Setting Guidelines - ABB RELION 670 Series Applications Manual

1MRK 511 364-UUS A
As the magnitude of the residual current is independent of the fault location, the selectivity of the
ground 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 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
Phase
ground
voltages
ANSI13000013 V1 EN-US
Figure 56: 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.
8.4.3

Setting guidelines

The sensitive ground-fault protection is intended to be used in high impedance grounded
systems, or in systems with resistive grounding where the neutral point resistor gives an ground-
fault current larger than what normal high impedance gives but smaller than the phase to phase
short circuit current.
Application manual
IN
VN
Current protection
ANSI13000013-1-en.vsd
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