ABB Relion 670 Series Applications Manual page 147

1MRK 511 407-UUS Rev. J
Phase
currents
Phase
ground
voltages
ANSI13000013 V1 EN-US
Figure 64: 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.
In a high impedance system the fault current is assumed to be limited by the system zero
sequence shunt impedance to ground and the fault resistance only. All the series impedances in
the system are assumed to be zero.
In the setting of ground-fault protection, in a high impedance grounded system, the neutral point
voltage (zero sequence voltage) and the ground-fault current will be calculated at the desired
sensitivity (fault resistance). The complex neutral point voltage (zero sequence) can be calculated
as:
Phasor measurement unit RES670
Application manual
IN
VN
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Current protection
ANSI13000013-1-en.vsd
Section 8
SEMOD171961-4 v10
141