a novel unit protection scheme for series compensated transmission line based on wavelet article 3

A Novel Unit Protection Scheme for Series Compensation Transmission Line Based on Wavelet Modulus Maxima

MS 08 Spain 1

A Novel Unit Protection Scheme for Series Compensated Transmission Line Based on Wavelet

Modulus MaximaS.M.Shahrtash

[email protected]

[email protected]

F.Haghjoo [email protected]

Sadegh Shahamati Beris [email protected]

Center of Excellence for Power Systems Automation and Operation (CEPSAO) Iran University of Science and Technology (IUST)

ABSTRACT

In this paper a protection algorithm based on traveling wave theory and wavelet analysis that can be implemented on series compensated transmission lines has been developed. A single-circuit transmission line has been simulated in EMTP_RV environment and main algorithm has been executed in MATLAB software. The algorithm's performance for each type of faults occurred in different distances for two compensation levels and configurations with different fault resistances has been tested and the results have been reported.

KEY WORDS

Modulus Maxima, Wavelet Transform, Traveling Wave, Unit Protection, Series Compensation lines.

RESEARCH FIELD

Power System Protection.

1. INTRODUCTION

Series compensation (SC) technique has been widely used in long transmission lines to increase the power transfer capability of the line, enhance transient and steady state stability, reduce both voltage drop and losses along the transmission line and improve economical loading. But, installing of series capacitor on the lines might cause relays mal-operation if not designed properly and given suitable settings. In Series compensated lines, relays may be exposed to voltage inversion, current inversion, sub harmonic oscillations, slow transients, fast transients, sub synchronous oscillations, under and overreaching problems [1]. Also the operation of both protective gaps and MOV, the main elements of the over voltage protection of series capacitors, make further changes in the voltage and current waveforms. According to these facts, the schemes based on fundamental frequency signals can be influenced by severe variations of circuit impedances. On the other hand, the fault generated transients which have vital information about nature of fault such as type, location and inception angle, are the most proper alternative to be used in protection scheme of series compensated lines. In [2] it has been shown that the wavefront of traveling waves is immune to presence of the series capacitors and if a pilot protection is constructed based on the wavefronts, the effect of SC will be eliminated. In this paper, a novel pilot protection has been developed which detects the wavefront of the fault initiated traveling waves by applying the wavelet transform and seeking for wavelet modulus maximas.

Sadegh Shahamati Beris F. Haghjoo S. H. Mortazavi Seyyed Mohammad Shahrtash

2 MS 08 Spain

2. THEORETICAL BACKGROUND

2.1. Traveling Wave theory

According to traveling wave theory, as a fault occurs the fault generated traveling waves travel along the line in both directions until to meet the discontinuous point of wave impedance, such as buses and fault point. Then a portion of wave will be reflected back and other portion continues to travel [3]. In the proposed algorithm the Forward Current Traveling Wave (FCTW) has been computed according to the following relation.

2&

)()()( 0

0

111

cf

ZR

R

tutiti

(1)

Where )(1 ti and )(1 tu are the current and voltage signals at the sending end, respectively and cZ

is the characteristic impedance of the transmission line. Using 0R instead of cZ itself, maintains the

sensitivity of the relay to both forward and backward traveling waves, i.e. the relay responds to either forward and reverse faults. Obviously, it is only for the external faults where the FCTW at one end has a similar waveform as the one found at the other end, provided that it is shifted in time by the travel time of the waves along the protected lines.

2.2. Wavelet Transform Wavelet Modulus Maxima

Traveling waves are usually sharply varying signals. Wavelet Transform (WT) is able to provide accurate transient information in both time and frequency domains. Extracting different decomposition levels the edge points of the FCTW has been revealed via Modulus Maxima calculations. The absolute local maximum values of wavelet coefficients are called wavelet modulus maxima (MM). If the mother wavelet is the first derivative of a smooth function, the edge of a signal can be represented by its wavelet modulus maxima [4].

|),(||),(| 0xsfWxsfW

(2)

Where the W denotes the wavelet transform and the

is the mother wavelet. In fact, the modulus

maxima are the maximum of pulse-like parts of the components in each decomposition level.

2.3. Applying Modal Transformation Concept

In Eq.(1), instead of phase voltages and currents, modal voltages and currents have been always used to simplify the analysis [5]. The modal parameters have been calculated by applying the following relation:

abco

abco

IQI

VSV

.

