Construction of dc machine: Yoke, Armature Winding, Commutator

A DC machine is an electromechanical device that converts electrical energy into mechanical energy, or vice versa, using direct current (DC). It works on the fundamental principle of electromagnetic induction, which was discovered by Michael Faraday. DC machines are classified into two main types: DC generators and DC motors. A DC generator converts mechanical energy into direct current electricity, while a DC motor performs the reverse operation, turning direct current electricity into mechanical motion.

CONSTRUCTION OF DC MACHINE

The essential construction of a DC machine includes two main parts: the stator and the rotor. The stator is the stationary part and contains the field windings or permanent magnets that produce a magnetic field. The rotor, also called the armature, is the rotating part that is placed inside the magnetic field. It carries conductors, which cut through the magnetic lines of force when the rotor rotates. This cutting of magnetic lines induces a voltage in the armature conductors, based on Faraday’s Law of Electromagnetic Induction.

An elementary DC machine consists of the following major parts:

1. Yoke (Magnetic Frame)
2. Main Poles
3. Field Winding
4. Armature Core
5. Armature Winding
6. Commutator
7. Carbon Brushes
8. End Covers
9. Shaft
10. Other Mechanical Parts

The yoke, main poles, and field winding together form the stationary part of the machine, known as the stator.

The armature core, armature winding, shaft, and commutator together form the rotating part of the machine, known as the armature.

In addition to these, a practical DC machine also includes:

• A pair (or more) of stationary carbon brushes
• A pair of end covers
• Other mechanical components necessary for proper operation

Yoke

The Yoke is like the outer body or frame of a DC machine. Just like our bones hold our body together, the yoke holds all the parts of the machine inside it safely.

It is shaped like a strong cylinder (a pipe-like shell), and both ends are covered with round caps called end covers. These end covers help the machine parts rotate smoothly by holding the bearings in place.

Most DC machines are placed flat on the ground using a special kind of base, called foot mounting. But sometimes, they are fixed to a wall or vertical surface using something called flange mounting—this is when one of the end covers is specially made to fit that way. This is a part of the CONSTRUCTION OF DC MACHINE

🛡️ What does the Yoke do?

The yoke has two main jobs:

1. It protects and holds everything inside – like a tough jacket that keeps all the machine parts safe and in the right place.
2. It helps the magnetic power flow properly – when the magnets inside the machine work, they create invisible magnetic lines, and the yoke gives them a smooth path to move through without any difficulty.

🛠️ How is the Yoke made?

• In big machines, the yoke is made by joining several parts together with welding, because one single piece would be too big.
• Then, the magnetic poles (which create magnetic power) are tightly fixed to the inside wall of the yoke.
• In small machines, like the motors inside a kitchen mixer, the yoke is made by stacking thin metal sheets and pressing them together. Sometimes, the magnets and the yoke are cut together from a single piece to save space and make it simpler.
  
  

Main Poles and Field Winding

Every DC machine has an important part called the stator, and inside it, we have main poles. These poles are not just random pieces – they are made from strong steel and fixed tightly inside a round frame called the yoke. And guess what? The number of poles is always even – like 2, 4, 6, and so on.

Each pole has two parts:

• Pole Core
• Pole Shoe

Now, let’s understand what they do.

What is Field Winding?

On the pole core, we wrap a special copper wire – this is called the field winding. When we send DC current (direct current) through this winding, it creates a magnetic field. This magnetic field flows across the small gap (called the air-gap) and reaches the armature, which is the rotating part of the machine. Then, it moves to the next pole.

Here’s something cool – the poles are arranged in such a way that every next pole has an opposite magnetic side. So if one is North, the next will be South. This pattern keeps repeating.

To know the direction of the magnetic field, you can use your right hand. If you wrap your fingers in the direction of current, your thumb will point in the direction of the magnetic field. (This is called the Right-Hand Thumb Rule.)

What are Pole Shoes?

The pole shoe is the flat, wide part at the bottom of the pole. It helps the magnetic field to spread over a bigger area of the armature. But there’s more – to reduce energy loss, the pole shoe is made by stacking thin metal sheets together. Each sheet is called a lamination, and they are all kept separate from each other using insulation. This clever trick helps reduce something called eddy current loss, which can waste energy.

Sometimes, both the pole core and the pole shoe are made from these thin laminations and put together as a single strong piece. This is a part of the CONSTRUCTION OF DC MACHINE.

Also, the shape of the pole shoe is designed in a special way – the air gap near the edge is made a little wider. This helps the magnetic field to become smooth and wavy, just like a sine wave. When this happens, the voltage and current that get produced in the armature also become smooth and clean.

Why Are the Poles Important?

