Recommendations For Current Transformers - ABB RELION REX640 Technical Manual

1MRS759142 C
4.3.3.8
REX640
Technical Manual
Table 596: Angle outputs when settings CT connection 1-2 and CT connection 1-3 match the
actual CT connections on windings 1, 2 and 3 but the phase B polarity is wrong
compared to other phases on winding 2
Angle output name
I_ANGL_A1_B1
I_ANGL_B1_C1
I_ANGL_C1_A1
I_ANGL_A2_B2
I_ANGL_B2_C2
I_ANGL_C2_A2
I_ANGL_A3_B3
I_ANGL_B3_C3
I_ANGL_C3_A3
I_ANGL_A1_A2
I_ANGL_B1_B2
I_ANGL_C1_C2
I_ANGL_A1_A3
I_ANGL_B1_B3
I_ANGL_C1_C3

Recommendations for current transformers

The more important the object to be protected, the more attention should be paid to the
CTs. Normally, it is not possible to dimension the CTs so that they repeat currents with
high DC components without saturating when the residual flux of the current
transformer is high. TR3PTDF operates reliably even though the CTs are partially
saturated. The purpose of the following current transformer recommendations is to
secure the stability of the relay at high through-currents and the quick and sensitive
operation of the relay at faults occurring in the protected area where the fault currents
can be high.
The accuracy class recommended for CTs to be used with TR3PTDF is 5P, where the
limit of the current error at the rated primary current is 1 percent and the limit of the
phase displacement is 60 minutes. The limit of the composite error at the rated
accuracy limit primary current is 5 percent.
The approximate value of the accuracy limit factor F
burden can be calculated on the basis of the rated accuracy limit factor F
rated burden, the rated burden S
the CT.
S S
+
in n
F F
= ⋅
a n
S S
+
in a
GUID-05F40171-2FE7-4A15-8D35-9B787BA380CD V1 EN
Angle value Possible reason if not OK
+120 OK
+120 OK
+120 OK
-60 Wrong polarity phase B
-60 Wrong polarity phase B
+120 OK
+120 OK
+120 OK
+120 OK
±180 OK
0 Winding 2, wrong polarity phase B
±180 OK
±180 OK
±180 OK
±180 OK
a
, the internal burden S
n
Section 4
Protection functions
corresponding to the actual CT
(ALF) at the
n
and the actual burden S
in
(Equation 120)
of
a
651