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Estimation of fault Location on UHV transmissionline using synchronized PMU measurements

K Ravishankar, D ThukaramDepartment of Electrical EngineeringIndian Institute of Science, Bangalore

Email: ravishankarkurre,[email protected]

Abstract—In this paper an accurate fault location algorithmfor adaptive fault detection/location on UHV transmission systemusing two end synchronized Phasor Measurement Unit (PMU)measurements is presented. The algorithm utilizes synchronizedmeasurements of voltages and currents from both ends of aline. The Electromagnetic Transients (EMT) program has beendeveloped to simulate a 765 kV Indian transmission System inwhich the distributed parameter line model is used. Simulationstudies have shown that the developed algorithm yields accurateresults independent of fault types and is insensitive to thevariation of source impedance, fault impedance, and line loading.The accuracy of fault location estimation achieved can be up to99.9% for many simulated cases. The technique will be verysuitable for implementation in an integrated digital protectionand control system for UHV transmission system. Illustrativeresults are presented for various type of faults.

I. INTRODUCTION

An accurate fault detection/location technique is of specialimportance in improving power system reliability includingrelaying, analysis for line inspection, and routine maintenance.Fault locator facilitates repair and restoration by immediateknowledge of the location and the nature (type and measuringdata) of the fault. A locator is also useful for transient faults,pointing to a weak spot that is threatening further trouble. Thelocator allows rapid arrival at the site before the evidence isremoved or the ”trail becomes cold”. Also, the knowledge thatrepeat faults are occurring in the same area can be valuable indetecting the cause. Weak spots that are not obvious may befound because a more thorough inspection can be focused inthe limited area defined by the fault locator. Distance relaysfor transmission-line protection provide some indication of thegeneral area where a fault occurred, but they are not designedto pinpoint the location [1].

Fault location schemes widely used are based on operatingprinciples of the travelling wave propagation on transmissionline. One approach is to observe the time at which a locatorof each terminal detects the first incoming fault surge from afaulted point. Another one is to transmit an electrical pulse intothe line, and to measure the period from emission to return ofthe pulse, thus known as a pulse radar method. This approachis based either on the travel time measurements using corre-lation techniques [2] or on the reconstruction of voltages andcurrents at the fault location. The traveling wave techniquesoffer some advantages but the computational complexity isincreased. The identification of the desired signal becomes

the essential problem of the usual kind of travelling waveprotection scheme. An adaptive travelling wave protectionalgorithm using two cross-correlation functions aid effectivelyin the identification of travelling wave. Fault location methodsutilizing travelling waves are independent of network configu-rations and devices installed in the network. But it is not easyto identify the local maximum of cross-correlation function forcalculating fault location. The other limitations of travellingwave techniques are that they require a very high samplingrate and cost.

Takagi et al. [3] proposed an approach based on thesuperposition theorem using the Laplace and the Fouriertransforms. The results obtained are quite accurate as long asthe assumptions are satisfied. A time domain representationof a transmission line model has also been considered byKezunovic et al. [4]. Data samples are considered as beingavailable from one end only. The voltage at the other end isestimated using pre-fault data. While one-terminal algorithmsprovide usefully accurate results, certain errors will remaindue to the inherent assumptions which are required in thealgorithms.The measurements from both ends provides suf-ficient number of equations to find the location of the fault[5]. Thukaram et al. applied Artificial Intelligence techniquesto fault location [6], [7] in absence of full information of fault.As the digital relays and communication systems provide theopportunity to perform fault locating using data from bothends in transmission lines, the fault location can be estimatedwith minimal assumptions and sources of errors.

