ABB RELION REX640 Technical Manual page 495

1MRS759142 F
Yo
≈ − ⋅
The result is valid regardless of the neutral earthing method.
In this case, the resistive part of the measured admittance is due to leakage losses
of the protected feeder. As they are typically very small, the resistive part is close
to zero. Due to inaccuracies in the voltage and current measurement, the small
real part of the apparent neutral admittance may appear positive. This should be
considered in the setting of the admittance characteristic.
Fault in the forward direction, that is, inside the protected feeder.
Unearthed network:
Yo Y
=
≈ ⋅
j
Compensated network:
Yo Y
=
I
Rcc
≈
High-resistance earthed network:
Yo Y
=
I
Rn
≈
Y
Bgtot
Y
CC
I
Rcc
Table continues on the next page
REX640
Technical Manual
I 10 A
eFd
j j
= − ⋅
U
15 3 kV
ph
Bgtot
 
−
I I
eTot eFd
 
 
U
 
ph
Y
+
Bgtot CC
(
( )
+ ⋅ j I ⋅ − 1 K − I
eTot eFd
U
ph
Y
+
Bgtot Rn
( )
+ ⋅ j I − I
eTot eFd
U
ph
Sum of the phase-to-earth admittances ( Y
network
Admittance of the earthing arrangement (compensation coil and parallel resistor)
Rated current of the parallel resistor
j 1 15 . milliSiemens
= − ⋅
)
Protection functions
, Y , Y ) of the background
BgA BgB BgC
(Equation 61)
(Equation 62)
(Equation 63)
(Equation 64)
(Equation 65)
(Equation 66)
(Equation 67)
495