4.3.3 Numerically stabilized low-impedance restricted ground-fault
protection 87LOZREF
4.3.3.1 Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Numerically stabilized low-impedance
restricted ground-fault protection
LREFPNDF dIoLo> 87LOZREF
4.3.3.2 Function block
GUID-136BBBB5-17AB-41B1-81B9-F89CC3E05227 V2 EN
Figure 266: Function block
4.3.3.3 Functionality
The numerically stabilized low-impedance restricted ground-fault protection function
87LOZREF 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 “Enable” and “Disable”.
The operation of 87LOZREF can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
Section 4 1MAC059074-MB A
Protection functions
538 615 series ANSI
Technical Manual
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