Auto Transformer

Auto Transformer :-- A transformer in which a part of the winding is common for both primary and secondary circuits, is called an auto transformer .Where as in two winding transformer both windings are electrically isolated but magnetically coupled .

Auto Transformer

Two winding transformer

Concept Of Maximum Power Transfer Theorem In Electrcial networks :---

Some times we need to transfer Maximum power from source side to load side ,then we have to apply Maximum Power Transfer Theorem in given circuit . But to gain  Maximum Power Transfer at load side we have to compermise with efficiency of the system ,i.e during 
Maximum Power Transfer  overall efficiency of the circuit is only 50% .

 Let a circuit in which we have to find a condition for Maximum Power Transfer  
 

To transfer  maximum power required condition is 

       load resistance = source resistance

  

 and maximum power  Pmax= (Vs)^2/4*Rs                                                                                                      

PHANTOM LOADING

What is Phantom loading ??

 When the current ratings of meter under test is very high,a test with actual load arrangements consumes considerable waste of power. To avoid this Phantom loading is used:-

Phantom loading consist of supplying the pressure circuit(voltage coil) from rated voltage supply and the current circuit from a low voltage supply. Thus it is possible to circulate the rated current through with the current circuit with low voltage supply as the circuit impedance is very low.

• The total power consumed by Phantom loading is very small as compared to direct loading.
• In Phantom loading  arrangement energy consumption in the calibration test of watt- meter is reduced because of the absence of load in the test.