ABB Relion 670 Series Applications Manual page 169

1MRK 511 401-UEN Rev. K
=
U
0
+
1
EQUATION1943 V1 EN-US
Where
U
phase
R
f
Z
0
The fault current, in the fault point, can be calculated as:
=
I 3I
j 0
EQUATION1944 V1 EN-US
The impedance Z
point apparatus) the impedance is equal to the capacitive coupling between the phase
conductors and earth:
= -
Z jX
0
EQUATION1945 V1 EN-US
Where
I
j
X
c
In a system with a neutral point resistor (resistance earthed system) the impedance Z
calculated as:
-
=
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
Bay control REC670
Application manual
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
×
3 U
=
phase
+ ×
Z 3 R
0 f
is dependent on the system earthing. In an isolated system (without neutral
0
×
3 U
= - phase
j
c
I
j
is the capacitive earth fault current at a non-resistive phase-to-earth fault
is the capacitive reactance to earth
×
jX 3R
c n
+
3R
c n
is the resistance of the neutral point resistor
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Current protection
(Equation 49)
(Equation 50)
(Equation 51)
(Equation 52)
can be calculated as:
0
Section 8
can be
0
163