No load equivalent circuit


No load equivalent circuit


The primary winding draws a small amount of alternating current of instantaneous value Io, called the exciting current, from the voltage source. The exciting current establishes flux f in the core.

When the primary side is connected to sinusoidal voltage source V1 a current known magnetizing current Im flows in it. This current set up a alternating flux in the core. Hence it is called a magnetizing current. The flux Φm is proportional to Im. Im lags behind the applied voltage v1 by 90.  











The flux Φm links with both the primary and the secondary winding. When it links with primary winding it produce self induce EMF E1 which is opposite to applied voltage. Similarly alternating flux links with secondary side its produce mutually induced EMF E2. Both E1 and E2 lag behind the Φ by 90 degree.
This can be shown by the phasor diagram.

Here the losses are neglected.
No load equivalent with losses
Here current need to supply the iron loss in the transformer core is known magnetizing component. It is also called as watt less component and is donated by Im or Ior.
                                                Im= IosinΦo
The current which is required to supply iron loss in core is called core loss component. It is also called as the watt full component. It is donated by Iw or Ioa
                                                Iw = Ic= IocosΦo
The no load component is summation of watt full and watt less component.

                                                Io = Iw  +  Im
No load current is about 3 to 5% of full load.
Phasor diagram at no load.


No load equivalent with losses.

click here to go KVL
click here to go nodal analysis

click here to go losses in transformer


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