This document provides an overview of fundamentals of distance protection for transmission lines. It discusses types of transmission lines and typical protection schemes used based on line length. It then describes what distance protection is and challenges in relay design related to transients. The document outlines considerations for distance relay characteristics, polarization, and schemes including non-pilot and pilot schemes. It discusses redundancy, security, out-of-step relaying and series compensation.

1. Fundamentals of Distance
Protection
GE Multilin

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April 11, 2023
Outline
• Transmission line introduction
• What is distance protection?
• Non-pilot and pilot schemes
• Redundancy considerations
• Security for dual-breaker terminals
• Out-of-step relaying
• Single-pole tripping
• Series-compensated lines

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Transmission Lines
A Vital Part of the Power System:
• Provide path to transfer power between generation and load
• Operate at voltage levels from 69kV to 765kV
• Deregulated markets, economic, environmental requirements
have pushed utilities to operate transmission lines close to their
limits.

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Transmission Lines
Classification of line length depends on:
 Source-to-line Impedance Ratio (SIR),
and
 Nominal voltage
Length considerations:
 Short Lines: SIR > 4
 Medium Lines: 0.5 < SIR < 4
 Long Lines: SIR < 0.5

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Typical Protection Schemes
Short Lines
• Current differential
• Phase comparison
• Permissive Overreach Transfer Trip (POTT)
• Directional Comparison Blocking (DCB)

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Typical Protection Schemes
Medium Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Inverse time overcurrent
• Current Differential

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Typical Protection Schemes
Long Lines
• Phase comparison
• Directional Comparison Blocking (DCB)
• Permissive Underreach Transfer Trip (PUTT)
• Permissive Overreach Transfer Trip (POTT)
• Unblocking
• Step Distance
• Step or coordinated overcurrent
• Current Differential

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What is distance protection?
For internal faults:
> IZ – V and V approximately
in phase (mho)
> IZ – V and IZ
approximately in phase
(reactance)
RELAY (V,I)
Intended
REACH point
Z
F1
I*Z
V=I*ZF
I*Z - V

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What is distance protection?
For external faults:
> IZ – V and V approximately
out of phase (mho)
> IZ – V and IZ
approximately out of phase
(reactance)
RELAY (V,I)
Intended
REACH point
Z I*Z
V=I*ZF
I*Z - V
F2

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What is distance protection?
RELAY
Intended
REACH point
Z

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April 11, 2023
Source Impedance Ratio,
Accuracy & Speed
Lin
e
System
Relay
Voltage at the relay:
SIR
f
f
V
V
PU
LOC
PU
LOC
N
R


]
[
]
[
Consider SIR = 0.1
Fault location Voltage
(%)
Voltage change
(%)
75% 88.24 2.76
90% 90.00 0.91
100% 90.91 N/A
110% 91.67 0.76

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Source Impedance Ratio,
Accuracy & Speed
Lin
e
System
Relay
Voltage at the relay:
SIR
f
f
V
V
PU
LOC
PU
LOC
N
R


]
[
]
[
Consider SIR = 30
Fault location Voltage
(%)
Voltage change
(%)
75% 2.4390 0.7868
90% 2.9126 0.3132
100% 3.2258 N/A
110% 3.5370 0.3112

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Challenges in relay design
> Transients:
– High frequency
– DC offset in currents
– CVT transients in
voltages
CVT output
0 1 2 3 4
steady-state
output
power cycles
-30
-20
-10
0
10
20
30
voltage,
V
C1
C2
2
3 5
6
1
4
7
High Voltage Line
Secondary
Voltage
Output
8

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Challenges in relay design
> Transients:
– High frequency
– DC offset in currents
– CVT transients in
voltages
C1
C2
2
3 5
6
1
4
7
High Voltage Line
Secondary
Voltage
Output
8
CVT
output
0 1 2 3 4
steady-state
output
-60
-40
-20
0
20
40
power cycles
voltage,
V
60

