This document provides an overview of a lecture on DC motors. It begins with preliminary notes stating that DC motors have applications in automobiles, aircraft and portable electronics due to their ability to easily control speed. It then discusses the simplest DC machine, which consists of a single rotating loop of wire. The document explains how a voltage is induced in the rotating loop and how a commutator can be added to convert the alternating voltage to a direct voltage. It further discusses how this simplest machine demonstrates the basic principles of induced voltage, torque, and commutation that apply to real DC machines.
This document provides a WhatsApp number for inquiries about available services. The number 8802731737 is listed for contacting via WhatsApp to ask questions or get more details regarding unspecified services that are available from the contact.
Компіляція для завантаження, друку і дати дітям. Колекція зображень малюнків у чорно- білому, з типовими різдвяними зображень у забарвленні. Типові сцени, які пов'язані з цією свят, які можна роздрукувати на домашньому принтері для дітей і фарби в кольорах. Креслення готові відправити друкованих та кольору. Корисно для матерів їх дітей або вчителів для дітей у школі.
This document provides a WhatsApp number for inquiries about available services. The number 8802731737 is listed for contacting via WhatsApp to ask questions or get more details regarding unspecified services that are available from the contact.
Компіляція для завантаження, друку і дати дітям. Колекція зображень малюнків у чорно- білому, з типовими різдвяними зображень у забарвленні. Типові сцени, які пов'язані з цією свят, які можна роздрукувати на домашньому принтері для дітей і фарби в кольорах. Креслення готові відправити друкованих та кольору. Корисно для матерів їх дітей або вчителів для дітей у школі.
Ознайомлення дошкільників з календарною обрядовістю.Lyi Tsvetkova
Ознайомлення дошкільників з календарною обрядовістю є одним із важливих напрямків роботи з народознавства. Презентація для педагогів розроблена до семінару з метою ознайомлення з основними народними святами
Поглиблювати навички роботи над оповіданнями; розвивати різні способи і види читання; збагачувати словниковий запас учнів; розвивати вміння спостерігати за природою, цінувати красу; виховувати любов до природи, бережливе і турботливе ставлення до неї.
Похід у театр сьогодні — вже не така урочиста подія, як століття тому. Тому вечірній одяг зовсім не обов’язковий. Чимало людей вирушають на виставу просто з роботи, і серед них занадто ошатний глядач може виглядати навіть смішно. Однак певні правила поведінки у театрі залишилися незмінними з давніх часів...
1) The document discusses the fundamentals of DC machinery, including the simplest DC machine consisting of a single rotating loop of wire. It describes how a voltage is induced in the loop due to rotation in a magnetic field and how a commutator can be used to produce DC voltage and current from the alternating voltage in the loop.
2) It then discusses a DC machine with a wound armature core and multiple loops of wire. It explains the commutation process which converts the AC voltages and currents in the rotor to DC voltages and currents at the machine terminals.
3) Finally, it illustrates commutation in a simple 4-loop DC machine, showing the induced voltages in each loop segment at a particular time step
1) DC machines operate based on the principles that voltage is induced in a conductor moving through a magnetic field (generator action) and a force is induced on a conductor with current in a magnetic field (motor action).
2) The simplest DC machine is a single loop of wire rotating through magnetic poles, which induces a voltage that can be extracted using a commutator and brushes.
3) Real DC machines have more complex windings and commutation systems to produce a DC output and overcome issues like armature reaction.
4) The main types of DC generators - separately excited, shunt, and series - have different characteristics based on how their fields are connected that determine how voltage and current vary with load
Ознайомлення дошкільників з календарною обрядовістю.Lyi Tsvetkova
Ознайомлення дошкільників з календарною обрядовістю є одним із важливих напрямків роботи з народознавства. Презентація для педагогів розроблена до семінару з метою ознайомлення з основними народними святами
Поглиблювати навички роботи над оповіданнями; розвивати різні способи і види читання; збагачувати словниковий запас учнів; розвивати вміння спостерігати за природою, цінувати красу; виховувати любов до природи, бережливе і турботливе ставлення до неї.
Похід у театр сьогодні — вже не така урочиста подія, як століття тому. Тому вечірній одяг зовсім не обов’язковий. Чимало людей вирушають на виставу просто з роботи, і серед них занадто ошатний глядач може виглядати навіть смішно. Однак певні правила поведінки у театрі залишилися незмінними з давніх часів...
1) The document discusses the fundamentals of DC machinery, including the simplest DC machine consisting of a single rotating loop of wire. It describes how a voltage is induced in the loop due to rotation in a magnetic field and how a commutator can be used to produce DC voltage and current from the alternating voltage in the loop.
2) It then discusses a DC machine with a wound armature core and multiple loops of wire. It explains the commutation process which converts the AC voltages and currents in the rotor to DC voltages and currents at the machine terminals.
3) Finally, it illustrates commutation in a simple 4-loop DC machine, showing the induced voltages in each loop segment at a particular time step
1) DC machines operate based on the principles that voltage is induced in a conductor moving through a magnetic field (generator action) and a force is induced on a conductor with current in a magnetic field (motor action).
2) The simplest DC machine is a single loop of wire rotating through magnetic poles, which induces a voltage that can be extracted using a commutator and brushes.
3) Real DC machines have more complex windings and commutation systems to produce a DC output and overcome issues like armature reaction.
4) The main types of DC generators - separately excited, shunt, and series - have different characteristics based on how their fields are connected that determine how voltage and current vary with load
- DC machines can operate as either generators or motors. A generator produces voltage when its coil rotates through a magnetic field, while a motor produces torque on its coil when current passes through it in a magnetic field.
- The simplest DC machine is a single loop of wire rotating through magnetic poles. Induced voltage and torque depend on flux, speed/current, and construction constants.
- Real DC machines use commutators and brushes to produce DC output from the AC voltage induced in the rotor coils. Problems during commutation like sparking are reduced by techniques like interpoles.
- The internal voltage and torque equations account for flux, speed/current, and construction constants. Power losses include copper, brush,
Construction and components of DC Machine – Principle of operation – Lap and wave windings-EMF equations– circuit model – armature reaction –methods of excitationcommutation – interpoles compensating winding –characteristics of DC generators.
The document describes the fundamentals of DC machines. It begins by introducing DC machines as generators that convert mechanical energy to electrical energy and motors that convert electrical energy to mechanical energy. It then discusses the basic principles of a simple rotating loop generator, including how a voltage is induced in the rotating loop and how a commutator and brushes can be used to produce a DC output. It also derives equations for the induced voltage and torque in a rotating loop motor. Finally, it examines in more detail how commutation works in a simple four-loop DC machine.
This document provides an overview of DC machines, including their construction, principles of operation, and characteristics. It discusses DC machines functioning as generators and motors. Key points include:
- DC machines can operate as generators, converting mechanical energy to electrical energy, or motors, converting electrical energy to mechanical energy.
- The main components are the stator (stationary part) and rotor (rotating part).
- In generator operation, relative motion between the magnetic field and armature windings induces an electromotive force (emf) based on Faraday's law of induction.
- In motor operation, current passing through the armature windings in a magnetic field experiences an electromagnetic force based on the left-hand
The document provides an outline and introduction to DC machines. It discusses the construction and basic parts of DC machines including the stator and rotor. It explains the principle of operation for both DC generators and DC motors. It discusses armature reaction, commutation, and characteristics of DC motors. It also covers the equivalent circuits of DC generators and motors and provides examples of calculating speed and induced emf in DC machines operating as generators and motors.
ENERGY_CONVERSION)During Motor Principle.pptdatamboli
1. A DC machine consists of a rotor with conducting loops rotating inside a stator with magnetic poles. As the loops rotate, a voltage is induced that can be converted to DC using a commutator and brushes.
2. When load is applied, armature reaction causes the magnetic neutral plane to shift. This leads to sparking at the brushes as they no longer short out loops with zero voltage. Armature reaction also causes flux weakening that reduces the generator's output voltage or can cause a motor to run away.
3. Changing current direction in commutator segments also induces voltages that can cause sparking if not addressed. Solutions are needed to address these commutation problems in real machines.
