 # Dc Motor Types-Dc Motor Magnet-Dc Motor Diagram.

The Dc Motor Types & Dc Motor is a Mechanism by which Electrical Energy is Converted into Mechanical Energy. Both in principle and in design, the D.C. motor is the reverse of a D.C. Generator.

## Dc Motor Magnet?

We know that Dc Motor Magnetic lines of force travel from North pole to South pole. The lines of force between these two poles in parallel.

When a coil starts rotating, after a very short time, the side of the coil B will come under the North pole and side A under the South pole. In this way, the current in coil side B is inward, while the coil side A it is outward, it is automatically changed with the help of the commutator. In this way, again an anticlock-wise force known as “Magnetic drag” will act on the coj) and the coj) will rotate continuously in a definite direction

1. If an Electric Current is passed Through a Conductor that is Perpendicular to the Card, The Dc Motor Magnetic lines of force will form a concentric circle.
2. The direction of the lines of force is Down with the help of arrows. This shows that in the upper side of the conductor, the lines of force travel from the left side to the right side, and on the lower side, these travel from the right side towards the left side. Now, if the conductor is aced between the magnetic pole.
3. The density of the flux rises above the conductor. Because of this, the field gets stronger above the conductor because on this side both the magnetic lines travel in the same direction and the part beneath the conductor becomes weak because the direction of the field is opposite.

The action between the magnetic force results in repulsion because of which the conductor moves from the stronger d to the weaker field i.e., downwards. Now, if the direction of the current is changed, there will be more magnetic lines wnward and less magnetic lines upward. At that time the conductor will start moving upward. The over all effect pends on motion of the armature. The direction in which the conductor moves can be determined by the Fleming’s left and rule and this whole phenomena is known as magnetic drag.

### What Is The Working Principle Of a D.C. Motor?

Working Principle Of Dc Motor: When a conductor carrying a current is placed in a magnetic field, it tends to move at the right angle to The field. In the figure, a two-pole motor is shown under the North and South poles.

1. Force will act on both sides of the coil which will tend to rotate e coil in the anticlockwise direction as given by the Fleming’s left hand rule.
2. This force will act till e conductor is in the magnetic field. The motion, however, is not smooth and to make the motor run smoothly, the single a is replaced by several coils set at equal inclination to each other.

## Types Of Dc Motor?

There are main Four Types Of D.C. Motors:

1. Series Wound Motor
2. Shunt Wound Motor.
3. Compound Wound Motor.
4. Permanent Magnet Dc Motor.

### What Is The Series Wound Motor?

In Series Wound Motor the field winding is connected in Series with the Series Wound – armature and carries the full armature current. The field winding has only a few turns of thick wire to keep the resista low and, hence to reduce the losses. As shown in Fig. 4.

When the load on the Series Wound Motor is light, only a small current is needed to produce the required torque, therefore, at loads, the flux is weak and the speed is high. But on heavy load the current is large and consequently, the flux is sin and the speed is low, therefore, the current of the motor depends upon the load.

This torque versus armature current begins to rise as a parab,After the saturation, with further increase in current.

Dc Motor Speed Characteristic:

At light loads, the current will be small, and hence there is weak, and the speed is high. As the load increases, the armature current and I flux increases and speed decreases rapidly.

The speed N is almost inversely proportional to armature current

hence the curve is a rectangular hyperbola as shown in Fig. As soon as the saturation state of iron is reached there is a little or no change in speed with any change in current and the curve flattens out.

At low loads, the speed rises quickly to a dangerous value. That is why a series motor should never be started without any load, or belts, etc., which might break and throw off the load. When the load increases the armature and field current increase, the flux increases, and the Motor speed drops.

Series Wound Motor Used?

The series motor is best suitable for traditional work, because of high starting torque. It is also used extensively for Cranes, Fans.

## What Is Dc Shunt Motor?

The Dc Shunt Motor, in which the field winding is connected acme that is, in parallel with the armature terminals is called a shunt motor. a very large resistance to keep the losses low, by being wound with wire of a large number of turns.

The speed of a Dc Shunt Motor remains almost constant and is not affected by Variation.

## Dc Compound Wound Motor?

This consists of Two Field Coils, one containing a large number of turns and is in parallel with the armature, and the other, containing only a few turns and is in series with the armature. This, thus, possesses the advantages of both the Series And Shunt Wound Motors.

### Types Of Compound Motors?

There are Two Types Of Compound Motors according to the Field Winding Connection.

1. Cumulative Compound Motor.
2. Differential Compound Motor.

### What is Cumulative Compound Motor?

A Cumulative Compound Motor is in which the Series Field Winding is so connected that its flux helps the flux produced by the shunt field winding as shown in Fig. 13. The armature torque is increased under heavy load or at starting.

