Hitachi Relion 670 Series Applications Manual page 165

1MRK506375-UEN Rev. N
Phase
currents
Phase-earth
voltages
IEC16000210 V1 EN-US
Figure 63:
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.
Directional and power functionality uses IN and UN. If a connection is made to GRPxN this signal is
used, else if connection is made only to inputs GRPxL1 and GRPxL2 the internally calculated sum of
these inputs (2I0 and 2U0) will be used.
8.5.3 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
IECEQUATION16029 V1 EN-US
Where
U is the phase voltage in the fault point before the fault,
phase
R is the resistance to earth in the fault point and
f
Z is the system zero sequence impedance to earth
0
The fault current, in the fault point, can be calculated as:

I 2 I
j
IECEQUATION16030 V1 EN-US
Railway application RER670
Application manual
IN
UN
Connection of SDEPSDE to analog preprocessing function block
U
phase

2 R

f
Z
0

2 U

phase
 
0
Z 2 R
0 f
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Section 8
Current protection
IEC16000210-1-en.vsdx
SEMOD171961-4 v11
(Equation 43)
(Equation 44)
159