TRANSFORMER

1. Principle of operation of a transformer is the mutual inductance. 

2. Primary winding Lp is connected to a voltage source that produces alternating current and the secondary winding Ls is connected across the load resistance RL.

3. The primary and secondary are not connected to each other, but power in the primary is coupled into the secondary by the magnetic field linking the two windings. 

4. A transformer is used when the load requires an ac voltage higher or lower than the generator voltage.


Step Up Transformer

ln a step-up transformer, Ns > Np, Vs > Vp and Is < Ip where Ns number of turns in the secondary and Np is number of turns in the primary.

Step Down Transformer

In a step down transformer, Np >Ns, Vp>Vs, and Ip < Is.





Turns Ratio

1. The ratio of the number of turns in the primary to the number in the secondary is the turns ratio of the transformer.

2. Turns ratio = Np/Ns.


Voltage Ratio 

1. The ratio of primary voltage to the secondary voltage is the voltage ratio.

2. Voltage ratio = Vp/Vs = Np/Ns.


Current Ratio 

1. Assuming zero losses for the transformer, the power in the secondary equals the power in the primary.

2. Vs Is = Vp Ip.


Losses In A Transformer

1. The ratio of output power to the input power is called transformer efficiency.

2. Efficiency = Pout /Pin ×100.


Types of Transformer


A) Power Transformers 

1. This transformer has one primary winding and several secondary windings.

2. The primary winding is always connected to ac main power supply.

3. Each secondary winding has induced voltage proportion to its turns ratio with the primary windings.


B) Isolation Transformer 

1. This is usual transfonner in which secondary it not directly connected to the ac power line in the primary. 

2. This isolation has an advantage in reducing the chance of electric shock.

3. Sometimes, a transformer with a 1:1 turns ratio is used just for isolation from the ac power line.


C) Auto Transformer 

1. An auto-transformer consists of one continuous coil with a tapped connection such as terminal 2 between the end terminals 1 and 3. 

2. Auto-transformers are also known as diminerstats. They are compact, Scent and usually cost less with only one winding.

3. But, the same set must be suitable for both the primary and secondary.