Voltage start value
= 0.15 × Un
According to
Figure 293
, this selection ensures at least a sensitivity
corresponding to a 2000 ohm fault resistance when the compensation
degree varies between 80% and 120%. The greatest sensitivity is achieved
when the compensation degree is close to full resonance.
An earth-fault current of 10 A can be converted into admittance.
Y
A
kV
j
Fdtot
= ≈ ⋅
10
15 3
1 15. mS
(Equation 71)
A parallel resistor current of 15 A can be converted into admittance.
(Equation 72)
According to
Equation 59
, during an outside fault EFPADM measures the
following admittance:
Yo Y j
Fdtot
= − ≈ − ⋅1 15. mS
(Equation 73)
According to
Equation 62
, during an inside fault EFPADM measures the
admittance after the connection of the parallel resistor:
Yo Y Y j B
Bgtot CC
= + ≈ + ⋅
( )
1 73. mS
(Equation 74)
Where the imaginary part of the admittance, B, depends on the tuning of the
coil (compensation degree).
The admittance characteristic is selected to be the combined
overconductance and oversusceptance characteristic ("Box"-characteristics)
with four boundary lines:
Operation mode
= "Go, Bo"
Directional mode
= "Non-directional"
The admittance characteristic is set to cover the total admittance of the
protected feeder with a proper margin, see
Figure 295
. Different setting
groups can be used to allow adaptation of protection settings to different
feeder and network configurations.
Conductance forward
This setting should be set based on the parallel resistor value of the coil. It must
be set to a lower value than the conductance of the parallel resistor, in order to
enable dependable operation. The selected value should move the boundary line
1MRS759142 F
Protection functions
REX640
Technical Manual
511
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