In this paper, new fault detection/location technique usingsynchronized fundamental voltage and current phasors at bothends of transmission line is presented. Using the accuratetiming signal provided by Global Positioning System (GPS)[8], [9] as common time base for measuring instrumentslocated at both ends of line, we can highly promote theaccuracy of synchronized measurements and reduce the costof equipment greatly. Because of low frequency of the timingsignal of GPS, it can not be used as sampling signal directly.This means that a timing device is needed to do frequencymultiplication/division task. The fault detection/location tech-nique incorporated with line parameter estimation forms anadaptive technique. The fault detection/location technique cancope with various factors associated with the accuracy of faultdetector/locator mentioned above. A new and unique algorithmto estimate and eliminate the decaying dc component in a

16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 722

Department of Electrical Engineering, Univ. College of Engg., Osmania University, Hyderabad, A.P, INDIA.

fault current signal is presented.The dc-removed current signalwas obtained by eliminating the dc component from the faultcurrent at each sampling instant. The algorithm can estimatethe dc component exactly from fault currents and is used forphasor extraction [10].

Electromagnetic Transients (EMT) program has been de-veloped to simulate a 765 kV Indian transmission Systemusing Dommel’s method [11]. The performance of the faultdetection/location algorithms are evaluated by simulating the765 kV Indian transmission System with respect to variousparameters such as fault resistance, source impedance varia-tion, line loading and fault incidence angle through the EMTPgenerated data.

II. CONFIGURATION OF FAULT LOCATOR FOR UHVTRANSMISSION SYSSTEM USING PMU MEASURMENTS

The overall diagram of the fault locator for UHV transmis-sion sysstem using PMU measurments is shown in Fig. 1. Thephasor measurement units are installed at both ends (sendingend S and receiving end R) of the transmission line. Thethree phase voltages and three phase currents are measuredby PMUs located at both ends of line simultaneously. Sincethe Global Synchronism Clock Generator (GSCG) has beenequipped in PMU to provide an extremely accurate and reli-able external reference clock signal, it can guarantee samplingsynchronization to an accuracy of better than 1 µ sec.

The EMTP simulated on 765 kV typical of an Indiantransmission System. Voltage and current waveforms wereconsidered to be directly taken as the synchronized sam-pled data (voltages and currents) from substations Anparaand Unnao. A new DFT method is used to extract close-infundamental phasors.

Display fault distance

If|Num|,|Den|>0

Synchronized phasors I I ,V VS SR R

GPS System

PMU at Substation S PMU at Substation R

Calculate Num, Den and p

Yes

No

Fig. 1. Fault locator for UHV transmission sysstem using PMU measurments

III. COMPUTATION OF FAULT DETECTION/LOCATIONINDEX

A. Single-phase Case:The index using the synchronized voltage and current sam-

ples at both ends of a transmission line to calculate the locationof the fault is presented in this section.

Consider an un-faulted single-phase (two-conductors in freespace) transmission line shown in Fig. 2. Under sinusoidalsteady state condition both voltage and current measured ata distance x km away from receiving end obey two lineardifferential equations

A homogeneous transmission line

Receiving end

I I

Sending end

Receiving end

I

Sending end

Is

Is

Vs

Vx=p dx=0

Faulted transmission line

Vs

IR

RIF

R

VR

F

Fig. 2. Transmission line under pre-fault and during fault conditions

dV (x)

dx= (R+ jωL) (1)

dI(x)

dx= (G+ jωC) (2)

Solving equations (1) and (2) by using boundary conditionswe get

V (x) =(VR + IRZC)e

γx

2+

(VR − IRZC)e−γx

2(3)

I(x) =(VR + IRZC)e

γx

2ZC+

(VR − IRZC)e−γx

2ZC(4)

where x is distance measured from receiving end

V (x) =(VS − ISZC)e

γx

2+

(VS + ISZC)e−γx

2(5)

I(x) =(VS − ISZC)e

γx

2ZC+

(VS + ISZC)e−γx

2ZC(6)

where x is distance measured from sending end

where ZC =√

(R+ jωL)/(G+ jωC)

and γ =√

(R+ jωL)(G+ jωC)

In case of a fault occurrence at the point F which is x = pdkm away from receiving end R on a transmission line S-Rshown in Fig. 2. d is the total length of the transmission line,and p is the per unit distance from receiving end to the faultand is also used as a fault detection/location index. When faultoccurred at the point F, the transmission line is thus dividedinto two homogeneous parts. Each section acts as independenttransmission line. Then the voltage VF at the point F usingboth ends boundary conditions is given by

