Effective Two-Terminal Single Line to Ground Fault

Location Algorithm

Muhd Hafizi Bin Idris Associate Professor Mohd Wazir MustafaYazhar Yatim

Presentation Outline

IntroductionResearch ObjectivePrevious ResearchThe Theories behind the TechniqueMethodologyResult & DiscussionConclusionReferencesQ & A

Research Objective

To design a new fault locating technique using two-terminal fault location algorithm.

Introduction

Fault has higher possibility to occur at transmission line because transmission line is exposed to the environment.The accurate fault location is very important because a small error in fault location may similar to several hundred meters or higher and this would delay the restoration time.Most of the fault are unbalanced faults where single line to ground fault contributes more than 90 % of the fault (TNB’s 5 years tripping statistics) [1].The categories of fault locating techniques are travelling wave and impedance based methods [2].

Cont..Impedance based method is widely used because of its simplicity and low cost. This technique uses the fundamental frequency of voltage and current phasors from installed transducers [2].For impedance based method, 2 categories applied that are one-terminal and two-terminal algorithms.One-terminal algorithm is commonly used because of limited access of data from both substation terminals.This algorithm requires many mathematical assumptions to eliminate the effect of fault resistance on fault location accuracy.

Cont.In term of accuracy, two-terminal is more accurate than one-terminal algorithm because the algorithm is not affected by the fault resistance and reactance effect.This algorithm requires communication channel to transfer the data between both substations.

Previous ResearchQ. Zhang et al. (1999) designed an algorithm to estimate fault location of a SLG fault on a two paralleled transmission line. The algorithm uses the faulted phase circuit and zero sequence circuit for fault location estimation and doesn’t require the source impedance data from remote end substation. The technique assumed that, in general, the load is not contained in the zero sequence circuit of the faulted phase. Thus, the effect of load disturbance on the accuracy of fault location can be eliminated [3].D. J. Lawrence et al. (1992) use ABCD parameters to define the transmission line and derive the equation for fault location. Different equations are derived based on fault types and the distance to fault location is derived from Newton’s technique for non-linear equations [4].

The Theories behind the Technique

The fault location is at m distance from substation A and (1-m) distance from substation B. The representation of SLG fault at a phase line can be extended to its’ sequence components as seen from both substations.

Cont..

Cont..Phase to ground fault voltage, VF seen from both substations can be written as;

Zero sequence components of phase currents from both substations are equal to;

Equalizing equation 1 & 2 and substituting IA0 and IB0 then rearranging for m:

Cont..

Equation 3 is in the complex form. To get the magnitude of m, the values of magnitude and phase angle of VA, VB, IA, IB, Z1, Z2 and Z0 must be available first. Magnitudes and phase angles of Z1, Z2 and Z0 can be taken directly from settings available in the protection relay while the magnitudes and phase angles of VA, VB, IA and IB which represent the post fault values can be extracted from the fault recorders or numerical protection relays.

Methodology

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Simulation Results

The errors between the estimated fault locations and actual fault locations were calculated using the formula:

Cont..

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Cont..Fault location errors for different fault locations and fault resistance, Rf

ConclusionThe algorithm proposed to estimate fault location for SLG fault in this paper presents quite accurate result. The algorithm is not subjected to fault resistance value. Fault location estimation can be carried out offline at the utility’s office or main substations where there are facilities to extract fault waveforms from fault/disturbance recorders or numerical protection relays using available communication channels.By knowing the value of m, fault resistance can be calculated directly by using (1) or (2).

References[1] A. M. Zin, S. P. A. Karim, “The Application of Fault Signature

Analysis in Tenaga Nasional Berhad Malaysia”, IEEE Transactions on Power Delivery, Vol. 22, No. 4, October 2007.

[2] Y. Cheng, J. Suonan, G. Song and X. Kang. “One- Terminal Impedance Fault Location Algorithm for Single Phase to Earth Fault of Transmission Line”, IEEE 2010.

[3] Q. Zhang, Y. Zhang, W. Song and Y. Yu. “Transmission Line Fault Location for Phase-to-Earth Using One Terminal Data”, IEE Proc.-Gener. Transm. Distrib., Vol. 146, No. 2. March 1999.

[4] D. J. Lawrence, L. Cabeza and L. Hochberg. “Development of an Advanced Transmission Line Fault Location System Part I1 – Algorithm Development and Simulation”, IEEE Transaction on Power Delivery, Vol. 7, No. 4, October 1992, pp. 1972-1983.

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