The poles inside the stator do 3 main jobs:

1. Hold the field winding safely in place.
2. Create the main magnetic field which runs through the motor.
3. Spread the magnetic field evenly for better performance.

How Many Poles Should a Motor Have?

The number of poles in a motor is chosen carefully. It depends on the size of the motor and how fast it should run. One big reason for choosing the number of poles is the frequency – that’s how fast the magnetic field switches back and forth as the armature rotates.

Here’s a simple formula:

f=P×N/120​

Where:

• f is the frequency (in Hertz),
• P is the number of poles,
• N is the speed (in rpm – rotations per minute).

If we use too many poles, the frequency goes up too much. This can cause extra heat and energy loss in the motor. That’s why engineers usually keep the frequency between 25 and 50 Hz in most machines.

Main point

• Main poles hold field windings and create the magnetic field.
• Field winding makes the machine work by building the main magnetic force.
• Pole shoes help spread the field smoothly.
• Laminations inside poles reduce energy waste.
• More poles mean smoother operation, but too many can cause energy loss.
  
  

Armature (आर्मेचर)

The armature is the part of a DC machine that rotates. You can think of it like the spinning heart of the machine. It plays a very important role in how the machine works.

The armature is made up of three main things:

1. A shaft (a long round rod in the center),
2. A drum-shaped magnetic core (like a thick, hollow cylinder),
3. And armature winding (wires wrapped around the core).

How it’s built

• The core is made of thin metal pieces stacked together, called laminations. These are used to reduce something called eddy current loss, which wastes energy.
• The laminations are only about 0.5 mm thick, and they are made from a special kind of steel that works well with magnets.
• Small holes (called air ducts) are made in the laminations so that cool air can flow inside and keep the machine from getting too hot.

In very large machines, there are radial ducts too, which allow air to move from the center outwards, helping even more with cooling. This is a part of the CONSTRUCTION OF DC MACHINE.

How it works

• On the outside of the armature core, there are slots cut into the metal. These slots are used to place the armature windings (the wires).
• When the armature spins, these wires need to stay in place. The slots help hold them tightly so they don’t fly out due to the spinning force.
• The main job of the magnetic core is to give the magnetic field a smooth and easy path to flow through. That’s why it is made from a material that allows magnetism to pass easily, with high permeability and high magnetic strength.

Other parts and support

• The armature is held up at both ends by bearings. These help the armature spin smoothly without wobbling.
• On one side of the shaft, there is a commutator. This is a round part that connects the wires from the armature to the rest of the machine. It helps in switching the direction of current in the windings at the right time.
• The shaft can be connected to another machine or motor using a coupling. This way, both machines can rotate at the same speed.
  
  
  

Commutator

Imagine you have a toy car that runs with the help of a small motor. Inside that motor, there is something very important called a commutator. Let’s understand what it does in a very simple way.

Inside a DC machine (a type of motor or generator), there are many coils of wire. You can think of these coils like loops or circles made of copper wire. When electricity flows through these loops, they help the motor spin and do its work.

Now, earlier, when we had only one coil, we used something called a split ring—it had just two copper parts, like two half circles, to connect the coil. But what happens when we have many coils? Two parts are not enough anymore!

That’s why we use a smart little device called a commutator.

What Exactly Is a Commutator?

A commutator is a round, drum-like piece that is fixed on the shaft of the motor (the part that spins). It is made up of many copper pieces (called segments), and each piece is kept separate from the others using insulating materials like mica, which stops electricity from leaking between them.

Each copper segment connects to the ends of the wire coils. This connection is made strong and permanent using a process called brazing (kind of like soldering).

The commutator helps the electricity flow in the right direction as the motor spins, so the motor keeps turning smoothly.

How It’s Made

• The segments are made of strong copper or copper mixed with silver.
• They are separated by thin slices of mica, which are about 0.8 mm thick.
• These segments have small raised parts called risers, which connect to the wire coils inside the motor.

Why the Commutator Is Important

Without a commutator, the motor wouldn’t work properly. It would stop and go, or maybe not work at all. The commutator makes sure that the direction of current keeps changing at the right time, so the motor runs smoothly and powerfully.

In short, the commutator is like the brain of the spinning part of the motor—it knows when and how to connect the wires, so everything works just right.

Brush Assembly and Brushes

A brush assembly is a small but very important part of a DC machine. It has two main parts – the brush holder and the brush itself.

This whole assembly is fixed on the machine’s outer cover (called the stationary end cover). It is placed in a round pattern around the commutator – that’s the rotating part inside the machine.

Now, let’s talk about the brushes.

These brushes are made from special materials like hard carbon, natural graphite, electro graphite, or metal graphite. Why these materials? Because they help carry electricity smoothly and don’t wear out too fast.

