ABB RELION REX640 Technical Manual page 556

Protection functions
RELEASE
RESET
BLOCK
Figure 319: Functional module diagram
General fault criterion
The General fault criterion ( GFC) module monitors the presence of earth faults
in the network and it is based on the value of the fundamental frequency zero-
sequence voltage defined as the vector sum of fundamental frequency phase
voltage phasors divided by three.
1
U
=
0
MFADPSDE supports zero-sequence voltage monitoring based on measurement
(from open-delta winding) or calculated (derived from phase-to-earth voltages).
When the magnitude of
is detected. The GFC module reports the exceeded value to the Fault direction
determination module and Operation logic. The reporting is referenced as General
Fault Criterion release.
The setting
avoid unselective start or operation,
the maximum healthy-state zero-sequence voltage value, considering network
topology changes, compensation coil and parallel resistor switching status and
compensation degree variations. The setting
selected based on the resonance curve calculated by the coil controller in
corresponding network conditions (see
556
Transient
detector
I
o
Multi-
IRES
frequency
admittance
U
o
URES
calculation
General
fault
criterion
( )
1 1 1
U U U
+ +
A B C
3
U
Voltage start value defines the basic sensitivity of MFADPSDE. To
Fault
direction
determination
1
Voltage start value , an earth fault
exceeds setting
o
Voltage start value must always be set above
Voltage start value can be easily
Figure 320
Operation
logic
Timer
).
Technical Manual
1MRS759142 F
PEAK_IND
INTR_EF
DIRECTION
FAULT_DIR
START
OPERATE
BLK_EF
(Equation 87)
REX640