ABB RELION Series Technical Manual page 294

Section 4
Protection functions
288
GUID-67BE307E-576A-44A9-B615-2A3B184A410D V2 EN
Figure 145: Definition of the relay characteristic angle, RCA=–90 degrees in an
isolated network
Directional earth-fault protection in an isolated neutral network
In isolated networks, there is no intentional connection between the system neutral
point and earth. The only connection is through the phase-to-earth capacitances (C
of phases and leakage resistances (R
capacitive and has a phase shift of -90 degrees compared to the polarizing voltage.
Consequently, the relay characteristic angle (RCA) should be set to -90 degrees and
the operation criteria to "IoSin" or "Phase angle". The width of the operating sector in
the phase angle criteria can be selected with the settings Min forward angle, Max
forward angle, Min reverse angle or Max reverse angle.
simplified equivalent circuit for an unearthed network with an earth fault in phase C.
For definitions of different directional earth-fault characteristics, see
Directional earth-fault
). This means that the residual current is mainly
0
Figure 146
principles.
1MRS758755 A
)
0
illustrates a
REC615 and RER615
Technical Manual