The brushes sit inside the brush holders and press against the commutator. But they don’t press too hard or too soft – just the right amount of pressure is applied using small stainless steel springs. These springs make sure the brushes stay in contact even when the commutator spins.

To let electricity flow in and out, flexible wires (called pigtails) are attached to the brushes. These wires also act like little arms that connect the brushes to the armature winding (the main winding that produces power).

So, in short:

• The brush assembly helps carry electricity between the moving and still parts of the machine.
• It uses brushes, holders, springs, and pigtails to do its job smoothly and safely.
  
  
  

Armature Winding –

The armature winding is like the heart of any rotating machine, whether it’s a motor or a generator. It plays a very important role in how the machine works. This is a main part of the CONSTRUCTION OF DC MACHINE.

Let’s first talk about a generator.

When a generator is turned by something like a turbine or engine (called a prime mover), it starts spinning. As it spins, it creates a kind of energy called electricity. This happens because of the movement inside the armature winding. The electric power that comes out is DC (direct current), and it flows through the wires when we connect something like a light bulb or heater to it.

Now, when current starts flowing in the armature, it also pushes back a little. This push is called counter torque. It tries to slow down the spinning. So, if the load (like a machine or device) takes more power, this push becomes stronger, and the speed of the generator might drop. To keep things steady, machines like power plants use special tools called governors to control the speed.

Now let’s look at the motor side.

If we use the same DC machine as a motor, something amazing happens. The current in the armature winding creates a force called the Lorentz force. This force makes the armature spin, and that’s how we get motion. This spinning force is called electromagnetic torque. It makes the motor turn in the direction we want.

What Is Inside the Armature Winding?

The armature winding has many small loops of wire, which we call coils. You can think of them like loops of thread wound carefully in a pattern. Each coil works with magnets in the machine to make or use electricity.

Before we go deeper into how these windings are made, let’s understand some simple words:

1. Armature Coil, Conductor, and End Connection – The basic parts of the winding.
2. Coil Span – The distance a coil covers.
3. Pole Pitch – The space between two magnetic poles.
4. Full-Pitched and Fractional-Pitched Coil – How much of the pole pitch the coil covers.
5. Front Pitch, Back Pitch, Resultant Pitch, and Average Pitch – Different ways to measure and connect the winding.
6. Commutator Pitch – How the winding is connected to the commutator, which helps change the direction of current.

In simple words, all these parts work together to make sure the machine runs smoothly—either creating power or using power.

When we talk about armature winding, we mean the way wires are arranged inside a motor or generator. These wires help create electricity or use it to do work, like turning a fan or running a machine.

Now, depending on how these wires are connected at one end (where the commutator is), armature winding is mainly divided into two types:

Wave Winding
Lap Winding

Armature Coil, Conductor, and End Connection

Let’s understand this in a very simple way.

Imagine you have a loop of wire. This loop is called an armature coil. It is made of copper wire and is placed inside a machine like a motor or generator.

Now, the straight parts of this loop that go inside the small grooves (called slots) of a round iron core are called conductors. These conductors are the parts that actually carry the electric current when the machine runs.

If the coil has only one turn, then there are just two conductors — one going in and one coming out. But if the coil is made with ‘n’ turns, then you will have 2n conductors — because each turn gives you two sides (one forward, one backward).

Now, think about the parts of the wire that are outside the slots, at the front and back of the core. These curved parts help complete the loop of the coil. They are not inside the slots, but they are very important. We call them end connections or winding overhangs.

So in simple words:
👉 Conductors go inside the slots.
👉 End connections stay outside to complete the loop.
👉 Together, they make one full armature coil.

In the end, the ends of all these coils are carefully joined with small metal pieces called commutator segments. This helps the current flow properly and makes the machine work smoothly.

What is Coil Span (or Coil Pitch)?

Imagine you have a coil — just like a simple loop of wire — placed inside a motor or generator. This coil has two sides (or arms), and both these sides sit inside slots on the armature (the rotating part).
Now, count how many slots are there between these two sides of the coil. That number is called the Coil Span or Coil Pitch.

📌 Simple Definition:
Coil Span is the distance between the two sides of a coil, counted in the number of armature slots.

⚡️ What is Pole Pitch?

Now let’s talk about poles — like the North and South poles of a magnet. In a motor or generator, the magnetic poles are fixed on the stator (the non-moving part). As the armature rotates, each pole affects a few armature slots or conductors (wires inside the slots).

So, if you count how many armature slots are covered by one magnetic pole, that number is called the Pole Pitch.

📌 Simple Definition:
Pole Pitch is the number of slots (or conductors) that come under one magnetic pole.

You can also think of it as the distance from one pole to the next, but measured in number of slots — not in centimeters or inches.