.1

1

(3)

101

011

111

3

1][][ 11 QS (4)

Then, the -mode of signal has been substituted in Eq.(1).


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3. PROPOSED ALGORITHM

The proposed algorithm is shown schematically in Fig.1. As shown the voltage and current data has been captured from the simulated circuit .Then the time delay that calculated based on the length of the line and sampling rate has been applied to the receiving end voltage and current waveforms. The modal transformation has been enforced to the three phase signals, and then FCTW waveform has been calculated according to Eq. (1) at both ends. In the next step the WT has been applied to the FCTWs and then the MM of third detail components has been computed, and the relevant time of occurrence for the top three of the MMs (the three with the larger magnitudes) have been saved for comparison in the next step. Finally based on conformity of MMs w.r.t. their times of occurrence, the internal faults has been distinguished against the external ones.

Figure 1. Proposed Algorithm Flowchart

Comparing Times of MMs

Internal Fault

UnCONFORMITY

External Fault

CONFORMITY

Modal Transformation

Applying

FCTW calculation

Using 3rd level of WT

Extracting MMs & It's Times

Modal Transformation

Applying

FCTW calculation

Using 3rd level of WT

Extracting MMs & It's Times

Time Delay

V & I Data Acquistion

V2

V1

Capacitor Capacitor

I2

I1

V1

Capacitor

V2


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4. ALGORITHM ROBUSTNESS TESTING

The proposed algorithm has been tested for different power system and operation conditions [6].

4.1. Transmission Line Configuration

Two basic configurations have been simulated in EMTP_RV environment and 256 fault cases have been implemented for each circuit. In the first configuration series compensation capacitors installed in the two ends of transmission lines as shown in Fig.1. and in the second the capacitor bank has been installed in the middle of the line as shown in Fig.1. In both circuits two compensation levels of 70 and 40 percent have been considered.

The characteristic of MOV has been considered as 23)(refV

Vpi , where refV has got two values of

200 and 500 kV.

4.2. Different Fault Conditions

Eight fault types included single, double and triple phases faults have been simulated. In each simulated circuit four locations considered for fault locations, two for External faults in the left and right sides of the transmission line and two points for internal faults in 100 km and 200 km distances far from the sending end. In addition, two fault resistances (Rf) of zero and 20 ohms have been simulated.

4.3. Algorithm Adjustments

For achieving the best operation results of the algorithm several adjustable parameters have been considered in the algorithm as follow:

4.3.1. Mother Wavelet

For achieving the best results of the algorithm it is necessary to choose a suitable mother wavelet. Generally, the cross-correlation factor can show compatibility of mother wavelets with related waveform, but in this study the signals waveforms have not a same shape and/or a same construction, because of different fault types and operation conditions. In [2], B-spline family of wavelets has been picked up for the protection purposes. But in this paper, after a careful investigation, where 12 functions have been tested, db3 has been chosen.

4.3.2. Peak Numbers

By appearance of the modulus maximas in the third detail components, the first 6 peaks have been considered and then the top three peaks have been selected.

4.3.3. Wavelet Decomposition Levels

Each scale in wavelet transform corresponds to a certain frequency band and the time window widths are changed with scale or frequency automatically. In this study 2nd to 5th levels of wavelet decompositions have been tested, and then based on the obtained best results, the 3rd detail component has been chosen.


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5. RESULTS OF THE ALGORITHM IMPLEMENTATION

In this section twelve case studies have been considered where their specifications have been mentioned below and their results have been reported.

Case 1: A101, External-Left, ag, Rf = 0 , SC = 70%, Two capacitors, Vref (MOV)= 500kV. Case 2: A202, External-Left, bg, Rf = 20 , SC = 70%, Two capacitors, Vref (MOV)= 500kV. Case 3: A303, External-Left, cg, Rf = 0 , SC = 70%, Two capacitors, Vref (MOV)= 200kV. Case 4: B714, External-Right, acg, Rf = 0 , SC = 40%, One capacitor, Vref (MOV)= 200kV. Case 5: B814, External-Right, acg, Rf = 20 , SC = 40%, One capacitor, Vref (MOV)= 200kV. Case 6: A814, External-Right, acg, Rf = 20 , SC = 40%, Two capacitors, Vref (MOV)= 200kV. Case 7: A322, Internal-100Km, acg, Rf = 0 , SC = 70%, Two capacitor, Vref (MOV)= 200kV. Case 8: A420, Internal-100Km, ab, Rf = 20 , SC = 70%, Two capacitor, Vref (MOV)= 200kV. Case 9: A521, Internal-100Km, bc, Rf = 0 , SC = 40%, Two capacitor, Vref (MOV)= 500kV. Case 10: B631, Internal-200Km, abc, Rf = 20 , SC = 40%, One capacitor, Vref (MOV)= 500kV. Case 11: B731, Internal-200Km, abc, Rf = 0 , SC = 40%, One capacitor, Vref (MOV)= 200kV. Case 12: A831, Internal-200Km, abc, Rf = 20 , SC = 40%, Two capacitors, Vref (MOV)= 200kV.

