ABB RELION REX640 Technical Manual page 670

Section 4
Protection functions
664
GUID-345732C2-CB61-4BF2-A9C5-26B5C5275AE2 V1 EN
Figure 365: 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.
Second harmonic blocking
This module compares the ratio of the current second harmonic (I
set value Start value 2.H. If the ratio (I
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 energization of a transformer running in parallel with the protected
transformer connected to the network.
_2H / I ) value exceeds the set value, the
0 0
1MRS759142 C
_2H) and I to the
0 0
REX640
Technical Manual