VF (x) =(VR + IRZC)e

γpd

2+

(VR − IRZC)e−γpd

2(7)

VF (x) =(VS − ISZC)e

γ(1−p)d

2+

(VS + ISZC)e−γ(1−p)d

2(8)



Eq. (7) and (8) gives the voltage at faulted point F in terms ofpost-fault receiving end and sending end measurements. Fromequations (7) and (8) fault detection index p is obtained as

p =(ln(Num/Den)

2γd(9)

where Num = (VR − IRZC)− (VS − ISZC)eγd (10)

Den = (VS + ISZC)e−γd − (VR + IRZC) (11)

Since no assumptions are for deriving index p, it is very robustand hardly effected by the variation of source impedanceloading change, fault impedance fault inception angle and faulttype. Simulations have shown that the proposed index canprovide accurate fault location. Absolute values of Num andDen can be used for fault detector. Pre-fault absolute Numand Den are equal to zero and during fault abruptly deviatedfrom zero.

B. Three-phase Case:

In case of thee-phase system, to eliminate coupling effectphase quantities are converted to modal quantities by usingdecoupling (Clark) transformation. Then the same above ap-proach can be applied. In the present paper mutual couplingis not considered. Hence the approach is applied directly.

IV. NEW DFT ALGORITHM TO REMOVE DC OFFSET FROMCURRENT

Full-cycle DFT filters are among the most popular inrelaying. For current waveform i(t) = A ∗ sin(ωt + θ), thefundamental frequency components are provided by [12].

IC =2

K

K−1∑k=0

ik cos(2πk

K) (12)

IS =2

K

K−1∑k=0

ik sin(2πk

K) (13)

where K is samples per cycle

phasor is I = IC + jIS

However, the DFT is not immune from the dc componentand the decaying dc component in the fault current can causeundesirable oscillations in the phasors. These oscillations cancause abnormal operation of protection system as well asinaccurate fault location.

Various Fault transients studies carried out for 765 kVtransmission systems [13] showed that the wave shape of faultcurrent significantly varying for the fault inception instant andalso the peak magnitude of fault currents are significantlylarge in UHV (765 kV) systems as compared with EHV(400 kV) systems.So estimation of DC offset in current signalis challenging when fault occurs on UHV transmission linebecause time constant and magnitude will depend on powersystem configuration at the moment of the fault and also

location of that fault on the line. It is a well established factthat line relays have a tendency to overreach in the presenceof DC offset components in faultcurrent waveforms. In faultlocation, the decaying component therefore has to be removedfrom these waveforms. A number of techniques have been putforward to deal with such situations [12], [14] In this paper anew and unique algorithm is presented to estimate and removethe decaying dc components in the fault current signal. Thefault current consisting of exponentially decaying component,fundamental and harmonic components can be expressed as

i(t) = I0e−t/τ +

k=n∑k=1

Ik sin(kωt+ θk) (14)

Where I0 is the magnitude of the decaying dc offset, is thetime constant of the decaying dc offset, k is the harmonicorder, Ik is the magnitude of the kth harmonic component, θkis the phase angle of the kth harmonic component, ω is thefundamental frequency and n is the maximum harmonic order.

If Eq. (14) is integrated during one period(T) the integralof the second term is zero and only the integral of the firstterm, which is related to the decaying dc component∫ t

t−T

i(t)dt =

∫ t

t−T

I0e−t/τdt

= −I0τe−t/τ (1− eT/τ )

= f(t) (15)

After simplifying eqution (15) we get time constant andmagnitude of the dc componet as follows

1

τ= (1− f(t+∆t)

f(t))1

∆t(16)

I0 =f(T )

−τ(e−T/τ − 1)(17)

By subtracting the calculted dc value from each of the sampleddata in buffers which contain one cycle of sample data we canextract fundamental componet axactly by applying DFT.

