Accurate Phase to Phase Fault Resistance Calculation Using Two Terminal Data

Muhd Hafizi Bin Idris, Surya Hardi, Mohd Zamri Hasan, Yazhar Yatim & Syafruddin Hasan School of Electrical System Engineering

University Malaysia Perlis Arau, Malaysia

hafiziidris@unimap.edu.my

Abstract— Faults can occurred at the transmission line due to lightning strike, broken conductor, cross arm or tower falls, danger tree, crane or animal encroachment, polluted insulator etc. Each type of fault will represents a fault resistance value. Fault resistance will affects the accuracy of protection relays in fault location and fault zone detection. Phase to phase fault is one type of unsymmetrical fault at the transmission line. This paper represents the accurate way to calculate the actual phase to phase fault resistance value by using data from both local and remote substations. From the finding, the actual fault resistance can be represented by fault resistance as seen from local substation in parallel with the fault resistance as seen from remote substation. To prove the finding, simulation has been carried out and the results show the validity of the proposed theory.

Keywords— phase to phase; two-terminal; fault resistance; fault location

I. INTRODUCTION

Faults occurrence at transmission line can be due to many circumstances such as tree or crane encroachment, lightning strike, insulation failure, instrument transformer explosion, animal intervention, and many others [1]. Fault can be classified as symmetrical and unsymmetrical faults. Three phase fault is the only symmetrical fault. Single phase to ground fault, phase to phase fault, double phase to ground fault and three phase to ground fault are unsymmetrical faults [2].

When a fault occurred at the transmission line, maintenance peoples have to locate the fault by using the fault location given by the fault recorder or numerical protection relay. The location given by this devices sometimes not very accurate and making it difficult to find the correct location of the fault. This is due to many factors such as current transformer and voltage transformer errors, line charging current, high fault resistance and many other factors. Fault resistance has a very great effect on the accuracy of fault location as has been proved in [3]. It will make the fault location becomes very inaccurate when the algorithm used to calculate the fault location does not consider its effects. A small error in fault location may similar to several kilometers at the actual transmission line.

There are 2 categories of fault location algorithm which are one-terminal and two-terminal algorithms. One-terminal algorithm uses data from one substation only which is from

local substation [4]. Two-terminal algorithm uses date from both local and remote substations [1,5]. Two-terminal data algorithm is more accurate than one-terminal data algorithm because of more data it uses to locate the fault [6]. Low speed communication channel can be used to transmit the data between local and remote substations or to a main substation.

In this paper, the authors present an accurate phase to phase fault resistance calculation using two-terminal data. By knowing the accurate value of fault resistance, the value can be used to accurately calculate the fault location. The fault impedance is assumed to be purely resistance [7].

II. THEORIES OF PHASE TO PHASE FAULT

Fig. 1 shows a case of phase to phase fault between red and yellow phases. There is a contact between red and yellow phase lines. This object represents a resistance value or typically called as fault resistance, RF. The parameters for phase to phase fault are shown in Table I.

Fig. 1. Phase to phase fault condition

TABLE I

PHASE TO PHASE FAULT PARAMETERS

No. Parameters Symbols Unit 1 Phase to ground voltage of red

phase from local substation. VRA kV

2 Phase to ground voltage of yellow phase from local substation

VYA kV

3 Phase current of red phase from local substation

IRA A

4 Phase to ground voltage of red phase from remote substation

VRB kV

5 Phase to ground voltage of yellow phase from remote substation

VYB kV

6 Phase current of red phase from remote substation

IRB A

7 Line impedance ZL Ω 8 Fault location m Per unit

This work was supported by Higher Education Ministry of Malaysia andUniversiti Malaysia Perlis through Research Acculturation Grant Scheme(RAGS, Project code: 9018-00020)

978-1-4799-7297-5/14/$31.00 ©2014 IEEE

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A. Equations seen from local substation

The voltage difference between red and yellow phase lines is, RF (1) Arranging for RF, RF 2 ⁄ (2) RF is then replaced with RFA to show that the fault resistance is seen from local substation as depicted by Fig. 2. RFA = RF (3)

Fig. 2. Phase to phase fault as seen from local substation.

