ABB RELION REX640 Technical Manual page 653

1MRS759142 C
REX640
Technical Manual
GUID-D5A18417-F6DE-4335-A47F-602D554A1BBC V1 EN
Figure 360: Example of two-winding power transformer differential protection
The rated load of the transformer can be calculated.
= 25 MVA / (1.732 ⋅ 110 kV) = 131.2 A
HV side: I
nT_Wnd1
= 25 MVA / (1.732 ⋅ 21 kV) = 687.3 A
LV side: I
nT_Wnd2
TR3PTDF settings:
CT ratio Cor Wnd 1 = 300 A / 131.2 A = 2.29
CT ratio Cor Wnd 2 = 1000 A / 687.3 A = 1.45
CT ratio Cor 3 is not applicable in this case.
Current group 3 type = "Not in use"
Phase Ref winding = "Winding 1" (source of power)
Zro A elimination = "Winding 1" (if winding 1 neutral is earthed)
Phase shift Wnd 1-2 = "330 deg" (for clock number 11)
Vector group matching and elimination of the zero-sequence
component
The vector group of the power transformer is numerically matched on the windings on
different sides of the transformer by the Phase shift Wnd 1-2 and Phase shift Wnd 1-3
settings. Thus no interposing CTs are needed if there is only a power transformer
inside the protected zone. The matching is based on phase shifting and a numerical
delta connection in the function.
If the neutral of a star-connected power transformer is earthed, any earth fault in the
network is perceived by the protection as differential current. The elimination of the
zero-sequence component can be selected to be on or off for that winding by the Zro
A elimination setting. By default, the elimination is done for every winding.
Section 4
Protection functions
647