V. SIMULATION RESULTS

A. Test system

The test system considered for studies is a 765kV typicalIndian transmission system connected between Anpara-Unnaoof UPSEB. Equalent system diagram is shown in Fig. 3Sending end bus(bus 3) is located at Anpara and Receivingend bus (bus4) is located at Unnao . Initially the system isassumed to be operating in steady state balanced conditionand delivering a load of 500 MW and 200MVAR. The pre-fault receiving end quantities are: 4000 MVA, 765 kV. Theinitial voltages at the buses are obtained from AC load flowsolution. The generator side the source strength considered tobe 5000 MVA and load side source strength is considered to be4000 MVA. Faults simulated at at ficticious bus 7 at variabledistances (p varying from 0.2 to 0.8) from the recienving endbus 4. Results for selected few cases are presented in this



paper. The faults for these cases assumed to occur at 0.040sec.Fault resistance RF is varied from 5.852Ω (0.001 p.u) to585.2Ω (0.1 p.u) All currents and voltages are expessed in perunit values on following base values

Base MVA=100 MVA, Base kV=765kV ;

~G

4 5

500km

321

15 kV 400kV 765kV 765kV 400kV 15kV

6

240MVAR 240MVAR

Fig. 3. Test system of 765kv Indian transmion system

B. Performance of the New DFT Algorithm

EMTP program has been doveloped to simultae 765kvIndian transmission system. The 765kv transmission systemcurrent signals generated from EMTP program are used fortesting the performance of the New DFT algorithm. Faultcurrent in line 3-7 for 3ph-g fault at a distance (p=0.8) of400km from Unnao is shown in Fig.4 The fault is created at0.4 sec. Fig. 5 and 6 shows the current phasor magnitude usingconventional DFT and modified DFT respectively.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2−40

−30

−20

−10

0

10

20

30

40

curre

nt in

pu

time in sec

iaibic

Fig. 4. Fault current in line 3-7 for 3ph-g fault for p=0.8 for fault at 0.4sec

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.24

6

8

10

12

14

16

18

20

22

time in sec

curre

nt in

pu

IaIbIc

Fig. 5. Current phasor for 3ph-g fault for p=0.8 using DFT(0.40sec)

Fault current in line 3-7 for 3ph-g fault at a distance(p=0.8)of 100km from Substation R. is shown in Fig.7 The faultis created at 0.45 sec. Fig. 8 and Fig.9 shows the currentphasor magnitude using conventional DFT and modified DFTrespectively. The results shows that the new DFT method givesthe phasors accurately with less oscillations in phasors.

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.26

8

10

12

14

16

18

20

time in sec

curre

nt in

pu

Ia

Ib

Ic

Fig. 6. Current phasor for 3ph-g fault for p=0.8 using modified DFT(0.40sec)

0 0.05 0.1 0.15 0.2−40

−30

−20

−10

0

10

20

30

40

curre

nt in

pu

time in sec

iaibic

Fig. 7. Fault current in line 3-7 for 3ph-g fault for p=0.8 for fault at 0.45sec

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.25

10

15

20

25

time in sec

cur

rent

in p

u

Ia

Ib

Ic

Fig. 8. Current phasor for 3ph-g fault for p=0.8 using DFT(0.45sec)

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.26

8

10

12

14

16

18

20

time in sec

curre

nt in

pu

IaIbIc

Fig. 9. Current phasor for 3ph-g fault for p=0.8 using modified DFT(0.45sec)

C. Performance of the fault Detection/Locattion Index p

1) Fault Detection and location of a-b fault: The fault canbe detected by observing the values of |Num| and |Den|.Pre-fault values of |Num| and |Den| will be zero ideally. SoPre-fault value of the Location index p will be undetermined.It can be proved by substituiting the measured voltages andcurrents at both ends in Eq. 10 and 11. Immediately after



the fault occurrence |Num| and |Den| will deviate from zerowhich is the indication of fault. The fault detector p gives thefault location from the bus 4 (Substation R)

The current and voltage signals at sending end bus(bus 3)located at Anpara substation are shown in Fig 10 and Fig 11and receiving end (bus4) at Unnao signals are shown in Fig12 and Fig 13 when a-b fault occured at a distance of 100kmfrom receiving end (bus4) at Anpara substation at time 0.4 secand fault resistance is 5.85Ω.

