Figure 247: Functional module diagram
General fault criterion
The General fault criterion ( GFC) module monitors the presence of earth fault 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 46)
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 the MFADPSDE
function. To avoid unselective start or operation,
Voltage start value must always
be set to a value which exceeds the maximum healthy-state zero-sequence
voltage value, taking into consideration of possible network topology changes,
compensation coil and parallel resistor switching status and compensation degree
variations.
As an alternative for internal residual zero-sequence overvoltage based start-
condition, MFADPSDE function can also be externally released by utilizing the
RELEASE
input. In this case, the external release signal overrides the
Voltage start
value setting and sets the internal limit to minimum value.
Multi-frequency admittance calculation
Multi-frequency admittance calculation module calculates neutral admittances
utilizing fundamental frequency and the 2nd, 3rd, 5th, 7th and 9th harmonic
components of residual current and zero-sequence voltage. The following
admittances are calculated, if the magnitude of a particular harmonic in residual
current and zero-sequence voltage are measurable by the protection relay.
Protection functions
1MRS757644 H
482
620 series
Technical Manual
