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Fundamentals of DistanceProtection
GE Multilin
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Outline
Transmission lin
e 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
Classification of line length depends on:
Source-to-line Impedance Ratio (SIR),
and Nominal voltage
Length considerations:
Short Lines: SIR > 4Medium Lines: 0.5 < SIR < 4
Long Lines: SIR < 0.5
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Typical Protection SchemesShort Lines
Current differential
Phase comparison
Permissive Overreach Transfer Trip (POTT)Directional Comparison Blocking (DCB)
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Typical Protection SchemesMedium Lines
Phase comparison
Directional Comparison Blocking (DCB)
Permissive Underreach Transfer Trip (PUTT)
Permissive Overreach Transfer Trip (POTT)
Unblocking
Step Distance
Step or coordinated overcurrentInverse time overcurrent
Current Differential
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Typical Protection SchemesLong 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:> IZV and Vapproximately
in phase (mho)
> IZVand IZapproximately 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:> IZVand Vapproximately
out of phase (mho)
> IZVand IZapproximately 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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Source Impedance Ratio,Accuracy & Speed
LineSystem
Relay
Voltage at the relay:SIRf
fVV
PULOC
PULOC
NR
][
][
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:SIRf
fVV
PULOC
PULOC
NR
][
][
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 involtages
CVT output
0 1 2 3 4
steady-stateoutput
power cycles
-30
-20
-10
0
10
20
30
voltage,
V
C1
C2
2
3 5
6
1
4
7
High Voltage Line
Secondar
yVoltage
Output
8
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Challenges in relay design
> Transients:
High frequency
DC offset in currents
CVT transients involtages
C1
C2
2
3 5
6
1
4
7
High Voltage Line
Secondar
yVoltage
Output
8
CVToutput
0 1 2 3 4
steady-stateoutput
-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, i
C
-0.5 0 0.5 1 1.5-100
-50
0
50
100
Reacta
ncecomparator[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 currentdepends on instant in the cycle at which fault
occurred
Rate of decay of dc offset depends onsystem X/R
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Zone 1 and CVT Transients
Capacitive Voltage Transformers (CVTs) create certainproblems 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 fora 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 isactually 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
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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
3442 44 Actual Fault
Location
LineImpedance
Trajectory(msec)
dynamic mhozone extendedfor 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 OverreachSolutions
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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 TransientsAdaptiveSolution
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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
XThe inner zone 1:
> has its reach dynamically
controlled by the voltage
magnitude
> is instantaneous
CVT TransientsAdaptiveSolution
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Desirable Distance RelayAttributesFilters:
> 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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Maximum Torque Angle
Angle at which mho element has maximum
reach
Characteristics with smaller MTA willaccommodate larger amount of arc resistance
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Traditional
Directional
angle lowered
and slammed
Directional angle
slammed
Both MHO anddirectional 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
LenticularCharacteristic
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 Quadrilateral
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 PolarizationjX
R
Dynamic MHO characteristic for a reverse faul
Dynamic MHO characteristic for a forward fa
Impedance During Close-up Faults
Static MHO characteristic (memory not established or
expired)
ZL
ZS
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Memory Polarization
Memory PolarizationImproved ResistiveCovera e
Dynamic MHO characteristic for a forward faul
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 togive more coverage for high resistance faults
> Directional discrimination based on the ground quantities is
fast:
Accurate angular relations between the zero andnegative sequence quantities establish very quicklybecause:
During faults zero and negative-sequencecurrents and voltages build up from very lowvalues (practically from zero)
The pre-fault values do not bias the developing
fault components in any direction
S
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Distance Schemes
Pilot Aided
Schemes
No Communicationbetween Distance
Relays
Communicationbetween Distance
relays
Non-Pilot Aided
Schemes
(Step Distance)
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Step Distance SchemesZone 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 cyclesZone 3:
Remote backup for relay/station failures at remoteterminal
Reaches beyond Z2, load encroachment a consideration
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Z1
Z1
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 utilizesimple on/off communications between relays, butcan also utilize peer-to-peer communications andGOOSE messaging over digital channels
Typical communications media include: Pilot-wire (50Hz, 60Hz, AT)
Power line carrier
Microwave
Radio
Optic fiber (directly connected or multiplexedchannels)
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Distance-based Pilot Protection
Pil t Aid d Di t B d S h
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Pilot-Aided Distance-Based Schemes
DUTTDirect Under-reaching Transfer Trip
PUTTPermissive Under-reaching Transfer
Trip
POTTPermissive Over-reaching Transfer Trip
Hybrid POTTHybrid Permissive Over-
reaching Transfer Trip
DCBDirectional Comparison Blocking
Scheme
DCUBDirectional Comparison Unblocking
Scheme
Di t U d hi T f T i
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Direct Underreaching Transfer Trip(DUTT)
Requires only underreaching (RU) functions whichoverlap in reach (Zone 1).
