ABB RELION 620 Series Technical Manual page 558

Section 4
Protection functions
552
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
• 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
• 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".
GUID-63BD73B4-7B60-4354-9690-E96C0A8076C7 V2 EN
Figure 279: Connection of the current transformers of Type 1. The connected
phase currents and the neutral current have opposite directions at an
external earth-fault situation. Both earthings are inside the area to be
protected.
1MRS757644 F
279 and 280.
281 and 282.
Technical Manual
620 series