TRANSFORMER ON NO-LOAD

When there is no load connected in secondary side operation of transformer is called no load operation in the case of transformer draw a small amount of current which is called no-load current (Io). No-load current is 5% to 10% of full load current.No load current is utilized for magnetizing to core and eddy current loss the hysteresis loss.It means Io has two component one is magnetizing component (Iu) and another is working component (Iw).Now from phasor diagram

Io=..

Iw=Iocos..

where cos is power factor in no load case and.. is phase angle between V1 and Io.Now power consumed on no-load operation

P=V1Iocos..

TRANSFORMER ON LOAD

When certain load is connected to transformer load current I2 start to flow in secondary coil.This current will set up () flux in the core in opposite direction to no-load flux ().() will link to primary winding and induced some voltage in the primary coil decreases.Now potential difference between supply and winding voltage will be increased.Hence additional current I2 will start to flow in addition to Io in primary side. Amount of I2 depends on amount of I2.Now I2 in primary side sets up into its own flux ().Hence () and () get conduced each other resulting only () in the core.Therefore in this transformer flux remains constant in the core.

N2I2=N1I2

N2/N1=I2/I2