fault location algorithm for series compensated

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Fault Location Algorithm for Series Compensated Transmission Lines

Using Fault Clearing Transients Independent of Line Parameters

Ismail Niazy, Javad Sadeh, Ebrahim Niazy [email protected], [email protected], [email protected]

Department of Electrical Engineering, Ferdowsi University of Mashhad, Iran

Keywords: Fault location, fault clearing transients, series compensated line, wavelet transform

Abstract This paper presents a novel fault location algorithm for series compensated transmission lines, which utilizes samples taken in just one terminal from voltage transients generated by fault clearing action of circuit breaker. In this algorithm, using wavelet transform, first and second inceptions of voltage traveling wave to the fault locator are detected and then actual wave speed is determined without any need to the line parameters and precise fault location is calculated. Because of using only one terminal data, algorithm does not need to communication equipments and data synchronization. Due to calculating of wave speed independent of line parameters, accuracy of algorithm is not affected by aging, change of climate and temperature, which modify wave speed. Fault resistance, fault inception angle and fault distance does not affect accuracy of the method. Extent simulations carried out with SimPowerSystem toolbox of MATLAB; confirm capability and high accuracy of the proposed algorithm. 1. Introduction

Use of series capacitor in long transmission lines is widely expanding due to

improving power-system stability, reducing transmission losses, enhancing voltage control, flexible power-flow control, reducing voltage drop, and economical reasons behind installing series capacitors [1-5]. In addition, series capacitors are used to avoid brownout of long-distance transmission lines and to suppress voltage fluctuation of flicker loads [6]. Accurate fault location reduces time and costs related to the dispatched crews searching to find the fault location and provides customers and consumers feeding with minimal interruption, also improves the performance of the power system [7] and identifies weak and vulnerable points in the system [8]. In addition, precise fault location improves the availability and reliability of the power supply [9]. Present fault location methods used to find location of fault in the transmission lines, are classified into two general categories [10]: impedance-based methods [11, 12] and traveling waves-based methods [13-16].

Use of traveling wave-based fault location algorithms is expanding due to these methods are insensitive to the fault resistance, power flow and source impedance, in addition, they are more accurate compare to impedance methods [13]. However, conventional

10-E-CAP-1534

Fault Location Algorithm for Series Compensated Transmission Lines Using Fault Clearing Transients Independent ...

25th International Power System Conference

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traveling wave methods, which are used to find location of fault in transmission lines, are sensitive to the fault inception angle, noises and faults occurred on the other lines and reflected waves from other terminals and equipments, which are outside from the fault locator and fault point and have problem with faults close to the relay [14, 17]. Utilizing fault-clearing transients is an alternative to eliminate such problems, therefore, in some papers it is suggested to use fault-clearing transients instead of fault-generated transients in order to take advantages of traveling wave methods whilst avoid their problems [14, 15, 17].

Because of non-linear characteristic of metal oxide varistor which is installed in parallel with series capacitor, impedance-based methods used to find location of fault in series compensated transmission lines, have difficulties in determining accurate fault location [3, 18].

In this paper, a novel algorithm is proposed to find location of faults occurred in the transmission lines, which are compensated with series capacitors. Proposed method utilizes voltage transients generated by clearing action of circuit breaker, which are sampled from one terminal. When the line is de-energized with opening action of circuit breaker, using wavelet transform, first and second inceptions of voltage traveling wave to the fault locator are detected and then the actual propagation speed of the wave in the transmission line is calculated independent of line parameters and finally accurate fault location is calculated. Presented method does not need to communication systems and data synchronization and because of sampling from just voltage in one terminal, compare to algorithms, which utilize voltage and currents and algorithms, which utilize data taken from both terminals is more economic. Presented algorithm, compare to algorithms that use voltage and current samples, has fewer measurement errors, because this algorithm uses less measurement instruments.

