ABB RELION REX640 Technical Manual page 538

Section 4
Protection functions
532
I I
EFFd detuning
+
 
atan
ϕ =
 
I
damping
 
GUID-16405161-8FB6-4E30-86F7-9CC0C424C2F0 V1 EN
I Earth-fault current produced by the protected feeder [A]
EFFd
I Detuning of the arc suppression coil [A]
detuning
I System damping [A]
damping
Example 1:
I = 30 A, I = +10 A and I
EFFd detuning
Tilt angle should not exceed ~10 deg.
Example 2:
I = 50 A, I = +10 A and I
EFFd detuning
Tilt angle should not exceed ~3 deg. However, such a low Tilt angle setting may
endanger the security of protection due to measurement errors of the CBCTs. In this
case, the phase angle of operation point should be increased by considering:
1. System damping increase by increasing the current value of the parallel resistor
of the coil
2. Reduction of the earth-fault current produced by the protected feeder by, for
example, installation of distributed compensation coils or by change of the feeder
topology
3. Reduction of overcompensation of the network. The recommendation is to use
the undercompensation mode.
The DIRECTION output indicates on which operating sector the current is measured.
The FAULT_DIR output indicates in which operation sector the fault current is
measured. The output is operational once the function is started.
To adapt the fault direction determination to a fault direction change during the fault,
for example, during manual fault location process, a cyclic accumulation of sum
admittance phasors is conducted. The duration of this directional evaluation cycle is
1.2 · Reset delay time (minimum 600 ms). If the fault direction based on the cyclic
phasor accumulation is opposite to the function direction output for Reset delay time
or 500 ms (minimum 500 ms), the function is reset and the fault direction calculation
of MFADPSDE is restarted.
If the earth-fault protection generates alarms, MFADPSDE also includes a RESET
input which can be used to externally re-trigger the fault direction determination if re-
evaluation of fault direction during a persistent earth fault is required.
It is also recommended to connect the start signal of non-directional earth fault
protection (EFxPTOC), set to operate in case of a cross-country fault, to RESET input
or BLOCK input of MFADPSDE to reset phasor accumulation during a cross-country
= 10 A. From Equation
damping
= 5 A. From Equation
damping
1MRS759142 C
(Equation 84)
84, = 76 deg. Thus
ϕ
84, = 85 deg. Thus
ϕ
REX640
Technical Manual