ABB RELION REX640 - Page 495

Yo j
I
U
j
A
kV
j
eFd
ph
≈ − ⋅ = − ⋅ = − ⋅
10
15 3
1 15. milliSiemens
(Equation 61)
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
Bgtot
=
(Equation 62)
≈ ⋅
−








j
I I
U
eTot eFd
ph
(Equation 63)
Compensated network:
Yo Y Y
Bgtot CC
= +
(Equation 64)
≈
+ ⋅ ⋅ −
( )
−
( )
I j I K I
U
Rcc eTot eFd
ph
1
(Equation 65)
High-resistance earthed network:
Yo Y Y
Bgtot Rn
= +
(Equation 66)
≈
+ ⋅ −
( )
I j I I
U
Rn eTot eFd
ph
(Equation 67)
Y
Bgtot
Sum of the phase-to-earth admittances ( Y
BgA
, Y
BgB
, Y
BgC
) of the background
network
Y
CC
Admittance of the earthing arrangement (compensation coil and parallel resistor)
I
Rcc
Rated current of the parallel resistor
Table continues on the next page
1MRS759142 F Protection functions
REX640
Technical Manual
495