Extensive simulations carried out in MATLAB software confirm capabilities and accuracy of proposed method in calculation of

fault location for different faults and conditions of the system. Proposed method is insensitive to the fault inception angle, fault resistance, source impedance, power flow, faults occurred in adjacent lines, waves reflected from other equipment and faults occurred in other lines and is capable to calculate faults occurred close to fault locator.

2. Proposed algorithm

Any sudden change in the power system, such as occurrence of fault and clearing action of circuit breaker, generates voltage and current traveling waves that propagate in both directions from the fault point over the transmission line. Mentioned signals propagate in transmission line to receive to the discontinuity points such as buses and fault point. On these points, some portion of the wave is let through and reminder is reflected and travels back. This condition is continued to wave attenuation [13].

When fault occurs in transmission line, traveling wave are generated which travel in transmission line. After fault detection, circuit breaker is opened in order to de-energize the transmission line, which is followed by generation of traveling waves that propagate from circuit breaker to the fault point and remote terminal. In order to distinguish between the fault generated transients and the fault clearing transients, Fig. 1 illustrates mentioned signals for the fault occurred at t = 20 msec and cleared at t = 70 msec. In addition, Fig. 2 obviously illustrates the lattice diagram of the fault clearing signals with the reflected and refracted signals from the fault point and remote terminal.

Fig. 1. Fault generated and fault clearing transients



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Fig. 2. Lattice diagram of the traveling waves generated by circuit breaker opening action

Voltage traveling waves in distance x from

fault locator in the time t in the lossless line can be described as the sum of two forward and backward waves as follow:

, (1)

where f1 and f2 are forward and backward waves, respectively; and u is voltage signal and v is the propagation speed of the wave. And,

(3)

√ (4)

where is the characteristic impedance of the transmission line and L and C are inductance and capacitance of the line per unit length. Nearly in all traveling wave-based fault location algorithms, which take sample just from one terminal, it is essential to compute wave speed using line parameters utilizing Eq. (3). It is clear that any change in the line parameters leads to change in wave speed. However, in most algorithms changes caused in the line parameters is not considered. Thus, the accuracy of the algorithms, which are based on the line parameters, will vary with aging, temperature and climate change and any other factor that changes the line parameters.

In this paper a novel fault location algorithm is presented, which despite of using only one terminal data, does not require to the line parameters. Proposed algorithm takes sample from transient voltage signals generated by circuit breaker opening action, then using modal decomposition, decomposes three phase voltage into modal components. It is available to detect the first and second

inceptions of alpha mode of voltage traveling wave signals to the fault locator using details of first level of wavelet transform. Thereupon real-time and accurate wave speed is calculated and precise fault location will be calculated.

In the three phase systems, forward and backward equations of the voltage and current are dependent to the voltage and current of the three phases and it should be considered that there is strong coupling between voltages and currents of phases. Presented algorithm in this paper, decomposes three phase voltages to the modal components, which can be analyzed independently as single-phase system. For this purpose, it is possible to use following relation to decompose voltage signal to the modal components:

(5)

where U is voltage component and the indices modal and phase are related to the modal and phase quantities; and T is the transformation matrix. For three-phase fully transposed line assumed in this paper, the Clarke’s transformation matrix can be used to obtain the ground and aerial mode signals from the three-phase transient signals [18]:

√

1 1 1√2 1 √2⁄ 1 √2⁄0 √3 2⁄ √3 2⁄

(7)

where U0 is the ground mode voltage component, and Uα and Uβ are known as the aerial mode voltage components for transposed lines. After that phasor components are decomposed to the modal components, it is possible to detect first and second inceptions of traveling wave, generated by fault clearing action of circuit breaker, using wavelet transform. The wavelet analyzes the signal at the different frequency bands with different resolutions by decomposing the signal into a coarse approximation and detail information and again each level can be decomposed more precise as shown in Fig. 3. In this paper, only details of first decomposition of Db4 transform are used to calculate the fault location.



