4.3.3.2 Function block
Figure 285: Function block
4.3.3.3 Functionality
The numerical stabilized low-impedance restricted earth-fault protection function
LREFPNDF for a two-winding transformer is based on the numerically stabilized
differential current principle. No external stabilizing resistor or non-linear resistor
are required.
The fundamental components of the currents are used for calculating the residual
current of the phase currents, the neutral current, differential currents and
stabilizing currents. The operating characteristics are according to the definite
time.
The function contains a blocking functionality. The neutral current second harmonic
is used for blocking during the transformer inrush situation. It is also possible to
block function outputs, timers or the function itself, if desired.
4.3.3.4 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of LREFPNDF can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 286: Functional module diagram
Earth fault detector
The operation is based on comparing the amplitude and the phase difference
between the sum of the fundamental frequency component of the phase currents
(ΣI, residual current) and the fundamental frequency component of the neutral
current (Io) flowing in the conductor between the transformer or generator's
neutral point and earth. The differential current is calculated as the absolute
1MRS757644 H
Protection functions
620 series
Technical Manual
559
To Next Page
Loading...
