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Principles of Electrical & Materials for Electrical Machines

BASIC PRINCIPLES OF ELECTRICAL MACHINES


All Electricals Machines are basically Electromagnetic devices. Among them the Rotating Machines are Electromechanical Energy Conversion devices but the transformer is a static Machine where energy conversion does not take place, only the level of Voltage changes.

All Electrical Machines are based upon three Principles namely :

(1) Induction

(2) Interaction and

(3) Alignment.

Transformer operation is based on Induction. Most of the Rotating Electrical Machines use the Principle of Induction as well as Interaction.


Electrical Materials
Electrical Materials


Only a few Machines such as reluctance motors are based on alignment.

Materials for Electrical Machines

The materials used in Electrical Machines can be divided into three categories viz.

a) Conducting Materials

b) Magnetic Materials and

c) Insulating Materials


(a) Electrical Conducting Materials


Silver, copper, aluminum are some of the important conducting materials.

Silver has Conductivity about 10% higher than that of copper, but it is never used in making Electrical Machines due to its higher cost.

Copper is the most widely used conducting materials due to its excellent Electrical and Mechanical properties.

The next important Conducting Material is
 Aluminum which is increasingly being used in many Electrical Engineering applications.


(b) Magnetic Materials 


Magnetic Materials may be classified into three board categories viz. Diamagnetic
Materials, paramagnetic Materials and ferromagnetic Materials.

From the Electrical Engineering point of view both the diamagnetic and paramagnetic Materials could be considered as non- Magnetic.

Ferromagnetic Materials ( such as nickel, Cobalt, iron, steel, silicon steel, permalloy and super - permalloy ) are further divided into two board groups, from Hysteresis loop point of view, viz. Hard Magnetic Materials and soft Magnetic Materials.

Hard Magnetic Materials ( Such as carbon steel, tungsten steel, Cobalt steel and hard Ferrites ) have a gradually rising Magnetization curve, large hyasteris loop area and consequently large energy loss per cycle of Magnetization and are used in making all kinds of Instruments and devices requiring permanent Magnets.


(c) Insulating Materials


There are quite a Large variety of Insulating Materials available having vastly different properties. 

Some of common Insulating Materials are paper, cotton, silk , cardboard, empire cloth, pressphan , mica, asbestos, Bakelite, micanite, resins , silicones, glass, ceramics, quartz, varnish, Transformer oil etc.

Insulting Materials normally used in Electrical machinery and apparatus, according to their thermal stability in service are grouped into seven classes viz. 

Classes Y, A, E, B, F, H, C capable of Operating at temperature 90°C, 105°C , 120°C , 130°C , 155°C, 180°C and above 180°C respectively safely.

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