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3. Fault location algorithm in series compensated

transmission lines

A new fault location algorithm is presented in this paper, which locates fault point in transmission lines compensated with series capacitor without using line parameters. To evaluate proposed method, a 50 Hz power system including a 300 km length transmission line with parameters provided in appendix is considered which series capacitors are installed exactly in the middle of transmission line. The compensation degree of 50% is obtained using capacitor banks with capacity of 51 μF installed on each phase. Fig. 4 shows such compensated transmission line with a three-phase to ground fault occurred.

Fig. 4. Series compensated transmission line with

three-phase to ground fault

When fault occurs in transmission line, circuit breaker is opened in order to deenergize the line. Opening of circuit breaker is followed by generation of high frequency voltage traveling waves, which propagate from circuit breaker to the fault point and remote bus. Voltage signal first arrives to the fault point, on this point some portion of the wave is reflected back to the fault locator and remainder refracts behind of the fault point and propagates to the remote terminal. Hence, after that circuit breaker is opened, two traveling waves arrive to the

fault locator. Now it is possible to calculate wave speed and fault location by detection of two mentioned inceptions and measuring the time of inceptions.

After that circuit breaker is opened, a transient voltage signal is generated and propagates to the fault point. Time of generation of mentioned signals is considered as the origin of time t = 0 as shown in Fig. 2. In the fault point, a portion of wave is reflected and reminder will refract. Reflection and refraction coefficients are obtained by:

(8)

1 (9)

where and Rf are the characteristic impedance of transmission line and fault resistance, respectively. If fault is in the second half of the transmission line, first inception to the fault locator is related to the wave, which is reflected from the fault point, and second wave is one reflected from the remote terminal. In this case, considering lattice diagram provided in Fig. 2, the times T1 and T2 are related to the mentioned incepted waves and propagation speed of traveling wave can be obtained by:

⁄ (10)

where is length of transmission line. Having actual wave speed and considering Fig. 2 it is possible to calculate fault location as follows:

(11)

It is clear from Eq (11) that in this paper, propagation speed of traveling wave is calculated independent of line parameters. Therefore, any change in the parameters of transmission line caused by aging, climate, temperature and pressure changes, does not affect the accuracy of proposed method.

If fault is in the first half of the transmission line, as illustrated in Fig. 5, first inception to the fault locator belongs to reflection from fault point and second inception is reflection from fault point too, so does not belong to reflection from remote terminal.



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Fig. 5. Lattice diagram for fault occurred in the first

half of transmission line

In this case belongs to wave reflected from fault point and belongs to this wave, which is reflected again from fault point. Therefore, it is necessary to identify this condition to judge that fault is occurred in the first half of transmission line. In such condition the time of second inception to the fault locator is twice of the first one, therefore simply it is identified that fault is in the first half. Now in order to calculate wave speed and fault location, it is essential to detect the wave reflected from remote terminal. For faults occurred in the first half of transmission line, the distance traveled by wave to arrive to the remote terminal and reflect to the fault locator is at least twice the distance to travel from fault locator to the fault point. Therefore, frequency of first incepted wave to the fault locator that belongs to the wave reflected from fault point which, is illustrated with in Fig. 5, is at least twice of the frequency of wave reflected from remote terminal, which is illustrated with . Theses frequencies are as follows:

(12)

(13) where x is the distance of fault from fault locator and is required time for traveling wave to arrive to the fault point and reflect and is the elapsed time to arrive to the remote terminal and reflect, respectively; and f1 and f2 are related frequencies, respectively. For the fault occurred in the first half of the transmission line, it is clear that and thus considering (12) and (13), it is clear that f 1 ≥ 2× f2. Now using a low pass filter, it is possible to eliminate f1 , therefore the

existent dominant frequency merely will be f2, thus, simply is calculated and wave propagation speed will be specified. For the fault occurred exactly in the half point, algorithm is similar to faults occurred in the first half of the line. Fig. 6 shows proposed filtering system.

