ABB RELION REX640 Technical Manual page 640

Section 4
Protection functions
634
tap position information is corrupted, the automatic tap changer position adaptation
does not try to adapt to any unrealistic position values.
Max winding tap
Tap nominal
Min winding tap
GUID-30DEED19-FDFF-4102-94E8-C3E64A0235BC V1 EN
Figure 349: Simplified presentation of the HV and LV windings of a two-winding
transformer with demonstration of the settings Max winding tap, Min
winding tap and Tap nominal
The position value is available in the Monitored data view on LHMI or through other
communication tools in TPOSYLTC. When the quality of the TAP_POS input value
is not good, the position information in the TAP_POS input is not used, and the last
value with the good quality information is used instead. In addition, the minimum
sensitivity of the biased stage, set by the Low operate value setting, is automatically
desensitized with the total range of the tap position correction. The new acting low
operate value can be calculated.
Desensitized Low operatevalue Low operatevalue ABS Max winding
GUID-4A0D2DFE-A5B0-4D0D-B31D-B36FE38D406F V1 EN
Second harmonic blocking
Transformer-magnetizing inrush currents occur when the transformer is energized
after a period of de-energization. The inrush current may be many times the rated
current, and the half-life can be up to several seconds. To the differential protection
relay, the inrush current represents a differential current that causes the protection
relay to operate almost always when the transformer is connected to the network.
Typically, the inrush current contains a large amount of second harmonics.
The blocking of the biased low stage of the protection relay at magnetizing inrush
current is based on the ratio of the amplitudes of the second harmonic to the
fundamental frequency component of the differential current (Id2f / Id1f).
The blocking also prevents an unwanted operation at recovery and a sympathetic
magnetizing inrush. At 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
(HV)
(
= +
1MRS759142 C
(LV)
t t ap Minwinding tap Step of tap ⋅ )
−
(Equation 116)
REX640
Technical Manual