ABB RELION 670 SERIES Applications Manual page 536

Section 9
Current protection
530
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 grounded networks, with
large capacitive ground 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 ground faults. In
addition, in low impedance grounded networks, the inverse time characteristic gives
better time-selectivity in case of high zero-resistive fault currents.
Phase
currents
IN
Phase
ground
voltages
VN
ANSI13000013 V1 EN
Figure 275: Connection of SDEPSDE to analog preprocessing function block
Overcurrent functionality uses true 3I0, i.e. sum of GRPxA, GRPxB and GRPxC. For 3I0
to be calculated, connection is needed to all three phase inputs.
Directional and power functionality uses IN and VN. If a connection is made to GRPxN
this signal is used, else if connection is made to all inputs GRPxA, GRPxB and GRPxC the
internally calculated sum of these inputs (3I0 and 3V0) will be used.
1MRK 506 369-UUS -
ANSI13000013-1-en.vsd
Line distance protection REL670 2.2 ANSI
Application manual