ABB Relion 620 Series, Technical Manual

Page: 548 / 1224

Example 2
Assuming that the actions according to alternative two above are taken in
order to improve the actual accuracy limit factor:
F
IrCT
IrTR
F
a n
= ×
(Equation 81)
IrTR 1000 A (rated secondary side current of the power transformer)
IrCT 1500 A (rated primary current of the CT on the transformer secondary side)
F
n
30 (rated accuracy limit factor of the CT)
F
a
(IrCT / IrTR) * Fn (actual accuracy limit factor due to oversizing the CT) =
(1500/1000) * 30 = 45
In TR2PTDF, it is important that the accuracy limit factors F
a
of the phase
current transformers at both sides correspond with each other, that is, the
burdens of the current transformers on both sides are to be as equal as
possible. If high inrush or start currents with high DC components pass
through the protected object when it is connected to the network, special
attention is required for the performance and the burdens of the current
transformers and for the settings of the function block.
4.3.2.6 CT connections and transformation ratio correction
The connections of the primary current transformers are designated as "Type 1" and
"Type 2".
• If the positive directions of the winding 1 and winding 2 protection relay
currents are opposite, the CT connection type setting parameter is "Type 1". The
connection examples of "Type 1" are as shown in Figure 281 and Figure 282 .
• If the positive directions of the winding 1 and winding 2 protection relay currents
equate, the
CT connection type setting parameter is "Type 2". The connection
examples of "Type 2" are as shown in
Figure 283
and
Figure 284
.
• The default value of the
CT connection type setting is "Type 1".
Protection functions 1MRS757644 H
548 620 series
Technical Manual