Setting Guidelines - ABB Relion REC670 Applications Manual

1MRK 511 358-UEN A
Phase
currents
Phase-
ground
voltages
IEC13000013 V1 EN-US
Figure 63: Connection of SDEPSDE to analog preprocessing function block
Overcurrent functionality uses true 3I0, i.e. sum of GRPxL1, GRPxL2 and GRPxL3. For 3I0 to be
calculated, connection is needed to all three phase inputs.
Directional and power functionality uses IN and UN. If a connection is made to GRPxN this
signal is used, else if connection is made to all inputs GRPxL1, GRPxL2 and GRPxL3 the
internally calculated sum of these inputs (3I0 and 3U0) will be used.
7.6.3

Setting guidelines

The sensitive earth fault protection is intended to be used in high impedance earthed systems,
or in systems with resistive earthing where the neutral point resistor gives an earth 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 earth and the fault resistance only. All the series impedances in
the system are assumed to be zero.
In the setting of earth fault protection, in a high impedance earthed system, the neutral point
voltage (zero sequence voltage) and the earth fault current will be calculated at the desired
sensitivity (fault resistance). The complex neutral point voltage (zero sequence) can be
calculated as:
=
U
0
+
1
EQUATION1943 V1 EN-US
Where
U
phase
R
f
Z
0
Application manual
IN
UN
U
phase
×
3 R
f
Z
0
is the phase voltage in the fault point before the fault,
is the resistance to earth in the fault point and
is the system zero sequence impedance to earth
Current protection
IEC13000013-1-en.vsd
(Equation 46)
Section 7
SEMOD171961-4 v8
135