Transformer
- A transformer is a device that is used to change the voltage of an alternating current.
- An alternating current is one that flows back and forth, continually reversing its direction.
- It is useful for
- transmitting electrical power from power stations to the consumers such as households and factories.
- regulating voltages for the proper use of electrical appliances such as a radio or a mains-operated television.
- It consists of two coils of wire:
- primary coil connected to the irnput voltage
- secondary coil connected to the output voltage
- These coils are wound around a laminated soft iron core at an appropriate number of turns.
- The soft iron core is laminated to reduce heat loss in the core.
- The transformer transfers electrical energy from the primary coil to the secondary coil by electromagnetic induction between both coils.
- At the primary coil, an alternating current (a.c.) is
- applied which sets up a changing magnetic field.
- This induces a voltage in the secondary coil.
Step-up and Step-down Transformers
- A step-up transformer
- has more turns in the secondary coil than in the primary coil.
- has a higher voltage in the secondary coil than in the primary coil.
- A step-down transformer
- has more turns in the primary coil than in the secondary coil.
- has a higher voltage in the primary coil than in the secondary coil.
- Usually, a transformer is not 100% efficient.
- This means that the power supplied to the primary coil is not transferred completely to the secondary coil.
- This is due to the resistance in the wire and heat loss in the core.
- The efficiency of the transformer can be increased by using copper wire (low resistance) and the laminated iron core.
Role of Transformers
- Electricity is generated in the power stations as large values of current.
- If transmitted through cables, a lot of energy may be lost as heat due to the resistance in the cables.
- To reduce power loss due to resistance, very thick cables can be used. However, the cables would be very heavy and uneconomical to use.
- A step-up transformer is used to increase the voltage so that less energy is lost in the form of heat in the transmission cables.
- The step-down transformer is then used to reduce the voltage at different stages before reaching homes and factories.
