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
1
Permanent Fault Need Immediate
Attention
We need accurate fault
location
Temporary Faults Needs Attention Too
Identify & Fix Damaged Insulators-Minimize Fault Recurrence
2
Hard to Find a Flashed Insulator
Finding Faults
3
Visual
Methods
Estimate Location From Current
“JM Drop” circa 1936
Approximate fault location was calculated based on system and
line parameters
4
Methods in Use
• Line impedance Based
♦
Measure impedance to fault
♦
Compare it to the actual line impedance
• Traveling Wave Based
♦
Measure wave arrival time
System OneOne-Line and Circuit
Representation of System Fault
S
VS
IS
m
VS
1–m
ZL
IS
IR
mZL
ZS
R
VR
IR
VR
(1 – m)ZL
IF
RF
5
ZR
Modified Takagi MethodMethod-Single Ended
(Negative Sequence)
V  m  Z1L  I  RF  IF
Multiply by I2 and save Imaginary part
Im V  I 2* 
m  Im Z1L  I  I 2*  RF  Im I F  I 2*
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”
6
Single End Impedance Method
m

Imag Va • I2*


Imag Z1L • Ia  k0 • Ig • I2*

Accuracy of
zero-sequence line
impedance


 System nonhomogeneity
Effect of zero-sequence
 Accuracy of
 mutual coupling from
measurements
parallel lines
 Accuracy of
 Time synchronization
Fault resistance
positive-sequence
line impedance
 Communication
 Radial topology
SE Impedance Fault Location
Phase--Ground Faults
Phase
7
SE Impedance Fault Location
Multi--Phase Faults
Multi
Fault Loop Selection and Reporting
• Select appropriate
Fault Loop
• Report a single fault
location value
8
♦
Select a window of data
from the fault data
♦
Provide the average
value of fault location
computed from the
selected window
Modified Takagi MethodMethod-Multi Ended
(Using Remote terminal current)
V  m  Z1L  I  RF  IF
Multiply by I2 and save Imaginary part
Im V  I 2* 
m  Im Z1L  I  I 2*  RF  Im I F  I F*
THIS IS ZERO
Multi--End I2 Total Current
Multi
FL_AGMEI 

Imag Va • I2T *


Imag Z1L Ia  k0 • IG  • I2T *

Accuracy of
 Fault resistance
 zero-sequence
line
 System nonhomogeneity
impedance
 Accuracy of
 Effect of zero-sequence
measurements
mutual coupling from
parallel lines
 Accuracy of
positive-sequence
 Time synchronization
line impedance
 Communication
9
ME_I Impedance Fault Location
Phase--Ground Faults
Phase
ME Impedance Fault Location
Multi--Phase Faults
Multi
10
Multi Ended Negative Sequence
Using Remote terminal voltage and current
Source S
Source R
Z1S
Z1L
Z1R
ref
I2S
Z2S
I2R
Z2L
Relay S
Z0S
Z0L
V2F
+
Z2R
Relay R
Z0R
ITOTAL
3RF
Use Synchronized Measurements to
Calculate Voltage at Fault Point
V 2 F  V 2 S  I 2 S  m  Z 2 L 
V2 F  V2 R  I 2 R  (1  m)  Z 2 L 
m
V 2 S  V 2 R  I 2 R  ZL 2
( I 2 S  I 2 R )  ZL 2
11
Double End With V2 and I2
 V2L  V2R  I2R • Z1L 
FL_UNBME  Real 

I2T • Z1L


Accuracy of
 Fault resistance
 zero-sequence
line
 System nonhomogeneity
impedance
 Accuracy of
 Effect of zero-sequence
measurements
mutual coupling from
parallel lines
 Accuracy of
positive-sequence
 Time synchronization
line impedance
 Communication
Multi-End Fault Location That Does
MultiNot Require Data Alignment
V2F  I2S  Z 2S  m  Z 2L 
V2F  I2R  Z 2R  1  m  Z2L 
• Each Relay Receives:
♦
♦
Magnitude and Angle of Z2R
I2R
12
Local and Remote Data
Necessary for Fault Location
I2R 
I2S  Z2S   m  I2S  Z2L 
Z 2R  Z2L   m  Z 2L 
• Rearrange Above Equation to Form a
Quadratic Equation
• Solve Quadratic for Fault Location m
Download Paper
Multi--End Methods Needs Time
Multi
Synchronized Data
• Synchrophasors
• Synchronized samples
♦
Devices with data acquisition synchronized
to a common time source
♦
Fixed sampling rate
13
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
Three
14
Reduce From ThreeThree-Terminal Line to
Two--Terminal Equivalent
Two
V2_SP = V2S – Z2L_SP • I2S
V2_TP = V2T – Z2L_TP • I2T
V2_UP = V2U – Z2L_UP • I2U
Same Result
Use TwoTwo-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 m 
 V2S – V2 _ Eq   Z2L _ SP • I2 _ Eq
Z 2L _ SP • I2S  I2 _ Eq 
15
Mutually Coupled Lines
Download Paper
Composite Lines
• Identifies faulted line section
• Calculates distance to fault
16
Intersection of Voltage Profiles
Identifies Faulted Section
Calculate Distance to Fault
Within Faulted Section using ME method
Download Paper
17
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
m

Imag Va • I2*


Imag Z1L • Ia  k0 • Ig • I2*

Multi-End Method using local voltage and currents, and remote
currents
Imag Va • I2T *
MEI FL_AGMEI  Imag Z1L Ia  k0 • IG • I2T*




Multi-End Method using local and remote voltage and currents
ME
 V2L  V2R  I2R • Z1L 
FL_UNBME  Real 

I2T • Z1L


18
Some of the Challenging Situations
for Z based Fault Location Methods
• Short faults: faster relays and breakersphasor 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
19
Lightning and Faults Launch
Traveling Waves
tL
m
tR
1
    tL – tR  v 
2
Download Paper
Double Ended TW Fault Location
1200
1000
Amps
800
600
400
200
0
-200
51.466
51.467
51.468
51.469
Time
20
51.47
51.471
51.472
Single--End TW Fault Locator
Single
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
21
Fault Location Results
(161kV, 117.11km long line)
Fault
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
BG
108.23
107.60
101.59
106.43
BG
98.85
98.98
95.20
98.37
Temporary Fault Due to Insulator
Flashover
22
Insulator Flashover
23