# Accurate Fault Location is Critical

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

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

Permanent Fault Need Immediate Attention
We need accurate fault location

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

Hard to Find a Flashed Insulator
Fault location investigations

Finding Faults

Visual Methods

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

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

System One-Line and Circuit Representation of System Fault

Modified Takagi Method-Single Ended (Negative Sequence)
Multiply by I2 and save Imaginary part Zero For: Rf=0 or system is homogeneous

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

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

SE Impedance Fault Location Phase-Ground Faults
𝑚𝐴𝐺= 𝐼𝑚 𝑉𝐴𝐺∙ 𝐼 2 𝑎 ∗ 𝐼𝑚 𝑍1𝐿∙ 𝐼𝐴𝐺+𝑘0∙𝐼𝐺 ∙ 𝐼 2 𝑎 ∗ 𝑚𝐵𝐺= 𝐼𝑚(𝑉𝐵𝐺∙ 𝐼 2 𝑏 ∗ ) 𝐼𝑚(𝑍1𝐿∙(𝐼𝐵𝐺+𝑘0∙𝐼𝐺)∙ 𝐼 2 𝑏 ∗ ) 𝑚𝐶𝐺= 𝐼𝑚 𝑉𝐶𝐺∙ 𝐼 2 𝑐 ∗ 𝐼𝑚 𝑍1𝐿∙ 𝐼𝐶𝐺+𝑘0∙𝐼𝐺 ∙ 𝐼 2 𝑐 ∗ 𝐼 2 𝑏 =𝑎∙𝐼 2 𝑎 𝐼 2 𝑐 = 𝑎 2 ∙𝐼 2 𝑎

SE Impedance Fault Location Multi-Phase Faults
𝑚𝐴𝐵= 𝐼𝑚 𝑉𝐴𝐵∙ 𝑗∙𝐼 2 𝑐 ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐵𝐶∙ 𝑗∙𝐼 2 𝑐 ∗ 𝑚𝐵𝐶= 𝐼𝑚 𝑉𝐵𝐶∙ (𝑗∙𝐼 2 𝑎 ) ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐵𝐶∙ (𝑗∙𝐼 2 𝑎 ) ∗ 𝑚𝐶𝐴= 𝐼𝑚 𝑉𝐶𝐴∙ (𝑗∙𝐼 2 𝑏 ) ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐶𝐴∙ (𝑗∙𝐼 2 𝑏 ) ∗ 𝑚3𝑃= 𝐼𝑚 𝑉∅∅∙ 𝐼∅∅ ∗ 𝐼𝑚 𝑍1𝐿∙𝐼∅∅∙ 𝐼∅∅ ∗ 𝐼 2 𝑏 =𝑎∙𝐼 2 𝑎 𝐼 2 𝑐 = 𝑎 2 ∙𝐼 2 𝑎

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

Modified Takagi Method-Multi Ended (Using Remote terminal current)
Multiply by I2 and save Imaginary part THIS IS ZERO

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

ME_I Impedance Fault Location Phase-Ground Faults
𝑚𝐴𝐺= 𝐼𝑚 𝑉𝐴𝐺∙ 𝐼 2𝑇 𝑎 ∗ 𝐼𝑚 𝑍1𝐿∙ 𝐼𝐴𝐺+𝑘0∙𝐼𝐺 ∙ 𝐼 2𝑇 𝑎 ∗ 𝑚𝐵𝐺= 𝐼𝑚(𝑉𝐵𝐺∙ 𝐼 2𝑇 𝑏 ∗ ) 𝐼𝑚(𝑍1𝐿∙(𝐼𝐵𝐺+𝑘0∙𝐼𝐺)∙ 𝐼 2𝑇 𝑏 ∗ ) 𝑚𝐶𝐺= 𝐼𝑚 𝑉𝐶𝐺∙ 𝐼 2𝑇 𝑐 ∗ 𝐼𝑚 𝑍1𝐿∙ 𝐼𝐶𝐺+𝑘0∙𝐼𝐺 ∙ 𝐼 2𝑇 𝑐 ∗ 𝐼 2𝑇 𝑏 =𝑎∙𝐼 2𝑇 𝑎 𝐼 2𝑇 𝑐 = 𝑎 2 ∙𝐼 2𝑇 𝑎 𝐼2𝑇=𝐼2𝐿𝑜𝑐𝑎𝑙+𝐼2𝑅𝑒𝑚𝑜𝑡𝑒

ME Impedance Fault Location Multi-Phase Faults
𝑚𝐴𝐵= 𝐼𝑚 𝑉𝐴𝐵∙ 𝑗∙𝐼 2𝑇 𝑐 ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐵𝐶∙ 𝑗∙𝐼 2𝑇 𝑐 ∗ 𝑚𝐵𝐶= 𝐼𝑚 𝑉𝐵𝐶∙ (𝑗∙𝐼 2𝑇 𝑎 ) ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐵𝐶∙ (𝑗∙𝐼 2𝑇 𝑎 ) ∗ 𝑚𝐶𝐴= 𝐼𝑚 𝑉𝐶𝐴∙ (𝑗∙𝐼 2𝑇 𝑏 ) ∗ 𝐼𝑚 𝑍1𝐿∙𝐼𝐶𝐴∙ (𝑗∙𝐼 2𝑇 𝑏 ) ∗ 𝑚3𝑃= 𝐼𝑚 𝑉∅∅∙ 𝐼∅∅𝑇 ∗ 𝐼𝑚 𝑍1𝐿∙𝐼∅∅∙ 𝐼∅∅𝑇 ∗ 𝐼 2𝑇 𝑏 =𝑎∙𝐼 2𝑇 𝑎 𝐼 2𝑇 𝑐 = 𝑎 2 ∙𝐼 2𝑇 𝑎 𝐼2𝑇=𝐼2𝐿𝑜𝑐𝑎𝑙+𝐼2𝑅𝑒𝑚𝑜𝑡𝑒 𝐼∅∅𝑇 =𝐼∅∅𝐿𝑜𝑐𝑎𝑙+𝐼∅∅𝑅𝑒𝑚𝑜𝑡𝑒

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

Use Synchronized Measurements to Calculate Voltage at Fault Point

        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

Multi-End Fault Location That Does Not Require Data Alignment
Each Relay Receives: Magnitude and Angle of Z2R ½I2R½

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

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

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

Three-Terminal Line

Reduce From Three-Terminal Line to Two-Terminal Equivalent
V2_SP = V2S – Z2L_SP • I2S V2_TP = V2T – Z2L_TP • I2T Same Result V2_UP = V2U – Z2L_UP • I2U

Use Two-Terminal Equivalent to Solve for m
I2_Eq = I2T + I2U V2_Eq = V2_TP Solve for m using SE or Multi-terminal (ME_I, ME) ME_I

Mutually Coupled Lines

Composite Lines Identifies faulted line section
Calculates distance to fault

Intersection of Voltage Profiles Identifies Faulted Section

Calculate Distance to Fault Within Faulted Section using ME method

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

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

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

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

Lightning and Faults Launch Traveling Waves

Double Ended TW Fault Location

Single-End TW Fault Locator

Image courtesy of Google
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

Fault Location Results (161kV, 117.11km long line)
TW Patrol SE_Z ME_Z_I ME_Z CG 109.74 109.29 105.44 106.24 106.56 BG 61.12 61.41 54.75 60.69 60.70 108.23 107.60 101.59 106.43 98.85 98.98 95.20 98.37

Temporary Fault Due to Insulator Flashover

Insulator Flashover

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