0 0.05 0.1 0.15 0.2−30

−20

−10

0

10

20

30

curre

nt in

pu

time in sec

X: 0.016Y: 7.009

iaibic

Fig. 10. Fault current in line 3-7 for a-b fault at 100km from substation R

0 0.05 0.1 0.15 0.2−1.5

−1

−0.5

0

0.5

1

1.5

volta

ge in

pu

time in sec

vavbvc

Fig. 11. Voltage at bus 3 a-b fault (100km from unnao)

0 0.05 0.1 0.15 0.2−40

−30

−20

−10

0

10

20

30

curre

nt in

pu

time in sec

iaibic

Fig. 12. Fault current in line 4-7 for a-b fault (100km from unnao)

These signals are considered to be time synchronised signalsobtained by GPS system. The phasors for these signals arecomputed by the PMU’s located at substations. The caclulatedfault detection indices |Num| and |Den| are shown in Fig 14and Fig 15 and the fault location index is shown in Fig 16 fromwhich it can be observed that the fault detection indices |Num|and |Den| are almost zero before fault (0.04 sec) and p hasno meaning before fault. Theoritically p should be indefinitebut practically it is a finite value. when the fault occured(after 0.04 sec the fault detection indices |Num| and |Den|are abruptly deviating from zero for faulted phases(a and b)and p converges to 0.1997 which is 0.03% where % error =(Estimated Location - Actual location)*100 /Total length

0 0.05 0.1 0.15 0.2−1.5

−1

−0.5

0

0.5

1

1.5

volta

ge in

pu

time in sec

vavbvc

Fig. 13. Voltage at bus 4 for a-b fault (100km from unnao)

0 0.05 0.1 0.15 0.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

faul

t loc

atio

n In

dex

Den

time in sec

a−phase

b−phase

c−phase

Fig. 14. Fault detection index Den for a-b fault (100km from substation R)

0.05 0.1 0.15 0.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

fault l

ocati

on In

dex N

um

time in sec

a−phaseb−phasec−phase

Fig. 15. Fault detection index Num for a-b fault (100km from substationR)

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.5

1

1.5

2

2.5

3

3.5

X: 0.06825Y: 0.1997

fault

loca

tion

Inde

x D

time in sec


Fig. 16. Fault location index p for a-b fault at 100km from substation R

2) Fault Detection and location of 3ph-g fault: The curentand voltage signals at sending end bus(bus 3) located at Anparasubstation are shown in Fig 17 and Fig 18 when 3ph-g faultoccured at a distance of 100km from receiving end (bus4) atUnnao substation at time 0.4 sec and fault resistance is 5.85Ω.The caclulated fault detection indices |Num| and |Den| areshown in Fig 20 and Fig 21 and the fault location index isshown in Fig 19. From the Fig 19, Fig 20 and Fig 21 it canbe observed that the fault detection indices |Num| and |Den|are almost zero before fault (0.04 sec) and p has no meaning



before fault. when the fault occured (after 0.04 sec the faultdetection indices |Num| and |Den| are abruptly deviatingfrom zero for faulted phases and p converges to 0.2001 whichis 0.01%

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2−30

−20

−10

0

10

20

30

40

curre

nt in

pu

time in sec

iaibic

Fig. 17. Fault current in line 3-7 for 3ph-g fault (100km from unnao)

0 0.05 0.1 0.15 0.2−2.5

−2

−1.5

−1

−0.5

0

0.5

1

1.5

2

volta

ge in

pu

time in sec

vavbvc

Fig. 18. Voltage at bus 3 for 3ph-g fault (100km from unnao)

0 0.05 0.1 0.15 0.20

0.5

1

1.5

2

2.5

3

3.5

4

X: 0.1543Y: 0.2001

fault l

ocati

on In

dex D

time in sec


Fig. 19. Fault location index p for 3ph-g fault (100km from unnao)

0 0.05 0.1 0.15 0.2−0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

fault

loca

tion

Inde

x Num

time in sec


Fig. 20. Fault detection index Num for 3ph-g fault (100km from unnao)

VI. CONCLUSION

A new fault detection/location algorithm using PMU mea-surments is presented. A modified DFT algorithm is usedto extract the phasors exactly. The algorithm is robust. Theperformance of algorithm has been verified with practical

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

X: 0.05145Y: 0.3138

fault l

ocati

on In

dex D

en

time in sec


Fig. 21. Fault detection index Den for 3ph-g fault (100km from unnao)

Indian transmission system simulated in developed EMTP.Simulation results show that this algorithm can detect andlocate the fault accurately.

