ABB 615 series Technical Manual page 341

1MAC059074-MB A
615 series ANSI
Technical Manual
Characteristic angle
= -90 deg
Forward
tripping zone
maximum torque line
(operating quantity)
GUID-04370359-62D0-4D09-B296-D72C961293C4 V1 EN
Figure 154: Definition of the relay characteristic angle, RCA=–90 degrees in an
isolated network
Directional ground-fault protection in an isolated neutral network
In isolated networks, there is no intentional connection between the system neutral point
and ground. The only connection is through the phase-to-ground capacitances (C
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.
equivalent circuit for an ungrounded network with a ground fault in phase C.
For definitions of different directional ground-fault characteristics, see
Directional ground-fault
Max forward angle
IG
Min forward angle
zero torque line
). This means that the residual current is mainly
0
Figure 155
principles.
Section 4
Protection functions
-VG (polarizing

quantity)
Backward
tripping zone
Min reverse angle
Max reverse angle
Min operate
current
0
illustrates a simplified
) of
335