ABB RELION REX640 Technical Manual page 465

1MRS759142 C
REX640
Technical Manual
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
GUID-50C19678-4C7E-47CD-8604-BE0F1538181B V1 EN
I I
 
−
eTot eFd
j
≈ ⋅
   
U
ph
 
GUID-68F98126-BC86-44CE-90DF-CBFAAF06CD10 V1 EN
Compensated network:
Yo Y Y
= +
Bgtot CC
GUID-194116F2-1A55-4B82-BA23-DD40E207D925 V1 EN
I j I 1 K
(
( )
+ ⋅ ⋅ − −
Rcc eTot
≈
U
ph
GUID-D7CB219D-7B2A-4B52-AD62-54D8A6DDEEC6 V1 EN
High-resistance earthed network:
Yo Y Y
= +
Bgtot Rn
GUID-DDD9549A-5C90-4C54-BC59-DCA834BB4A35 V1 EN
I j I I
( )
+ ⋅ −
Rn eTot eFd
≈
U
ph
GUID-B3DA7BF8-49C6-4E66-99F7-C3017DA9702E V1 EN
Y Sum of the phase-to-earth admittances (Y
Bgtot
Y Admittance of the earthing arrangement (compensation coil and parallel resistor)
CC
I Rated current of the parallel resistor
Rcc
I Magnitude of the earth-fault current of the protected feeder when the fault resistance is zero ohm
eFd
I Magnitude of the uncompensated earth-fault current of the network when Rf is zero ohm
eTot
K Compensation degree, K = 1 full resonance, K<1 undercompensated, K>1 overcompensated
I Rated current of the neutral earthing resistor
Rn
Equation 50 shows that in case of a fault inside the protected feeder in unearthed
networks, the measured admittance equals the admittance of the background network.
The admittance is dominantly reactive; the small resistive part of the measured
I
)
eFd
, Y
BgA BgB
Section 4
Protection functions
, Y ) of the background network
BgC
(Equation 50)
(Equation 51)
(Equation 52)
(Equation 53)
(Equation 54)
(Equation 55)
459