Download - 10 DP Schemes
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Distance Protection Schemes
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Z3
Z3
Z1
Z1
Z2
Z2
Z3
Z2
Z1 1
.T2
T3
Trip
T2
1
. T2
T3
Trip
T2
Basic Distance Scheme
Z1
Z2
Z3
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Basic Distance Scheme - Disadvantages
Zone 1 set to 80% leaves 2 end zones
Faults in end zone results in instantaneoustripping at one end and time delayed at the
other
Time delay may lead to system stabilityproblems
Sequential clearance leaves no dead time for
high speed A/R cycle (transient fault becomes
permanent)
Longer clearance times - More damage
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Zone 1 Extension Scheme
Z3
Z2
Z3
Z1X
Z1X
Z2
Z1
Z1
Z3
Z2
Z1 1
.T2
T3
Trip
&
1
Z1X
A/R
Z2
Z1
Z3
1
. T2
T3
Trip
&
1
Z1X
A/R
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Zone 1 Extension - Advantages
No signalling channel required (may be used
as temporary replacement for carrier aided
scheme when comms. channel out of service)
Provides fast fault clearance at both ends for a
transient fault anywhere along the line length
Allows the use of high speed A/R cycle
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Zone 1 Extension Scheme - Disadvantages
Tripping can occur for external faults (but will be
followed by an autoreclose)
Basic distance scheme logic applies following
reclose (i.e. potential for time delayed clearancefor permanent faults)
Only suitable to systems where autoreclose isused (for example can not be used on cable
circuits)
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Loss of Load Accelerated Trip
Z3
Z3
Z1
Z1
Z2
Z2
T1 = 40ms (allows for slowest pickup of Zone 2)
T2 = 18ms (prevents LOL trip for external fault withCB pole scatter)
Z2
.
.&
.
.
.
&
&
.
1
.
LDA
LDB
LDC
0
T2
T1
0Trip
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Loss of Load Scheme
Fast fault clearance without the need for a
signalling channel
Only applicable where 3 phase tripping is used
Only operates for unbalanced faults
Load current (above the current detector
settings) must exist prior to the fault to arm thescheme
Can be used as back up to signal aided scheme
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Channel Dependant Schemes
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Unit Protection Schemes
Provide high speed clearance for all faults on line
(for example current differential)
Do not provide inherent back-up protection
SOLUTION IS TO PROVIDE DISTANCE PROTECTION FOR
BACK-UP PROTECTION OF ADJACENT LINES WITH AN AIDED
TRIPPING SCHEME FOR HIGH SPEED PROTECTION OF WHOLE
LINE
Requires the use of an ON/OFF signalling
channel between line ends (i.e. HF/VF/Fibre
Optic/Radio)
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Types of Aided Tripping Schemes
Acceleration
Transfer tripping
Direct
Permissive Underreach
Permissive Overreach
Blocking
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Direct Transfer Trip
Z3
Z3
Z1
Z1
Z2
Z2
Z3
Z2
Z1 1
.T2
T3
Trip
Z3
Z2
Z11
. T2
T3
Trip
Tx
Rx
Tx
Rx
Send Logic : Z1
Trip Logic : Rx
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Direct Transfer Trip - Advantages
All faults anywhere along the protected line can
be cleared instantaneously at both line ends
Scheme can be advantageous for protecting 3
terminal lines due to ease of application
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Direct Transfer Trip - Disadvantages
A very secure signalling channel is required :-
incorrect operation leads to false tripping
Circuit breakers at both line ends must be closed
and contribute fault current to obtain high speedfault clearance
If the channel fails only the Basic scheme logicwill be provided
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Acceleration Scheme (for Reach Stepped Relay)
Z3
Z3
Z1
Z1
Z2
Z2
Change
Z1
reach
Z3
Z1/Z2 1
.
T2
Trip
T3
1
. T3
T2
Trip
Tx
Rx
Tx
Rx
1
.
1
.
