ABB RELION REX640 Technical Manual page 497

1MRS759142 F
Uo
Figure 281: Admittance calculation during a forward fault
REX640
Technical Manual
E
A
~
E
B
~
E
C
~
R
n
L
cc
R
cc
Forward fault,
unearthed network:
Yo ≈ j*(I -I )/U
eTot eFd ph
Reverse fault:
Yo ≈ -j*I
When the network is fully compensated in compensated networks,
theoretically during a forward fault, the imaginary part of the measured
admittance equals the susceptance of the protected feeder with a
negative sign. The discrimination between a forward and reverse fault
Io
A B C
Im(Yo)
/U
eFd ph
Forward fault, compensated network:
Yo ≈ (I + j*(I *(1-K) - I
rcc eTot
Protection functions
Protected feeder
Y
Fd
I
eFd
Background network
Y
Bg
Forward fault,
high resistance earthed network:
Yo ≈ (I +j*(I -I ))/U
Rn eTot eFd
Under-comp. (K<1)
Re(Yo)
Resonance (K=1)
Over-comp. (K>1)
))/U
eFd ph
Forward
Fault
I
eTot
(I - I )
eTot eFd
ph
497