Oltc & avr

CFVV vs VFVVTransformer actionTransformer equation V= 4.44 f N Eqn -1Where E= Induced voltage = Max flux.F= frequencyN = number of turns

From eqn-1: = V/4.44 f NThis means that flux is directly proportional to voltage and inversely proportional to number of turns and frequency.Transformer ActionAlso N1/N2 = V1/V2Eqn-2From this equation it can be equated that V1/N1 equals V2/N2.This means that the voltage per turn in a transformer remains same throughout irrespective of primary or secondary winding.

Voltage changing In order to vary the secondary voltage of transformer we have two optionsChange the number of turns of primaryChange the number of turns of secondaryTo increase the voltage on the secondary we have to either increase the no of turns on secondary side or decrease the number of turns on primary side.

Changing the turns on primary sideOn Load Tap ChangerWhen the turns are changed on primary side, due to variation of incoming voltage on primary side, the control is called constant flux variable voltage control.Because under this condition, due to decrease in incoming voltage, the number of turns are on primary side are decreased in order to increase the secondary voltage. So in this case, ( = V/4.44 f N) the ratio of V/N remains constant .Changing the turns on Secondary sideOff Load Tap ChangerWhen the turns are changed on secondary side, due to variation of incoming voltage on primary side, the control is called variable flux variable voltage control.Because under this condition, due to decrease in incoming voltage, the number of turns are on Secondary side are increased in order to increase the secondary voltage. So in this case, ( = V/4.44 f N) the ratio of V/N does not remain constant .

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