ABB Relion REC615, Техническое руководство

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4.2.7.4 Operation principle
The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of MFADPSDE can be described using a module diagram. All the
modules in the diagram are explained in the following sections.
Figure 195: 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 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
Protection functions 1MRS758755 C
390 REC615 & RER615
Technical Manual