ABB REL 356 Current Differential Protection
3-9
Settings and Application
Sequence Coefficients (C0, C1, C2)
REL 356 uses sequence filters to obtain positive, negative and zero sequence currents. These currents are then com-
bined into one quantity:
currents.
sequence
negative
the
and
sequence
positive
the
sequence,
zero
the
are
and
,
2
1
0
2
1
0
2
1
0
I
I
I
where
I
C
I
C
I
C
IT
⋅
+
⋅
−
⋅
=
In order to minimize the influence of load, C1 should be set to a relatively low value. We recommend to use C1 = 0.1.
C0 and C2 will both multiply fault currents. Setting recommendations C1 and C2 for three cases are made:
Case 1) Minimum fault current for a ground fault I
F
Gmin
> 50% of minimum fault current for a three phase fault, I
3
F
min
.
Case 2) Minimum fault current for a ground fault I
F
Gmin
< 50% of minimum fault current for a three phase fault, I
3
F
min
.
Case 3) Minimum fault current for a ground fault I
F
Gmin
< 12.5% of minimum fault current for a three phase fault, I
3
F
min
.
Case 1
Either C2 or C0 can be used for fault detection of any unsymmetrical fault. The use of negative sequence, C2, is
preferable as the negative sequence currents are more consistent at the two line terminals. We therefore recommend to
set C0 = 0.
A high value of C2 would increase the sensitivity but in order not to make the relay responding to system unbalances a
“moderate” setting is recommended. Good sensitivity with high security is achieved with setting C2 = 0.7.
The recommended settings
C1 = 0.1
C2 = 0.7
C0 = 0.0
gives the following sensitivity for different faults:
Three phase faults
min
3
min
3
min
1
.
0
1
φ
φ
I
I
C
IT
⋅
−
=
⋅
−
=
Phase-phase faults
min
3
min
3
min
min
60
min
33
.
0
2
3
38
.
0
38
.
0
)
2
1
(
3
1
φ
φ
φφ
φφ
I
I
I
I
e
C
C
IT
j
⋅
=
⋅
⋅
=
⋅
=
⋅
⋅
+
−
=
±
ο
Single phase to ground faults
min
min
min
2
.
0
)
0
2
1
(
3
1
G
G
I
I
C
C
C
IT
φ
φ
⋅
=
⋅
+
+
−
=
3
.
0
80
.
0
2
3
.
0
8
.
0
2
)
(
8
.
0
2
1
1
min
min
⋅
⋅
⋅
=
⋅
⋅
⋅
=
−
⋅
≤
I
C
ITL
RES
OP
OTH
and for single end infeed:
Summary of Contents for REL 356
Page 23: ...ABB REL 356 Current Differential Protection 1 10 Product Overview and Specifications ...
Page 83: ...ABB REL 356 Current Differential Protection 3 36 Settings and Application ...
Page 127: ...ABB REL 356 Current Differential Protection 5 28 Testing ...
Page 186: ...LINE SECTIONALIZING USING A PLC AND ABB PROTECTIVE RELAY Page 49 of 53 ...
Page 187: ...LINE SECTIONALIZING USING A PLC AND ABB PROTECTIVE RELAY Page 50 of 53 ...
Page 188: ...LINE SECTIONALIZING USING A PLC AND ABB PROTECTIVE RELAY Page 51 of 53 ...
Page 189: ...LINE SECTIONALIZING USING A PLC AND ABB PROTECTIVE RELAY Page 52 of 53 ...
