Electrical steel is a special type of steel used in the construction the cores of transformers and the stator of motors and generators.  This steel is also known as silicon steel.  It is an alloy of Iron with silicon. The silicon content can be upto 15%  The silicon increases the resistivity of steel minimizing eddy currents and the resulting heat loss.

Electrical steel also has a small hysteresis curve, reducing iron losses.  Heat treatment is done which increases the grain size of the steel and reduces the hysterisis loss.

In grain-oriented silicon steel, the orientation of the grain structure is made in a specific direction in order to increase the flux density and reduce the magnetic saturation.  This type of steel is used in the construction of transformer core where the direction of the magnetic field is predictable and in a specific direction.  The orientation of the grain structure ensures that all the molecules have poles are in the same direction.  This reduces the hysteresis loss.  This is usually more expensive.

In motors and generators though, the magnetic circuit is more complex, hence non-oriented silicon steel may be used.

In electric machines such as transformers, motors, etc., the steel is made in the form of thin sheets which are laminated on both sides. This is done in order to prevent eddy currents from circulating in the core. 

Electrical steel should be handled carefully.  Wrong bending or rough handling can adversely affect the magnetic properties of the steel.



Hot washing of insulators refers to cleaning the insulators in transmission lines when the lines are live. Transmission lines can afford very little downtime. Cleaning the hundreds of insulators has to be carried out when the lines are live with voltage.

Insulators get dirty due to dust, moisture, bird droppings and chemicals from smoke. These deposits will form a layer over the surface and can contribute to a flashover between the conductor and the grounded frame of the transmission tower. Thus, periodic cleaning of the insulators is essential.

Hot washing involves cleaning the insulator surfaces with de-mineralized water. De-mineralized has high resistivity (greater than 50000 ohm cm). The water is pressurized and sprayed in jets from special cleaning machines. These cleaning machines are stationed on the ground or in some cases fixed on helicopters which hover near the lines and clean the insulators.

The Hot washing is usually carried out from the bottom of the insulator. The whole insulator is not made wet at any given point of time. The bottom of the insulator is washed and then the washing proceeds to the middle sections and the then to the top of the insulator.

The water spray from cleaning one insulator should not fall on another insulator. This may cause a flashover. The wind direction should also be taken into account.




Paper being an insulating and dielectric medium finds wide application as an insulation for cables. Paper is made up of cellulose a very good dielectric.

Some of the common types of insulation paper are the kraft paper and the crepe paper.  kraft paper is obtained from the pulp of soft wood.  When this kraft paper is impregnated with liquids to enhance BDV and maintain pH, crepe paper is obtained.

Crepe paper is flexible and tough which enables it to be wound over sharp turns in the windings.  Semi-conducting insulation paper is used in some transformer winding to ground the leakage winding.  

Transformerboard is a kind of paper insulation which provides has a rigid structure.  It is widely used for transformer insulation.

Fish Paper is another kind of insulating paper which is vulcanized.  Fishpaper can even be machined to form a specific shape.  It has excellent insulating and mechanical properties