ABB RELION 620 Series Technical Manual page 543

1MRS757644 F
4.3.2.6
620 series
Technical Manual
• a CT with a higher rated burden S
higher rated accuracy limit F
• a CT with a higher nominal primary current I
can be chosen
Example 2
Assuming that the actions according to alternative two above are taken in order to
improve the actual accuracy limit factor:
IrCT
F F
= ×
a n
IrTR
GUID-31A3C436-4E17-40AE-A4EA-D2BD6B72034E V2 EN
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 30 (rated accuracy limit factor of the CT)
n
F (IrCT / IrTR) * Fn (actual accuracy limit factor due to oversizing the CT) = (1500/1000) * 30 = 45
a
In TR2PTDF, it is important that the accuracy limit factors F
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.
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
• 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
• The default value of the CT connection type setting is "Type 1".
Protection functions
can be chosen (which also means a
n
)
n
(but the same rated burden)
1n
of the phase current
a
Figure 271
Figure 273 and Figure
Section 4
(Equation 80)
and Figure 272.
274.
537