ABB RELION REX640 Technical Manual page 686

Protection functions
winding tap parameter tells the tap position number resulting in the maximum
effective number of winding turns.
The
compensation algorithm know in which direction the compensation is being made.
This ensures also that if the current tap position information is corrupted for some
reason, the automatic tap changer position adaptation does not try to adapt to any
unrealistic position values.
Figure 389: Simplified presentation of the high voltage and medium voltage
windings with demonstration of the Max winding tap, Min winding tap and Tap
nominal parameters
The position value is available through the Monitored data view on LHMI or through
other communication tools in the tap position indication function. When the quality
of the TAP_POS value is not good, the position information in TAP_POS is not used
but the last value with the good quality information is used instead. In addition, the
minimum sensitivity of the biased stage, set by the
automatically desensitized with the total range of the tap position correction. The
new acting low operate value is
Desensitized Low operate value = Low operate value ABS MaxWi
Second harmonic blocking
The transformer magnetizing inrush currents occur when energizing the
transformer after a period of de-energization. The inrush current can be many
times the rated current and the halving time can be up to several seconds. To
the differential protection, the inrush current represents a differential current,
which would cause the differential protection to operate almost always when the
transformer is connected to the network. Typically, the inrush current contains a
large amount of second harmonics.
Blocking the operation of the TR2PTDF biased low stage at a magnetizing inrush
current is based on the ratio of the amplitudes of the second harmonic digitally
filtered from the differential current and the fundamental frequency (Id2f /Id1f).
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
686
Min winding tap and Max winding tap parameters help the tap position
Low operate value setting, is
( n n ding tap Min winding tap
+ −
1MRS759142 F
× ) Step of tap
(Equation 162)
REX640
Technical Manual