ABB REL 356 Current Differential Protection
3-25
Settings and Application
With the recommended 20% margin, OTH should then be set to:
OTH < 0.80 (OP
min
– RES
min
) = 0.80 x ITL x 0.3 = 0.80 x C1I1 x 0.3
Different CT ratios can be used in the two line ends by adjusting the operating threshold, OTH, so that the same level
is achieved on a primary basis. For example, if one end has a ratio of 240 and OTH is set to 0.5 A, the other end with
ratio 120 should have an OTH setting of 1.0 A. Note that the sequence filter settings, C1, C2 and C0, should always
be the same at the two line ends.
Note that for versions 1.15 and earlier, OTH is set in peak value why the above setting recommendations
should be
adjusted with a factor
.
This means that the recommended setting for double end infeed is:
and for single end infeed:
Sequence Coefficients (C0, C1, C2)
C0 = 0.0, C1 = 0.1, C2 = 0.7
REL 356 uses sequence filters to obtain positive, negative and zero sequence currents. These currents are then
combined into one quantity:
The sequence filter settings, C1, C2 and C0, should always be the same at the two line ends.
In order to minimize the influence of load, C1 should be set to a relatively low value. We recommend to use C1 = 0.1.
2
)
(
8
.
0
2
min
min
RES
OP
OTH
−
⋅
⋅
≤
3
.
0
80
.
0
2
3
.
0
8
.
0
2
)
(
8
.
0
2
1
1
min
min
⋅
⋅
⋅
=
⋅
⋅
⋅
=
−
⋅
≤
I
C
ITL
RES
OP
OTH
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
⋅
+
⋅
−
⋅
=
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
.
Minimum fault current for internal phase to ground fault 2400 A primary = 67% of three phase fault current
Þ
use settings according to Case 1
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.
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 ...