B. Equations seen from remote substation The voltage difference between red and yellow phase lines is, RF (4) Arranging for RF, RF 2 ⁄ (5) RF is then replaced with RFB to show that the fault resistance is seen from remote substation as depicted by Fig. 3. RFB = RF (6)

Fig. 3. Phase to phase fault as seen from remote substation.

C. Parallel connection of fault resistances seen by both substations

If we look at the fault resistance seen from local substation

RFA and the fault resistance seen from remote substation RFB, it can be said that the actual fault resistance value, RF can be represented by fault resistances seen from both substations

connected in parallel as depicted by Fig. 4. By using (7), fault resistance, RF can be directly calculated using simple parallel connection formula.

RF RFA xRFB ⁄ RFA RFB (7)

As seen from Fig. 4 (b), the phase current from each substation will flow and circulate through fault resistance seen by each side respectively. Simulation has been carried out to prove the equivalent circuit of parallel connection to represent the fault resistance, RF which is discussed in the next section.

Fig. 4. Fault resistance, RF represented by an equivalent parallel connection of

fault resistances seen from both substations.

III. MODELING USING MATLAB SIMULINK

Table II shows the parameters used for modeling the source, transmission line and phase to phase fault. For this model, it was assumed that the positive and zero sequence capacitances of the transmission line are very small because of the transmission line is short.

Fig. 5 shows the overall simulation model developed for this research. It can be seen that there are two blocks at the right side of Fig. 5 used to calculate the fault resistances seen from each substation. Fault Resistance Calculation A block is used to calculate the fault resistance seen from local substation, RFA while Fault Resistance Calculation B block is used to calculate the fault resistance seen from remote substation, RFB. The values of RFA and RFB then will be used to calculate the fault resistance value, RF. In this simulation, the fault location m from local substation is assumed to be known before the simulation is carried out to get the results of fault resistance.

TABLE II SOURCE, TRANSMISSION LINE AND FAULT PARAMETERS.

Parameters Value Unit

Source Voltage 132 kV

Phase angle of phase A 0 degree Nominal frequency 50 Hz

3 phase short circuit MVA 1044 MVA X/R ratio 1 -

Transmission Line Line length 47 km

Positive sequence resistance 0.045531917 Ω / km Zero sequence resistance 0.151489359 Ω / km

Positive sequence inductance 0.0006176566 H / km Zero sequence inductance 0.001533982 H / km

Positive sequence capacitance 1e-9 F / km Zero sequence capacitance 1e-9 F / km

Fault Fault resistance 2, 10 Ω Fault location 5, 10, 15, 20, 25, 30, 35,

40, 45 km

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Fig. 5. Overall simulation model

The function of Analog Low Pass Filter block is to filter

any harmonic component which might appear in the voltage and current signals and only fundamental component of the signals will be passed through for calculation in the next steps. The function of Fourier Analysis block is to extract the magnitude and phase angle of voltage and current signals. The Degree to radian block is used to convert the phase angle from degree to radian for calculation purpose.

IV. SIMULATION RESULTS

This section represents the results to prove that the fault resistance, RF can be determined by calculating the equivalent resistance of parallel connection between fault resistance seen from local substation, RFA and fault resistance seen from remote substation, RFB. The error between calculated RF and actual fault resistance is determined using (8).

%Error Calculated RF Actual RF Actual RF⁄ x100 (8)

The simulation was carried out for two conditions which are for fault resistance RF = 2 Ω and RF = 10 Ω. For each fault resistance value, fault location was varied from 5 km until 45 km from local substation. Table III and Table IV represent the results for RF = 2 Ω and RF = 10 Ω respectively. Fig. 6 and Fig. 7 show the plot of calculated and actual fault resistances for the results from Table III and Table IV respectively.

From the results, it can be proved that the calculated RF for each fault location (in km) is almost similar to actual fault resistance by a small error. From both tables also, it can be seen that even though the fault location was varied, the calculated RF is still almost similar to actual fault resistance and this proved the theory which has been explained in section II.

