Transformers

Tranformer:

"In sort we can say" : A transformer is a static device which consist of two or more stationary electric circuit interlinked by a common magnetic circuit for the purpose transferring electrical energy between them while keeping the frequency of operation constants.

• Basic principal behind the transformer action is Faradays law of electromagnetic induction.
• Tranformer is a constant frequency and constant power device.

• 

  Transformer

Ideal tranformer:

• The tranformer core has infinite permeability . So flux established without any magnetising current.
• The primary and secondary winding have Zero resistance . So there is no ohmic power loss and no resistive voltage drop in it.
• In Ideal tranformer there is no magnetic leakage flux.
• The core loss considered to be zero.

 

Types of Tranformer Construction:

1. Core type  2. Shell type

Core types:

1. It have a series magnetic circuit.
2. It consist 2 limb and 2 yoke
3. Suitable for low flux density application.
4. It required more amount of copper.
5. Required less amount of insulation so suitable for high voltage ad high power applications.

Shell type:

1. It have a parallel magnetic circuit.
2. It consist 3 limb and 2 yoke.
3. Suitable for high flux density application.
4. It required less amount of copper.
5. Suitable for low voltage and lower power applications.

Losses in Transformer:

1. Copper loss (Pcu):

• This loss is Variable loss
• Total copper loss = Primary copper loss + Secondary copper loss

2. Iron loss (Pi):

• This loss is Constant loss
• Iron loss= Hystersis loss + Eddy Current loss

Hysteris loss        =         P_h=K_hfB_m^x

• K_{h = Proportionality constant depends upon volume, quality of the core material and units used}
• B_{m= Maximum flux density in the core}
• _{f    = Supply frequency}
• _{x    = Steinmetz exponent (1.5 to 2.5)}
• _{But if V/f is constant}  
•    P_{h α f}

        Eddy current loss    =          Pe=K_ef²Bm²t²  

• K_{e    = proportionality constant depend upon volume and resistivity of the core material}
• f       = Supply frequency
• Bm   = Maximum flux density
• t       = Thickness of lamination
• But if V/f is constant
• P_{e α f}²