This document provides an overview of transformers and their operation. It discusses:
- The history and development of transformers from the 1880s to present day
- The basic components and construction of transformers
- How an ideal transformer works based on Faraday's law of induction
- How voltages and currents are related in an ideal transformer based on turn ratios
- How real transformers approximate ideal transformer behavior
- Examples of analyzing circuits containing transformers by referring their sides
- The theory of operation for real single-phase transformers based on mutual and leakage fluxes
This document provides information about synchronous machines and their construction. It discusses how synchronous generators and motors work, including how they are constructed, how their rotor magnetic fields are produced, and how different types of rotors and field windings are used. It also covers the internal voltage generation of synchronous generators and how their equivalent circuits are modeled, including how armature reaction affects the relationship between internal and terminal voltages. Phasor diagrams are introduced as a way to represent the AC voltages and currents in synchronous machines.
1) This document discusses the course "Electric Machines" which introduces the theory, operation, and performance of electrical machines and motors. It covers topics like DC motors, power transformers, and AC induction motors.
2) The course is evaluated based on a final exam worth 70% and classwork worth 30%, which includes a midterm exam, reports, and attendance.
3) Chapter 1 introduces electrical machines and drive systems, including definitions, classifications, voltage and torque equations, and the primitive machine model to explain basic operation of motors and generators.
This document discusses the construction and operation of synchronous machines. It describes how synchronous generators have rotors that produce a rotating magnetic field from DC current in field windings. Synchronous motors have stators that produce a rotating magnetic field to turn the rotor. Large generators use brushless exciters to supply DC current to rotor windings without mechanical contact. Equivalent circuits are presented showing how armature reaction affects the relationship between internally generated and terminal voltages. Phasor diagrams illustrate voltage and current relationships for different power factors.
- DC generators and motors operate using the principle of electromagnetic induction. When a conductor moves through a magnetic field, an electromotive force (emf) is induced in the conductor.
- The basic components of a DC generator are a magnetic field (produced by poles and field windings) and a conductor (armature) that rotates within the magnetic field. This motion induces an emf in the armature.
- A commutator is used to convert the alternating current from the armature into direct current that can be supplied to a load. Brushes make contact with the commutator segments to carry the output current.
The document discusses direct current (DC) machines and their operation. It provides details on:
1) The basic components and construction of a DC machine including its armature winding, commutator, and field poles.
2) How an alternating current induced in the armature coils is converted to direct current via the commutator and brush assembly.
3) Different types of armature windings including lap and wave windings.
4) Factors that affect the performance of DC machines such as armature reaction and how it can be mitigated through techniques like using interpoles.
5) Equations for calculating the generated electromotive force (EMF) in a DC generator.
Electrical Power Systems 3 phase apparatusMubarek Kurt
This document discusses 3-phase power apparatus and provides information on various electrical machine concepts including:
- The basic concept of magnetic fields and flux in electrical machines
- The rotating components and applications of rotating machines like generators, motors, and alternators
- The structures and operating principles of different types of AC and DC machines including synchronous and induction machines
It also covers topics like induced voltages and torque in electrical machines, power flows and losses, efficiency, voltage regulation, and speed regulation.
1) Synchronous machines have a rotor supplied by an external DC source that produces a rotating magnetic field. This induces a voltage in the stator windings.
2) The rotor can have either salient or non-salient poles and is laminated to reduce eddy currents. DC power is supplied to the rotor via slip rings and brushes or a brushless exciter.
3) An equivalent circuit model represents the internal generated voltage and accounts for armature reaction, inductance, and resistance effects on the terminal voltage.
Types of armature winding of dc generator manoharpitchai
This document discusses the constructional features of DC machines, including:
- The function of the commutator and brushes is to convert the alternating voltage induced in the armature coils into direct current by means of mechanical rectification.
- Armature windings can be of two types - lap winding or wave winding. Lap winding connects coil ends to consecutive commutator segments, while wave winding connects ends approximately two pole pitches apart.
- The number of parallel paths in the armature is equal to the number of poles for lap winding, and is equal to 2 for wave winding. Understanding armature windings and parallel paths is important for analyzing DC machine performance.
This document provides information about experiments conducted in an electrical machines lab at Mehran University of Engineering and Technology. It includes an index listing 12 experiments conducted between August and October on topics like DC generators, motors, and control systems. Practical 1 provides an introduction to electrical machine equipment like DC motors, generators, transformers, and control panels. It describes the components and operating principles. The document also includes circuit diagrams, readings tables and conclusions from experiments verifying open circuit characteristics of separately excited DC generators and self-excited series DC generators.
BEE - DC Machines basic of electronic and electrical enginnerringkavi7010764469
The document discusses the construction and working principles of DC machines. It describes how DC machines can operate as either generators or motors. As a generator, a DC machine converts mechanical energy into electrical energy via electromagnetic induction. As a motor, it converts electrical energy into mechanical torque by applying a current-carrying conductor in a magnetic field. The key components of a DC machine include an armature, commutator, field coils, and poles which allow it to generate or be driven by a DC current based on Faraday's law of induction.
Basic concepts of electricity last two week convertedASHISH DHAMANDA
This document discusses alternating current (AC) and how it differs from direct current (DC). It explains that AC is generated from rotating magnets in generators, which produces a reversing voltage polarity over time. AC generators and motors have simpler designs than DC versions because they do not require brushes. Transformers are also discussed, which use mutual induction between coils to step voltages up or down, enabling efficient long-distance power transmission. The key advantages of AC that the document outlines are simpler generator/motor construction and enabling power distribution via step-up and step-down transformers, which is not possible with DC.
Similar to 1337683622.6252Lecture 05 - DC motors.ppt (20)
This document discusses issues related to integrating distributed energy resources (DER) into electric power grids. It provides background on DER definitions and classifications. It addresses grid integration and interconnection standards, including requirements for steady state and transient operations, protection, and islanding detection. The document outlines considerations for DER protection and control requirements to safely interconnect DER while maintaining grid reliability. It also presents examples of DER installations and research on advanced relay techniques for islanding detection.
This document discusses unintentional islanding of power systems with distributed resources like solar PV. It defines intentional and unintentional islands, and issues with unintentional islands like safety hazards, overvoltages, and loss of protection. Methods to detect unintentional islands are described, like reverse power relays and active techniques. Simulation results show one technique detecting an island within 0.5 cycles. Guidelines for assessing islanding risk are provided, and the future of anti-islanding techniques discussed, like the potential need for multiple active methods with reduced grid stiffness.
The document discusses several methods for detecting power islands in grid-connected distributed generation systems. Passive detection schemes have a large non-detection zone while active methods can degrade power quality. Intelligent methods that use artificial intelligence techniques like neural networks, fuzzy logic, genetic algorithms and expert systems show promise for quickly and accurately detecting and classifying islanding conditions. The key advantages of these methods are their ability to learn adaptively and generalize while accurately detecting islanding conditions.
This document provides an overview of a course on power generation systems. The course covers conventional power sources like thermal and hydroelectric plants as well as non-conventional renewable sources like solar and wind. It discusses different methods of power generation including using steam to turn turbines, using the kinetic energy of moving water or wind, and exploiting nuclear reactions. The document compares various energy sources based on their initial costs, running costs, limitations, and sustainability. Students will learn about electrical power generation and the key players and sources that make up Pakistan's power sector.
This document discusses the implications of distributed generation islanding on power system dynamics. It begins by defining islanding as the phenomenon where a distributed generator continues to power a location even after that location is electrically isolated from the central distribution network. If unintentional islanding occurs, it can pose safety hazards and damage equipment if the distributed generator's voltage and frequency are not properly regulated. The document also discusses out-of-phase reclosing, which produces high transient currents that can damage equipment. It then examines various active anti-islanding methods and notes their dynamic impacts, such as unnecessary tripping from undervoltage events. While anti-islanding protection prevents problems now, the document warns its effects could degrade power quality and stability as distributed
The document provides installation instructions and specifications for capacitors, including that a minimum 50mm gap is required between capacitors, the air temperature must not exceed 65 degrees Celsius, and the bottom of copper bars should be at least 180mm above capacitor terminals to avoid magnetic interference. It also lists technical parameters for the capacitors such as voltage, frequency, amps, weight, and individual kvar and MFD specifications for 5 capacitors along with an internal wiring diagram and date.