Fig. 6. Proposed filter for extracting f2

Computational error for the distance calculated as fault location can be obtained by: % C A

T 100 (14)

4. Evaluation of proposed algorithm

To evaluate performance of proposed algorithm, extensive simulations been carried out using SimPowerSystem toolbox of MATLAB software. For this purpose a 132 kV, three-phase system similar to the system shown in Fig. 4 with 300 km length is considered. Simulations for different single, double and three phases to ground faults and similarly for double and three phases faults occurred in different distances from fault locator are performed. Fault resistances prompted to change between zero and 100 Ω and fault inception angles between zero and 90˚ are considered.

As an example, if a double-phase to ground fault with resistance of 10 Ω and 30˚ fault inception angle occurs in distance 210 km far from fault locator, three phase voltage signals and their modal decomposition are shown in Figs. 7 and 8, respectively. It is assumed that fault occurred in 30 msec and cleared at 70 msec. Applying wavelet transform, details and approximations of alpha mode component of the decomposed signal are obtained which is presented in Fig. 9. Proposed algorithm just uses details of alpha mode signal in first level of wavelet transform. Using details signal, time which incident wave is generated is detected at t =



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0.070232 sec. Similarly, first and second inceptions to the fault locator are detected in t = 0.071657 sec and t = 0.072268 sec. Using Eq (10) wave speed is determined 294,659.323 km/sec and using Eq (11) fault location will be 209.944 km which has 0.0187% error.

Fig. 7. Three phase voltage signals for double phase

to ground fault occurred in distance 210 km

Fig. 8. Modal component voltage signals for double phase to ground fault occurred in distance 210 km

Fig. 9. Wavelet transform of alpha mode signal for

fault occurred in 210 km

As another example, if a single phase to ground fault with 14 Ω fault resistance and zero fault inception angle occurs in distance 140 km from fault locator, incident wave is generated in t = 0.070123 sec. First and second inceptions to the fault locator are detected at t = 0.071074 sec and t = 0.072025 sec, respectively. Therefore, T1 and T2 are determined 0.000951 sec and 0.001902 sec, respectively. Fig. 10 shows wavelet transform of alpha signal, which include first and second inceptions to the fault locator. It is clear that T2 = 2×T1 and it is identified that fault is in the first half of transmission line. Using a low pass filter, such as one shown in Fig. 11, first and second inceptions are eliminated and, wave reflected from remote terminal is detected which is shown in Fig. 12. Arrival time of this wave is detected at t = 0.072159 sec and wave speed is obtained 294,659.323 km/sec and fault location is calculated 140.110 km which has 0.037% computational error.

To demonstrate the effect of different parameters on the accuracy of proposed algorithm, the following subsections discuss about the influence of fault resistance, fault inception angle, fault location and fault type on the algorithm.

4.1 Influence of fault resistance About 80% of the faults occurred in

transmission lines are single phase to ground case [19] which the line is short circuited to the earth without or via a fault resistance. Majority of the fault location algorithms take effect from fault resistance, therefore it is essential to study the effect of fault resistance on the accuracy of proposed algorithm. To evaluate the influence of the fault resistance, simulation results for single and double-phase to ground faults occurred in distance167 km of transmission line with different fault resistances are presented in Table 1.



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Table 1.Influence of fault resistance on the accuracy of the proposed method for faults occurred in 167

km

Error % Calculated distance

Fault Resistance Fault type

-0.0093 166.972 0 Single phase to ground 0.0297 167.089 50

0.0247 167.074 100 -0.0323 166.903 0 Double phase to

ground -0.0350 166.895 50 -0.0183 166.945 100 0.0283 167.085 0 Three phase to

ground 0.0150 167.045 50 -0.0220 166.934 100

It is clear from results presented in Table 1,

that the fault resistance has no significant effect on the accuracy of the proposed algorithm. 4.2. Effect of fault inception angle

Most of traveling wave-based fault location algorithms suffer from the fault inception angle. To evaluate the influence of the fault inception angle on the accuracy of the proposed algorithm, simulations for double-phase and three-phase faults occurred in 245 km distance from fault locator with different fault inception angles are carried out, and the obtained results are shown in Table 2.

