ABB Relion 620 Series - Page 563

normally applied when the transformer is earthed solidly or through low-impedance
resistor (NER). LREFPNDF can be also applied on the delta side of the transformer
if an earthing transformer (zig-zag transformer) is used there. In LREFPNDF, the
difference of the fundamental component of all three phase currents and the
neutral current is provided to the differential element to detect the earth fault
in the transformer winding based on the numerical stabilized differential current
principle.
Connection of current transformers
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 figures Figure 289 and Figure
290 .
• 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 figures Figure 291 and Figure 292 .
• The default value of the CT connection type setting is "Type 1".
In case the earthings of the current transformers on the phase side and the
neutral side are both either inside or outside the area to be protected, the setting
parameter CT connection type is "Type 1".
If the earthing of the current transformers on the phase side is inside the area to be
protected and the neutral side is outside the area to be protected or if the earthing
on the phase side is outside the area and on the neutral side inside the area, the
setting parameter CT connection type is "Type 2".
1MRS757644 H
Protection functions
620 series
Technical Manual
563