# Speed Control of DC Motors

Personalized homework help for all major subjects.

Order confidently with our risk free, 14-day money-back guarantee.

• ✔️ No sign-up required
• | 🔒 100% Confidential

## Our Expert Writers

We proudly boast a team of expert professionals with verified academic credentials, selected for their proven skills and flexibility through a strict process.

Engage with experts from the top universities across the globe.

## Get Homework Help Instantly

Say goodbye to homework stress! 📚 Just share your details and we’ll whip up an affordable quote in no time – often within 15 minutes.

Get started now for FREE!

### Submit Your Homework

Let our experts help you with your college homework

8.1 Factors controlling the speed

Since, DC motors are readily available for adjustment of their operating speed hence the DC machines are considered as adaptable to the varying speed.  The speed of DC motor varies over the wide range. There are several methods of varying the speed of the DC motors and that is why DC motor has wide range of applications in the modern industries.

The speed of DC motors can be given as:

V-IaRa

N α Φ

where, Φ is the electric field, V is voltage, R is Rheostat measure and N is speed of DC motor.

Thus, it can be said that speed of Dc motor can be controlled by Φ, V or R.

8.2 Field control method

This is the method in which there is an advantage of shunt motors.  It is the most common method of controlling the speed of DC motors as well as the compound motors. When the field is excited separately, the field current, flux and speed are adjusted with the adjustment of shunt field circuit resistance. This is done in the most simple and an inexpensive way without causing changes in the motor loss.

Speed is inversely proportional to the field current,

N α 1/ If α 1/ Φ

When there is a maximum field current, there is a lowest speed. The highest speed of the DC motor is limited electrically due to the armature reaction effects under the weak field. This causes the motor to become unstable.

A constant output is delivered when the voltage remains constant throughout the motor.

Advantages of field control method

Some of the advantages of using this method for speed control are:

• Even the minute speed can be controlled
• Higher efficiency to work
• Controlling equipments are compact
• Inexpensive and simple method
• Can be done automatically as well as manually
• Access to the smooth and stepless method of controlling speed
• Speed control is not affected due to field control within the limit. No matter whether it is shunt motor, compound motor or series motor.

Disadvantages of field control method

Some of the disadvantages of using this method for speed control are:

• speed cannot be control beyond the basic speed
• Armature reaction causes instability at higher speed
• Commutation gets difficult and  commutator can be damaged at the higher speeds

Shunt motors

Change in the shunt field current with the help of shunt field rheostat causes changes in the flux of DC shunt motors. The wastage of power while controlling the resistance is quite less because of the small field current.

Speed of the motor can be increased in the ratio of 2:1 with the help of this method in non-interpolar machines.

Series motors

In this type of motor, the afflux can be changes with the help of following methods:

• Armature Divertor: The divertors across the armature is used to get the speeds lower than the normal speed
• Field Divertor: This is the invariable resistance and shunts the series windings by adjusting the resistance of this divertor any amount of current can be passed through it. When the flux is decreased, the speed of the motor is increased.
• Parallel field coils: In this method, by regrouping of the field coils, several speeds can be obtained.
• Tapped field control: In this method, the numbers of tapping are brought outside from the field. Hence the number of series of filed can be short circuited. The motor works at higher speed when all field turn in the circuit and works at low speed when some series field turns are cut down.

8.3 Rheostatic control

It is the method of speed control of DC motors in which the series resistance is inserted in the armature circuit. This method can be used with the shunt, series and compound motors.  In the shunt and compound motors, resistor is  connected between the armature and shunt. This method of speed control is common in series motors and is used when there is a need of the low load speed.

Advantages of Rheostatic control method

The advantages of this method include:

• Easy connection and simple to use
• Speed lower than the basic speed can be achieved
• Functionality of motor starting can be controlled with the speed control

Disadvantages of Rheostatic control method

The advantages of this method include:

• Less efficient
• Speed regulation is not good
• High cost of operation due to the presence of variable resistors
• Problem in getting the stepless control of speed in high power

Shunt motors

In this method, the voltage across the armature changes due to the insertion of the variable resistance or rheostat. This type of resistance is also called as controller resistance. When the controller resistance is increased, the potential difference across the armature is decreased which ultimately lowers the speed of the armature. Speed is proportional to the potential difference across armature for getting the constant torque. Thus, it can be said the higher is the resistance, the higher is the reduction in speed.

When there is a certain value of load current and the speed is zero in the motor, this is the condition of maximum current and it is also called as the stalling current.

This method is quite wasteful and expensive one, also not appropriate when the load is variable. By using the divert or across the armature, the operation of the motor can be made stable. The change in the armature current because of the change in the potential difference is negligible hence there is no effect on the change of speed of the armature.

Voltage applied across the armature can be reduced with the increased in resistance in series. The speed will also be reduced with the decrease in voltage across the armature. A very low power is wasted due to the passage of full motor current through resistance. Variable voltage supply is helpful in controlling the motion of the DC motors.

Series parallel control

In electrical tractation, this method is widely used. In this, coupled motors are used that are mechanically similar. The motors which are at the low speed are joined in series and when the motors attain the specific speed the additional resistance is cut down with the help of the controller.  There is no wastage of power because no additional resistance in the circuits hence the motor is highly effective.

8.4 Voltage method

In this method, the speed is controlled by regulating the motor’s terminal voltage when the constant field current is maintained. The change in speed is proportional to the change in voltage. Though, the output changes directly with the change in speed when the torque is constant. The application of voltage control is limited as the voltage is needed to be regulated without causing changes in the field.

