ABB RELION REX640 Technical Manual page 589

1MRS759142 F
Maximum fault current value is obtained when fault resistance (
Equation 104
Interpretation of
damping and imaginary part due to network detuning. Fault current magnitude
increases when damping or detuning increases.
The effect of fault resistance to fault current magnitude can be written as:
where
Interpretation of
magnitude is proportional to scaling the fault current magnitude at zero fault
resistance with the per unit value of residual voltage (
Minimum fault current magnitude is always obtained at resonance, when detuning
I
( ) is zero, in case
v
At resonance, fault current is only due to system resistive shunt losses i.e. due to
network damping (
In case of unearthed network, detuning value (
fault current due to total network phase-to-earth capacitance value. In case of high
resistance earthed network detuning value (
REX640
Technical Manual
can be written as:
Equation 105
is that fault current has resistive part due to network
Equation 106 is that effect of fault resistance to fault current
Equation 104
can be written as:
I
) and possible harmonic components.
d
Protection functions
R
F
) due to fault resistance.
I
) equals the uncompensated earth-
v
I
) equals the uncompensated earth-
v
(Equation 104)
) is zero, in case of
(Equation 105)
(Equation 106)
(Equation 107)
(Equation 108)
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