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Challenges in relay design
-0.5 0 0.5 1 1.5
-100
-80
-60
-40
-20
0
20
40
60
80
100
Voltage
[V]
-0.5 0 0.5 1 1.5
-3
-2
-1
0
1
2
3
4
5
Current
[A]
vA
vB vC
iA
iB
,iC
-0.5 0 0.5 1 1.5
-100
-50
0
50
100
Reactance
comparator
[V]
power cycles
SPOL
SOP
Sorry… Future (unknown)
> In-phase = internal
fault
> Out-of-phase =
external fault

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Transient Overreach
• Fault current generally contains dc offset in
addition to ac power frequency component
• Ratio of dc to ac component of current
depends on instant in the cycle at which fault
occurred
• Rate of decay of dc offset depends on
system X/R

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Zone 1 and CVT Transients
Capacitive Voltage Transformers (CVTs) create certain
problems for fast distance relays applied to systems with
high Source Impedance Ratios (SIRs):
> CVT-induced transient voltage components may
assume large magnitudes (up to 30-40%) and last for
a comparatively long time (up to about 2 cycles)
> 60Hz voltage for faults at the relay reach point may be
as low as 3% for a SIR of 30
> the signal may be buried under noise

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CVT transients can cause distance relays to overreach.
Generally, transient overreach may be caused by:
> overestimation of the current (the magnitude of the
current as measured is larger than its actual value,
and consequently, the fault appears closer than it is
actually located),
> underestimation of the voltage (the magnitude of the
voltage as measured is lower than its actual value)
> combination of the above
Zone 1 and CVT Transients

19. Distance Element Fundamentals
XL
XC
R
Z1 End Zone

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-10 -5 0 5 10
-5
0
5
10
15
Reactance
[ohm]
Resistance [ohm]
18
22
26
30
34
42
44 Actual Fault
Location
Line
Impedance
Trajectory
(msec)
dynamic mho
zone extended
for high SIRs
Impedance locus may pass
below the origin of the Z-plane -
this would call for a time delay
to obtain stability

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> apply delay (fixed or adaptable)
> reduce the reach
> adaptive techniques and better filtering
algorithms
CVT Transient Overreach
Solutions

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> Optimize signal filtering:
– currents - max 3% error due to the dc component
– voltages - max 0.6% error due to CVT transients
> Adaptive double-reach approach
– filtering alone ensures maximum transient
overreach at the level of 1% (for SIRs up to 5) and
20% (for SIRs up to 30)
– to reduce the transient overreach even further an
adaptive double-reach zone 1 has been
implemented
CVT Transients – Adaptive
Solution

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The outer zone 1:
> is fixed at the actual reach
> applies certain security delay to cope with CVT transients
Delayed
Trip
Instantaneous
Trip
R
X
The inner zone 1:
> has its reach dynamically
controlled by the voltage
magnitude
> is instantaneous
CVT Transients – Adaptive
Solution

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Desirable Distance Relay
Attributes
Filters:
> Prefiltering of currents to remove dc decaying transients
– Limit maximum transient overshoot (below 2%)
> Prefiltering of voltages to remove low frequency transients
caused by CVTs
– Limit transient overreach to less than 5% for an SIR of
30
> Accurate and fast frequency tracking algorithm
> Adaptive reach control for faults at reach points

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Distance Relay Operating Times

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Distance Relay Operating Times
20ms
15ms
25ms 30ms
35ms

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Distance Relay Operating Times
SLG faults LL faults
3P faults

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0 5 10 15 20 25 30
0
10
20
30
40
50
60
70
80
90
100
Maximum
Rach
[%]
SIR
Actual maximum reach curves
Relay 1
Relay 3
Relay 2
Relay 4

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Maximum Torque Angle
• Angle at which mho element has maximum
reach
• Characteristics with smaller MTA will
accommodate larger amount of arc resistance

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Traditional
Directional
angle lowered
and “slammed”
Directional angle
“slammed”
Both MHO and
directional angles
“slammed” (lens)
Mho Characteristics

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Typical load characteristic
impedance
+R
Operate
area
No Operate area
+XL
+ = LOOKING INTO LINE
normally considered
forward
Load
Trajectory
Load Swings

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Load swing
“Lenticular”
Characteristic
Load Swings

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Load Encroachment Characteristic
The load encroachment element responds to positive
sequence voltage and current and can be used to
block phase distance and phase overcurrent
elements.

