- When the supply
voltage V
_{1}is given to the transformer primary winding, the no load current I_{0}flows through the primary winding. This current sets up flux in the core. - Due to varying flux core loss or iron loss occurs in the core material, the no load input power is given by

W

_{0 }= V_{1}I_{0 }Cos F_{0}
Where

V

_{1}= Primary Supply Voltage
I

_{0}= No load current- Therefore
the no load input current has to supply ( I ) Iron losses in the core and ( II
) Small amount of copper loss in the primary winding ( no copper loss in the
secondary winding because it is open circuited therefore the no load current
lags behind V
_{1}by angle F_{0}. (F_{0}< 90° ) - The no load current has two components

__( I ) Loss component current ( I___{w})- The
function of the I
_{w}is to supply iron loss in the core. - It is in
phase with voltage V
_{1}.

I

_{w }= I_{0}Cos F_{0}……………( 1 )

__( II ) Magnetizing Current ( I___{µ})- The
function of the magnetizing current I
_{µ}is to create flux in the core. It is in quadrature with voltage V_{1}.

I

_{µ}= I_{0}Sin F_{0}……………..( 2 )
Therefore
I

_{0}= √ ( I_{µ}^{2}+ I_{w}^{2})
Also
tan F

_{0}= I_{µ}/ I_{w}**What percentage of no load current that of full load primary current? Why?**

- The no load primary current is only 2 to 5% of full load current because the core of the transformer has low reluctance path.

**Why the waveform of the exciting current is not sinusoidal?**

- The permeability of the core varies with the exciting current therefore the waveform of the exciting current is not sinusoidal.

**Why the angle between supply voltage V1 and no load current is always less than 90**

^{0 }?- The no load current is not wholly reactive.
- It has to supply amount of iron losses
and relative large amount of magnetizing current therefore the input power factor of the no load current always less than 90
^{0}.

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