ABB 615 series Technical Manual page 547

1MAC059074-MB A
615 series ANSI
Technical Manual
GUID-4BF3E289-E355-4C31-B87E-151DFDDCEBA8-ANSI V1 EN
Figure 269: Setting range of the operating characteristics for the stabilized differential
current principle of the ground-fault protection function
The Trip 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 Trip 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.
Second harmonic blocking
This module compares the ratio of the current second harmonic (IG_2H) and IG to the set
value Pickup value 2.H. If the ratio (IG_2H / IG) value exceeds the set value, the BLK2H
output is activated.
The blocking also prevents unwanted operation at the recovery and sympathetic
magnetizing inrushes. At the recovery inrush, the magnetizing current of the transformer
to be protected increases momentarily when the voltage returns to normal after the
clearance of a fault outside the protected area. The sympathetic inrush is caused by the
Section 4
Protection functions
541