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Blinders
• Blinders limit the operation of distance relays
(quad or mho) to a narrow region that parallels
and encompasses the protected line
• Applied to long transmission lines, where
mho settings are large enough to pick up on
maximum load or minor system swings

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Quadrilateral Characteristics

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Ground Resistance
(Conductor falls on ground)
R Resultant impedance outside of
the mho operating region
Quadrilateral Characteristics

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Mho Quadrilatera
l
Better coverage for
ground faults due
to resistance added
to return path
Lenticular
Used for phase elements
with long heavily loaded
lines heavily loaded
Standard for phase
elements
JX
R
Distance Characteristics -
Summary

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Distance Element Polarization
The following polarization quantities are commonly
used in distance relays for determining directionality:
• Self-polarized
• Memory voltage
• Positive sequence voltage
• Quadrature voltage
• Leading phase voltage

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Memory Polarization
> Positive-sequence memorized voltage is used for
polarizing:
– Mho comparator (dynamic, expanding Mho)
– Negative-sequence directional comparator (Ground
Distance Mho and Quad)
– Zero-sequence directional comparator (Ground
Distance MHO and QUAD)
– Directional comparator (Phase Distance MHO and
QUAD)
> Memory duration is a common distance settings (all zones,
phase and ground, MHO and QUAD)

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Memory Polarization
jX
R
Dynamic MHO characteristic for a reverse fault
Dynamic MHO characteristic for a forward fau
Impedance During Close-up Faults
Static MHO characteristic (memory not established or
expired)
ZL
ZS

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Memory Polarization
Memory Polarization…Improved Resistive
Coverage
Dynamic MHO characteristic for a forward fault
Static MHO characteristic (memory not established or
expired)
jX
R
ZL
ZS
RL

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Choice of Polarization
• In order to provide flexibility modern distance
relays offer a choice with respect to
polarization of ground overcurrent direction
functions:
–Voltage polarization
–Current polarization
–Dual polarization

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Ground Directional Elements
> Pilot-aided schemes using ground mho distance relays
have inherently limited fault resistance coverage
> Ground directional over current protection using either
negative or zero sequence can be a useful supplement to
give more coverage for high resistance faults
> Directional discrimination based on the ground quantities is
fast:
– Accurate angular relations between the zero and
negative sequence quantities establish very quickly
because:
 During faults zero and negative-sequence
currents and voltages build up from very low
values (practically from zero)
 The pre-fault values do not bias the developing
fault components in any direction

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Distance Schemes
Pilot Aided
Schemes
No Communication
between Distance
Relays
Communication
between Distance
relays
Non-Pilot Aided
Schemes
(Step Distance)

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Step Distance Schemes
• Zone 1:
– Trips with no intentional time delay
– Underreaches to avoid unnecessary operation for faults
beyond remote terminal
– Typical reach setting range 80-90% of ZL
• Zone 2:
– Set to protect remainder of line
– Overreaches into adjacent line/equipment
– Minimum reach setting 120% of ZL
– Typically time delayed by 15-30 cycles
• Zone 3:
– Remote backup for relay/station failures at remote
terminal
– Reaches beyond Z2, load encroachment a consideration

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Z1
Z1
Local
Remote
Step Distance Schemes

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Z1
Z1
End
Zone
End
Zone
Local
Remote
Step Distance Schemes

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Z1
Z1
Breaker
Tripped
Breaker
Closed
Local
Remote
Step Distance Schemes

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Z1
Z1
Z2 (time delayed)
Remote
Local
Step Distance Schemes
Z2 (time delayed)

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Z1
Z2 (time delayed)
Step Distance Schemes
Z3 (remote backup) …