Synchronous motors and generators operate by synchronizing the rotation of the rotor's magnetic field with the rotating magnetic field produced by the stator windings. Synchronous motors are used for constant-speed applications like propulsion for large ships. They work by locking the rotor's magnetic field to the rotating stator field. Synchronous generators can be produced by transitioning a synchronous motor driven by a turbine from motor to generator operation as the power angle shifts from negative to positive.
Basic Power Electronics Concepts_Ozipineci_ORNL.pdfgulie
This document provides an introduction to power electronics. It defines power electronics as technology used to change the characteristics of electrical power to suit applications. The document outlines the history and types of power semiconductor devices like diodes, thyristors, MOSFETs and IGBTs. It also describes different types of power converters including rectifiers, inverters, and DC-DC converters. Thermal management of power devices is also discussed.
Electrical Engineering Objective Type Questions.pdfgulie
This document contains a list of objective type questions for the Electrical Engineering department at Government College of Engineering in Bargur, prepared by assistant professor V. Arivumani. It includes 875 total questions organized under various topics related to electrical engineering, such as DC generators, DC motors, transformers, induction motors, synchronous motors, transmission and distribution, and cables. The questions cover concepts like generator construction, winding types, armature reaction, commutation, and parallel operation of generators. Sample questions and answers are provided for the topic of DC generators.
This document provides job hunting techniques for those seeking employment in the United Arab Emirates (UAE). It outlines steps such as defining one's career interests, obtaining necessary documents like a passport and degree attestation, creating a strong resume and cover letter, applying for jobs online from home country or during a visit to UAE, and preparing for interviews. Useful online resources and job sites are also listed to facilitate the job searching process in UAE.
This document presents a fractional order PID controller (FOPID)-Toolbox to design robust fractional PID controllers. The toolbox uses nonsmooth optimization techniques to optimize the parameters of fractional PIαDβ and (PID)n controllers to achieve a desired crossover frequency and phase margin. The goal is to develop a systematic method to optimize the parameters of these fractional order controllers based on expressing the control problem and requirements in terms of a desired open-loop response and using a loop shaping configuration. An algorithm is proposed that initializes the fractional orders, computes the gradient with respect to the orders, and iteratively updates the orders using steepest descent until convergence.
This document describes research into using a fractional order PID (FOPID) controller to control voltage fluctuations in an islanded microgrid with a single power source. The proposed FOPID controller has more tuning parameters than a standard PID controller, allowing it to better regulate the microgrid's output voltage under different load conditions and uncertainties. The controller is designed using an optimization technique to maximize system performance. Simulation results show the FOPID controller is effective at reducing voltage fluctuations and provides a fast, robust response for the microgrid system.
This document discusses unintentional islands in power systems with distributed resources and methods to prevent them. It defines types of islands and issues they can cause. It outlines standard testing and requirements for distributed resources to detect and cease energizing an unintentional island within 2 seconds. Various passive, active and communication-based anti-islanding protection methods are described to meet this requirement.
SVM-plus-Phase-Shift Modulation Strategy for Single-Stage.pdfgulie
This document proposes a new modulation strategy called SVM-plus-phase-shift (SVM-PS) modulation for a single-stage three-phase resonant AC-DC matrix converter with an LCL resonant tank. The strategy aims to achieve unity power factor and flexible control of active and reactive power transfer. It derives the relationship between switch states and line-frequency phase currents based on the fundamental component of the tank current. This allows simple control of current amplitude and phase via modulation of the AC and DC side switches based on voltage and current references. Simulation results show the proposed strategy reduces current distortion and ripple compared to conventional SVM.
This document discusses multiphase power converters. It begins by defining multiphase converters as those with more than three phases, which are an extension of three-phase converters with additional legs. Multiphase converters are used in applications involving AC to DC, DC to AC, AC to AC, and DC to DC conversion. They provide advantages like enhanced torque density, lower torque pulsation, higher frequency ripple, lower per-leg current rating, greater fault tolerance, and lower harmonic losses. The document goes on to describe types of multiphase converters and their applications in areas like adjustable speed drives, renewable energy systems, and electric vehicles.
Grid Converters for Photovoltaic and Wind Power Systems - 2010 - Teodorescu -...gulie
This document summarizes space vector transformations of three-phase systems. It discusses symmetrical components analysis in the frequency and time domains, which allows decomposition of an unbalanced three-phase system into positive, negative, and zero sequence components. It also describes Clarke's transformation to a stationary αβ0 reference frame, which defines three independent real components from the complex positive and negative sequence components.
This document discusses space vector pulse width modulation (SVPWM) techniques for multilevel inverters. It begins by introducing SVPWM and explaining that it provides advantages over sinusoidal PWM, including better fundamental output voltage and improved harmonic performance. It then defines two-dimensional and three-dimensional space vectors and discusses how SVPWM can be implemented in both 2D and 3D. The document focuses on SVPWM for three-leg voltage source inverters, describing the voltage space vectors and how SVPWM can be used to synthesize the required output voltage vector through PWM of the switching state vectors.
This document provides an introduction to using the ATP/EMTP software for simulating electrical systems transients. It discusses how to create data files for simulations using either ATPDraw, a graphical preprocessor, or by directly editing text files. It also describes running simulations and viewing results. The document is intended to introduce beginners to the ATP/EMTP software by following existing manuals on its usage and capabilities. It emphasizes that expertise requires experience working with the software and suggests consulting manuals and experts for in-depth knowledge of complex simulations.
Electrical power systems design and analysis mohamed e. el-hawarygulie
The document discusses the benefits of exercise for mental health. Regular physical activity can help reduce anxiety and depression and improve mood and cognitive function. Exercise causes chemical changes in the brain that may help protect against mental illness and improve symptoms.
Redefining brain tumor segmentation: a cutting-edge convolutional neural netw...IJECEIAES
Medical image analysis has witnessed significant advancements with deep learning techniques. In the domain of brain tumor segmentation, the ability to
precisely delineate tumor boundaries from magnetic resonance imaging (MRI)
scans holds profound implications for diagnosis. This study presents an ensemble convolutional neural network (CNN) with transfer learning, integrating
the state-of-the-art Deeplabv3+ architecture with the ResNet18 backbone. The
model is rigorously trained and evaluated, exhibiting remarkable performance
metrics, including an impressive global accuracy of 99.286%, a high-class accuracy of 82.191%, a mean intersection over union (IoU) of 79.900%, a weighted
IoU of 98.620%, and a Boundary F1 (BF) score of 83.303%. Notably, a detailed comparative analysis with existing methods showcases the superiority of
our proposed model. These findings underscore the model’s competence in precise brain tumor localization, underscoring its potential to revolutionize medical
image analysis and enhance healthcare outcomes. This research paves the way
for future exploration and optimization of advanced CNN models in medical
imaging, emphasizing addressing false positives and resource efficiency.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
TIME DIVISION MULTIPLEXING TECHNIQUE FOR COMMUNICATION SYSTEMHODECEDSIET
Time Division Multiplexing (TDM) is a method of transmitting multiple signals over a single communication channel by dividing the signal into many segments, each having a very short duration of time. These time slots are then allocated to different data streams, allowing multiple signals to share the same transmission medium efficiently. TDM is widely used in telecommunications and data communication systems.
### How TDM Works
1. **Time Slots Allocation**: The core principle of TDM is to assign distinct time slots to each signal. During each time slot, the respective signal is transmitted, and then the process repeats cyclically. For example, if there are four signals to be transmitted, the TDM cycle will divide time into four slots, each assigned to one signal.
2. **Synchronization**: Synchronization is crucial in TDM systems to ensure that the signals are correctly aligned with their respective time slots. Both the transmitter and receiver must be synchronized to avoid any overlap or loss of data. This synchronization is typically maintained by a clock signal that ensures time slots are accurately aligned.
3. **Frame Structure**: TDM data is organized into frames, where each frame consists of a set of time slots. Each frame is repeated at regular intervals, ensuring continuous transmission of data streams. The frame structure helps in managing the data streams and maintaining the synchronization between the transmitter and receiver.
