ABB RET670 Applications Manual page 461

1MRK504116-UUS C
Application manual
- ×
jX 3R
=
Z c n
0
- +
jX 3R
c n
EQUATION1946 V1 EN
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
= - =
Z jX // 3R // j3X
0 c n n
EQUATION1947 V1 EN
Where
X is the reactance of the Petersen coil. If the Petersen coil is well tuned we have 3X
n
case the impedance Z
Now consider a system with an grounding via a resistor giving higher ground-fault
current than the high impedance grounding. The series impedances in the system can
no longer be neglected. The system with a single phase to ground-fault can be
described as in figure 200.
9R X X
n n c
(
+ × -
3X X j3R 3X X
n c n n c
will be: Z = 3R
0 0 n
Section 3
IED application
can be calculated as:
0
)
n
(Equation 356)
(Equation 357)
= X In this
c
455