As the load increases, the speed decreases in the same way as the series motor. When the load suddenly decreases, the shunt field prevents the motor from speeding up beyond safe value, therefore, the motor has approximately constant speed at different loads within the capacity of the motor.

### What Is Differential Compound Dc Motor?

The Dc Motor in which the series winding is so connected that its field opposes the shunt winding field is called a Differential Compound Motor.

The series field winding is short circuited when starting up, otherwise, the series field would rise to its full value before the shunt field. This will cause the motor to start in the opposite direction. These motors are very rarely used.

### Differential Compound Dc Motor Types?

1. Long Shunt Compound Motor.
2. Short Shunt Compound Motor

Long Shunt Compound Motor.

When the shunt field is connected across the armature and series field, the motor is called a Long Shunt Compound Motor.

Short Shunt Compound Motor

When the shunt field is connected across the armature alone, the motor is called a Short Shunt Compound Dc Motor.

### Use of Compound Motors?

These motors are used where the load varies

Compound characteristic suddenly from no load to full load as in Punch Presses, Rolling Mills, Printing Press, Flour Mill etc.

#### Characteristics of Compound Motor.

The speed of the Cumulative Compound Motor is maximum at no load and slightly 15 to 20 % between no Series characteristic load and full load drop. But in differential compound motor speed drops down very rapidly with the increase of load. The figure shows the characteristics of cumulative and differential compound motor.

### Emf Of Dc Motor?

Due to the rotation of the armature coil in the magnetic field, the Dc Motor Types also works as a generator and an induced E.M.F. acts in the armature conductors which opposes the applied E.M.F. (according to Lenz’s Law) This is called back e.m.f. and goes on increasing with the speed.

### What Is Dc Motor Equations?

It is the turning and twisting moment of a force about an axis. It is the product of the force and the radius at which this force acts.

Torque = ForcConsider a pulley of radius ‘r’ metre, ‘F’ be the force acting on a pulley which revolves at a speed ‘N’ rev./sec.

Torque (T) = F xr Nw-m.

Work done in one revolution of armature = F2ar Joules.

Work done in one sec = F x 2 ar x N joules.

## Armature Torque Of Dc Motor?

In a Dc Motor, each conductor lying under a pole face exerts a torque tending to turn the armature. The sum of all these Torque Is Called The Armature Torque. (T.) or It is the torque developed in the armature for turning it.

### How Is Shaft Torque Calculated?

The Shaft Torque available at the shaft for doing useful work is called shaft torque (Tan). The horse power obtained using the shaft torque is called the brake horse power (B.H.P.).

The difference between the armature torque and shaft torque is known as lost torque.

## Dc Motor Parts Name?

The Parts of a Dc Motor is almost similar to a D.C. generator (Explained in Dc. generator chapter), like how to identify dc motor part name?

1. Yoke.
2. Armature.
3. Pole core and shoes.
4. Commutator.
5. Carbon brush.
6. Brush holder.
7. Front and rear endplates.
8. Bearings.
9. Shaft and pulley.
10. Eye bolt.
11. Bed (Base) plate.
12. Series Winding Terminal box.

## Armature Reaction Definition.

The Reaction of the Armature Field on the main field of a generator (as mentioned in D.C. generator chapter) has its counter part in a motor, so that the field distortion will, if incorrect, make sparkless commutation possible only on a displaced neutral axis.

In a motor, the field distortion is in the reverse direction to that of a generator and the angle of lead in a generator becomes the angle of lag in a motor.

The angle of lag will vary in a shunt motor with the armature current and would require a different brush position with every change of load. Moreover when a motor is reversed the brush position would require a large adjustment.

### What Is a Commutation In Dc Motor?

Commutation in D.C. Motors is exactly similar to D.C. generators. When a carbon brush touches two or more than two segments, the coils which are connected to the segments get short.

As a result, the current in the coils changes its direction, and this change in the direction of the flow of current is called commutation. This commutation leads to the sparking in the brushes. To remove them inter poles are used, as explained in D.C. Generator chapter.

Example: A 250 volts shunt motor takes a current of 20 amperes. If the shunt field resistance is 200 ohms and armature resistance is 0.3 ohm, find (A) the armature current (B) the back E.M.F, Dc Motor Types.

Motor voltage (V) = 250 volts.

Shunt field resistance (Rsh) = 200 ohms.

Armature resistance (R.) = 0.3 ohm.

Load current (1) = 20 amps.

Armature current (1) = ?.

### Necessity of D.C. motor starter?

It is a safety device of the motor. When a motor is at rest there is no back e.m.f. If the armature is connected directly to the supply, the starting current will be very high.

For example, a 100 volt 15 H.P. motor has a cold armature resistance of 0.042 ohms and a full load current of 126 amperes. If this motor is connected directly to the supply, a current of 100/0.042 = 2380 amperes would flow.