The variable DC Voltage source can be the DC Vacuum tube, there at on tube or gas tube, three phase operating, semi conductor amplifier and single phase AC supply. By using this method, the motors of upto 75kW can be controlled by using magnetic amplifiers as a source of an adjustable DC voltage. Large DC motors can be controlled with rotary amplifiers. Ward Leonard control system is the example.

Advantages

• It helps in eliminating the need of series armature starting resistance
• Uniform acceleration
• Better regulation of the speed

Disadvantages

• Arrangement cost of expensive
• Efficiency of the overall system is low

Application of this method

It is used in steel mills for reversing the rolling mills, high and medium speed elevators, paper machines, seamless tube mills and shovels.

Ward Leonard control system

This method   of speed control provides an array of speed of operating speeds and reduces the wastage of energy.

In the system of Ward Leonard control, there is a main motor whose speed is controlled, a separately excited generator that feed the armature of the motor, an exciter which offer excitation of the field and the driving motor with a constant speed. The motor is the shunt motor when there is a DC supply and the driving motor is used when AC supply is used. Excitor is not important during the DC supply.

Working of the Ward Leonard control system

Generator and excitor are driven by the motor and the voltage is fed with controlled varying settings. Change in voltage is applied for the change in motor’s speed.  This speed can be adjusted from zero to maximum in any of the direction with the help of rheostat and switch. When the sliding contact of the rheostat is at the extreme hand side the motor runs at the full speed and when the slider is on the left hand side, the speed of the motor becomes slowest or zero. The sliding contact of the rheostat is shifted to the extreme left to reverse the motor’s speed.

There is a modification in this type of control system by the use of small motor generator which reduces the fluctuations in the power’s demand from the supply circuit.

Advantage of Ward Leonard control system

The main advantages include;

• Instant reversal without causing high armature currents
• Variable speed from zero to highest, can be obtained
• Stepless control is there
• Easily adaptable to the intermediate electronic, magnetic amplifier and semi conductor for the amplification of the large motors.
• Ideal for the speed regulation

Disadvantages of Ward Leonard control system

The main disadvantages include;

• High cost of installation
• Effectiveness and efficiency of the system is less as compared to the filed control method.

Links of Previous Main Topic:-

Links of Next Electrical Engineering Topics:-

Your Price: \$11.00 \$10.00

Pricing may change based on requirements

l

## FAQ - Frequently Asked Questions

Discover quick answers in our FAQ, covering the most common customer questions about our homework help service.

### Is your homework service confidential?

M
L

Absolutely! Confidentiality is one of the basic guarantees of our service at MyHomeworkHelp.com.

When our customers make their homework orders, they know their information remains 100% confidential.

Even your homework writer will not be provided with your personal details. So, when you hire a professional homework helper on our website, rest assured that your information will remain private and safe.

For a comprehensive understanding of how we protect your privacy, please refer to our Privacy Policy.

### Who will help me with my homework?

M
L

We work with subject experts from all over the world. We hire them with the help of complex tests in the disciplines of their expertise. We also verify the IDs and academic transcripts of our homework writers to be sure that our experts have a bachelor's or master’s or a PhD degree. This is how we can be sure of the proficiency of our panel of experts who will help you with your homework.

### Is it legal to ask for help with homework?

M
L

Seeking homework help is perfectly fine and shows your proactive approach to overcoming challenges. But it's important to use our homework service to enhance your understanding, not to replace your own efforts.

Our homework service offers original solutions for personal use, including:

• Generating ideas or arguments for your research.
• Deepening your subject comprehension.
• Direct citation, with proper referencing.

However, it's crucial to avoid plagiarism by not submitting our work as your own. Make sure to check your institution's academic integrity policies before using our services. Our goal is to support your educational journey in a responsible and beneficial way. Refer our honor code for more details.

### Is myhomeworkhelp.com legit?

M
L

Yes, myhomeworkhelp.com is completely legitimate. We've been successfully connecting students with top experts worldwide since 2012, offering direct, secure communication for a seamless learning experience. With over thousands of students helped and a commitment to innovative, effective education tools, we're dedicated to making learning easier and more accessible for everyone.

You can read our reviews here on Trustpilot and Sitejabber (Independent, verified reviews from buying customers) like you!

### Is there a possibility of plagiarism in my completed order?

M
L

Unlike our competitors who use cheap and ineffective in -house plagiarism software, MyHomeworkHelp.com uses credible software to check your homework solution originality. We guarantee that your paper will pass TurnItIn checks with a low percentage of similarity. In addition, we also check submitted papers for ai-content using Originality.ai.

You will receive a complemantary plagiarism free report with your completed order.

### What makes you one of the best homework help website?

M
L

We are not number 1 (yet!). We're an independent, bootstrapped business standing up to Big EdTech for last 12 years. So it means a lot that folks like you are willing to consider our services for your educational needs.

Myhomework Help is recognized as one of the premier websites for homework answers for three key reasons.

1. Firstly, we pride ourselves on the expertise and qualifications of our tutors/experts, who are selected through a rigorous vetting process to ensure they can provide best academic assistance across a wide range of subjects.
2. Secondly, our response time to student inquiries is fast (as early as few minutes), reflecting our understanding of the importance of timely support in an academic setting.
3. Lastly, we keep our pricing very student friendly. Our aim is to provide the best learning experience to students like yourself without burning a hole in your pockets.