ABB RER620 Technical Manual page 151

1MAC309294-MB F
RER620
Technical Manual
Characteristic angle
= -90 deg
maximum torque line
Figure 61: 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 line-to-ground capacitances (C
and leakage resistances (R
capacitive and has a phase shift of –90 degrees compared to the residual voltage (-V
Consequently, the relay characteristic angle (RCA) should be set to -90 degrees and the
operation criteria to I sin(φ) or phase angle. The width of the operating sector in the phase
0
angle criteria can be selected with the settings Min forward angle, Max forward angle, Min
reverse angle or Max reverse angle. The figure below describes how ground fault current
is defined in isolated neutral networks.
For definitions of different directional ground-fault characteristics, see
Directional ground-fault principles.
Max forward angle
I
0
(operating quantity)
Min forward angle
zero torque line
). This means that the zero sequence current is mainly
0
Section 4
Protection functions
- V (polarizing quantity)
0
Min reverse angle
Max reverse angle
Min operate
current
) of phases
0
).
0
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