- Transformer is a device which transfers electrical energy from one circuit to another circuit without change in frequency but voltage level is usually changed.
- The basic principle of transformer is electromagnetic induction.
- Transformer has two windings (i) primary winding and (ii) secondary winding
- Primary and secondary windings are magnetically coupled (not electrically connected).
- If the primary voltage is less than secondary voltage, such transformer is called step-up.
- If the primary voltage is greater than secondary voltage such transformer is called step down.
Classification of transformers
- Power transformers: used for transmission of electric power.
- Distribution transformers: used for distribution of electric power.
- Autotransformers: used to start induction motors.
- Isolation transformers: used to isolate the electronic circuits from the main electrical lines.
- Instrument transformers: to measure high voltages and currents in power system potential transformer (P.T.) and current transformer (C.T.).
Applications of Transformer
- Transformers are used in generating station to step-up the voltage. Transformer transfer electrical power from a generated voltage of about 11KV to higher values of 132KV, 220KV, 400KV and 765KV.
- Transformers are used to reduce these high voltages to a safe level 440/230 volts for use in industries, homes, offices etc.
- Transformers are also used in communication circuits for impedance matching purposes.
- Transformers are also used in electronics circuits.
Construction of transformer
- The main elements of a transformer are ; two coils and laminated core.
- The core of the transformer is constructed from laminated silicon steel.
- Laminated core is used to reduce eddy current losses.
- Silicon steel is used to reduce to hysteresis losses.
- The thickness of laminations varies from 0.35 mm to 0.5 mm for a frequency of 50Hz.
- The transformer is divided into two types (i) core type and (ii) shell type.
- Core type transformer has two limbs or legs.
- Core type transformers are used for high voltage applications (e.g. Power transformers, distribution transformers, autotransformers).
- Shell type transformer has three limbs or legs.
- Shell type transformers are used for low voltage applications (e.g. in electronics circuits).
- In shell type both primary and secondary windings are placed on the central limb side by side or concentrically.
- Low voltage winding placed nearer the core and high voltage winding is placed outside the low voltage winding to reduce the cost of insulation placed between core and low voltage winding.