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Fault Location EE 526 Venkat Mynam Senior Research Engineer Schweitzer Engineering Laboratories

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Accurate Fault Location is Critical Expedite Service Restoration Reduce outage times Identify insulator problems Prevent potential recurring faults Verify Protective Relay Performance

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Permanent Fault Need Immediate Attention We need accurate fault location

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Temporary Faults Needs Attention Too Identify & Fix Damaged Insulators-Minimize Fault Recurrence

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Hard to Find a Flashed Insulator

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Finding Faults

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Visual Methods

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Estimate Location From Current “JM Drop” circa 1936 Approximate fault location was calculated based on system and line parameters

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Methods in Use Line impedance Based ♦ Measure impedance to fault ♦ Compare it to the actual line impedance Traveling Wave Based ♦ Measure wave arrival time

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System One-Line and Circuit Representation of System Fault

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Modified Takagi Method-Single Ended (Negative Sequence) Multiply by I 2 and save Imaginary part Zero For: Rf=0 or system is homogeneous

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IEEE Guide Defines Homogeneous System “A transmission system where the local and remote source impedances have the same angle as the line impedance”

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Single End Impedance Method Fault resistance System nonhomogeneity Accuracy of measurements Accuracy of positive-sequence line impedance Accuracy of zero-sequence line impedance Effect of zero-sequence mutual coupling from parallel lines Time synchronization Communication Radial topology

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SE Impedance Fault Location Phase-Ground Faults

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SE Impedance Fault Location Multi-Phase Faults

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Fault Loop Selection and Reporting Select appropriate Fault Loop Report a single fault location value ♦ Select a window of data from the fault data ♦ Provide the average value of fault location computed from the selected window

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Modified Takagi Method-Multi Ended (Using Remote terminal current) Multiply by I 2 and save Imaginary part THIS IS ZERO

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Multi-End I2 Total Current Fault resistance System nonhomogeneity Accuracy of measurements Accuracy of positive-sequence line impedance Accuracy of zero-sequence line impedance Effect of zero-sequence mutual coupling from parallel lines Time synchronization Communication

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ME_I Impedance Fault Location Phase-Ground Faults

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ME Impedance Fault Location Multi-Phase Faults

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V2F + ref Multi Ended Negative Sequence Using Remote terminal voltage and current

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Use Synchronized Measurements to Calculate Voltage at Fault Point

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Double End With V2 and I2 Fault resistance System nonhomogeneity Accuracy of measurements Accuracy of positive-sequence line impedance Accuracy of zero-sequence line impedance Effect of zero-sequence mutual coupling from parallel lines Time synchronization Communication

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Multi-End Fault Location That Does Not Require Data Alignment Each Relay Receives: ♦ Magnitude and Angle of Z 2R ♦ I 2R

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Local and Remote Data Necessary for Fault Location Rearrange Above Equation to Form a Quadratic Equation Solve Quadratic for Fault Location m Download Paper

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Multi-End Methods Needs Time Synchronized Data Synchrophasors Synchronized samples ♦ Devices with data acquisition synchronized to a common time source ♦ Fixed sampling rate

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Series Compensated Lines Line Side PT Bus Side PT Challenges Steady State Transient (phasor estimate is not stable) Subsynchronous MOV and bypass breaker switching Download Paper

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Three-Terminal Line

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Reduce From Three-Terminal Line to Two-Terminal Equivalent V 2_SP = V 2S – Z 2L_SP I 2S V 2_TP = V 2T – Z 2L_TP I 2T V 2_UP = V 2U – Z 2L_UP I 2U Same Result

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Use Two-Terminal Equivalent to Solve for m I 2_Eq = I 2T + I 2U V 2_Eq = V 2_TP Solve for m using SE or Multi-terminal (ME_I, ME) ME_I

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Mutually Coupled Lines Download Paper

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Composite Lines Identifies faulted line section Calculates distance to fault

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Intersection of Voltage Profiles Identifies Faulted Section

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Calculate Distance to Fault Within Faulted Section using ME method Download Paper

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Impedance Method Approach Summary Measure VA, VB, VC, IA, IB, IC Extract fundamental components Determine phasors and fault type Apply impedance algorithm

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Impedance Fault Location Methods Multi-End Method using local and remote voltage and currents Multi-End Method using local voltage and currents, and remote currents Single-End Method using local voltage and currents SE MEI ME

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Some of the Challenging Situations for Z based Fault Location Methods Short faults: faster relays and breakers- phasor estimate is not stable Faults associated with time-varying fault resistance-phasor estimate is not stable Series compensation

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Short Duration Faults Raw-Blue, Cosine Filtered-Green Magnitude of Filtered Quantity-Red

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Lightning and Faults Launch Traveling Waves tLtL tRtR Download Paper

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Double Ended TW Fault Location

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Single-End TW Fault Locator

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Results From Field 117.11km, 161 kV line 18 sections with 4 different tower configurations Challenges with existing impedance based fault location methods Image courtesy of Google

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FaultTWPatrolSE_ZME_Z_IME_Z CG109.74109.29105.44106.24106.56 BG 61.12 61.4154.7560.6960.70 BG108.23107.60101.59106.43 BG 98.85 98.9895.2098.37 Fault Location Results (161kV, 117.11km long line)

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Temporary Fault Due to Insulator Flashover

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Insulator Flashover

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