Table 2.Effect of fault inception angle on the accuracy of proposed algorithm for faults occurred

in 245 km


Fault inception angle (degree) Fault type

0.0373 245.112 0 Double-phase fault -0.0143 244.957 45

0.0257 245.077 90 -0.0340 244.898 0 Three-phases

fault 0.0343 245.103 45 0.0093 245.972 90

From Table 2 it is clear that the inception

angle of the fault has no significant effect on the accuracy of the algorithm so, the accuracy is not influenced by the variations of the fault inception angle. 4.3. Effect of fault distance

To investigate the effect of fault distance on the accuracy of proposed method, results for single-, double- and three-phase to ground faults occurred in different distances on the

transmission line with 75˚ fault inception angle and 80 Ω fault resistance are shown in Table 3.

Table 3.Effect of fault distance on the accuracy of proposed method


Actual fault distance Fault type

-0.0150 2.955 3 Single phase to ground -0.0220 102.934 103

0.0077 203.023 203 0.0216 3.065 3 Double phase to

ground -0.0260 102.922 103 0.0177 203.047 203 0.0117 3.035 3 Three phase to

ground -0.0167 102.950 103 0.0020 203.066 203

4.4. Effect of fault type

The proposed algorithm in this paper is capable to find location of various types of faults occurred in transmission lines compensated with series capacitors. To understand the effect of fault type on the accuracy of the proposed method, simulation results for single, double- and three-phase to ground faults and double and three-phase faults occurred with 60˚ fault inception angle and 25 Ω fault resistance are presented in Table 4.

Table 4.Effect of fault type on the accuracy of

proposed method


Actual fault distance Fault type

-0.0150 2.955 3 Single phase to ground -0.0220 102.934 103

0.0077 203.023 203 0.0216 3.065 3 Double phase

to ground -0.0260 102.922 103 0.0177 203.047 203 0.0117 3.035 3 Three phase to

ground -0.0167 102.950 103 0.0020 203.066 203 0.0330 3.099 3 Double-phase

fault -0.0376 102.887 103 0.0383 203.115 203 0.0073 3.022 3 Three-phases

fault -0.0323 102.903 103 0.0223 203.067 203

Presented results in Table 4 confirm that

the accuracy of the proposed algorithm is similar for different types of faults occurred in the transmission line.



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5. Conclusion In this paper, a novel fault location

algorithm is presented which uses just voltage samples taken from one-terminal to find location of faults occurred in transmission lines compensated with series capacitors. The wavelet-based algorithm utilizes high frequency fault clearing voltage transients. After that circuit breaker is opened, applying wavelet transform first and second inceptions of traveling waves to the locator point are detected. Thereafter, actual propagation speed of the traveling wave is calculated and accurate fault location is determined without need to line parameters. Extensive simulations performed using SimPowerSystem toolbox of MATLAB software, for different fault types and conditions confirm the capability and accuracy of the proposed algorithm. The presented results show that fault inception angle, fault resistance, fault type and distance of fault do not affect the accuracy of the proposed algorithm. Presented method despite of using only one terminal data provides so accurate results, such that in the worst case, computational error does not exceed 0.04 %, in addition, algorithm does not need to the communication systems and data synchronization. References [1] M.A. Dabbagh and S.K. Kapuduwage, “Using

Instantaneous Values for Estimating Fault Locations on Series Compensated Transmission Lines”, Electric Power Systems Research, Vol. 76, pp. 25–32, 2005.

[2] A.S.B Jayasinghe, R.K. Aggarwal, AT. Johns and Z.Q. Bo, “A Novel Non-Unit Protection for Series Compensated EHV Transmission Lines Based on Fault Generated High Frequency Voltage Signals”, IEEE Transactions on Power Delivery, Vol. 13, pp. 405-413, 1998.