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Step Distance Protection

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Local Relay – Z2
Zone 2 PKP
Local Relay Remote Relay
Remote Relay – Z4
Zone 4 PKP
Over Lap
Distance Relay Coordination

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Communication
Channel
Local
Relay
Remote Relay
Need For Pilot Aided Schemes

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Pilot Communications Channels
• Distance-based pilot schemes traditionally utilize
simple on/off communications between relays, but
can also utilize peer-to-peer communications and
GOOSE messaging over digital channels
• Typical communications media include:
– Pilot-wire (50Hz, 60Hz, AT)
– Power line carrier
– Microwave
– Radio
– Optic fiber (directly connected or multiplexed
channels)

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Distance-based Pilot Protection

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Pilot-Aided Distance-Based Schemes
 DUTT – Direct Under-reaching Transfer Trip
 PUTT – Permissive Under-reaching Transfer
Trip
 POTT – Permissive Over-reaching Transfer Trip
 Hybrid POTT – Hybrid Permissive Over-
reaching Transfer Trip
 DCB – Directional Comparison Blocking
Scheme
 DCUB – Directional Comparison Unblocking
Scheme

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Direct Underreaching Transfer Trip
(DUTT)
• Requires only underreaching (RU) functions which
overlap in reach (Zone 1).
•Applied with FSK channel
– GUARD frequency transmitted during normal
conditions
– TRIP frequency when one RU function operates
• Scheme does not provide tripping for faults beyond
RU reach if remote breaker is open or channel is
inoperative.
• Dual pilot channels improve security

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Bus
Line
Bus
Zone 1
Zone 1
DUTT Scheme

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Permissive Underreaching
Transfer Trip (PUTT)
• Requires both under (RU) and overreaching
(RO) functions
• Identical to DUTT, with pilot tripping signal
supervised by RO (Zone 2)

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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1
To protect end of
line
& Local Trip
Zone 2
Rx PKP
OR
Zone 1
PUTT Scheme

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Permissive Overreaching Transfer
Trip (POTT)
• Requires overreaching (RO) functions (Zone
2).
• Applied with FSK channel:
–GUARD frequency sent in stand-by
–TRIP frequency when one RO function
operates
• No trip for external faults if pilot channel is
inoperative
• Time-delayed tripping can be provided

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Bus
Line
Bus
Zone 1
Zone 2
Trip
Line
Breakers
OR
t
Rx
Tx
AND
(Z1)
(Z1)
o
Zone 1
Zone 2
Zone 2
Zone 1
POTT Scheme

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POTT Scheme
POTT – Permissive Over-reaching Transfer
Trip
End
Zone
Communication
Channel

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Local Relay Remote Relay
Remote
Relay FWD
IGND
Ground Dir OC Fwd
OR
Local Relay – Z2
ZONE 2 PKP
Local Relay
FWD IGND
Ground Dir OC Fwd
OR
TRIP
Remote Relay – Z2
POTT TX
ZONE 2 PKP
POTT RX
Communicatio
n Channel
POTT Scheme

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POTT TX 4
POTT TX 3
POTT TX 2
POTT TX 1 A to G
B to G
C to G
Multi Phase
Local Relay Remote Relay
POTT RX 4
POTT RX 3
POTT RX 2
POTT RX 1
Communications
Channel(s)
POTT Scheme

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Local Relay Remote Relay
POTT TX ZONE 2 OR
GND DIR OC FWD
Communication
Channel
TRIP
GND DIR OC REV
GND DIR OC REV POTT RX
Start
Timer
Timer
Expire
GND DIR OC FWD
POTT Scheme
Current reversal example

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Local Relay
Open
Remote Relay
Remote FWD
IGND
POTT TX
Remote – Z2
Communication
Channel
POTT RX
OPEN
POTT TX
Communication
Channel
POTT RX
TRIP
POTT Scheme
Echo example

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Hybrid POTT
• Intended for three-terminal lines and weak
infeed conditions
• Echo feature adds security during weak
infeed conditions
• Reverse-looking distance and oc elements
used to identify external faults

