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 motors 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 the Dc shunt motor, dc compound motor, and dc series motor.
In this post, we will cover the detail of the dc series motor, its construction working, operation, application, and related parameters. So let’s get started with Introduction to DC Series Motor.
Introduction to DC Series Motor
- The DC series Motor is such a dc motor that is used in such applications where a high quantity of torque is needed.
- Its construction is such that armature windings and field windings are linked in a 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, and 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 that flux has a direct relation with the current flowing through the 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 the increment in flux speed of the motor reduces.
- In a result, the torque-speed curve of the motor is sharply dropping.
- The induced torque for this motor is mentioned here.
Tind=KΦIA
- As the flux for this motor has a direct relation with the IA for the saturation point of material used in the motor rotor. The equation for flux will be.
φ=cIA
- Here C is constant. The equation for the 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 prefers such applications where high torque is required. Like stator motors in cars, elevators, and tractors.
Terminal Characteristics 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 a 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.
- The 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 the link large load to the motor when it is starting so motor operates tremendously which causes the damage 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 the same.
- So current passing in the motor relies on the value of resistance. So if we increase resistance current will decrease.
- The expression for voltage and speed can be seen as.
N ∝ Eb/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.
How does a Series DC Motor Work?
A series DC motor has the field winding and the armature winding is connected in series combination with each other. It means that similar currents pass through both windings
The field winding causes a magnetic field and the armature winding rotates in this magnetic field. When a current passes through the armature winding, it bears a force due to the magnetic field. This force helps the armature to rotate.
The amount of torque generated by a series DC motor is a direct relation to the square of the current passing through the motor. This means that a small increment in current can cause a large increase in torque. This makes series DC motors good for applications that need high starting torque, like traction motors for trains and elevators.
The speed of a series DC motor has an inverse relation with the current flowing through the motor. That defines that a small increase in current can cause a large decrease in speed. This makes series DC motors difficult to control, and they are not normally used in applications where accurate speed control is needed
Here is a step-by-step explanation of how a series DC motor works:
- The motor is attached to a DC power supply.
- Current passes through the field winding, producing a magnetic field.
- Current also passes through the armature winding, which rotates in the magnetic field.
- The armature experiences a force due to the magnetic field, which resulted in rotation.
- The rotation of the armature causes the commutator to rotate.
- The commutator switches the current in the armature winding so that the armature continues to rotate in a similar direction.
- The motor continues to rotate when current passes through it
Why Series Motor is Started with No-Load
A series motor must not be started without load. It is due to that speed of the motor is in direct relation to the applied voltage and inverse relation with field flux. When a motor is started without load there is no load current that produces field flux. It means that motor speed will be high which can damage the rotor.
Here are the main causes why a series motor should not be started on no load:
- High starting current: When a series motor is started on no load, the armature current will be very high. it is that motor windings are in series combination with field windings, so full supply voltage about armature windings exists. The high current can damage motor insulation and windings.
- High speed: The high starting current also resulted in the motor operating at a very high speed. Since the speed of a series motor is direction proportional to armature current. The high speed can damage the motor mechanically and cause the motor to overheat.
- Excessive sparking: The high starting current can also result in excessive sparking at the commutator. it is due to the commutator is not able to accurately distribute the current to the armature windings. Extra sparking can damage the commutator and brushes.
Faqs
- What is a series DC motor?
A series DC motor has the armature and field windings are connected in series. it shows that the same current flows through both windings. So, the speed of a series DC motor is inverse relation to the armature current.
- What are the advantages of series DC motors?
Series DC motors have these benefits
- High starting torque: Series DC motors have very high starting torque, making them best for applications that need a large amount of torque at startup, like trains, elevators, and hoists.
- Simple construction: Series DC motors are relatively easy to make, making them less costly than other types of DC motors.
- Rugged construction: These motors are rugged and can handle harsh operating conditions.
- What are the disadvantages of series DC motors?
Series DC motors some disadvantages explained
- Poor speed regulation: The speed of a series DC motor is sensitive to vary in the load or the applied voltage. This makes it difficult to change the speed of a series DC motor correctly
- High speed: Series DC motors can work at very high speeds, which can be dangerous.
- High current draw: Series DC motors have high currents, which can overload the power supply.
- What are the applications of series DC motors?
Series DC motors are used in a variety of applications, that are
- Electric traction: These motors are used in trains, trams, and trolleybuses.
- Cranes: They are used in cranes to lift heavy loads.
- Air compressors: used in air compressors to produce high-pressure air.
- Elevators: These motors are also used in elevators to move people and cargo between floors.
- Hoists: It is used in hoists to lift heavy loads.
- Toys: They are mostly used in toys, such as toy cars and trains.
- How does a series DC motor work?
A series DC motor works on the principle of electromagnetic induction. When a current passes through the armature winding, it produces a magnetic field. This magnetic field interacts with the magnetic field produced by the field winding to generate torque. The torque rotates the armature, which in turn rotates the shaft of the motor.
- What is the speed equation for a series DC motor?
The speed equation for a series DC motor is:
speed = K / I
where:
- K is a constant of the motor
- I is the armature current
This expression shows that the speed of a series DC motor is inversely proportional to the armature current.
- How can the speed of a series DC motor be controlled?
The speed of a series DC motor can be regulated as
- Changing the applied voltage: Increasing the voltage provided will increase the speed of the motor, and reducing the applied voltage will reduce the speed of the motor.
- Changing the load: Increasing the load will reduce the speed of the motor, and decreasing the load will increase the speed of the motor.
- Using a series resistor: A series resistor can be positioned in series with the armature winding to decrease the current flow and hence the speed of the motor.
- What are the safety precautions for series DC motors?
Series DC motors can be dangerous if not used properly. The following safety precautions must be considered when using series DC motors:
- Always wear safety glasses when working with series DC motors.
- Try to avoid the armature or field windings while the motor is running.
- Ensure the motor is properly grounded.
- Use a series resistor to reduce the current flow if the motor is overloaded.
- Do not operate the motor at speeds that exceed the rated speed.
- What are the maintenance requirements for series DC motors?
Series DC motors need regular maintenance to keep them running in good condition. The following maintenance workings must be performed on a regular basis:
- Check the brushes for wear and tear.
- Clean the commutator.
- Lubricate the bearings.
- Inspect the insulation for damage.
- Replace any damaged parts as needed.
- Where can I learn more about series DC motors?
There are different sources available to learn more about series DC motors. Here are some explained
- The book “DC Motors” by Thomas A. Lipo is a comprehensive resource on the design, operation, and maintenance of DC motors.
- The website of the American Society of Mechanical Engineers (ASME) has a section on DC motors that includes technical papers, standards, and other resources.
So that is a detailed post about the series dc motor if you have any further queries ask in the comments. Thanks for reading. Have a nice day.