[3] J. Sadeh, N. Hadjsaid, A.M. Ranjbar and R. Feuillet, “Accurate Fault Location Algorithm for Series Compensated Transmission Lines”, IEEE Trans. on Power Delivery, Vol. 15, pp. 323-328, 2000.

[4] A.I. Megahed, A.M. Moussa and A.E. Bayoumy, “Usage of Wavelet Transform in the Protection of Series-Compensated Transmission Lines”, IEEE Transactions on Power Delivery, Vol. 21, pp. 1213-1221, 2006.

[5] F. Ghassemi, J. Goddarzi and A.T. Johns, “Method to Improve Digital Distance Relay Impedance Measurement When used in SC Lines Protected by a Metal Oxide Varistor”, IEE Proceedings on Generation, Transmission and Distribiution, Vol. 145, pp. 403–408, 1998.

[6] T. Maekawa, Y. Obata, M. Yamaura, Y. Kurosawa and H. Takani, “Fault Location for Series Compensated Parallel Lines”, IEEE/PES Transmission and Distribution Conference and Exhibition, Asia Pacific, Vol. 2, pp. 824-829, 2002.

[7] IEEE Power Engineering Society, IEEE Guide for Determining Fault Location on AC Transmission and Distribution Lines, IEEE Std C37.114 ™ -2004.

[8] A.J. Mazon, I. Zamora, J.F. Minambres, M.A. Zorrozua, J.J. Barandiaran and K. Sagastabeitia, “A New Approach to Fault Location in Two-Terminal Transmission Lines Using Artificial Neural Networks”, Electr. Power Syst. Res. Vol. 56, pp. 261-266, 2000.

[9] J. Sadeh and A. Adinehzadeh, “Accurate Fault Location Algorithm for Transmission Line in the Presence of Series Connected FACTS Devices”, Int. J. Electr. Power Energy Syst. Vol. 32, pp. 323-328, 2010.

[10] J. Suonan and J. Qi, “An Accurate Fault Location Algorithm for Transmission Line Based on R–L Model Parameter”, Electr. Power Syst. Res. Vol. 76, pp. 17-24, 2005.

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[12] A. J. Mazon, I. Zamora, J.F. Miñambres, M.A. Zorrozua, J.J. Barandiaran and K. Sagastabeitia, “A New Approach to Fault Location in Two-Terminal Transmission Lines Using Artificial Neural Networks”, Electr. Power Syst. Res. Vol. 56, pp. 261-266, 2000.

[13] A. Abur and F.H. Magnago, “Use of Time Delays Between Modal Components in Wavelet Based Fault Location”, Int. J. Electr. Power Energy Syst. Vol. 22, pp. 397-403, 2000.

[14] V. Faybisovich and M.I. Khoroshev, “Frequency Domain Double-Ended Method of Fault Location for Transmission Lines”, Transmission and Distribution Conference and Exposition, Southern California, Alhambra, April 2008.

[15] I. Niazy and J. Sadeh, “Using Fault Clearing Transients for Fault Location in Combined Line (Overhead/Cable) by Wavelet Transform”, 24nd Int. Power Syst. Conf. (PSC’09), November, Tehran, Iran (in Persian), 2009.



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[16] M.I. Gilany, E.M.T. Eldin, M.M.A. Aziz and D.K. Ibrahim, “Traveling Wave-Based Fault Location Scheme for Aged Underground Cable Combined with Overhead Line”, Int. J. of Emerging Electr. Power Syst. Vol. 2, pp. 1032, 2005.

[17] L. Yongli, Z. Yi and M. Zhiyu, “Fault Location Method Based on the Periodicity of the Transient Voltage Traveling Wave”, IEEE Proceedings. PowerCon. International Conference on Power System Technology, Vol. 3, Tianjin China, pp. 389-392, Nov. 2004.

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fault location algorithm for series compensated

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