REFERENCES

[1] L. Eriksson, M. M. Saha, and G. D. Rockefeller, “An accurate faultlocator with compensation for apparent reactance in the fault resistanceresulting from remote-end infeed,” IEEE Trans. Power App. Syst, vol.PAS-104, no. 1, pp. 424–436, Feb. 1985.

[2] L. Jie, S. Elangovan, and J. B. X. Devotta, “Adaptive travelling waveprotection algorithm using two correlation functions,” IEEE Transactionson Power Delivery, vol. 14, no. 1, Jan. 1999.

[3] T. Takagi, Y. Yamakoshi, J. Baba, K. Uemura, and T. Sakaguchi, “Faultlocation for ehv/uhv transmission lines: Part 1- fourier transformationmethod,” IEEE Transactions on Power Apparatus and Systems, vol. PAS-100, no. 3, pp. 1316–1323, March 1981.

[4] M. Kezunovic, J. Mrkic, and B. Perunicic, “An accurate fault locationalgorithm using synchronized sampling,” Electric Power Systems Re-search, vol. 29, pp. 161–169, 1994.

[5] J. Izykowski, R. Molag, E. Rosolowski, and M. M. Saha, “Accuratelocation of faults on power transmission lines with use of two-endunsynchronized measurements,” IEEE Trans. Power Del, vol. 21, no. 2,pp. 627–633, Apr. 2006.

[6] D. Thukaram, H. P. Khincha, and H. P. Vijayanarasimha, “Artificialneural network and support vector machine approach for locating faultsin radial distribution systems,” IEEE Trans. Power Delivery, vol. 20,no. 2, pp. 710–721, Apr. 2005.

[7] G. K. Purushothama, A. Narendranath, D. Thukaram, andK. Parthasarathy, “Ann applications in fault locators,” ElectricPower and Energy Systems, vol. 23, pp. 491–506, 2001.

[8] D. Novosel, D. G. Hart, E. Udren, and J. Garitty, “Unsynchronized two-terminal fault location estimation,” IEEE Trans. Power Del, vol. 11,no. 1, pp. 130–138, Jan. 1996.

[9] A. Jiang, J.-Z. Yang, Y.-H. Lin, C.-W. Liu, and C. Ma, “An adaptive pmubased fault detection/location technique for transmission lines-i. theoryand algorithms,” IEEE Trans. Power Del, vol. 15, no. 2, pp. 486–493,Apr. 2000.

[10] Y.-S. Cho, C.-K. Le, G. Jang, and H. J. Lee, “An innovative decaying dccomponent estimation algorithm for digital relaying,” IEEE Transactionson Power Delivery, vol. 24, no. 1, pp. 73–78, Jan. 2009.

[11] H. W. Dommel, Electromagnetic Transients Program Theory Book.BPA, Jul. 1994.

[12] A. Phadke and J. Thorp, Computer Relaying For Power Systems. JohnWiley & Sons, 1988.

[13] D. Thukaram, S. R. Kolla, K. Ravishankar, and A. Rajendra Kumar,“Switching and fault transient analysis of 765 kv transmission systems,”Third International Conference on Power Systems, Kharagpur, INDIA,no. 122, Dec. 2009.

[14] T. S. Sidhu, X. Zhang, F. Albasri, and M. S. Sachdev, “Discretefourier-transform-based technique for removal of decaying dc offset from phasorestimates,” Proc. Inst. Elect. Eng., Gen.., Transm. Distrib, vol. 150, no. 6,pp. 745–752, Nov. 2003.

