Figure 287: Operating characteristics of the stabilized earth-fault protection
function
Figure 288: Setting range of the operating characteristics for the stabilized
differential current principle of the earth-fault protection function
The
Operate value
setting is used for defining the characteristics of the function.
The differential current value required for tripping is constant at the stabilizing
current values 0.0 < IB/In < 1.0, where In is the nominal current, and the In in this
context refers to the nominal of the phase current inputs. When the stabilizing
current is higher than 1.0, the slope of the operation characteristic (ID/IB) is
constant at 50 percent. Different operating characteristics are possible based on
the
Operate value
setting.
For the protection of the trip, the measured neutral current has to be above 4
percent. When the condition has been fulfilled, the measured neutral current must
stay above 2 percent, otherwise reset time is started.
To calculate the directional differential current ID_COSPHI, the fundamental
frequency amplitude of both the residual and neutral currents has to be above 4
percent of In. If neither or only one condition is fulfilled at a time, the cosφ term
is forced to 1. After the conditions are fulfilled, both currents must stay above 2
percent of In to allow the continuous calculation of the cosφ term.
1MRS757644 H
Protection functions
620 series
Technical Manual
561
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