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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1 Zone 4
Local
Remote
Weak
system
Hybrid POTT

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Directional Comparison Blocking
(DCB)
• Requires overreaching (RO) tripping and blocking
(B) functions
• ON/OFF pilot channel typically used (i.e., PLC)
– Transmitter is keyed to ON state when blocking
function(s) operate
– Receipt of signal from remote end blocks
tripping relays
• Tripping function set with Zone 2 reach or greater
• Blocking functions include Zone 3 reverse and low-
set ground overcurrent elements

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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1
Local
Remote
DCB Scheme

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End Zone
Communication Channel
Directional Comparison Blocking
(DCB)

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Directional Comparison Blocking
(DCB)
Internal Faults
Local Relay Remote Relay
Local Relay – Z2
Zone 2 PKP
TRIP Timer
Start
FWD IGND
GND DIR OC Fwd
OR
Dir Block RX
NO
TRIP
Expired

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Local Relay Remote Relay
Remote Relay – Z4
Zone 4 PKP
REV IGND
GND DIR OC Rev
OR
DIR BLOCK TX
Local Relay – Z2
Zone 2 PKP
Dir Block RX
Communication
Channel
FWD IGND
GND DIR OC Fwd
OR
TRIP Timer
Start No TRIP
Directional Comparison Blocking
(DCB)
External Faults

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Directional Comparison
Unblocking (DCUB)
• Applied to Permissive Overreaching (POR)
schemes to overcome the possibility of carrier signal
attenuation or loss as a result of the fault
• Unblocking provided in the receiver when signal is
lost:
– If signal is lost due to fault, at least one
permissive RO functions will be picked up
– Unblocking logic produces short-duration TRIP
signal (150-300 ms). If RO function not picked
up, channel lockout occurs until GUARD signal
returns

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Bus
Line
Bus
Trip
Line
Breakers
Tx1
(Un-Block)
Forward
Forward
Tx2
(Block)
Forward
Rx2
Rx1
t
o
AND t
o
AND
AND
AND
Lockout
(Block)
(Un-Block)
DCUB Scheme

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End Zone
Communication Channel
Directional Comparison Unblocking
(DCUB)

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Directional Comparison Unblocking
(DCUB)
Normal conditions
Local Relay Remote Relay
GUARD1 TX
GUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
NO Loss of Guard
FSK Carrier FSK Carrier
NO Permission
NO Loss of Guard
NO Permission
Load Current

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Directional Comparison Unblocking
(DCUB)
Normal conditions, channel failure
Local Relay Remote Relay
GUARD1 TX
GUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
FSK Carrier FSK Carrier
Loss of Guard
Block Timer Started
Loss of Guard
Block Timer Started
Load Current
NO RX
NO RX
Block DCUB
until Guard OK
Expired
Block DCUB
until Guard OK
Expired
Loss of Channel

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Directional Comparison Unblocking
(DCUB)
Internal fault, healthy channel
Local Relay Remote Relay
GUARD1 TX
GUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
FSK Carrier FSK Carrier
Loss of Guard
Permission
TRIP1 TX
Local Relay – Z2
Zone 2 PKP
TRIP1 RX
TRIP2 TX
TRIP
Remote Relay – Z2
ZONE 2 PKP
TRIP Z1
TRIP2 RX

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Directional Comparison Unblocking
(DCUB)
Internal fault, channel failure
Local Relay Remote Relay
GUARD1 TX
GUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
FSK Carrier FSK Carrier
TRIP1 TX
Local Relay – Z2
Zone 2 PKP
NO RX
TRIP2 TX
TRIP
Remote Relay – Z2
ZONE 2 PKP
TRIP Z1
NO RX
Loss of Guard
Loss of Channel
Loss of Guard
Block Timer Started
Duration Timer Started
Expired

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Redundancy Considerations
• Redundant protection systems increase dependability of the
system:
 Multiple sets of protection using same protection principle
and multiple pilot channels overcome individual element
failure, or
 Multiple sets of protection using different protection
principles and multiple channels protects against failure of
one of the protection methods.
• Security can be improved using “voting” schemes (i.e., 2-out-
of-3), potentially at expense of dependability.
• Redundancy of instrument transformers, battery systems, trip
coil circuits, etc. also need to be considered.