Applied with FSK channel
GUARD frequency transmitted during normalconditions
TRIP frequency when one RU function operates
Scheme does not provide tripping for faults beyond
RU reach if remote breaker is open or channel isinoperative.
Dual pilot channels improve security
DUTT S h
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Bus
Line
Bus
Zone 1
Zone 1
DUTT Scheme
P i i U d hi
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Permissive UnderreachingTransfer Trip (PUTT)
Requires both under (RU) and overreaching
(RO) functions
Identical to DUTT, with pilot tripping signal
supervised by RO (Zone 2)
PUTT S h
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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1
To protect end ofline
& Local TripZone 2
Rx PKP
ORZone 1
PUTT Scheme
P i i O hi T f
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Permissive Overreaching TransferTrip (POTT)
Requires overreaching (RO) functions (Zone2).
Applied with FSK channel:
GUARD frequency sent in stand-by
TRIP frequency when one RO functionoperates
No trip for external faults if pilot channel isinoperative
Time-delayed tripping can be provided
POTT S h
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Bus
Line
Bus
Zone 1
Zone 2
TripLine
Breakers
OR
t
Rx
Tx
AND
(Z1)
(Z1)
o
Zone 1
Zone 2
Zone 2
Zone 1
POTT Scheme
POTT Scheme
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POTT Scheme
POTTPermissive Over-reaching Transfer
TripEnd
Zone
CommunicationChannel
POTT Scheme
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Local Relay Remote Relay
Remote
Relay FWD
IGND
Ground Dir OC Fwd
OR
Local RelayZ2
ZONE 2 PKP
Local Relay
FWD IGND
Ground Dir OC Fwd
OR
TRIP
Remote RelayZ2
POTT TX
ZONE 2 PKP
POTT RX
Communicatio
n Channel
POTT Scheme
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
Com
munications
C
hannel(s)
POTT Scheme
POTT Scheme
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Local Relay Remote Relay
POTT TX ZONE 2 OR
GND DIR OC FWD
CommunicationChannel
TRIP
GND DIR OC REVGND DIR OC REV POTT RX
StartTimerTimerExpire
GND DIR OC FWD
POTT SchemeCurrent reversal example
POTT Scheme
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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 SchemeEcho example
Hybrid POTT
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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
Hybrid POTT
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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1 Zone 4
LocalRemote
Weak
system
Hybrid POTT
Directional Comparison Blocking
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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 blockingfunction(s) operate
Receipt of signal from remote end blockstripping relays
Tripping function set with Zone 2 reach or greaterBlocking functions include Zone 3 reverse and low-set ground overcurrent elements
DCB Scheme
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Bus
Line
Bus
Zone 1
Zone 2
Zone 2
Zone 1
LocalRemote
DCB Scheme
Directional Comparison Blocking
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End Zone
Communication Channel
Directional Comparison Blocking
(DCB)
Directional Comparison Blocking
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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
ORDir Block RXNO
TRIP
Expired
Directional Comparison Blocking
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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
Directional Comparison
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Directional ComparisonUnblocking (DCUB)
Applied to Permissive Overreaching (POR)schemes to overcome the possibility of carrier signalattenuation or loss as a result of the fault
Unblocking provided in the receiver when signal islost:
If signal is lost due to fault, at least onepermissive RO functions will be picked up
Unblocking logic produces short-duration TRIPsignal (150-300 ms). If RO function not pickedup, channel lockout occurs until GUARD signalreturns
DCUB Scheme
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Bus
Line
Bus
TripLine
Breakers
Tx1(Un-Block)
Forward
Forward
Tx2(Block)
Forward
Rx2
Rx1
to
AND to
AND
AND
AND
Lockout
(Block)
(Un-Block)
DCUB Scheme
Directional Comparison Unblocking
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End Zone
Communication Channel
Directional Comparison Unblocking
(DCUB)
Directional Comparison Unblocking
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Directional Comparison Unblocking
(DCUB)Normal conditions
Local Relay Remote RelayGUARD1 TXGUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RXNO Loss of Guard
FSK Carrier FSK Carrier
NO Permission
NO Loss of Guard
NO Permission
Load Current
Directional Comparison Unblocking
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Directional Comparison Unblocking
(DCUB)Normal conditions, channel failure
Local Relay Remote RelayGUARD1 TXGUARD1 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
Directional Comparison Unblocking
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Directional Comparison Unblocking
(DCUB)Internal fault, healthy channel
Local Relay Remote RelayGUARD1 TXGUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
FSK Carrier FSK Carrier
Loss of Guard
Permission
TRIP1 TX
Local RelayZ2
Zone 2 PKP
TRIP1 RX
TRIP2 TX
TRIP
Remote RelayZ2
ZONE 2 PKP
TRIP Z1
TRIP2 RX
Directional Comparison Unblocking
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Directional Comparison Unblocking
(DCUB)Internal fault, channel failure
Local Relay Remote RelayGUARD1 TXGUARD1 RX
Communication
Channel
GUARD2 TX GUARD2 RX
FSK Carrier FSK Carrier
TRIP1 TX
Local RelayZ2
Zone 2 PKP
NO RX
TRIP2 TX
TRIP
Remote RelayZ2
ZONE 2 PKP
TRIP Z1
NO RX
Loss of Guard
Loss of Channel
Loss of Guard
Block Timer Started
Duration Timer StartedExpired
Redundancy Considerations
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Redundancy Considerations
Redundant protection systems increase dependability of thesystem:Multiple sets of protection using same protection principle
and multiple pilot channels overcome individual elementfailure, or
Multiple sets of protection using different protectionprinciplesand multiple channels protects against failure ofone 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, tripcoil circuits, etc. also need to be considered.
