example, the IoCos mode in the directional ground-fault protection function 67/51N,
67/50N.
32N measures the ground-fault power 3UoIoCosφ and gives a trip signal when the
residual current IG, residual voltage VG and the ground-fault power exceed the set limits
and the angle (φ) between the residual current and the residual voltage is inside the set
operating sector, that is, forward or backward sector. The operating time characteristic can
be selected to be either definite time (DT) or a special wattmetric-type inverse definite
minimum type (wattmetric type IDMT).
The wattmetric-based ground-fault protection is very sensitive to current transformer
errors and it is recommended that a core balance CT is used for measuring the residual
current.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.
4.2.6.4 Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are “Enable” and “Disable”.
For 32N, certain notations and definitions are used.
Residual voltage VG or V0 = (VA+VB+VC)/3 = V
0
, where V
0
= zero-
sequence voltage
Residual current IG or I0 = -(IA+IB+IC) = 3×- I
0
, where I
0
= zero-
sequence current
The minus sign (-) is needed to match the polarity of calculated and
measured residual currents.
The operation of 32N can be described with a module diagram. All the modules in the
diagram are explained in the next sections.
Section 4 1MAC059074-MB A
Protection functions
410 615 series ANSI
Technical Manual
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