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.
4.6.1.4
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.
GUID-F8C2915F-CA7B-4830-B748-3E19E26803CC V1 EN
Figure 144:
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 (IG) flowing in the
conductor between the transformer or generator's neutral point and ground. The
differential current is calculated as the absolute value of the difference between the
residual current (the sum of the fundamental frequency components of the phase currents
I_A, I_B and I_C) and the neutral current. The directional differential current
ID_COSPHI is the product of the differential current and cosφ. The value is available in
the monitored data view.
Section 4
1MRS240050-IB C
Protection functions
302
REF615R
Technical Manual
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