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# Electrical machines and appliances theory for engineers beginners

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## Winding coil

A length of wire lying in the magnetic field and in which an EMF is induced is called a coil. The coils used in windings are shown in Figure 1.

Figure 1(a) represents a coil with only one turn in it. Each coil has active and inactive sides. A coil can in general have any number of turns. A single turn/coil has two active sides, or otherwise called as conductors. Similarly, a two turn coil has four conductors and a three turn coil has 6 conductors.

Generally, the total number of conductors per coil:

ZC = 2T

and, the total number of conductors for a given machine:

Z = ZCC

where:

• ZC = total number of conductors per coil
• C = number of coils
• Z = total number of conductors
• T = number of turns per coil

Figure 1(b) represents multi turn coil.

#### Active side of a coil

It is the part of a coil which lies in the slots under a magnetic pole and EMF is induced in this part only.

In Figure 1(a), coil sides AB and CD are called as active sides. For a double layer winding, one half portion of the coil drawn with solid line corresponds to the coil side lying on the top of a slot, and the dotted line corresponds to the coil side lying in the bottom layer of another slot.

This type of representation is used for double layer winding. For a single layer winding, the complete coil is represented by a solid line.

#### Inactive side of a coil

The inactive side of a coil consists of two portions, namely the front end side and the back end side. In Figure 1(a), the portion of the conductor which joins the two active sides and placed around the core, is called the back end side of the coil.

The portions which are used to connect other coils are called front end side. These ends have two leads called as starting end S and finishing end F of a coil.

In Figure 1(a), AD and BC represents the inactive sides of a coil.