power transformers

Useful Information

Useful Information:

Electricity and magnetism: In the late 19th century, Orsted accidentally found that when a magnet is brought near a current carrying conductor, it gets deflected.

The basic reason for this is that the electricity in the conductor produces a magnetic field in its vicinity and drops off when the electric source is removed.

It is known that the atoms of all basic elements have some charge in the form of electrons, which exhibit a magnetic field around each atom. However it had been found that not all matter in the universe creates magnetic fields around their atoms though all atoms consist of electrons. It had been discovered that the atomic configuration of the materials is responsible for their magnetic characteristics.

All matter can be either termed ‘magnetic’ or ‘nonmagnetic’ depending upon its atomic configuration and its ability to retain/create magnetic fields. Magnetic materials have their magnetic fields aligned in a particular direction so that they have a cumulative magnetic property, which can be confirmed through experiments.

However in non-magnetic materials, the arrangement of electrons is such that the magnetic fields get cancelled. The net effect is that they do not have the capacity to retain/produce magnetic fields when they are in the vicinity of electric currents.

Figure 2.4

Typical magnetic fields in a permanent magnet

12 Practical Power Transformers: Operation, Maintenance & Testing

Figure 2.4

Typical magnetic fields in a non-magnetic material

The magnetic materials can be classified further as Permanent and Ferro Magnetic. A permanent magnet will have its magnetic fields aligned in one direction and hence always exhibits the magnetic property irrespective of any external source. On the other hand, ferro-magnetic materials have the magnetic fields of individual atoms aligned in one direction but the orientation of a domain is random. Hence they do not show magnetic properties under normal conditions. When an external magnetic field is applied to them (through an electric source), the magnetic fields of the individual domains tend to line up in the direction of this external field, which causes the external magnetic field to be enhanced.


This property of magnetic materials is important in building up the core of a transformer, which is the path of magnetic flux. It is necessary that the core of a transformer be built with magnetic material.