ABB RELION Series Technical Manual page 336

Section 4
Protection functions
330
E
A
E
B
E
C
R
n
Uo
L
cc
R
cc
Reverse fault:
Yo ≈ -j*I
eFd
GUID-B852BF65-9C03-49F2-8FA9-E958EB37FF13 V1 EN
Figure 167: 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 10
eFd
Yo j j
≈ − ⋅ = − ⋅
U
15
ph
GUID-E2A45F20-9821-436E-94F1-F0BFCB78A1E3 V1 EN
Io
A B C
~
~
~
Im(Yo)
/U
ph
A
j 1 15 . milliSiemens
= − ⋅
3 kV
Protected feeder
Y
Fd
Background network
Y
Bg
(I - I )
eTot eFd
Re(Yo)
REC615 and RER615
Technical Manual
1MRS758755 A
Reverse
Fault
I
eFd
(Equation 15)