ABB RELION RER670, Applications Manual

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has -90º phase shift compared to the residual voltage (2U
0
). The characteristic
angle is chosen to -90º in such a network.
In resistance earthed networks or in Petersen coil earthed, with a parallel resistor,
the active residual current component (in phase with the residual voltage) should be
used for the earth fault detection. In such networks, the characteristic angle is
chosen to 0º.
As the amplitude of the residual current is independent of the fault location, the
selectivity of the earth fault protection is achieved by time selectivity.
When should the sensitive directional residual overcurrent protection be used and
when should the sensitive directional residual power protection be used? Consider
the following:
• Sensitive directional residual overcurrent protection gives possibility for better
sensitivity. The setting possibilities of this function are down to 0.25 % of
IBase, 1 A or 5 A. This sensitivity is in most cases sufficient in high
impedance network applications, if the measuring CT ratio is not too high.
• Sensitive directional residual power protection gives possibility to use inverse
time characteristics. This is applicable in large high impedance earthed
networks, with large capacitive earth fault currents. In such networks, the
active fault current would be small and by using sensitive directional residual
power protection, the operating quantity is elevated. Therefore, better
possibility to detect earth faults. In addition, in low impedance earthed
networks, the inverse time characteristic gives better time-selectivity in case of
high zero-resistive fault currents.
Phase
currents
IN
Phase-earth
voltages
UN
IEC16000210-1-en.vsdx
IEC16000210 V1 EN-US
Figure 57: Connection of SDEPSDE to analog preprocessing function block
Overcurrent functionality uses true 2I0, i.e. sum of GRPxL1 and GRPxL2. For 2I0
to be calculated, connection is needed to both two phase inputs.
1MRK 506 375-UEN A
Section 8
Current protection
Railway application RER670 2.2 IEC 175
Application manual