Question

Transformers either increase or decrease AC voltage.
(A) State the principle of a transformer.
(B) Explain with the help of a labelled diagram the working of a transformer.
(C) Explain briefly any three energy losses in a transformer.

Answer 1

Hint: The transformer works on basic principles of electromagnetic induction and mutual induction. A transformer consists of two main parts- the core and the windings, which are insulated from each other. Energy losses mainly take place through the core and windings.

Complete Step by Step Solution: A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits.
The transformer works on the principle of Faraday’s law of electromagnetic induction and mutual induction. There are usually two coils, primary coil and secondary coil on the transformer core. The core laminations are joined in the form of strips. The two coils have high mutual inductance. When an alternating current pass through the primary coil, forms a varying magnetic flux as per faraday’s law of electromagnetic induction and this change in magnetic flux induces an emf (electromotive force) in the secondary coil which is linked to the core having a primary coil. This is mutual induction.
The major parts of a single-phase transformer consist of:

1. Core of a transformer: The core acts as a support to the winding in the transformer and provides a low reluctance path to the flow of magnetic flux. It is made up of a laminated soft iron core in order to reduce the losses in a transformer.
2. Windings: Windings are the set of copper wires wound over the transformer core. Windings are of two types- primary windings and secondary windings.
Primary winding is the set of turns of windings to which supply current is feed while secondary winding is the set of turns of winding from which output is taken.
The primary and secondary windings are insulated from each other using insulation coating agents.
3. Insulation Agents: Insulation is necessary for transformers to separate windings from shorting the circuit and thus facilitating the mutual induction. Insulation agents have influence in durability and the stability of a transformer.
The input line connects to the 'primary' coil, while the output lines connect to ‘secondary’ coils. The alternating current in the primary coil induces an alternating magnetic flux that 'flows' around the ferromagnetic core, changing direction during each electrical cycle. The alternating flux in the core in turn induces an alternating current in each of the secondary coils. The voltage at each of the secondary coils is directly related to the primary voltage by the turns ratio, or the number of turns in the primary coil divided by the number turns in the secondary coil.
Transformer energy losses are dominated by winding and core losses.
1. Winding losses: Current flowing through a winding's conductor causes joule heating due to the resistance of the wire. As frequency increases, skin effect and proximity effect causes the winding resistance and, hence, losses to increase.
2. Hysteresis losses: The core is magnetized and demagnetized alternately when AC current flows through the primary coil. Energy is lost during this process. This is known as Hysteresis. This effect is reduced by using a soft iron core.
3. Eddy current losses: Eddy currents are induced in the conductive metal transformer core by the changing magnetic field, and this current flowing through the resistance of the iron dissipates energy as heat in the core. Eddy current losses can be reduced by making the core of a stack of laminations (thin plates) electrically insulated from each other.
Hysteresis and eddy current losses are subdivisions of core loss.

Note: Faraday's law of induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF)—a phenomenon known as electromagnetic induction. It is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators and solenoids.