Answer Posted / hin sothea(ctl)

OLTC On Load Tap Changer in Tr. Is mean that the changing
Tap of Transformer is according to the changing of loads
at low voltage side. Any way chang Tap mean chang the turn
winding of Primary side of Tr.
Eg: VL=VHx(NL/NH)
V=P/I

If current at lower side is increased, the voltage at lower
side will be decreased and also for the voltage at higher
side.To make the voltage at lower side stable, the turn
winding at higher side must be higher than it befor. When
the turn is chang it is mean the Tap is chang.

By Ohm Law:

P : Stable
I :→∞
V :→0
VL :constant,Low side Voltage(We need it be constang)
VH :constant,High side Voltage
NL :constant,Low side turn winding
NH :High side turn winding

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