4. **Multiplexer and Demultiplexer**: At the transmitting end, a multiplexer combines multiple input signals into a single composite signal by assigning each signal to a specific time slot. At the receiving end, a demultiplexer separates the composite signal back into individual signals based on their respective time slots.
### Types of TDM
1. **Synchronous TDM**: In synchronous TDM, time slots are pre-assigned to each signal, regardless of whether the signal has data to transmit or not. This can lead to inefficiencies if some time slots remain empty due to the absence of data.
2. **Asynchronous TDM (or Statistical TDM)**: Asynchronous TDM addresses the inefficiencies of synchronous TDM by allocating time slots dynamically based on the presence of data. Time slots are assigned only when there is data to transmit, which optimizes the use of the communication channel.
### Applications of TDM
- **Telecommunications**: TDM is extensively used in telecommunication systems, such as in T1 and E1 lines, where multiple telephone calls are transmitted over a single line by assigning each call to a specific time slot.
- **Digital Audio and Video Broadcasting**: TDM is used in broadcasting systems to transmit multiple audio or video streams over a single channel, ensuring efficient use of bandwidth.
- **Computer Networks**: TDM is used in network protocols and systems to manage the transmission of data from multiple sources over a single network medium.
### Advantages of TDM
- **Efficient Use of Bandwidth**: TDM all
A SYSTEMATIC RISK ASSESSMENT APPROACH FOR SECURING THE SMART IRRIGATION SYSTEMSIJNSA Journal
The smart irrigation system represents an innovative approach to optimize water usage in agricultural and landscaping practices. The integration of cutting-edge technologies, including sensors, actuators, and data analysis, empowers this system to provide accurate monitoring and control of irrigation processes by leveraging real-time environmental conditions. The main objective of a smart irrigation system is to optimize water efficiency, minimize expenses, and foster the adoption of sustainable water management methods. This paper conducts a systematic risk assessment by exploring the key components/assets and their functionalities in the smart irrigation system. The crucial role of sensors in gathering data on soil moisture, weather patterns, and plant well-being is emphasized in this system. These sensors enable intelligent decision-making in irrigation scheduling and water distribution, leading to enhanced water efficiency and sustainable water management practices. Actuators enable automated control of irrigation devices, ensuring precise and targeted water delivery to plants. Additionally, the paper addresses the potential threat and vulnerabilities associated with smart irrigation systems. It discusses limitations of the system, such as power constraints and computational capabilities, and calculates the potential security risks. The paper suggests possible risk treatment methods for effective secure system operation. In conclusion, the paper emphasizes the significant benefits of implementing smart irrigation systems, including improved water conservation, increased crop yield, and reduced environmental impact. Additionally, based on the security analysis conducted, the paper recommends the implementation of countermeasures and security approaches to address vulnerabilities and ensure the integrity and reliability of the system. By incorporating these measures, smart irrigation technology can revolutionize water management practices in agriculture, promoting sustainability, resource efficiency, and safeguarding against potential security threats.
KuberTENes Birthday Bash Guadalajara - K8sGPT first impressionsVictor Morales
K8sGPT is a tool that analyzes and diagnoses Kubernetes clusters. This presentation was used to share the requirements and dependencies to deploy K8sGPT in a local environment.
DEEP LEARNING FOR SMART GRID INTRUSION DETECTION: A HYBRID CNN-LSTM-BASED MODELgerogepatton
As digital technology becomes more deeply embedded in power systems, protecting the communication
networks of Smart Grids (SG) has emerged as a critical concern. Distributed Network Protocol 3 (DNP3)
represents a multi-tiered application layer protocol extensively utilized in Supervisory Control and Data
Acquisition (SCADA)-based smart grids to facilitate real-time data gathering and control functionalities.
Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
Understanding Inductive Bias in Machine LearningSUTEJAS
This presentation explores the concept of inductive bias in machine learning. It explains how algorithms come with built-in assumptions and preferences that guide the learning process. You'll learn about the different types of inductive bias and how they can impact the performance and generalizability of machine learning models.
The presentation also covers the positive and negative aspects of inductive bias, along with strategies for mitigating potential drawbacks. We'll explore examples of how bias manifests in algorithms like neural networks and decision trees.
By understanding inductive bias, you can gain valuable insights into how machine learning models work and make informed decisions when building and deploying them.
Literature Review Basics and Understanding Reference Management.pptxDr Ramhari Poudyal
Three-day training on academic research focuses on analytical tools at United Technical College, supported by the University Grant Commission, Nepal. 24-26 May 2024
Batteries -Introduction – Types of Batteries – discharging and charging of battery - characteristics of battery –battery rating- various tests on battery- – Primary battery: silver button cell- Secondary battery :Ni-Cd battery-modern battery: lithium ion battery-maintenance of batteries-choices of batteries for electric vehicle applications.
Fuel Cells: Introduction- importance and classification of fuel cells - description, principle, components, applications of fuel cells: H2-O2 fuel cell, alkaline fuel cell, molten carbonate fuel cell and direct methanol fuel cells.
1. ELEN 3441 Fundamentals of Power Engineering Spring 2008
1
Lecture 5: DC motors
Instructor:
Dr. Gleb V. Tcheslavski
Contact:
gleb@ee.lamar.edu
Office Hours:
TBD; Room 2030
Class web site:
http://ee.lamar.edu/gleb/
Index.htm
2. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Preliminary notes
DC power systems are not very common in the contemporary engineering
practice. However, DC motors still have many practical applications, such
automobile, aircraft, and portable electronics, in speed control
applications…
An advantage of DC motors is that it is easy to control their speed in a
wide diapason.
DC generators are quite rare.
Most DC machines are similar to AC machines: i.e. they have AC voltages
and current within them. DC machines have DC outputs just because they
have a mechanism converting AC voltages to DC voltages at their
terminals. This mechanism is called a commutator; therefore, DC
machines are also called commutating machines.
3. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
The simplest DC rotating machine
consists of a single loop of wire
rotating about a fixed axis. The
magnetic field is supplied by the
North and South poles of the
magnet.
Rotor is the rotating part;
Stator is the stationary part.
4. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
We notice that the rotor lies in a slot curved
in a ferromagnetic stator core, which,
together with the rotor core, provides a
constant-width air gap between the rotor and
stator.
The reluctance of air is much larger than the
reluctance of core. Therefore, the magnetic
flux must take the shortest path through the
air gap.
As a consequence, the magnetic flux is perpendicular to the rotor surface
everywhere under the pole faces.
Since the air gap is uniform, the reluctance is constant everywhere under the pole
faces. Therefore, magnetic flux density is also constant everywhere under the pole
faces.
5. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
1. Voltage induced in a rotating loop
If a rotor of a DC machine is rotated, a voltage will be induced…
The loop shown has sides ab and cd perpendicular to the figure
plane, bc and da are parallel to it.
The total voltage will be a sum of voltages induced on each
segment of the loop.
Voltage on each segment is:
ind
e
v×B l (5.5.1)
6. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
1) ab: In this segment, the velocity of the wire is tangential to the path of rotation.
Under the pole face, velocity v is perpendicular to the magnetic field B, and the
vector product v x B points into the page. Therefore, the voltage is
into page under the pole face
0 beyond the pole edges
ba
vBl
e
v×B l
2) bc: In this segment, vector product v x B is perpendicular to l. Therefore, the
voltage is zero.
3) cd: In this segment, the velocity of the wire is tangential to the path of rotation.
Under the pole face, velocity v is perpendicular to the magnetic flux density B,
and the vector product v x B points out of the page. Therefore, the voltage is
out of page under the pole face
0 beyond the pole edges
dc
vBl
e
v×B l
4) da: In this segment, vector product v x B is perpendicular to l. Therefore, the
voltage is zero.
(5.6.1)
(5.6.2)
7. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
The total induced voltage on the loop is:
tot ba cb dc ad
e e e e e
2
0
tot
vBl under the pole faces
e
beyond the pole edges
When the loop rotates through 1800,
segment ab is under the north pole
face instead of the south pole face.
Therefore, the direction of the voltage
on the segment reverses but its
magnitude reminds constant, leading
to the total induced voltage to be
(5.7.1)
(5.7.2)
8. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
The tangential velocity of the loop’s edges is
v r
(5.8.1)
2
0
tot
r Bl under the pole faces
e
beyond the pole edges
where r is the radius from the axis of rotation to
the edge of the loop. The total induced voltage:
(5.8.2)
The rotor is a cylinder with surface area 2rl.
