ABB Relion 670 Series Applications Manual page 148

Section 8
Current protection
V
=
V
0
+
1
EQUATION2020-ANSI V1 EN-US
Where
V
phase
R
f
Z
0
The fault current, in the fault point, can be calculated as:
=
I 3I
j 0
EQUATION2021 V1 EN-US
The impedance Z
point 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
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
142
phase
×
3 R
f
Z
0
is the phase voltage in the fault point before the fault,
is the resistance to ground in the fault point and
is the system zero sequence impedance to ground
×
3 V
= phase
+ ×
Z 3 R
0 f
is dependent on the system grounding. In an isolated system (without neutral
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
is the resistance of the neutral point resistor
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1MRK 511 407-UUS Rev. J
can be calculated as:
0
Phasor measurement unit RES670
Application manual
(Equation 43)
(Equation 44)
(Equation 45)
can be
0
(Equation 46)