TABLE III

SIMULATION RESULTS FOR RF = 2 Ω WITH VARIED FAULT LOCATION

Fault location from local substation

5 km 10 km 15 km 20 km 25 km 30 km 35 km 40 km 45 km

RFA (Ω) 3.36 3.42 3.619 3.863 4.07 4.326 4.607 4.922 5.264 RFB (Ω) 5.048 4.731 4.436 4.161 3.929 3.728 3.46 3.304 3.336

Calculated RF (Ω) 2.017 1.985 1.993 2.003 1.999 2.002 1.976 1.977 2.042 % Error 0.85 0.75 0.35 0.15 0.05 0.1 1.2 1.15 2.1

TABLE IV

SIMULATION RESULTS FOR RF = 10 Ω WITH VARIED FAULT LOCATION

Fault location from local substation

5 km 10 km 15 km 20 km 25 km 30 km 35 km 40 km 45 km

RFA (Ω) 16.58 17.26 18.26 19.22 20.35 21.61 22.96 24.55 26.34 RFB (Ω) 25.17 23.65 22.13 20.84 19.66 18.6 17.73 16.81 15.76

Calculated RF (Ω) 9.996 9.978 10.005 9.999 10 9.996 10.004 9.978 9.86 % Error 0.04 0.22 0.05 0.01 0 0.04 0.04 0.22 1.4

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Fig. 6. Simulation results for RF = 2 Ω with varied fault location

Fig. 7. Simulation results for RF = 10 Ω with varied fault location

V. CONCLUSION

This paper presents the theory developed to calculate fault resistance value for phase to phase fault. First the fault resistances seen from both substations will be calculated using

(2) and (5). Then by using (7), the actual fault resistance can be estimated by calculating the equivalent fault resistance of parallel connection between those two fault resistances calculated earlier. The results proved that the calculated fault resistance is almost similar to actual fault resistance by small error and the different fault locations can be said that do not influence the fault resistance calculation. Fault resistance estimation in transmission line fault analysis is very important because it has a great effect on the accuracy of fault location. By accurately estimates the fault resistance, compensation can be made to fault location algorithm thus accurate fault location can be gained.

VI. REFERENCES

[1] M. H. Idris, M. W. Mustafa & Y. Yatim, Effective Two-Terminal Single Line to Ground Fault Location Algorithm, IEEE International Power Engineering and Optimization Conference (PEOCO), Melaka, Malaysia: 6-7 June 2012.

[2] H. Saadat, Power System Analysis, WCB/McGraw-Hill, 1999. [3] M. H. Idris, M. S. Ahmad, A. Z. Abdullah & S. Hardy, Adaptive Mho

Type Distance Relaying Scheme with Fault Resistance Compensation, IEEE International Power Engineering and Optimization Conference (PEOCO), Langkawi, Malaysia: 3-4 June 2013.

[4] Anamika Jain, A. S. Thoke, Ebha Koley & R. N. Patel, Fault Classification and Fault Distance Location of Double Circuit Transmission Lines for Phase to Phase Faults using only One Terminal Data, 3rd International Conference on Power Systems, Kharagpur, India, December 27-29 2009.

[5] Eduardo G. Silveira & Clever Pereira, Transmission Line Fault Location Using Two-Terminal Data Without Time Synchronization, IEEE Transactions on Power Systems, Vol. 22, No. 1, February 2007.

[6] Wen-Hao Zhang, Umar Rosadi, Myeon-Song Choi, Seung-Jae Lee & Ilhyung Lim, A Robust Fault Location Algorithm for Single Line-to-ground Fault in Double-circuit Transmission Systems, Journal of Electrical Engineering & Technology, Vol. 6, No. 1, pp. 1-7, 2011.

[7] Marija Bockarjova, Antans Sauhats & Goran Andersson, Statistical Algorithms for Fault Location on Power Transmission Lines, IEEE Power Tech, Russia, 27-30 June 2005.

3.36 3.42 3.6193.863 4.07

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5.0484.731

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3.929 3.7283.46 3.304 3.336

0

1

2

3

4

5

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5 10 15 20 25 30 35 40 45

Faul

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Fault location from local substation (km)

Simulation Results for RF = 2 Ω with Varied Fault Location

RFARFBCalculated RFActual RF

16.58 17.26 18.26 19.2220.35

21.6122.96

24.5526.34

25.1723.65

22.1320.84

19.6618.6 17.73 16.81

15.76

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5

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15

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25

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5 10 15 20 25 30 35 40 45

Faul

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Fault location from local substation (km)

Simulation Results for RF = 10 Ω with Varied Fault Location

RFARFBCalculated RFActual RF

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