ABB RELION REX640 Technical Manual page 586

Protection functions
defined as the vector sum of fundamental frequency phase voltage phasors divided
by three.
When the magnitude of U
detected and EF_IND output is set to TRUE. Setting value
is given in per unit format with system nominal phase-to-earth value (U
reference.
IFPTOC supports fundamental frequency residual voltage monitoring based on
measured U
connected phase-to-earth voltages.
The setting
in terms of fault resistance. Fault detection sensitivity in terms of fault resistance
can be estimated using the equation below:
where U
[A],
unit.
In compensated networks the minimum value for the setting
be easily selected based on the resonance curve calculated by the coil controller
considering different network topologies and conditions, refer to
586
from open-delta winding or internally calculated U
o
Input EXT_RELEASE is alternative method for internal GFC and validity
check modules to indicate the presence of earth fault in the protected
feeder and to release the calculation of IFPTOC function. Activation of
EXT_RELEASE will also override earth-fault validity check criterion i.e.
earth-fault current estimate is considered as valid when EXT_RELEASE
is activated. It is therefore mandatory that EXT_RELEASE is based on
start of directional earth-fault detection function, such as MFADPSDE or
DEFxPDEF.
Voltage start value defines the basic sensitivity of the IFPTOC function
is the system phase-to-earth voltage [V],
PE
I
is the network detuning value [A] and
v
Voltage start value , an earth fault is
exceeds setting
o
U
o_pu
1MRS759142 F
(Equation 100)
Voltage start value
derived from
o
(Equation 101)
I
is the total system damping
d
Voltage start value in per
is setting
Voltage start value can
Figure 336
Technical Manual
) as
n_PE
.
REX640