input current values on the side where the tap changer resides are scaled to match
the currents on the other side.
A correct scaling is determined by the number of steps and the direction of the
deviation from the nominal tap and the percentage change in voltage resulting
from a deviation of one tap step. The percentage value is set using the
Step of tap
parameter.
The operating range of the tap changer is defined by the
Min winding tap
and
Max winding tap
parameters. The
Min winding tap
parameter tells the tap position
number resulting in the minimum effective number of winding turns on the side
of the transformer where the tap changer is connected. Correspondingly, the
Max
winding tap
parameter tells the tap position number resulting in the maximum
effective number of winding turns.
The
Min winding tap
and
Max winding tap
parameters help the tap position
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 269: 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
Low operate value
setting, is
automatically desensitized with the total range of the tap position correction. The
new acting low operate value is
Desensitized Low operate value = Lowoperate value ABS MaxWi+ ( nnding tap Min winding tap Step of tap− ×)
(Equation 74)
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
Protection functions
1MRS757644 H
524 620 series
Technical Manual
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