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End Zone
Communication Channel 1
Communication Channel 2
Loss of Channel 2
AND Channels:
POTT Less Reliable
DCB Less Secure
OR Channels:
POTT More Reliable
DCB More Secure
More Channel Security More Channel Dependability
Redundant Communications

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Redundant Pilot Schemes

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• Integrated functions:
weak infeed
echo
line pick-up (SOTF)
• Basic protection elements used to key the
communication:
distance elements
fast and sensitive ground (zero and negative
sequence) directional IOCs with current,
voltage, and/or dual polarization
Pilot Relay Desirable Attributes

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Pre-programmed distance-based pilot schemes:
 Direct Under-reaching Transfer Trip (DUTT)
 Permissive Under-reaching Transfer Trip (PUTT)
 Permissive Overreaching Transfer Trip (POTT)
 Hybrid Permissive Overreaching Transfer Trip (HYB
POTT)
 Blocking scheme (DCB)
 Unblocking scheme (DCUB)
Pilot Relay Desirable Attributes

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Security for dual-breaker terminals
• Breaker-and-a-half and ring bus terminals are
common designs for transmission lines.
• Standard practice has been to:
– sum currents from each circuit breaker
externally by paralleling the CTs
– use external sum as the line current for
protective relays
• For some close-in external fault events, poor CT
performance may lead to improper operation of line
relays.

88. 88 /
GE /
April 11, 2023
Security for dual-breaker terminals
Accurate CTs preserve the
reverse current direction
under weak remote infeed

89. 89 /
GE /
April 11, 2023
Security for dual-breaker terminals
Saturation of CT1 may
invert the line current as
measured from externally
summated CTs

90. 90 /
GE /
April 11, 2023
Security for dual-breaker terminals
• Direct measurement of currents
from both circuit breakers allows
the use of supervisory logic to
prevent distance and directional
overcurrent elements from
operating incorrectly due to CT
errors during reverse faults.
• Additional benefits of direct
measurement of currents:
 independent BF protection
for each circuit breaker
 independent autoreclosing
for each breaker

91. 91 /
GE /
April 11, 2023
Security for dual-breaker terminals
Supervisory logic should:
– not affect speed or sensitivity of protection elements
– correctly allow tripping during evolving external-to-
internal fault conditions
– determine direction of current flow through each
breaker independently:
• Both currents in FWD direction  internal fault
• One current FWD, one current REV  external fault
– allow tripping during all forward/internal faults
– block tripping during all reverse/external faults
– initially block tripping during evolving external-to-
internal faults until second fault appears in forward
direction. Block is then lifted to permit tripping.

92. 92 /
GE /
April 11, 2023
Single-pole Tripping
• Distance relay must correctly identify a SLG
fault and trip only the circuit breaker pole for
the faulted phase.
• Autoreclosing and breaker failure functions
must be initiated correctly on the fault event
• Security must be maintained on the healthy
phases during the open pole condition and any
reclosing attempt.

93. 93 /
GE /
April 11, 2023
Out-of-Step Condition
• For certain operating conditions, a severe
system disturbance can cause system
instability and result in loss of synchronism
between different generating units on an
interconnected system.

94. 94 /
GE /
April 11, 2023
Out-of-Step Relaying
Out-of-step blocking relays
– Operate in conjunction with mho tripping relays
to prevent a terminal from tripping during severe
system swings & out-of-step conditions.
– Prevent system from separating in an
indiscriminate manner.
Out-of-step tripping relays
– Operate independently of other devices to
detect out-of-step condition during the first pole
slip.
– Initiate tripping of breakers that separate system
in order to balance load with available
generation on any isolated part of the system.

