ABB RELION Series, Техническое руководство

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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
0
)
of phases and leakage resistances (R
0
). This means that the residual current is mainly
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 . Figure 146 illustrates a
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 principles .
Section 4
1MRS758755 A
Protection functions
288 REC615 and RER615
Technical Manual