Redundant Communications
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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
Redundant Pilot Schemes
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Redundant Pilot Schemes
Pilot Relay Desirable Attributes
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Integrated functions:
weak infeedecho
line pick-up (SOTF)
Basic protection elements used to key thecommunication:
distance elements
fast and sensitive ground (zero and negative
sequence) directional IOCs with current,voltage, and/or dual polarization
Pilot Relay Desirable Attributes
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 (HYBPOTT)
Blocking scheme (DCB)
Unblocking scheme (DCUB)
Pilot Relay Desirable Attributes
Security for dual-breaker terminals
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Security for dual breaker terminals
Breaker-and-a-half and ring bus terminals arecommon 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 linerelays.
Security for dual-breaker terminals
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Security for dual breaker terminals
Accurate CTs preserve thereverse current direction
under weak remote infeed
Security for dual-breaker terminals
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Security for dual breaker terminals
Saturation of CT1 may
invert the line current as
measured from externally
summated CTs
Security for dual-breaker terminals
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Security for dual breaker terminals
Direct measurement of currents
from both circuit breakers allowsthe 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 breakerindependent autoreclosing
for each breaker
Security for dual-breaker terminals
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Security for dual breaker terminalsSupervisory 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 eachbreaker independently:
Both currents in FWD directioninternal 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 forwarddirection. Block is then lifted to permit tripping.
Single-pole Tripping
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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 anyreclosing attempt.
Out-of-Step Condition
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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 aninterconnected system.
Out-of-Step Relaying
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Out of Step Relaying
Out-of-step blocking relays
Operate in conjunction with mho tripping relaysto prevent a terminal from tripping during severesystem 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 poleslip.
Initiate tripping of breakers that separate systemin order to balance load with available
generation on any isolated part of the system.
Out-of-Step Tripping
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Out of Step TrippingThe 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 elementis ready to trip
Power Swing Blocking
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Power Swing Blocking
Applications:
> Establish a blocking signal for stable power swings (PowerSwing Blocking)
> Establish a tripping signal for unstable power swings (Out-
of-Step Tripping)
Responds to:> Positive-sequence voltage and current
Series-compensated lines
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Series compensated lines
EXs SC XL Infinte
Bus
Benefits of series capacitors:
Reduction of overall XLof long linesImprovement 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
Series-compensated lines
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p
EXs 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
Series-compensated lines
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pSeries Capacitor with MOV
Series-compensated lines
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p
Series-compensated lines
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pDynamic Reach Control
Series-compensated lines
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pDynamic Reach Control for External Faults
Series-compensated lines
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pDynamic Reach Control for External Faults
Series-compensated lines
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pDynamic Reach Control for Internal Faults
Distance Protection Looking
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gThrough 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 transformerGiven 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
Transformer Group Compensation
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p p
Depending on locat ion o f VTs and CTs, distance relays need to
compensate for the phase shi f t and magni tude change caused by the
power transformer
Setting Rules
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g
Transformer positive sequence impedance must beincluded in reach setting only if transformer liesbetween VTs and intended reach point
Currents require compensation only if transformer
located between CTs and intended reach pointVoltages require compensation only if transformerlocated between VTs and intended reach point
Compensation set based on transformer connection
& vector group as seen from CTs/VTs toward reachpoint
Distance Relay Desirable
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> 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 distanceapplications with power transformers
yAttributes
Distance Relay Desirable
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> 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
yAttributes
Distance Relay Desirable
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>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
Attributes
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