ABB RELION REX640, Техническое руководство, Страница: 556 / 1960

IRES
URES
Transient
detector
General
fault
criterion
Operation
logic
BLOCK
RELEASE
RESET
Multi-
frequency
admittance
calculation
OPERATE
START
BLK_EF
INTR_EF
PEAK_IND
Fault
direction
determination
Timer
I
o
U
o
FAULT_DIR
DIRECTION
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.
U
U U U
A B C
0
1
1 1 1
3
=
+ +
( )
(Equation 87)
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
U
o
1
exceeds setting
Voltage start value, an earth fault
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
Voltage start value defines the basic sensitivity of MFADPSDE. To
avoid unselective start or operation,
Voltage start value must always be set above
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
Voltage start value can be easily
selected based on the resonance curve calculated by the coil controller in
corresponding network conditions (see
Figure 320
).
Protection functions 1MRS759142 F
556 REX640
Technical Manual