ABB RELION REX640 Technical Manual page 429

1MRS759142 C
REX640
Technical Manual
GUID-3287CC33-2A56-4625-BE74-BD3F6893EDB6 V1 EN
Figure 225: 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
Protection functions
). This means that the residual current is mainly
0
Figure 226
characteristics.
Section 4
)
0
illustrates a
423