c
n
0
c
n
jX 3R
Z
jX
3R
-
×
=
-
+
EQUATION1946 V1 EN
(Equation 198)
Where
R
n
is the resistance of the neutral point resistor
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
0
can be
calculated as:
(
)
n
n
c
0
c
n
n
n
c
n
n
c
9R X X
Z
jX // 3R // j3X
3X X
j3R
3X
X
= -
=
+
×
-
EQUATION1947 V1 EN
(Equation 199)
Where
X
n
is the reactance of the Petersen coil. If the Petersen coil is well tuned we have 3X
n
= X
c
In this
case the impedance Z
0
will be: Z
0
= 3R
n
Now consider a system with an earthing via a resistor giving higher earth fault current
than the high impedance earthing. The series impedances in the system can no longer
be neglected. The system with a single phase to earth fault can be described as in
Figure
.
Section 9
1MRK 502 071-UEN -
Current protection
360
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Содержание Relion REG670
Страница 1: ...RELION 670 SERIES Generator protection REG670 Version 2 2 IEC Application manual...
Страница 2: ......
Страница 108: ...102...
Страница 132: ...126...
Страница 324: ...318...
Страница 442: ...436...
Страница 476: ...470...
Страница 628: ...622...
Страница 718: ...712...
Страница 728: ...722...
Страница 768: ...762...
Страница 778: ...772...
Страница 779: ...773...