Maximum torque line
Min forward angle
Min reverse angle
Min operate
current
Max forward angle
Max reverse angle
Backward
operating zone
Zero torque line
Non-operating zone
Forward
operating zone
Characteristic angle
= -90°
Io
(Operating quantity)
-Uo
(Polarizing quantity)
GUID-E829A47B-A6C1-46AD-99B8-5F3E9D234B70 V1 EN
Figure 61: Definition of the relay characteristic angle, RCA = -90° in an isolated
network
Directional earth-fault detection 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 (C0)
of phases and leakage resistances (R0). This means that the residual current is mainly
capacitive and has a phase shift of -90° compared to the polarizing voltage.
Consequently, the relay characteristic angle (RCA) should be set to -90° 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 62 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.
1MRS757488 H Section 6
Commissioning
RIO600 107
Installation and Commissioning Manual
To Next Page
Loading...