Since there are two poles, the area of the rotor
under each pole is Ap = rl. Therefore:
2
0
p
tot
A B under the pole faces
e
beyond the pole edges
(5.8.3)
9. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
Assuming that the flux density B is constant everywhere in the air gap under the
pole faces, the total flux under each pole is
p
A B
The total voltage is
2
0
tot
under the pole faces
e
beyond the pole edges
The voltage generated in any real machine depends on the following
factors:
1. The flux inside the machine;
2. The rotation speed of the machine;
3. A constant representing the construction of the machine.
(5.9.1)
(5.9.2)
10. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
2. Getting DC voltage out of a rotating
loop
A voltage out of the loop is alternatively a
constant positive value and a constant
negative value.
One possible way to convert an alternating
voltage to a constant voltage is by adding a
commutator
segment/brush
circuitry to the
end of the loop.
Every time the
voltage of the
loop switches
direction,
contacts switch
connection.
11. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
segments
brushes
12. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
3. The induced torque in the
rotating loop
Assuming that a battery is connected
to the DC machine, the force on a
segment of a loop is:
F i
l×B
And the torque on the segment is
sin
rF
Where is the angle between r and F.
Therefore, the torque is zero when
the loop is beyond the pole edges.
(5.12.1)
(5.12.2)
13. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
When the loop is under the pole faces:
1. Segment ab:
2. Segment bc:
3. Segment cd:
4. Segment da:
ab
F i ilB
l×B
sin sin90
ab rF r ilB rilB ccw
(5.13.1)
(5.13.2)
0
ab
F i
l×B
sin 0
ab rF
(5.13.3)
(5.13.4)
ab
F i ilB
l×B
sin sin90
ab rF r ilB rilB ccw
(5.13.5)
(5.13.6)
0
ab
F i
l×B
sin 0
ab rF
(5.13.7)
(5.13.8)
14. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The simplest DC machine
The resulting total induced torque is
The torque in any real machine depends on the following factors:
1. The flux inside the machine;
2. The current in the machine;
3. A constant representing the construction of the machine.
2
0
ind
i under the pole faces
beyond the pole edges
ind ab bc cd da
2
0
ind
rilB under the pole faces
beyond the pole edges
(5.14.1)
(5.14.2)
Since Ap rl and p
A B
(5.14.3)
(5.14.4)
15. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
Commutation is the process of converting the AC voltages and currents in
the rotor of a DC machine to DC voltages and currents at its terminals.
A simple 4-loop DC machine has four complete loops buried in slots curved in the
laminated steel of its rotor. The pole faces are curved to make a uniform air-gap.
The four loops are laid into the slots in a special manner: the innermost wire in
each slot (end of each loop opposite to the “unprimed”) is indicated by a prime.
Loop 1 stretches
between
commutator
segments a and
b, loop 2
stretches
between
segments b and
c…
16. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
At a certain time instance, when t
= 00, the 1, 2, 3’, and 4’ ends of the
loops are under the north pole face
and the 1’, 2’, 3, and 4 ends of the
loops are under the south pole face.
The voltage in each of 1, 2, 3’, and
4’ ends is given by
positive, out of the page
ind
e vBl
v×B ×l
positive, into the page
ind
e vBl
v×B ×l
The voltage in each of 1’, 2’, 3, and 4 ends is
(5.16.1)
(5.16.2)
If the induced voltage on any side of a loop is (5.16.1), the total voltage at the
brushes of the DC machine is
4 0
E e at t
(5.16.3)
17. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
We notice that there are two parallel paths for current through the
machine! The existence of two or more parallel paths for rotor current is
a common feature of all commutation schemes.
18. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
If the machine keeps rotating, at t = 450, loops 1 and 3 have rotated into the gap
between poles, so the voltage across each of them is zero. At the same time, the
brushes short out the commutator segments ab and cd.
This is ok since
the voltage across
loops 1 and 3 is
zero and only
loops 2 and 4 are
under the pole
faces. Therefore,
the total terminal
voltage is
2 45
E e at t
(5.18.1)
19. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
At t = 900, the loop ends 1’, 2, 3, and 4’ are under
the north pole face, and the loop ends 1, 2’, 3’, and
4 are under the south pole face. The voltages are
built up out of page for the ends under the north
pole face and into the page for the ends under the
south pole face. Four voltage-carrying ends in each
parallel path through the machine lead to the
terminal voltage of
4 90
E e at t
(5.16.3)
We notice that the voltages in loops 1 and 3 have
reversed compared to t = 00. However, the loops’
connections have also reversed, making the total
voltage being of the same polarity.
20. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Commutation in a simple 4-loop
DC machine
When the voltage reverses in a loop, the connections of the loop are also switched
to keep the polarity of the terminal voltage the same.
The terminal voltage of this 4-loop DC
machine is still not constant over time,
although it is a better approximation to a
constant DC level than what is produced
by a single rotating loop.
Increasing the number of loops on the
rotor, we improve our approximation to
perfect DC voltage.
Commutator segments are usually made out of copper bars and the brushes are
made of a mixture containing graphite to minimize friction between segments and
brushes.
22. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
1. Armature reaction
If the magnetic field windings of a DC machine are connected to the power
source and the rotor is turned by an external means, a voltage will be
induced in the conductors of the rotor. This voltage is rectified and can be
supplied to external loads. However, if a load is connected, a current will
flow through the armature winding. This current produces its own magnetic
field that distorts the original magnetic field from the machine’s poles. This
distortion of the machine’s flux as the load increases is called armature
reaction and can cause two problems:
1) neutral-plane shift: The magnetic neutral plane is the plane within the
machine where the velocity of the rotor wires is exactly parallel to the
magnetic flux lines, so that the induced voltage in the conductors in the
plane is exactly zero.
23. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
A two-pole DC machine: initially, the pole flux is
uniformly distributed and the magnetic neutral plane is
vertical.
The effect of the air gap on the pole flux.
When the load is connected, a current – flowing
through the rotor – will generate a magnetic field from
the rotor windings.
24. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
This rotor magnetic field will affect the original
magnetic field from the poles. In some places
under the poles, both fields will sum together, in
other places, they will subtract from each other
Therefore, the net magnetic field will not be
uniform and the neutral plane will be shifted.
In general, the neutral plane shifts in the direction
of motion for a generator and opposite to the
direction of motion for a motor. The amount of the
shift depends on the load of the machine.
25. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
The commutator must short out the commutator segments right at the
moment when the voltage across them is zero. The neutral-plane shift may
cause the brushes short out commutator segments with a non-zero voltage
across them. This leads to arcing and sparkling at the brushes!
26. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
2) Flux weakening.
Most machines operate at flux densities
near the saturation point.
At the locations on the pole surfaces
where the rotor mmf adds to the pole
mmf, only a small increase in flux occurs
(due to saturation).
However, at the locations on the pole
surfaces where the rotor mmf subtracts
from the pole mmf, there is a large
decrease in flux.
Therefore, the total average flux under
the entire pole face decreases.
27. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
Observe a considerable decrease in
the region where two mmfs are
subtracted and a saturation…
In generators, flux weakening
reduces the voltage supplied by a
generator.
In motors, flux weakening leads to
increase of the motor speed.
Increase of speed may increase
the load, which, in turns, results in
more flux weakening. Some shunt
DC motors may reach runaway
conditions this way…
28. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
2. L di/dt voltages
This problem occurs in
commutator segments being
shorten by brushes and is called
sometimes an inductive kick.
Assuming that the current in the
brush is 400 A, the current in
each path is 200 A. When a
commutator segment is shorted
out, the current flow through that
segment must reverse.
Assuming that the machine is
running at 800 rpm and has 50
commutator segments, each
segment moves under the brush
and clears it again in 0.0015 s.
29. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Problems with commutation in
real DC machines
The rate of change in current in the shorted loop averages
400
266 667 /
0.0015
di
A s
dt
Therefore, even with a small
inductance in the loop, a very large
inductive voltage kick L di/dt will be
induced in the shorted commutator
segment.