Figure 2. Result of A101,A202&A303 coded fault cases

0 1000 2000 3000 4000 5000 6000 7000-500

0

5003rd detail Sending End (A101) RESULT:EL

0 1000 2000 3000 4000 5000 6000 7000-100

-50

0

50

1003rd detail Receiving End (A101) RESULT:EL

0 500 1000 1500 2000 2500 3000 3500 4000-500

0


0 500 1000 1500 2000 2500 3000 3500 4000-40

-20

0

20


0 500 1000 1500 2000 2500 3000 3500 4000-4

-2

0


0 500 1000 1500 2000 2500 3000 3500 4000-10

-5

0

5


Fault Type 1st MM 2nd MM 3rd MM

S 1002 1255 1506

A101

R 1003 1254 1505

S 1002 1253 1504

A202

R 1004 1255 1505

S 1002 1253 1506

A303

R 1003 1254 1505


6 MS 08 Spain

Figure 3. Result of B714,B814&A814 coded fault cases

The results of the first three cases have been shown in Fig.2. As the faults are external and beyond the sending end, obviously, it is for the positive shift of time for the FCTW at the receiving end that the time conformity of MMs has been achieved. These results have been shown in the table inside the Fig.2. The results of the next three cases, which are the external faults beyond the receiving end, have been shown in Fig.3. In these cases, with negative shift of time for the FCTW at the receiving end, the time conformity of MMs has been verified (refer to the table in the Fig.3).The key point of true operation of the algorithm in these cases is implementing the R0 instead of the Zc in the calculations that cause to appear the small MMs in the receiving end. The next six cases are the internal faults at different distance (from the sending end).referring to Fig.4 and 5, it has been shown that neither positive, nor negative time shift can result to the time conformity of MMs. Indeed, the performance of the proposed algorithm has been investigated under 512 different cases (with different specifications) and in all of them it has been shown accurate selectivity and sensitivity and/or dependability and security.

Fault Type 1st MM 2nd MM 3rd MM

S 1004 1254 1505

B714

R 1002 1254 1506

S 1004 1254 1505

B814

R 1002 1254 1504

S 1003 1254 1507

A814

R 1002 1254 1506

0 500 1000 1500 2000 2500 3000 3500 4000

-100

-50

0

50

1003rd detail Sending End (B714) RESULT:ER

0 500 1000 1500 2000 2500 3000 3500 4000-100

-50

0

50

1003rd detail Receiving End (B714) RESULT:ER

0 500 1000 1500 2000 2500 3000 3500 4000-100

-50

0

50

1003rd detail Sending End (B814) RESULT:ER

0 500 1000 1500 2000 2500 3000 3500 4000-100

-50

0

50

1003rd detail Receiving End (B814) RESULT:ER

0 500 1000 1500 2000 2500 3000 3500 4000-100

-50

0

50

1003rd detail Sending End (A814) RESULT:ER

0 500 1000 1500 2000 2500 3000 3500 4000-50

0

50

1003rd detail Receiving End (A814) RESULT:ER


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Figure 4. Result of A322,A420&A521 coded fault cases

6. CONCLUSION

An application of traveling waves and wavelet modulus maxima have been presented in scheme for unit protection of series compensated transmission lines. The performance of the proposed algorithm under several different conditions has been evaluated and the maximum possible accuracy has been obtained. The algorithm not only distinguishes between internal faults and external ones, but also differences between left and right external faults. The proposed algorithm has been improved and applied to the compensated lines which has mutual coupling with another circuit and the results which will be reported in the next paper have shown high accuracy, as well.

