ABB RELION REX640 Technical Manual page 464

Section 4
Protection functions
458
E
A
E
B
E
C
R
n
Uo
L
cc
R
cc
Reverse fault:
Yo ≈ -j*I
eFd
GUID-E45A96D0-0B28-45A7-A497-EAA52D24F82E V1 EN
Figure 247: Admittance calculation during a reverse fault
R Resistance of the parallel resistor
CC
L Inductance of the compensation coil
CC
R Resistance of the neutral earthing resistor
n
Y Phase-to-earth admittance of the protected feeder
Fd
Y Phase-to-earth admittance of the background network
Bg
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.
I A
10
eFd
Yo j j
≈ − ⋅ = − ⋅
15
U
kV
ph
3
GUID-97427224-8935-47DE-9FFC-FB954B687742 V1 EN
Io
A B C
Protected feeder
~
~
~
Background network
Im(Yo)
Re(Yo)
/U
ph
j mS
1 15 .
= − ⋅
1MRS759142 C
Y
Fd
Reverse
Fault
Y
Bg
(I - I )
I
eTot eFd
eFd
(Equation 49)
REX640
Technical Manual