This voltage causes sparkling at the
brushes.
30. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
1. Commutating poles or interpoles
To avoid sparkling at the brushes while the machine’s load changes, instead of
adjusting the brushes’ position, it is possible to introduce small poles (commutating
poles or interpoles) between the main ones to make the voltage in the commutating
wires to be zero. Such poles are located directly over the conductors being
commutated and provide the flux that can exactly cancel the voltage in the coil
undergoing commutation. Interpoles do not change the operation of the machine
since they are so small that only affect few
conductors being commutated. Flux
weakening is unaffected.
Interpole windings are connected in series
with the rotor windings. As the load increases
and the rotor current increases, the magnitude
of neutral-plane shift and the size of Ldi/dt
effects increase too increasing the voltage in
the conductors undergoing commutation.
31. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
However, the interpole flux increases too producing a larger voltage in the
conductors that opposes the voltage due to neutral-plane shift. Therefore,
both voltages cancel each other over a wide range of loads. This approach
works for both DC motors and generators.
The interpoles must be of the same polarity as the next upcoming main
pole in a generator;
The interpoles must be of the same polarity as the previous main pole in a
motor.
The use of interpoles is very common because they correct the sparkling
problems of DC machines at a low cost. However, since interpoles do
nothing with the flux distribution under the pole faces, flux-weakening
problem is still present.
32. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
2. Compensating windings
The flux weakening problem can be very severe for large DC motors.
Therefore, compensating windings can be placed in slots carved in the
faces of the poles parallel to the rotor conductors. These windings are
connected in series with the rotor windings, so when the load changes in
the rotor, the current in the compensating winding changes too…
33. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
Sum of these three fluxes equals to the
original pole flux.
Pole
flux
Rotor
and
comp.
fluxes
34. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
The mmf due to the compensating
windings is equal and opposite to
the mmf of the rotor. These two
mmfs cancel each other, such that
the flux in the machine is
unchanged.
The main disadvantage of
compensating windings is that
they are expensive since they
must be machined into the
faces of the poles. Also, any
motor with compensative
windings must have interpoles
to cancel L di/dt effects.
35. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Solutions to the problems with
commutation
A stator of a
six-pole DC
machine with
interpoles and
compensating
windings.
pole
interpole
36. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Power flow and losses in DC machines
Unfortunately, not all electrical power is converted to mechanical power by a motor
and not all mechanical power is converted to electrical power by a generator…
The efficiency of a DC machine is:
100%
out
in
P
P
100%
in loss
in
P P
P
or
(5.36.1)
(5.36.2)
37. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The losses in DC machines
There are five categories of losses occurring in DC machines.
1. Electrical or copper losses – the resistive losses in the armature and field
windings of the machine.
Armature loss:
2
A A A
P I R
Field loss:
2
F F F
P I R
(5.37.1)
(5.37.2)
Where IA and IF are armature and field currents and RA and RF are armature and
field (winding) resistances usually measured at normal operating temperature.
38. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The losses in DC machines
2. Brush (drop) losses – the power lost across the contact potential at the
brushes of the machine.
BD BD A
P V I
(5.38.1)
Where IA is the armature current and VBD is the brush voltage drop. The voltage
drop across the set of brushes is approximately constant over a large range of
armature currents and it is usually assumed to be about 2 V.
Other losses are exactly the same as in AC machines…
39. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The losses in DC machines
4. Mechanical losses – losses associated with mechanical effects: friction
(friction of the bearings) and windage (friction between the moving parts of the
machine and the air inside the casing). These losses vary as the cube of rotation
speed n3.
3. Core losses – hysteresis losses and eddy current losses. They vary as B2
(square of flux density) and as n1.5 (speed of rotation of the magnetic field).
5. Stray (Miscellaneous) losses – losses that cannot be classified in any of the
previous categories. They are usually due to inaccuracies in modeling. For many
machines, stray losses are assumed as 1% of full load.
40. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The power-flow diagram
On of the most convenient technique to account for power losses in a
machine is the power-flow diagram.
For a DC
motor:
Electrical power is input to the machine, and the electrical and brush losses must be
subtracted. The remaining power is ideally converted from electrical to mechanical
form at the point labeled as Pconv.
41. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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The power-flow diagram
The electrical power that is converted is
conv A A
P E I
And the resulting mechanical power is
conv ind m
P
After the power is converted to mechanical form, the stray losses, mechanical
losses, and core losses are subtracted, and the remaining mechanical power is
output to the load.
(5.41.1)
(5.41.2)
42. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Equivalent circuit of a DC motor
The armature circuit (the entire
rotor structure) is represented by
an ideal voltage source EA and a
resistor RA. A battery Vbrush in the
opposite to a current flow in the
machine direction indicates brush
voltage drop.
The field coils producing the
magnetic flux are represented by
inductor LF and resistor RF. The
resistor Radj represents an
external variable resistor
(sometimes lumped together with
the field coil resistance) used to
control the amount of current in
the field circuit.
43. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Equivalent circuit of a DC motor
Sometimes, when the brush drop voltage is small, it may be left out. Also, some
DC motors have more than one field coil…
The internal generated voltage in the machine is
A
E K
The induced torque developed by the machine is
ind A
K I
Here K is the constant depending on the design of a particular DC machine (number
and commutation of rotor coils, etc.) and is the total flux inside the machine.
Note that for a single rotating loop K = /2.
(5.43.1)
(5.43.2)
44. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Magnetization curve of a DC machine
The internal generated voltage EA is directly proportional to the flux in the machine
and the speed of its rotation.
The field current in a DC machine produces a field mmf F = NFIF, which produces
a flux in the machine according to the magnetization curve.
or in terms
of internal
voltage vs.
field
current for
a given
speed.
To get the maximum possible power per weight out of the machine, most motors
and generators are operating near the saturation point on the magnetization curve.
Therefore, when operating at full load, often a large increase in current IF may be
needed for small increases in the generated voltage EA.
45. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Motor types: Separately excited
and Shunt DC motors
Separately excited DC motor:
a field circuit is supplied from a
separate constant voltage power
source.
Shunt DC motor:
a field circuit gets its power from the
armature terminals of the motor.
Note: when
the voltage to
the field circuit
is assumed
constant,
there is no
difference
between
them…
For the armature circuit of these motors:
T A A A
V E I R
(5.45.1)
46. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
A terminal characteristic of a machine is a plot of the machine’s output
quantities vs. each other.
For a motor, the output quantities are shaft torque and speed. Therefore, the
terminal characteristic of a motor is its output torque vs. speed.
If the load on the shaft increases, the load torque load will exceed the induced
torque ind, and the motor will slow down. Slowing down the motor will decrease
its internal generated voltage (since EA = K), so the armature current
increases (IA = (VT – EA)/RA). As the armature current increases, the induced
torque in the motor increases (since ind = KIA), and the induced torque will
equal the load torque at a lower speed .
2
T A
ind
V R
K K
(5.46.1)
47. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
Assuming that the terminal voltage and other terms are constant, the motor’s
speed vary linearly with torque.
However, if a motor has an armature reaction, flux-weakening reduces the flux
when torque increases. Therefore, the motor’s speed will increase. If a shunt (or
separately excited) motor has compensating windings, and the motor’s speed
and armature current are known for any value of load, it’s possible to calculate
the speed for any other value of load.
48. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
– Example
Example 5.1: A 50 hp, 250 V, 1200 rpm DC shunt motor with compensating windings
has an armature resistance (including the brushes, compensating windings, and
interpoles) of 0.06 . Its field circuit has a total resistance Radj + RF of 50 , which
produces a no-load speed of 1200 rpm. The shunt field winding has 1200 turns per
pole. a) Find the motor speed when its input current is 100 A.
b) Find the motor speed when its input current is 200 A.
c) Find the motor speed when its input current is 300 A.
d) Plot the motor torque-speed characteristic.
49. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
– Example
The internal generated voltage of a DC machine (with its speed expressed in rpm):
A
E K
Since the field current is constant (both field resistance and VT are constant) and
since there are no armature reaction (due to compensating windings), we
conclude that the flux in the motor is constant. The speed and the internal
generated voltages at different loads are related as
2 2 2
1 1 1
A
A
E K n
E K n
Therefore:
2
2 1
1
A
A
E
n n
E
At no load, the armature current is zero and therefore EA1 = VT = 250 V.
50. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
– Example
a) Since the input current is 100 A, the armature current is
250
100 95
50
T
A L F L
F
V
I I I I A
R
Therefore: 250 95 0.06 244.3
A T A A
E V I R V
and the resulting motor speed is:
2
2 1
1
244.3
1200
250
1173
A
A
E
n n m
E
rp
b) Similar computations for the input current of 200 A lead to n2 = 1144 rpm.
c) Similar computations for the input current of 300 A lead to n2 = 1115 rpm.
d) To plot the output characteristic of the motor, we need to find the torque
corresponding to each speed. At no load, the torque is zero.
51. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
– Example
Since the induced torque at any load is related to the power converted in a DC
motor:
conv A A ind
P E I
the induced torque is
A A
ind
E I
For the input current of 100 A:
2443 95
190
2 1173/ 60
ind N m
-
For the input current of 200 A:
For the input current of 300 A:
2383 195
388
2 1144 / 60
ind N m
-
2323 295
587
2 1115 / 60
ind N m
-
52. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: terminal characteristic
– Example
The torque-speed
characteristic of the motor is:
53. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Nonlinear analysis
The flux and, therefore the internal generated voltage EA of a DC machine are
nonlinear functions of its mmf and must be determined based on the magnetization
curve. Two main contributors to the mmf are its field current and the armature
reaction (if present).
Since the magnetization curve is a plot of the generated voltage vs. field current,
the effect of changing the field current can be determined directly from the
magnetization curve.
If a machine has armature reaction, its flux will reduce with increase in load. The
total mmf in this case will be
net F F AR
N I
F F (5.53.1)
It is customary to define an equivalent field current that would produce the same
output voltage as the net (total) mmf in the machine:
* AR
F F
F
I I
N
F
(5.53.2)
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Shunt motor: Nonlinear analysis
Conducting a nonlinear analysis to determine the internal generated voltage in a
DC motor, we may need to account for the fact that a motor can be running at a
speed other than the rated one.
The voltage induced in a DC machine is
A
E K
For a given effective field current, the flux in the machine is constant and the
internal generated voltage is directly proportional to speed:
0 0
A
A
E n
E n
Where EA0 and n0 represent the reference (rated) values of voltage and speed,
respectively. Therefore, if the reference conditions are known from the magnetization
curve and the actual EA is computed, the actual speed can be determined.
(5.54.1)
(5.54.2)
55. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Nonlinear analysis –
Example
Example 5.2: A 50 hp, 250 V, 1200 rpm DC shunt motor without compensating
windings has an armature resistance (including the brushes and interpoles) of 0.06
. Its field circuit has a total resistance Radj + RF of 50 , which produces a no-load
speed of 1200 rpm. The shunt field winding has 1200 turns per pole. The armature
reaction produces a demagnetizing mmf of 840 A-turns at a load current of 200A.
The magnetization curve is shown.
a) Find the motor speed when its input
current is 200 A.
b) How does the motor speed compare to
the speed of the motor from Example 5.1
(same motor but with compensating
windings) with an input current of 200 A?
c) Plot the motor torque-speed
characteristic.
56. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Nonlinear analysis –
Example
a) Since the input current is 200 A, the armature current is
250
200 195
50
T
A L F L
F
V
I I I I A
R
Therefore: 250 195 0.06 238.3
A T A A
E V I R V
At the given current, the demagnetizing mmf due to armature reaction is 840 A-
turns, so the effective shunt field current of the motor is
0
0
238.3
1200
2
1227
33
A
A
r
E
pm
n n
E
* 840
5 4.3
1200
AR
F F
F
I I A
N
F
From the magnetization curve, this effective field current will produce an internal
voltage of EA0 = 233 V at a speed of 1200 rpm. For the actual voltage, the speed is
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Shunt motor: Nonlinear analysis –
Example
b) A speed of a motor with compensating windings was 1144 rpm when the input
current was 200 A. We notice that the speed of the motor with armature reactance
is higher than the speed of the motor without armature reactance. This increase is
due to the flux weakening.
c) Assuming that the mmf due to
the armature reaction varies
linearly with the increase in current,
and repeating the same
computations for many different
load currents, the motor’s torque-
speed characteristic can be plotted.
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Shunt motor: Speed control
There are two methods to control the speed of a shunt DC motor:
1. Adjusting the field resistance RF (and thus the field flux)
2. Adjusting the terminal voltage applied to the armature
1. Adjusting the field resistance
1) Increasing field resistance RF decreases the field current (IF = VT/RF);
2) Decreasing field current IF decreases the flux ;
3) Decreasing flux decreases the internal generated voltage (EA = K);
4) Decreasing EA increases the armature current (IA = (VT – EA)/RA);
5) Changes in armature current dominate over changes in flux; therefore,
increasing IA increases the induced torque (ind = KIA);
6) Increased induced torque is now larger than the load torque load and, therefore,
the speed increases;
7) Increasing speed increases the internal generated voltage EA;
8) Increasing EA decreases the armature current IA…
9) Decreasing IA decreases the induced torque until ind = load at a higher speed .
59. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Speed control
The effect of increasing the field
resistance within a normal load
range: from no load to full load.
Increase in the field resistance
increases the motor speed. Observe
also that the slope of the speed-torque
curve becomes steeper when field
resistance increases.
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Shunt motor: Speed control
The effect of increasing the field
resistance with over an entire load
range: from no-load to stall.
At very slow speeds (overloaded
motor), an increase in the field
resistance decreases the speed. In this
region, the increase in armature current
is no longer large enough to
compensate for the decrease in flux.
Some small DC motors used in control circuits may operate at speeds close to stall
conditions. For such motors, an increase in field resistance may have no effect (or
opposite to the expected effect) on the motor speed. The result of speed control by
field resistance is not predictable and, thus, this type of control is not very common.
61. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Speed control
2. Changing the armature voltage
This method implies changing the voltage applied to the armature of the
motor without changing the voltage applied to its field. Therefore, the
motor must be separately excited to use armature voltage control.
Armature
voltage speed
control
62. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Speed control
1) Increasing the armature voltage VA increases the armature current (IA = (VA -
EA)/RA);
2) Increasing armature current IA increases the induced torque ind (ind = KIA);
3) Increased induced torque ind is now larger than the load torque load and,
therefore, the speed ;
4) Increasing speed increases the internal generated voltage (EA = K);
5) Increasing EA decreases the armature current IA…
6) Decreasing IA decreases the induced torque until ind = load at a higher speed .
Increasing the armature voltage of a
separately excited DC motor does not
change the slope of its torque-speed
characteristic.
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Shunt motor: Speed control
If a motor is operated at its rated terminal voltage, power, and field current, it will be
running at the rated speed also called a base speed.
Field resistance control can be used for speeds above the base speed but not
below it. Trying to achieve speeds slower than the base speed by the field circuit
control, requires large field currents that may damage the field winding.
Since the armature voltage is limited to its rated value, no speeds exceeding the
base speed can be achieved safely while using the armature voltage control.
Therefore, armature voltage control can be used to achieve speeds below the base
speed, while the field resistance control can be used to achieve speeds above the
base speed.
Shunt and separately excited DC motors have excellent speed control
characteristic.
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Shunt motor: Speed control
For the armature voltage control, the flux in the motor is constant. Therefore, the
maximum torque in the motor will be constant too regardless the motor speed:
max ,max
A
K I
(5.64.1)
Since the maximum power of the motor is
max max
P
(5.64.2)
The maximum power out of the motor is directly proportional to its speed.
For the field resistance control, the maximum power out of a DC motor is
constant, while the maximum torque is reciprocal to the motor speed.
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Shunt motor: Speed control
Torque and power limits as functions of motor speed for a shunt (or separately
excited) DC motor.
