maximum torque line
Min forward angle
Min reverse angle
Min operate
current
Max forward angle
Max reverse angle
Backward
tripping zone
zero torque line
Non-trip
pin
g zo
ne
Forward
tripping zone
Characteristic angle
= -90 deg
IG
(operating quantity)
-VG
(polarizing
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
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
illustrates a simplified
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 principles
1MAC059074-MB A
Section 4
Protection functions
615 series ANSI
335
Technical Manual
Summary of Contents for Relion 615 series
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