So, it is unsafe, which would damage the motor and blow off the main fuse or circuit breakers. To avoid this excessive starting current resistance is inserted in series with the armature and gradually cut out as the motor gains speed and develops the back e.m.f. which then regulates its speed.

When the Dc Motor is running normally on load, it draws from the supply just sufficient current to develop the required torque. It is limited by the back e.m.f. of the motor.

## Types Of Dc Motor Starters?

There are two Types Of Dc Motor of starters used for starting the D.C. shunt and compound motor.

1. D.C. three point starter.
2. D.C. four point starter.

### D.C. three point starter.

The starter has got only three terminals namely line (L), armature (A) and field (F or Z), so it is called a three point starter.

#### Parts of a D.C. Three Point Starter?

he following are the main parts of a three point starter.

• Variable Resistance.
• Handle
• Spring.

Variable Resistance: It is made of an alloy. It is connected with the armature Studs circuit in series. The resistance is designed for heavy current and low resistance values. It is wound in a spiral shape and placed on the porcelain or asbestos sheet. A number of tapping are connected with the studs. When the motor starts, full resistance is connected in series.

Handle: It is made of iron and is insulated from the starter. A copper strip | o.lclul is placed under the handle to make contact with the studs. It has a soft iron piece that is attracted by the no-volt coil and the handle remains in ON position as long as the current flows through the no-volt coil.

Spring: It is a wound on the handle of the starter. The function of a spring is to bring the handle in the OFF position when the supply fails. The tension of the spring is LF A placed in such a manner so that the handle comes at the OFF position immediately after the no-volt coil is demagnetized.

### DC Motor Four Point Starter Function:

A four point starter is used with a Shunt Or Compound Motor. It has four terminals marked L+, L-, A, and F or Z. In this starter, the no volt coil is connected NVC directly across the line through a protecting resistance.

unlike the three point starter, in which it is in series with the field. Its construction is similar to that of a 3 point starter as shown in the figure.

This starter is used at places where much speed regulation is required. For the maximum variation of speed, a high resistance O.L.C. is connected in series with the shunt field winding.

If this resistance is used in three point starter, it will reduce the shunt field winding current. It means the Lever current passing through the N.V.C. is also decreased.

Therefore, the no volt coil will not be able to produce sufficient magnetic strength and therefore, release the handle to the OFF position. This problem has been rectified in four point starter so that N.V.C. is able to make a strong magnet.

### D.C. Series Motor Starter And Its Function?

To start the D.C. series motor a Two point Dc Series Motor Starter is used. A simple two point starter is connected in series with a Dc series motor.

The resistance of the starter is sub-divided into a number of steps and is made of low value and a high current carrying capacity and is cut out of the circuit one after the other as the motor attains normal speed.

This resistance is inserted in the circuit because the motor takes high current at the time of starting as the resistance of the armature and field is very low and there is no back e.m.f. in it.

The starter resistance can be used as a speed regulator if it is designed for continuous rating. The starter contains two protective devices such as no volt coil and overload coil. Their function is the same as explained earlier.

Precaution: The starting handle must be held at every resistance stud for a few seconds to give the motor time to build up speed. A too-quick movement of the handle defeats the very purpose of the Dc Motor Starter.

On the other hand, the handle should not be moved too slowly, as the starting resistance which is Lever →L A. designed to carry the current only for a few seconds, will be damaged by the Dc Series Motor Starter heavy starting current.

## Dc Motor Forward Reverse Switch?

Whenever D.C. series motor require to operate forward and backward direction, a drum type starter is used which is similar to D.C. series starter.

It is a wooden or insulated thin sheet drum having a number of resistance and carbon brush. The drum is filled with insulating oil. About fourteen numbers of thin copper sheet pieces are attached with the help of screws called Finger which make a connection with carbon brush.

Motor, supply, and resistance are connected with these fingers. At starting the handle of the starter rotate towards the forwarding position which connects the field and armature of the Dc Motor and it starts to rotate them gradually and slowly resistance is cut off from the motor circuit.

Now, in the case anticlockwise direction, the handle of the starter is to be rotated another direction, thus direction and speed of the motor can be controlled.

Note: Due to carbon brush, the spark is produced in the starter so to minimize this effect a blow-out coil is connected in series with the load as shown in the figure.

### How does a reversible DC motor work?

Reversal of D.C. Motors: The direction of rotation (D.O.R.) of a D.C. motor can be reversed by changing the direction of current either in Armature, or Field winding. If the direction of current in both is changed, there will be no reversal change.

Reversal of Series Motor: To reverse the direction of rotation of a series motor, reverse the direction of current either in the armature or field. The connection of a series motor is shown, in Fig. 27(a). The change in the direction of the current in armature is shown in Fig. 27(b). The change in the direction of the current infield.

