What is winding?

A winding is one or more turns of wire through which an electric current can pass. It is usually made of copper and is used in transformers, generators, and motors. Winding can be of different types, depending upon its shape, cross-sectional area, and nature of orientation.

Types of winding in generator

The different types of winding in generators are:

• Stator winding
• Rotor winding

The field winding is placed on the stator that creates a magnetic field and is stationary. The stator winding is usually made of copper. The stator winding's cross-section and the number of turns depends on the machine. To supply terminals in shunt type of machines, the field winding or the stator winding is connected in parallel. Usually, supply terminals will have high voltage so the stator winding is connected across a high voltage source. Whereas, in series machines, the stator winding is connected in series with the armature winding or rotor winding. As armature winding carries a large amount of current, so if the current is high then the number of turns must be decreased to keep the magnetomotive force constant.

The armature winding is placed in the rotor slots and is made up of copper material. Armature windings are always closed and form a closed-loop structure.

The armature windings are of two types:

1) Double layer winding

2) Single layer winding

In double-layer winding, more than one coil is placed in one slot. If two windings are placed in one slot, then the number of coils becomes double that of single-layer winding.

Number of coils = 2 x S/2

= S

According to this, number of coils = number of slots

A coil can not occupy both the top and bottom positions in one slot. A coil occupies the top position in one slot and the bottom position in another slot.

Coil span

Coil span is the number of slots between the two sides of the same coil.

Commutator pitch

Every coil is connected to the commutator. The number of segments lying between the ends of the coil is known as the commutator pitch. The commutator is also known as a reverser.

Pole pitch

Pole pitch is the electrical angle between the north pole and the south pole.

Lap winding and wave winding

The most important part of rotating machines is armature winding. The mechanical energy is converted into electrical energy here and vice versa. The armature windings are mostly classified into two types:

Lap winding

In the case of lap winding, the conductors are joined in such a way so that their poles are equal to their parallel paths in number. The end of each coil's side is connected to the adjacent segment of the commutator. The number of brushes is equal to the number of parallel paths in the case of lap winding. These brushes are further divided into negative and positive polarities. They are mainly used for low voltage and high current applications. They are of three types:

1. Simplex lap winding: In this type of winding, the terminating end of one coil is connected to the commutator segment and the starting end of the next coil is connected under the same pole. Here, the number of poles is equal to the number of parallel paths.
2. Duplex lap winding: In this type of winding, the number of parallel paths is equal to double the number of poles. It is mainly used for heavy current applications. Here, this kind of winding is obtained by placing two types of similar winding on the same armature and by connecting the even number of commutator bars to one and the odd number of commutator bars to the second winding.
3. Triplex lap winding: The windings are connected to one-third of the commutator bars.

In the case of lap winding, the cost is increased because it requires many conductors.

Wave winding

In this type of winding, only two parallel paths are present between the positive and negative brushes. The finishing end of one coil is connected to the starting end of the other coil commutator segment at some distance, apart from each other. Here, irrespective of the number of poles, the conductors are connected to two parallel paths. They are mainly used for high voltage and low current applications. The winding is called a progressive winding when the winding progresses from left to right and the winding is called retrogressive winding when the winding advances from right to left.

Closed winding terms

Back pitch: It is the distance between the top and bottom sides of one coil.

Front pitch: It is the distance between the sides that are connected to the same commutator segment.

Winding pitch: It is the distance between two consecutive similarly top and bottom coil sides.

Note: In the case of DC motors, the winding remains the same but in the case of synchronous machines (alternator and electric motor), the windings that are the stator and rotor windings are reversed that is the field winding is put in the rotor (cylindrical and salient pole rotor) and the armature windings are put in the stator. DC motor testing can be done using an ohmmeter or multimeter.

Context and Applications

The topic is significant in the professional courses like-

1. Bachelors of Technology in Electrical Engineering
2. Masters of Technology in Electrical Engineering

Practice Problems

Q 1. What is the number of brushes in a lap winded P pole DC Motor?

1. 2
2. 3
3. P
4. 2P

Answer: Option c

Explanation: In DC Motor, the number of brushes is equal to P.

Q 2. What is known as the distance between the segments to which the ends of coils are connected in armature type of winding?

1. Resultant pitch
2. Back pitch
3. Winding pitch
4. Commutator pitch

Answer: Option d

Explanation: The distance between the segments to which the ends of coils are connected is called commutator pitch.

Q 3. What kind of material is used for motor winding?

1. Enameled copper wires
2. Rolled copper bars
3. Super enameled copper wires
4. Silver

Answer: Option a

Explanation: The coils are generally wounded with enameled copper wire also called magnetic wires in case of motor winding.

Q 4: How much a wave winding must go at least around the armature before it goes back to where it had started?

1. Twice
2. Thrice
3. Once
4. None

Answer: Option a

Explanation: A wave winding must go at least twice around the armature before it goes back to where it had started.

Q 5. What is the pole pitch for a four-pole motor winding machine which has 16 coils and has two layers of lap-winding?

1. 8
2. 32
3. 16
4. 4

Answer: Option a

Explanation: Pole pitch = S/P = 16/2 = 8

Related concepts

• Armature reaction
• EMF equation
• Losses in DC machines