Fault Type

Del

ay

Terminal 1st MM 2nd MM 3rd MM

+ S

R

1044 961

1129 1045

1212 1130 A322

- S R

920 1086

1003 1170

1088 1254

+ S R

1044 961

1212 1129

1296 1297 A420

- S R

920 1086

1171 1254

1255 1422

+ S R

1044 961

1128 1045

1212 1129 A521

- S R

919 1086

1087 1170

1171 1253

0 1000 2000 3000 4000

-1000

-500

0

5003rd detail Sending End (A420) IL(+)

0 1000 2000 3000 4000-1000

-500

0

5003rd detail Receiving End (A420) IL(+)

0 1000 2000 3000 4000-1000

-500

0

500

10003rd detail Sending End (A420) IR(-)

0 1000 2000 3000 4000-400

-200

0

2003rd detail Receiving End (A420) IR(-)

0 1000 2000 3000 4000-400

-200

0


0 1000 2000 3000 4000-400

-200

0


0 1000 2000 3000 4000-400

-200

0

200


0 1000 2000 3000 4000-200

-100

0


0 1000 2000 3000 4000-400

-200

0


0 1000 2000 3000 4000-200

-100

0


0 1000 2000 3000 4000-400

-200

0


0 1000 2000 3000 4000-100

-50

0

50



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Figure 5. Result of B631,B731&A831 coded fault cases

REFERENCEs

[1]. Zijun Huang, Yunping Chen, Qingwu Gong; "A Protection and Fault Location Scheme for EHV Line with Series Capacitor based on Travelling Waves and Wavelet Analysis"; Power system Technology, 2002, proceeding. PowerCon2002, International Conference on Volume: 1, On page(s): 290- 294 Vol.1.

[2]. Su Bin, Dong Xinzhou, Sun Yuanzhang; "A New Traveling Wave Differential Relay for Series Compensated EHV Transmission Line"; Developments in Power System Protection, 2004. Eighth IEE International Conference on Volume: 2, On page(s): 420- 423 Vol.2.

[3]. Z Chen, Xiang-ning Lin, Z Q Bo; "Wavelet Transform based Boundary Protection Scheme for Series Compensated Lines"; Developments in Power System Protection, 2004. Eighth IEE International Conference on Volume 1, Issue, 5-8 April 2004 Page(s): 56 - 59 Vol.1.

[4]. L. Shang, G. Herold, J. Jaeger, R. Krebs, A. Kumar; " Analysis and Identification of HVDC System Faults Using Wavelet Modulus Maxima"; Friedrich-Alexander University of Erlangen Nuremberg; Siemens AG, Germany.

[5]. J.Liang, S.Elangovan, J.B.X.Devotta; "Application of wavelet transform in traveling wave protection"; International Journal of Electrical Power & Energy Systems; Volume 22, Issue 8, 1 November 2000, Pages 537-542.

[6]. Sadegh Shahamati Beris, Seyed Mohammad Shahrtash; "Investigation of Wavelet Differential Relay Operation on Series Compensated Transmission Line"; 2nd Conference on Power System Protection & Control (PSPC2008), Tehran Iran; available at: www.pspacc.org/pspacc/pspacc2008/articles/main113.pdf.

Fault Type

Del

ay

Terminal 1st MM 2nd MM 3rd MM

+ S R

1097 972

1285 1035

1473 1160 B631

- S R

972 1034

1160 1097

1349 1159

+ S R

1097 972

1285 1035

1474 1223 B731

- S R

972 1034

1161 1097

1349 1159

+ S R

1089 920

1254 1087

1422 1171 A831

- S R

961 1044

1129 1212

1297 1296

0 1000 2000 3000 4000

-500

0

500

10003rd detail Sending End (B631) IL(+)

0 1000 2000 3000 4000-1000

-500

0

5003rd detail Receiving End (B631) IL(+)

0 1000 2000 3000 4000-500

0

500

10003rd detail Sending End (B631) IR(-)

0 1000 2000 3000 4000-1000

-500

0

500

10003rd detail Receiving End (B631) IR(-)

0 1000 2000 3000 4000-500

0

500

10003rd detail Sending End (B731) IL(+)

0 1000 2000 3000 4000-1000

-500

0

5003rd detail Receiving End (B731) IL(+)

0 1000 2000 3000 4000-500

0

500

10003rd detail Sending End (B731) IR(-)

0 1000 2000 3000 4000-1000

-500

0

500

10003rd detail Receiving End (B731) IR(-)

0 1000 2000 3000 4000-400

-200

0


0 1000 2000 3000 4000-1000

-500

0

500


0 1000 2000 3000 4000-1000

-500

0


0 1000 2000 3000 4000-1000

-500

0


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