ABB RELION REX640 Technical Manual page 742

Protection functions
If the actual burden of the current transformer (S
reduced enough to provide a sufficient value for F
• A current transformer with a higher rated burden S
means a higher rated accuracy limit F
• A current transformer with a higher nominal primary current I1
rated burden) can be chosen.
Example 2
Assuming that the actions according to the current transformer with a
higher nominal primary current I1
to improve the actual accuracy limit factor (F
I
rTR
I
rCT
F = 30
n
F = (I
a
F = (1500/1000) · 30 = 45
a
In differential protection it is important that the accuracy limit factors
(F ) at both sides of the phase CTs correspond with each other, that is,
a
the burdens of the CTs on both sides should be as equal as possible. If
high inrush or start currents with high DC components flow through the
protected object when it is connected to the network, special attention
should be paid to the performance and the burdens of the CTs and to the
settings of the function block.
4.3.3.9 Signals
TR3PTDF Input signals
Table 671: TR3PTDF Input signals
Name
I3P1
I3P2
I3P3
BLOCK
BLK_OPR_LS
BLK_OPR_HS
742
= 1000 A Rated secondary current of the transformer
= 1500 A Rated primary current of the CT on the transformer secondary
side
Rated accuracy limit factor of the CT
/ I ) · F Actual accuracy limit factor due to oversizing the CT
rCT rTR n
Type
SIGNAL
SIGNAL
SIGNAL
BOOLEAN
BOOLEAN
BOOLEAN
Equation 173
) in
a
, there are two alternatives.
a
n
) or
n
(but the same rated burden) are taken
n
):
a
Default
-
-
-
0=False
0=False
0=False
1MRS759142 F
cannot be
can be chosen (which also
(but the same
n
Description
Three-phase currents
1
Three-phase currents
2
Three-phase currents
3
Block
Blocks operate out-
puts from biased
stage
Blocks operate out-
puts from instantane-
ous stage
REX640
Technical Manual