Reversal of Series Inter Pole Motor: To reverse the direction of rotation of series Inter Pole Motor, reverse the direction of current either in the armature and Inter Pole both or in the field, because the Inter Pole is connected in series with the armature.

## Armature Control Method?

In this method, a variable resistance is connected in series with the armature circuit. If the resistance is increased, the voltage across armature terminals is decreased, thereby decreasing the armature speed.

But the change in resistance does not affect the Field Current because the shunt field is directly connected to the supply voltage.

• There is a lot of wastage of power in the resistance (Rheostat).
• The speed available will be lower than the normal speed.
•  This method is employed for a short period only.

## What Is The Field Control Method?

If the flux per pole, \$ is kept constant, the speed N will be approximately proportional to the applied voltage V, since \$, depends upon the exciting current (or field current) Shunt Field obviously if this current is varied, the speed will vary.

A variable resistance (Rheostat) is connected in series with the shunt field By Variable Resistance increasing the series resistance, the field current may be decreased and thus the field weakens, and the speed increases and vice-versa.

• Losses are small.
• A speed variation of 15% to 30 % can be obtained.
• This method is economical and more useful.
• This method gives a higher speed than the rated speed of the motor.

### Disadvantages Of Field Control Method?

The reduction of flux causes an increase in the armature current, therefore, the size of the motor is required to be kept large.

• This method is expensive.
• It is seldom used.
•  It consumes more power.
•  The speed obtained is lower than the normal speed of the motor.

## What Is A Ward Leonard Method?

In Ward Leonard Method, the variable voltage is applied to the armature of the main motor. This variable voltage is obtained from the motor-generator set which consists of either a D.C. or A.C. motor mechanically Coupled To a Generator.

The field regulator of the generator is of maximum range to vary the voltage from zero to the maximum value. A reversing switch is inserted in the field winding of the generator.

If it is desired to change the direction of rotation, speed is varied by shunt field regulator. The field of the main motor is permanently connected across the supply. All three machines are mounted on a common shaft.

## What Is a Flux Control Method?

A variable Resistance is connected in parallel with the series field winding as shown in Diagram. This resistance is called a Flux Control Method And diverter. By reducing the diverter, resistance weakens the field current and flux, which results the motor speed-up.

Advantages : The speed of a motor higher than normal can be obtained by this method.

### What Is A Armature Diverter Method?

A variable resistance is connected in parallel with the armature as shown in Diagram By decreasing the diverter resistance, the armature current (1.) is reduced, then field flux o must increase which results in an increase in current drawn from the supply and the speed drops.

### How Do You Calculate The Efficiency Of a Dc Motor?

It is a ratio between output and input of the motor and always expressed in Fig. No. 38 Variable resistance method. percentage. Its symbol is n.

The output of the motor is the mechanical power taken from the motor’s shaft. The input of the motor is the electrical power supplied to the motor.

Rating of D.C. motors: The rating of the motor is generally mentioned on the name plate of the motor as given below.

Example: Horse power (H.P.) 10 h.p.

Voltage 230 Volt

Current 33 Amp

Speed 2800 R.p.m.

Type compound motor.

It means that when a D.C. compound motor is running at 2800 r.p.m. with a 230 V supply voltage it is capable of delivering 10 h.p. when it takes a current of 33 amperes.

### Dc Motor Speed Regulation?

The Speed Regulation In Dc Motor is the change caused in speed when the load on the motor is increased from no-load to full-load at the full load speed. It is generally expressed as a percentage.

## Dc Motor Full Load Current?

### What is in a DC motor and Dc Motor Types?

The Dc Motor Types & Dc Motor is a Mechanism by which Electrical Energy is Converted into Mechanical Energy. Both in principle and in design, the D.C. motor is the reverse of a D.C. Generator.

### Which magnet is used in the DC motor?

We know that Dc Motor Magnetic lines of force travel from North pole to South pole. The lines of force between these two poles in parallel.

### what is the working principle of DC machines and Dc motor?

The Working Principle Of Dc Motor: When a conductor carrying a current is placed in a magnetic field, it tends to move at the right angle to The field. In the figure, a two-pole motor is shown under the North and South poles.

### What is the most common type of dc motor?

• There are main Four Types Of D.C. Motors:
• Series Wound Motor
• Shunt Wound Motor.
• Compound Wound Motor.
• Permanent Magnet Dc Motor.

### What is a compound motor?

This consists of Two Field Coils, one containing a large number of turns and is in parallel with the armature, and the other, containing only a few turns and is in series with the armature.

### how to identify dc motor part name?

The Parts of a Dc Motor is almost similar to a D.C. generator (Explained in Dc. generator chapter), like how to identify dc motor part name?

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