Hitachi Relion 670 Series Applications Manual page 139

1MRK511407-UUS Rev. N
V
=
V
0
+
1
EQUATION2020-ANSI V1 EN-US
Where
V is the phase voltage in the fault point before the fault,
phase
R is the resistance to ground in the fault point and
f
Z is the system zero sequence impedance to ground
0
The fault current, in the fault point, can be calculated as:
=
I 3I
j 0
EQUATION2021 V1 EN-US
The impedance Z
apparatus) the impedance is equal to the capacitive coupling between the phase conductors and ground:
= -
Z
0
EQUATION2022-ANSI V1 EN-US
Where
I
j
X
c
In a system with a neutral point resistor (resistance grounded system) the impedance Z
calculated as:
-
jX 3R
=
Z
0
-
jX
EQUATION1946 V1 EN-US
Where
R is the resistance of the neutral point resistor
n
In many systems there is also a neutral point reactor (Petersen coil) connected to one or more
transformer neutral points. In such a system the impedance Z
Phasor measurement unit RES670
Application manual
phase
×
3 R
f
Z
0
×
3 V
= phase
+ ×
Z 3 R
0 f
is dependent on the system grounding. In an isolated system (without neutral point
0
×
3 V
= -
phase
jX j
c
I
j
is the capacitive ground fault current at a non-resistive phase-to-ground fault
is the capacitive reactance to ground
×
c n
+
3R
c n
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can be calculated as:
0
Section 8
Current protection
(Equation 43)
(Equation 44)
(Equation 45)
can be
0
(Equation 46)
133