🧮 How to Calculate Pole Pitch?

Let’s say:

• Z is the total number of armature conductors
• P is the total number of poles

Then the Pole Pitch is:

👉 Pole Pitch = Z / P

This formula gives the number of conductors under each pole.

🔁 What is a Full Pitched Coil?

Imagine placing a coil so that:

• One side of the coil is right under the center of a North Pole, and
• The other side is right under the center of the next South Pole

This coil is called a Full Pitched Coil.

Why is this important?

Because:

• The two sides of the coil feel opposite magnetic poles.
• So, the emf (electric pressure) produced in each side is also in opposite direction.
• These two emfs are like mirror images — they are 180° apart electrically.
• But together, they add up and make a strong total emf.

📌 In simple words:
A Full Pitched Coil gives us the maximum possible voltage from that coil.

📐 Electrical Degree vs Mechanical Degree

• Electrical degree tells us about the phase or timing of electricity.
• Mechanical degree is about the actual physical rotation.

They are different, but related. The relation depends on the number of poles in the machine.

Full Pitched and Fractional Pitched Coils

Let’s understand this with a simple idea.

When we make a coil in a motor or generator, we place two sides of the coil in the magnetic field. Now, if the distance between those two sides is exactly equal to the distance between two magnetic poles (this distance is called one pole pitch), then we call it a full pitched coil.

In a full pitched coil, both sides of the coil cut the magnetic field strongly and completely — one side cuts the North pole and the other cuts the South pole. Because of this, both sides produce equal and opposite voltage (EMF), and when we add them, the result is strong and powerful. So, the total voltage in a full pitched coil is maximum.

But sometimes, the coil is made a little shorter than one pole pitch. This is called a fractional pitched coil.

In a fractional pitched coil, the two sides of the coil don’t cut the magnetic field fully. So, the voltage produced in them is not as strong as in a full pitched coil. That’s why the total voltage in a fractional pitched coil is less.

In most DC machines, we use full pitched coils, because they give us more voltage and better performance.

Front Pitch, Back Pitch, Resultant Pitch, and Average Pitch

When we look at a DC machine (like a motor or generator), there are many wires (conductors) placed on a part called the armature. These wires are connected in a special way to make the machine work properly. This is a part of the CONSTRUCTION OF DC MACHINE.

Let’s understand some important words used to describe how these wires are connected:

1. Front Pitch (Yf)

When two wires (conductors) are joined together at the front side (near the commutator), the distance between them is called Front Pitch.
👉 Imagine looking at the front of the machine – the gap between two connected wires there is the front pitch.

2. Back Pitch (Yb)

Now, go to the back side of the machine. When two wires of the same coil are connected there, the distance between them is called Back Pitch.
👉 It’s just like the front pitch, but this time we are looking from the back of the armature.

3. Resultant Pitch (Yr)

Now let’s say one coil starts from a certain point. The distance between the start of this coil and the start of the next coil is called Resultant Pitch.
👉 It tells us how far apart the starting points of two coils are.

4. Average Pitch (Ya)

We have two main pitches – front and back. If we want to find an average, we add both pitches and divide by 2.
That means:
Average Pitch = (Front Pitch + Back Pitch) ÷ 2
👉 It gives a middle value between the front and back pitch.

note point

• Front Pitch = Distance at front (commutator side) between connected conductors
• Back Pitch = Distance at back (rear side) between connected conductors
• Resultant Pitch = Distance from start of one coil to start of next coil
• Average Pitch = (Front Pitch + Back Pitch) ÷ 2
  
  
  

Commutator Pitch and Number of Commutator Segments

Let’s understand this in a very easy way.

Inside a DC machine (like a motor or generator), there is a round part called the commutator. It is made of small copper pieces placed next to each other in a circle. These pieces are called commutator segments. This is a part of the CONSTRUCTION OF DC MACHINE.

Now, there are also many coils of wire inside the machine. Each coil has two ends. These two ends are connected to two commutator segments.

The distance between these two segments is called the commutator pitch.

👉 Simply put,
Commutator Pitch is the number of segments between the two ends of the same coil.

For example, if one end of a coil is connected to segment 1, and the other end is connected to segment 3, then the commutator pitch is 2.

This pitch is not measured in centimeters or inches — it is measured by counting the number of segments between the two connections.

Also remember,
The total number of commutator segments is always equal to the total number of coils in the armature.

Let’s sum it up in a very simple way:

• A commutator segment is a copper piece on the commutator.
• A coil has two ends, and each end is joined to one commutator segment.
• The gap (in segment count) between these two connected segments is called the commutator pitch.
• The number of segments = number of coils.

This is how the coil and commutator work together to make the machine run smoothly.

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