Hi reader welcomes to another interesting post. in this post, we will have a detailed look at DC Series Motor Working and Applications. With respect to construction or physical dimension, there are 2 basic categories of dc motor first one is self-excited and the second one is a separately excited dc motor. There are further three subtypes of self-excited dc motor which are Dc shunt motor, dc compound motor, and dc series motor.

In this post, we will cover the detail about the dc series motor, its construction working, operation, application, and related parameters. So let’s get started with Introduction to DC Sereis Motor.

Introduction to DC Series Motor

The DC series Motor is such dc motor that used in such applications where a high quantity of torque needed.
Its construction is such that armature windings and field windings are linked in series combination. Such configuration helps to generate a large quantity of torque.

The number of turns required in field windings is less than the turns of windings used in armature windings.

In the below figure the equivalent circuit of a series dc motor can be seen. You can see that in this circuit same current passing through the armature windings, field windings.
If we apply KVL to this circuit then we have.

VT=EA+IA(RA+RS)

Induced Torque in Series DC Motor

The terminal characteristics of the series dc motor is like the parameters of the shunt dc motor.
Its operation is based on the that flux has a direct relation with the current flowing through armature or IA till the point where we get saturation.
With the increment in the load connected to the motor flux also rises. Due to increment in flux speed of motor reduces.
In result, the torque-speed curve of motor is sharply drooping.
The induced torque for this motor is mention here.

Tind=KΦIA

As the flux for this motor has a direct relation with the IA for saturation point of material used in the motor rotor. The equation for flux will be.

φ=cIA

Here C is constant. The equation for induced torque of this motor will become.

Tind=KΦIA

=KcIA∧2

From this equation, we can see that torque has a direct relation to the square of the armature. So this motor gives high torque than any other type of motor.
So it prefferd such application where high torque is required. Like stator motor in cars, elevators, and tractors.

Terminal Characteristic of Series DC Motor

For discussing the terminal characteristic of this motor we will make assumptions related to the linear magnetization curve and study the effect of saturation in the graph.
The supposition of the linear magnetization curve indicates that flux in the motor has value.

KcIA∧2

This equation will help us to make the torque-speed characteristic curve of the series motor.
According to KVL law we have.

VT=EA+IA(RA+RS)—–A

IA= √Tind/KC

Putting the value of E=Kw Φ in equation A we have.

VT= KwΦ+√Tind/KC (RA+RS)

If flux is deleted from the equation so there will be a direct relation between torque and speed of motor.

Deleting flux from the equation note that.

IA=Φ/C

We equation for induced torque become.

Tind=K/c Φ²

Construction of Series DC Motor

The main parts of this motor are armature windings commutator stator field windings and brushes.
Its outer part is stator that is created through the steel and provides cover to the internal parts of the motor. Here in the place of electromagnet poles are also used in some cases.
Rotor of this motor comprises of armature windings these windings are linked to the commutators..
The external power to this motor is given by the carbon brushes than armature windings.

Why Series Motor is Started with No-Load

The value of the armature current of this motor depends on the load linked to the motor. When there is no load small armature current passes in the motor.
But if we connect link large load to the motor when it is starting so motor operatees tremendously that cause the damaging of motor windings.

Speed control of DC series Motor

Normally three methods are used for speed control of this motor that are described here.
- Armature resistance control
- Tapped Field control
- Field control

Armature Resistance Control Method

The circuit for this speed control method can be seen in the below figure.

From this circuitry, you can observe that the change in resistance speed is changed. As there is a series combination between field and armature windings and current flow also same.
So current passing in the motor relies on the value of resistance. So if we increase resistance current will decreases.

The expression for voltage and speed can be seen as.

N ∝ E_b/ɸ

Speed has an inverse relation to the field current.

Field Control Method

The circuit for this method can be seen here.
In this circuit field, the diverter is linked to the field windings that is in series combination to the armature.
The usage of this diverter is to help bypass the quantity of armature current in the motor.
The changes in IA speed of the motor can be varied similar to the above-mentioned method. With the difference that in this current of armature windings I bypassed through the passing the field windings.
For this resistance, if linked to the field windings. If the value of resistance offered by the diverted is high current passing in the field windings.