is successfully applied for effective detection and classification and approximate location of faults in TEED transmission lines. Synchronized sampling of three phase currents and voltages at the three terminals of TEED transmission line are carried out to improve the reliability of the protection system. Three phase currents are analyzed with mother wavelet i.e., ior2.2. Detail decomposition is used for detection, classification and location purpose. Fault detection and classification is accomplished using detail D1- coefficients (obtained with ior2.2) of currents at the three ends which are added up to get resultant detail coefficients at each terminal. es are calculated using the resultant detail coefficients and compared with their respective threshold values for the purpose of detection and classification of faults in TEED transmission line. On the basis of results presented that Wavelet based protection algorithm proposed can be used to protect TEED transmission line effectively. ILIOGRPHY [1] pplication of Phase and Ground Distance Relays To Three Terminal Lines G. E. lexander J. G. ndricha, GE Protection & ontrol Malvern, P. [2] High-Resistance Faults On Multi Terminal Line:- nalysis, Simulated Studies nd n daptive Distance Relaying Scheme Y.Q. Xia. K. David K. K. Li, IEEE Transactions on Power Delivery, Vol. 9, No. 1, January [3] EMTP pplied To Evaluate Three-Terminal Line Distance Protection Schemes K. M. Silva, W. L.. Neves and.. Souza, Presented at the International onference on Power Systems Transients (IPST 7) in Lyon, France on June 4-7, 27. [4] Digital Differential Protection Of Four nd More Ended Transmission Lines y ndrew Leach, urtin University of technology.e Thesis [5] Unique urrent Differential ased lgorithm For Protection Of Multi-Terminal Lines 1-Fahri, Senior Member, IEEE.Elagtal, 21 IEEE. [6] omputer-ided Design Of New Nonunit Protection Scheme For EHV Teed ircuits.m. arter R. K. ggarwal.t. Johns Z.Q. o, IEE Proc.- Gener. Transm. Distrib., Vol. 143, No. 2, March 1996 [7] New Directional omparison Technique For The Protection Of Teed Transmission ircuits D R M Lyonette, Z Q o, G Weller, F Jiang, IEEE [8] Fault Location of a Teed-Networ with Wavelet Transform and Neural Networs L L Lai E Vaseear H Subasinghe N Rajumar a arter J Gwyn, IEEE. [9] New Digital Relaying Scheme for EHV Three Terminal Transmission Lines M.M. Eissa, Electric Power Systems Research 73 (25) [1] Practical pproach to ccurate Fault Location on Extra High Voltage Teed Feeders R K ggarwal DV oury T Johns Kalam, IEEE Transactions on Power Delivery, Vol. 8, No. 3, July 1993 [11] New Fault Location Technique for Two and Three Terminal Lines dly. Girgis David G. Hart William L. Peterson, Transactions on Power Delivery, Vol. 7 No.1, January 1992 [12] New Fault Locator for Three-Terminal Transmission Lines Using Two-Terminal Synchronized Voltage and urrent Phasors Ying- Hong Lin, hih-wen Liu, Member, IEEE, and hi- Shan Yu, IEEE transactions on power delivery, vol. 17, no. 2, pril 22. [13] fault detection and faulted phase selection approach for Transmission lines with Haar wavelet Transform Joe-ir Jiang,Ping-Lin Fan,hing-Shan hen,hi-shan Yu nd Jin-Yi Sheu, IEEE 23. [14] Wavelet Networ-ased Detection and lassification of Transients Leopoldo ngrisani, Pasquale Daponte, Senior Member, IEEE, and Massimo D puzzo, IEEEtransactions on instrumentation and measurement, vol. 5, no. 5, october 21. [15] pplication of Wavelet Theory to Power Distribution Systems for Fault Detection James Momoh D. Tom Ruy, 1996 IEEE. ISSN: