ABB Relion 670 Series Applications Manual page 245

1MRK 511 401-UEN Rev. K
= + 
C
L1l
= 
C 2 C
IECEQUATION19026 V1 EN-US
Where,
f is the number of fuse blown
u
C is the capacitance of the left section of phase L1
L1l
C is the capacitance of the healthy section
If an element fails in the left section, the unbalance current flowing through the neutral is
calculated by applying Thevenin theorem. Apply Thevenin theorem and calculate:
1. The open-circuit neutral voltage V
2. The open-circuit impedance (Z
=
V V
th N 1
æ
C
=
ç L1l
V
th
è
IECEQUATION19027 V1 EN-US
Assuming that there is no asymmetrical system unbalance on the system so that the negative
and zero sequence component of the phase voltages are zero.
V
=
L 1
V
0
IECEQUATION19028 V1 EN-US
so,
æ
=
ç
V
th
è
IECEQUATION19029 V1 EN-US
æ
=
ç
V
th
è
C
ANSIEQUATION19029 V1 EN-US
æ
=
ç
Z
ç (
th
è
IECEQUATION19030 V1 EN-US
=
I
UNBL1
IECEQUATION19031 V1 EN-US
Bay control REC670
Application manual
( )
− −
C C P f 1
x u u u
e
-
V
N 2
( )
´ + ´ + ö
+
æ
V C V V V V
-
L1 L2 L 3 ÷ L1
ç
+ ´
è
ø
C 2 C 3
L1l
+ +
V V
=
L 2 L 3
0
3
ö
-
C C
´
L1l ÷
V
+ ´
L1
ø
C 2 C
L1l
- ö
C C
´
÷
Al
V
+ ´
A
ø
2 C
Al
ö
+ ´
æ ö
C 5 C
1
´
÷
L1l
ç ÷
) ÷
+ ´ ´ ´
è ø
C 2 C 3 C w
ø
L1l
æ - ö
V C C
= ´ ´ ´ ´
th ç L1l ÷
V w 3 C
+ ´
L1
è ø
Z C 5 C
th L1l
© Copyright 2017 Hitachi Power Grids. All rights reserved
.
th
) between N and N
th 1
+
ö
V
L 2 L3
÷
ø
by using the following equations:
2
Section 10
Unbalance protection
(Equation 108)
(Equation 109)
(Equation 110)
(Equation 111)
(Equation 111)
(Equation 112)
(Equation 113)
239