The document presents a technical overview of distance protection in electrical systems, detailing the principles, characteristics, and operational parameters of various protective zones. It covers relay performance, fault simulations, and the impact of resistive faults, emphasizing the importance of accurate reach settings and load encroachment considerations for effective fault detection. Additionally, it includes a discussion on remote backup strategies and the influence of fault resistance on distance protection performance.

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Technical Presentation On
Protection
Distance Protection Basics

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Agenda
1 2 3 4 5 6
Basics Characteristics
Load
Encroachment
Zones of
Protection
Resistive Faults
Remote Infeed

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Principle of Distance Protection
ZK=Uk/ Ik
Uk=0Uk
IkZ<
A B
metallic faultZk
The impedance is proportional to the distance!

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Relay Performance Parameters
Reach Accuracy
• Reach accuracy is a
comparison of the actual
ohmic reach of the relay
under practical conditions
with the relay setting value
in ohms.
• Reach accuracy particularly
depends on the level of
voltage presented to the
relay under fault conditions.
Operating Time
• Operating times vary with
Depending on the
measuring techniques
employed, transient errors
etc.
• Operating Time
Specification is more often
used in electromechanical/
static relays.

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Zones of Protection
Zone-4
•TimeDelayed
•ReverseDirection
•10-25%ofZab
Zone-1
•InstantaneousTrip
•Underreaching
•80-85%ofZab
Zone-3
•TimeDelayed
•RemoteBackup
•120%of(Zab+Zbc)
Zone-2
•TimeDelayed
•Coveradjacentline
•120%ofZab
RA
~~
RB
BUS A BUS B BUS CZab Zbc

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Simulation of Zone Trips
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R3
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R1
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R2
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R4R1-Z1
R1-Z2
R1-Z3
R2-Z1
R2-Z2
R2-Z3
R3-Z1
R3-Z2
R3-Z3
R4-Z1
R4-Z2
R4-Z3
NORMAL OPERATING CONDITION

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Simulation of Zone Trips
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R3
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R1
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R2
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R4R1-Z1
R1-Z2
R1-Z3
R2-Z1
R2-Z2
R2-Z3
R3-Z1
R3-Z2
R3-Z3
R4-Z1
R4-Z2
R4-Z3
FAULT NEAR TO RELAY R1

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Simulation of Tele Transfer Trips
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R3
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R1
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R2
21
-
Z1
21
-
Z2
21
-
Z3
0.2 s
0.6 s
R4R1-Z1
R1-Z2
R1-Z3
R2-Z1
R2-Z2
R2-Z3
R3-Z1
R3-Z2
R3-Z3
R4-Z1
R4-Z2
R4-Z3
FAULT NEAR TO RELAY R1
POTT POTT
Rx
Tx
Rx
Tx

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Distance Characteristics
Characteristic Reactance Impedance Mho Quadrilateral
R-X Diagram
Directionality Non directional Non directional Directional Directional
Applications Short Lines where
arc resistance is
the same order of
the line length
Fault Location
purposes.
Operate for Bus
Faults also
Commonly
Used in Long
Lines. Do not
operate for bus
side faults
Commonly used
due to
independent
setting for R
and X Reach
R
X
Operate
Restrain
R
X
Operate
Z
Restrain
R
X
Operate
Max sen. Line
Restrain
δ, RCA
R
X
Operate
Restrain
Restrain

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Mapping of Faults in R-X Plane
METALLIC FAULT RF=0
120%
40% 60%
80% 100%
20%
140%
XL
RL R
jX
ZL=RL + jXL
ZL
WITH FAULT RESISTANCE
Distance Proportional to ZL.
ZL
RF
120%
40% 60%
80% 100%
20%
140%
XL
RL R
jX
ZL=RL+RF + jXL
1Ω 2Ω 3Ω 4Ω
•Distance Proportional to RF+ZL.
•RF=RARC + RTOWER FOOTING
The relay measures the sum between line impedance (if fault at 100% of the line) and
the fault resistance

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Quadrilateral Characteristics
R1
R2
R3
R4
R5
Z1
ZN
The Grey region is the impedance
locus we want to cover with the
distance protection characteristic.

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MHO Vs. Quad Characteristics
ZL
X
LOAD
RF
Quad
Rf Mho
Short line
ZL
X
LOAD
Long line

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During Double Infeed
F
A
B
FA
A
A
m R
I
I
RZ
I
V
Z   FBAAAA RIIIZV 
• The fault has more or less fault resistance.
• If the fault is an arcing fault the fault resistance is normally very small.
• The influence of the fault resistance depends on the fault current infeed from the
remote line end.
• The fault resistance seen by the distance protection is increased compared to its
real value. This applies if EA &EB are approximately in phase i.e no load transfer
across the feeder.

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Resistive Fault During Double Infeed
FR
F
A
B
R
I
I

AZ
UNDERREACH!

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Remote Backup
• Due to fault current contribution substation B (not ”seen” by relay in ”A), the distance
protection in station A will measure a higher impedance than the "true" impedance to
the fault.
• The relay will under reach and this means in practice it can be difficult to get a
remote back-up.
 1 2A L A A B B FV Z I I I I Z     
Z<
IA IB2
IB1 If=IA+IB1+IB2
ZL
ZFUA
1 2A A B B
m L F
A A
V I I I
Z Z Z
I I
 
   
In feed Factor
A B

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Load Encroachment
X
Zone 01
Zone 02
Zone 03 Remote back-up
R
Zone 05
Remote fault
that has to be
detected
Zone 04 Remote back-up

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Reduced Resistive Reach
X
Zone 01
Zone 02
Zone 03 Remote back-up
R
Zone 05
Remote fault that has to be
detected. But Can’t Detect due
to reduced Resistive Reach
Setting
Zone 04 Remote back-up

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Customized Reach Setting
X
Zone 01
Zone 02
Zone 03 Remote back-up
Zone 04 Remote back-up
R
Zone 05
Remote fault to be detected

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Remote Backup with Load Encroachment
scheme
Zone 03
Zone 02
Zone 01
Zone 04
The green area represents the load encroachment area and “cuts” any impedance
protection that might enter in it

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Any Questions???