Send Logic : Z1Trip Logic : Rx + Z2
Z1/Z2
Z3
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Permissive Schemes
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Permissive Underreach Scheme
Z3
Z3
Z1
Z1
Z2
Z2
Tx
Rx
Tx
Rx
Send Logic : Z1
Trip Logic : Rx + Z2
Z3
Z2
Z1 1
.T2
T3
Trip
T2
&
1
. T2
Z3
Z2
Z1
T3
Trip
T2
&
100
0100
0
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Permissive Underreach Scheme
A
21
C
B
D
A
C
B
D
Send
Fault
Fault
Race between relay at D
picking up and signal
send from relay at C
resetting, following
opening of breaker at C
If signal send from Cresets before relay D
operates then aided
tripping will not occur
To prevent this a 100ms
delay on drop off of the
signal send is used in
the scheme logic
21
21 21
Rx + Z2
Rx + Z2
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Permissive Underreach Transfer Trip - Advantages
Only a simplex signalling channel required
Scheme is very secure as signalling channelonly keyed for internal fault (Zone 1 initiation)
Permissive Underreach Transfer Trip -
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Permissive Underreach Transfer Trip -Disadvantages
If one terminal of the line is open then only
Basic scheme logic will apply
If there is a weak infeed at one terminal then
only Basic scheme logic will apply
If signalling channel fails then only Basic
scheme logic will apply
Resistive coverage is governed by Zone 1
setting (may be limited on short lines)
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Permissive Overreach Scheme Internal Fault
Z3
Z3
Z2
Z1 1
.T2
T3
Trip
&
T2
Z3
Z2
Z11
. T2
T3
Trip
&
T2
Rx
Tx
Rx
Tx
Z3
Z1
Z1
Z2
Z2
Send Logic : Z2
Trip Logic : Rx + Z2
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Permissive Overreach Scheme External Fault
Z3
Z3
Z2
Z1 1
.T2
T3
Trip
&
T2
Z3
Z2
Z11
. T2
T3
Trip
&
T2
Rx
Tx
Rx
Tx
Z3
Z1
Z1
Z2
Z2
Send Logic : Z2
Trip Logic : Rx + Z2
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Permissive Overreach Scheme (CB Echo Logic)
Z3
Z3
Z2
Z1
T2
T3
Trip
&
T2
Z3
Z2
Z1
T2
T3
Trip
&
T2
&
1
Rx
Tx
CB open &
1
Rx
Tx
CB open
Z3
Z1
Z1
Z2
Z2
1
.
1
.
Send Logic : Z2
Trip Logic : Rx + Z2Open terminal echo : CB Open + Rx
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Permissive Overreach Scheme (WI Echo Logic)
Z4
Z2
Z1
Z1Z2
Send Logic : Z2
Trip Logic : Rx + Z2Open terminal echo : CB Open + Rx
Weak Infeed echo : Z4 + RxZ4
Z3
Z2
Z1
T2
T3
Trip
T2
Z3
Z2
Z1
T2
T3
Trip
T2
&
Z4
CB open &
Z4
CB open
1
& &
&Rx
Tx &Rx
Tx
1
.
1
.
1
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Permissive Overreach Weak Infeed Trip Scheme
Z4
Z2
Send Logic : Z2
Trip Logic : Rx + Z2
Open terminal echo : CB Open + Rx
Weak Infeed echo : Z4 + Rx
Weak Infeed trip : Z4 + LDOV reset + Rx
Z1
Z1Z2
Z4
Z3
Z2
Z1
T3
Trip
&
T2
&LDOV
Z3
Z2
Z1
T3
Trip
&
T2
&
&Rx
TxZ4
CB open &Rx
Tx
LDOV
Z4
CB open
& &
1
.
1
.
1 1
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Permissive Overreach Transfer Trip - Advantages
Provides better resistive coverage, especially
on short lines, where MHO measuringelements are used
For cases where one line terminal is open,open breaker echo logic can be used
For cases of weak or zero infeed at one lineterminal weak infeed logic can be used
(reverse looking zone required)
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Permissive Overreach Transfer Trip - Disadvantages
Duplex signalling channel required
Scheme is theoretically less secure then PUR
as signalling channel is keyed for external
faults
If signalling channel fails then only Basic
scheme logic will apply
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Blocking Schemes
Bl ki S h I t l F lt
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Blocking Scheme - Internal Fault
Z3
Z2
Z3
Z2
Z1
T3
Trip
&
T2
&Rx
Tx
1
.
