- 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

_{0 }= V

_{1}I

_{0 }Cos F

_{0}

Where

Cos F

_{0}= No load input power factor- 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 V**

_{1}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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