G. Ziegler. Digital Differential Protection
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G. Ziegler, 10/2005 page 195
Differential Protection Symposium
Belo HorizonteNovember 2005
Q
1/4 cycle
ΔT)
4n
1n
n
I
2
5n
i
2
n
i
(
4Tt
t
dtI(t)Q ⋅
+
+
+
+
+≈
+
⋅=
∑
∫
n-1
n
n+1
n+2
n+3
n+4
n+5
with ∆T= 1 ms (18
O
el.)
7SD52/7SD61: Charge comparison protection supplement
speed 2 relays 3 relays 6 relays
64 kbit/s 21 ms 21 ms 41 ms
128 kbit/s 16 ms 16 ms 24 ms
512 kbit/s (FO) 14 ms 14 ms 17 ms
0
0
Q
rest
= Σ Q errors
Q
Diff
=
│Q
1
+Q
2
+Q
3
│
Trip
Area
Restrain
Area
Q
Diff
>>
Settable pick-up value
Q
1
Q
2
Q
3
Calculation of the charge
G. Ziegler, 10/2005 page 196
Differential Protection Symposium
Belo HorizonteNovember 2005
Year
1986
1992
1998
2004
Memory
192 kB
768 kB
8.5 MB
28 MB
Bus width
16 bit
16 bit
32 bit
32 bit
Processing
power
0.5 MIPS
1.0 MIPS
35 MIPS
80 MIPS
Communication
19.2 kbps
115.2 kbps
1.5 Mbps (LAN)
100 Mbps (LAN)
Development of IED processing and communication power
G. Ziegler, 10/2005 page 197
Differential Protection Symposium
Belo HorizonteNovember 2005
21 & 87 Relay
United full scheme distance and differential protection
87
21
Copy of well proven
features
2 in 1
87
I
Rest
∆I
21 & 87
81
59 27
49
51/51N
21, 21N
85 -21
27 WI68, 68T
67N 85 -67N
2579
50 BF
G. Ziegler, 10/2005 page 198
Differential Protection Symposium
Belo HorizonteNovember 2005
For all kind of lines
Short to long lines
Parallel lines
Multi-terminal lines
Tapped lines
Transformer lines
Series comp. lines
87 Differential
21 Distanceline protection
67 DEF
For all kind of communication:
Traditional : PLC, Pilot wires, Microwave
Dedicated OF
Digital microwave
Commsnetworks
For all kind of operation
Single and/or three-pole ARC
Universal line protection relay
G. Ziegler, 10/2005 page 199
Differential Protection Symposium
Belo HorizonteNovember 2005
Net
Net
87
21
87
21
87
21
&
Permissive
tripping
Line with larger transformer taps
Release of 87 by 21 distance overreaching zone
Allows low setting of 87 pick-up!
G. Ziegler, 10/2005 page 200
Differential Protection Symposium
Belo HorizonteNovember 2005
l
3
= 5 km
X
L3
=
2.0 Ω
l
1
= 8 km
X
L1
=
3.2 Ω
Net
Net
∆I
∆I
20 MVA
u
T
=12 %
X
SC-T
= 73 Ω
5 MVA
u
K
=8 %
X
SC-T
= 194 Ω
10 MVA
u
K
=10 %
X
SC-T
= 121 Ω
l
4
= 4 km
X
L4
=
1.6 Ω
110 kV
S
SC2
‘‘=1000 MVA
Z
S2
= 12.1 Ω
110 kV
S
SC1
‘‘=2000 MVA
Z
S1
= 6.05 Ω
l
2
= 10 km
X
L2
=
4.0 Ω
400/1 A
400/1 A
A 957
Ω 73
kV 3110/1.1
T
X
3/
N
U1.1
SC
I =
⋅
=
−
⋅
≈
SC
A
kV
MVA
N
U
TN
S
Rush
I 918
1103
35
5
3
5 =
⋅
⋅=
⋅
−
⋅≈Σ
∑
u Settingpick-up value ∆I > 1.3·957 A
u or blocking ∆I via remote signalling when tap protection operates
u or release of ∆I by an overreaching distance zone
Line differential relay with digital communication (7SD61)
Application to tapped line, Example
G. Ziegler, 10/2005 page 201
Differential Protection Symposium
Belo HorizonteNovember 2005
Fully redundant line protection
using dissimilar protection and commsprinciples
PLC
PLC
commsnet
21
87
21
87
21
87
21
87
MUXMUX
Fully redundant 87 and 21 teleprotectionremains in operation
in each combination of relay and communication failure!
G. Ziegler, 10/2005 page 202
Differential Protection Symposium
Belo HorizonteNovember 2005
Pha -E
Phb -E
Phase selective fault clearance and auto-reclosingalso with multiple-faults
87 differential
and
21 pilot protection
Phase segregated 87 differential and 21 distance pilot protection:
Enhanced selectivity with multiple faults
G. Ziegler, 10/2005 page 203
Differential Protection Symposium
Belo HorizonteNovember 2005
Pha -E
Phb -E
Phase selective fault clearance and auto-reclosingalso with multiple-faults
87 differential
and
21 pilot protection
Phase segregated 87 differential and 21 distance pilot protection:
Enhanced selectivity with multiple faults
G. Ziegler, 10/2005 page 204
Differential Protection Symposium
Belo HorizonteNovember 2005
U1
U2
Distance
X
L
•I
1
X
L
•I
2
Grid1 Grid2
I
1
I
2
U
1
U
2
(I
1
+I
2
)•R
F
Two-sided fault locator using 87&21 relay
communication
Digital comms