Z1
Z1Z2
Send Logic : Z3 + Z2
Trip Logic : Rx + Z2
Z3
Z3
Z2
Z1
T2
T3
Trip
&
T2
&Rx
Tx
1
.
Bl ki S h E t l F lt
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Blocking Scheme - External Fault
Z3
Z2
Z3
Z2
Z1
T3
Trip
&
T2
&Rx
Tx
1
.
Z1
Z1Z2
Send Logic : Z3 + Z2
Trip Logic : Rx + Z2
Z3
Z1
Z2
Z3
T2
T3
Trip
&
T2
&Rx
Tx
1
.
Bl ki S h Ad t
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Blocking Scheme - Advantages
Only simplex signalling channel required
Provides better resistive coverage than PUR onshort lines where MHO elements are used
Fast tripping will still be possible at closed end ofline for all fault positions with remote breaker
open
Fast tripping will still be possible at strong infeed
terminal for all fault positions where remote
terminal has no or weak infeed
Bl ki S h Di d t
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Blocking Scheme - Disadvantages
Only 2 forward zones of protection available(unless relay has >3 Zones)
If signalling channel fails then only Basic schemelogic will apply
Current sensitivity is lower as tripping elements(Z2) are controlled by high set current level
detectors (to ensure blocking elements (Z3/Z4)
are more sensitive than tripping elements)
Permissive Schemes vs Blocking Schemes
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Permissive Schemes vs Blocking Schemes
Permissive less reliable - require a signal from
remote relay plus local operation to trip
Blocking less secure - require a signal from
remote relay to prevent a trip
Permissive schemes are marginally faster and
more sensitive (timer plus high set currentelements on Blocking scheme)
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Teed Feeders
Teed Feeders No Zone 1 Coverage
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Teed Feeders - No Zone 1 Coverage
B
AC'A'B'
B'
A'
C
A-A - Zone 1 reach of relay at A
B-B - Zone 1 reach of relay at B
C-C - Zone 1 reach of relay at C
ABC Zone not covered by Zone 1 from any terminal.
Hence schemes reliant on Zone 1 operation would not
work (Z1 ext, PUR)
Teed Feeders Underreaching
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Teed Feeders - Underreaching
B
A CZc
Zb
Za
Ia Ic
Actual impedance to fault from terminal A = Za + Zb
Measured voltage at terminal A V = Ia.Za + (Ia + Ic).Zb
Measured current at terminal A I = Ia
Impedance measured by relay A V/I = Za + Zb + (Ic/Ia).Zb
Relay therefore measures a greater impedance than the actual impedance
and underreaches. Must allow for this underreach when setting Zone 2
elements to ensure correct scheme operation
Teed Feeders - No/Weak Infeed at One Terminal
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Teed Feeders No/Weak Infeed at One Terminal
B
A C
No infeed from terminal B.
Fault therefore not covered by Zone 1 from any
terminal. Hence schemes reliant on Zone 1
operation would not work (Z1 ext, PUR)
Teed Feeders - Problems (1)
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Teed Feeders - Problems (1)
B
A C
Relay at terminal B sees a reverse fault. Noscheme will operate at this terminal. Fault
clearance will be sequential following opening of
breaker A from relay A Zone 1 element.
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Directional Earth Fault (DEF)
Directional Earth Fault Schemes
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Directional Earth Fault Schemes
DEF schemes are identical to Distance
schemes
DEF Forward replaces Zone 2, DEF Reverse
replaces Zone 3/4 Reverse No equivalent to Zone 1 as the DEF elements
can not have a defined reach, hence no
schemes using Zone 1 can be replicated (Z1ext, PUR)
Directional Earth Fault Schemes
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Directional Earth Fault Schemes
21
Ea E
b
67N
21
RF
Independent
signallingchannel67N
Independent signalling channels allows the use of
different schemes for the distance and DEF
elements, for example PUR distance with POR DEF
Directional Earth Fault Schemes
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Directional Earth Fault Schemes
21
EaEb
67N
21
RF
Shared Channel
67N
Shared signalling channels limits the use of
schemes for the distance and DEF elements.
Both use the same scheme logic.