95. 95 /
GE /
April 11, 2023
Out-of-Step Tripping The locus must stay
for some time
between the outer
and middle
characteristics
Must move and stay
between the middle
and inner
characteristics
When the inner
characteristic is
entered the element
is ready to trip

96. 96 /
GE /
April 11, 2023
Power Swing Blocking
Applications:
> Establish a blocking signal for stable power swings (Power
Swing Blocking)
> Establish a tripping signal for unstable power swings (Out-
of-Step Tripping)
Responds to:
> Positive-sequence voltage and current

97. 97 /
GE /
April 11, 2023
Series-compensated lines
E
Xs SC XL Infinte
Bus
Benefits of series capacitors:
• Reduction of overall XL of long lines
• Improvement of stability margins
• Ability to adjust line load levels
• Loss reduction
• Reduction of voltage drop during severe disturbances
• Normally economical for line lengths > 200 miles

98. 98 /
GE /
April 11, 2023
Series-compensated lines
E
Xs SC XL Infinte
Bus
SCs create unfavorable conditions for protective relays and
fault locators:
• Overreaching of distance elements
• Failure of distance element to pick up on low-current faults
• Phase selection problems in single-pole tripping
applications
• Large fault location errors

99. 99 /
GE /
April 11, 2023
Series-compensated lines
Series Capacitor with MOV

100. 100 /
GE /
April 11, 2023
Series-compensated lines

101. 101 /
GE /
April 11, 2023
Series-compensated lines
Dynamic Reach Control

102. 102 /
GE /
April 11, 2023
Series-compensated lines
Dynamic Reach Control for External Faults

103. 103 /
GE /
April 11, 2023
Series-compensated lines
Dynamic Reach Control for External Faults

104. 104 /
GE /
April 11, 2023
Series-compensated lines
Dynamic Reach Control for Internal Faults

105. 105 /
GE /
April 11, 2023
Distance Protection Looking
Through a Transformer
• Phase distance elements can be set to see beyond
any 3-phase power transformer
• CTs & VTs may be located independently on
different sides of the transformer
• Given distance zone is defined by VT location (not
CTs)
• Reach setting is in sec, and must take into
account location & ratios of VTs, CTs and voltage
ratio of the involved power transformer

106. 106 /
GE /
April 11, 2023
Transformer Group Compensation
Depending on location of VTs and CTs, distance relays need to
compensate for the phase shift and magnitude change caused by the
power transformer

107. 107 /
GE /
April 11, 2023
Setting Rules
• Transformer positive sequence impedance must be
included in reach setting only if transformer lies
between VTs and intended reach point
• Currents require compensation only if transformer
located between CTs and intended reach point
• Voltages require compensation only if transformer
located between VTs and intended reach point
• Compensation set based on transformer connection
& vector group as seen from CTs/VTs toward reach
point

108. 108 /
GE /
April 11, 2023
> Multiple reversible distance zones
> Individual per-zone, per-element characteristic:
– Dynamic voltage memory polarization
– Various characteristics, including mho, quad,
lenticular
> Individual per-zone, per-element current supervision
(FD)
> Multi-input phase comparator:
– additional ground directional supervision
– dynamic reactance supervision
> Transient overreach filtering/control
> Phase shift & magnitude compensation for distance
applications with power transformers
Distance Relay Desirable
Attributes

109. 109 /
GE /
April 11, 2023
> For improved flexibility, it is desirable to have the following
parameters settable on a per zone basis:
– Zero-sequence compensation
– Mutual zero-sequence compensation
– Maximum torque angle
– Blinders
– Directional angle
– Comparator limit angles (for lenticular characteristic)
– Overcurrent supervision
Distance Relay Desirable
Attributes

110. 110 /
GE /
April 11, 2023
> Additional functions
– Overcurrent elements (phase, neutral, ground,
directional, negative sequence, etc.)
– Breaker failure
– Automatic reclosing (single & three-pole)
– Sync check
– Under/over voltage elements
> Special functions
– Power swing detection
– Load encroachment
– Pilot schemes
Distance Relay Desirable
Attributes

111. 111 /
GE /
April 11, 2023