ABB RELION Series, Technical Manual

Page: 381 / 804

The operation of MFADPSDE can be described using a module diagram. All the
modules in the diagram are explained in the following sections.
GUID-C69174FA-2E03-4582-A479-107B655C136E V1 EN
Figure 196: 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
= + +
( )
/
GUID-0E55584E-A887-4A4B-B8E0-5CDCEDFCFC55 V1 EN
(Equation 31)
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.
1MRS758755 A
Section 4
Protection functions
REC615 and RER615 375
Technical Manual