ABB Relion 620 Series - Page 433

~
~
~
A B C
U
o
E
A
E
B
E
C
Io
Reverse
Fault
Y
Fd
L
cc
R
cc
Y
Bg
I
eFd
(I
eTot
- I
eFd
)
R
n
Protected feeder
Background network
Im(Yo)
Re(Y
o)
Reverse fault:
Y
o ≈ -j*I
eFd
/U
ph
Figure 214: Admittance calculation during a reverse fault
R
CC
Resistance of the parallel resistor
L
CC
Inductance of the compensation coil
R
n
Resistance of the neutral earthing resistor
Y
Fd
Phase-to-earth admittance of the protected feeder
Y
Bg
Phase-to-earth admittance of the background network
For example, in a 15 kV compensated network with the magnitude of the earth-fault
current in the protected feeder being 10 A (Rf = 0 Ω), the theoretical value for the
measured admittance during an earth fault in the reverse direction, that is, outside
the protected feeder, can be calculated.
Yo j
I
U
j
A
kV
j
eFd
ph
≈ − ⋅ = − ⋅ = − ⋅
10
15 3
1 15. milliSiemens
(Equation 30)
The result is valid regardless of the neutral earthing method.
1MRS757644 H
Protection functions
620 series
Technical Manual
433