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Shunt motor: Speed control: Ex
Example 5.3: A 100 hp, 250 V, 1200 rpm DC shunt motor with an armature
resistance of 0.03 and a field resistance of 41.67 . The motor has compensating
windings, so armature reactance can be ignored. Mechanical and core losses may
be ignored also. The motor is driving a load with a line current of 126 A and an initial
speed of 1103 rpm. Assuming that the armature current is constant and the
magnetization curve is
a) What is the motor speed if the field
resistance is increased to 50 ?
b) Calculate the motor speed as a function
of the field resistance, assuming a
constant-current load.
c) Assuming that the motor next is
connected as a separately excited and is
initially running with VA = 250 V, IA = 120 A
and at n = 1103 rpm while supplying a
constant-torque load, estimate the motor
speed if VA is reduced to 200 V.
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Shunt motor: Speed control: Ex
shunt separately-excited
For the given initial line current of 126 A, the initial armature current will be
1 1 1
250
126 120
41.67
A L F
I I I A
Therefore, the initial generated voltage for the shunt motor will be
1 1 250 120 0.03 246.4
A T A A
E V I R V
68. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Speed control: Ex
After the field resistance is increased to 50 Ω, the new field current will be
2
250
5
50
F
I A
The ratio of the two internal generated voltages is
2 2 2 2 2
1 1 1 1 1
A
A
E K n
E K n
Since the armature current is assumed constant, EA1 = EA2 and, therefore
1 1
2
2
n
n
The values of EA on the magnetization curve are directly proportional to the flux.
Therefore, the ratio of internal generated voltages equals to the ratio of the fluxes
within the machine. From the magnetization curve, at IF = 5A, EA1 = 250V, and at
IF = 6A, EA1 = 268V. Thus:
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Shunt motor: Speed control: Ex
1 1 1 1
2
2 2
268
1103 1187
250
A
A
n E n
n rpm
E
b) A speed vs. RF characteristic
is shown below:
70. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Shunt motor: Speed control: Ex
c) For a separately excited motor, the initial generated voltage is
1 1 1
A T A A
E V I R
2 2 2 2 2
1 1 1 1 1
A
A
E K n
E K n
Since
and since the flux is constant
2 1
2
1
A
A
E n
n
E
Since the both the torque and the flux are constants, the armature current IA is
also constant. Then
2 2
2 1
1 1
200 120 0.03
1103 879
250 120 0.03
T A A
T A A
V I R
n n rpm
V I R
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Shunt motor: The effect of an
open field circuit
If the field circuit is left open on a shunt motor, its field resistance will be
infinite. Infinite field resistance will cause a drastic flux drop and, therefore,
a drastic drop in the generated voltage. The armature current will be
increased enormously increasing the motor speed.
A similar effect can be caused by armature reaction. If the armature
reaction is severe enough, an increase in load can weaken the flux
causing increasing the motor speed. An increasing motor speed increases
its load, which increases the armature reaction weakening the flux again.
This process continues until the motor overspeeds. This condition is called
runaway.
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Motor types: The permanent-magnet
DC motor
A permanent magnet DC (PMDC) motor is a motor whose poles are
made out of permanent magnets.
Advantages:
1. Since no external field circuit is needed, there are no field circuit copper
losses;
2. Since no field windings are needed, these motors can be considerable
smaller.
Disadvantages:
1. Since permanent magnets produces weaker flux
densities then externally supported shunt fields,
such motors have lower induced torque.
2. There is always a risk of demagnetization from
extensive heating or from armature reaction
effects (via armature mmf).
73. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Motor types: The permanent-
magnet DC motor
Normally (for cores), a ferromagnetic
material is selected with small residual
flux Bres and small coercive
magnetizing intensity HC.
However, a maximally large residual
flux Bres and large coercive
magnetizing intensity HC are desirable
for permanent magnets forming the
poles of PMDC motors…
74. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Motor types: The permanent-
magnet DC motor
A comparison of magnetization
curves of newly developed
permanent magnets with that of a
conventional ferromagnetic alloy
(Alnico 5) shows that magnets made
of such materials can produce the
same residual flux as the best
ferromagnetic cores.
Design of permanent-magnet DC
motors is quite similar to the design
of shunt motors, except that the flux
of a PMDC motor is fixed.
Therefore, the only method of speed
control available for PMDC motors
is armature voltage control.
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Motor types: The series DC motor
A series DC motor is a DC motor whose field windings consists of a
relatively few turns connected in series with armature circuit. Therefore:
( )
T A A A s
V E I R R
(5.75.1)
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Series motor: induced torque
The terminal characteristic of a series DC motor is quite different from that of the
shunt motor since the flux is directly proportional to the armature current
(assuming no saturation). An increase in motor flux causes a decrease in its
speed; therefore, a series motor has a dropping torque-speed characteristic.
The induced torque in a series machine is
(5.76.1)
ind A
K I
Since the flux is proportional to the armature current:
A
cI
(5.76.2)
where c is a proportionality constant. Therefore, the torque is
2
ind A
KcI
(5.76.3)
Torque in the motor is proportional to the square of its armature current. Series
motors supply the highest torque among the DC motors. Therefore, they are used
as car starter motors, elevator motors etc.
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Series motor: terminal characteristic
Assuming first that the magnetization curve is linear and no saturation occurs, flux
is proportional to the armature current:
A
cI
Since the armature current is
ind
A
I
Kc
and the armature voltage A
E K
The Kirchhoff’s voltage law would be
( ) ind
T A A A S A S
V E I R R K R R
Kc
2 2
ind A
K
KcI
c
(5.77.1)
(5.77.2)
(5.77.3)
(5.77.4)
(5.77.5)
Since (5.77.1), the torque:
78. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Series motor: terminal characteristic
Therefore, the flux in the motor is
ind
c
K
The voltage equation (5.77.4) then becomes
ind
T ind A S
c
V K R R
K Kc
(5.78.1)
(5.78.2)
which can be solved for the speed:
1 A S
T
ind
R R
V
Kc
Kc
(5.78.3)
The speed of unsaturated series motor inversely proportional
to the square root of its torque.
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Series motor: terminal characteristic
One serious disadvantage of
a series motor is that its
speed goes to infinity for a
zero torque.
In practice, however, torque
never goes to zero because
of the mechanical, core, and
stray losses. Still, if no other
loads are attached, the
motor will be running fast
enough to cause damage.
Steps must be taken to ensure that a series motor always has a load! Therefore,
it is not a good idea to connect such motors to loads by a belt or other mechanism
that could break.
80. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Series motor: terminal
characteristic – Example
Example 5.4: A 250 V series DC motor with compensating windings has a total
series resistance RA + RS of 0.08 . The series field consists of 25 turns per pole
and the magnetization curve is
a) Find the speed and induced
torque of this motor when its
armature current is 50 A.
b) Calculate and plot its torque-
speed characteristic.
a) To analyze the behavior of a series
motor with saturation, we pick points
along the operating curve and find the
torque and speed for each point. Since
the magnetization curve is given in
units of mmf (ampere-turns) vs. EA for
a speed of 1200 rpm, calculated
values of EA must be compared to
equivalent values at 1200 rpm.
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Series motor: terminal
characteristic – Example
For IA = 50 A
( ) 250 50 0.08 246
A T A A S
E V I R R V
Since for a series motor IA = IF = 50 A, the mmf is
25 50 1250
NI A turns
F
From the magnetization curve, at this mmf, the internal generated voltage is
EA0 = 80 V. Since the motor has compensating windings, the correct speed of the
motor will be
0
0
246
1200 3690
80
A
A
E
n n rpm
E
The resulting torque:
246 50
31.8
3690 2 60
A A
ind
E I
N m
-
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Series motor: terminal
characteristic – Example
b) The complete torque-
speed characteristic
We notice severe over-
speeding at low torque
values.
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Series motor: Speed control
The only way to control speed of a series DC motor is by
changing its terminal voltage, since the motor speed is
directly proportional to its terminal voltage for any given
torque.
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Motor types: Compounded DC motor
A compounded DC motor is a motor with both a shunt and a series field.
Long-shunt
connection
Short-shunt
connection
Current flowing into a dotted
end of a coil (shunt or
series) produces a positive
mmf.
If current flows into the
dotted ends of both coils, the
resulting mmfs add to
produce a larger total mmf –
cumulative compounding.
If current flows into the dotted end of
one coil and out of the dotted end of
another coil, the resulting mmfs
subtract – differential compounding.
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Motor types: Compounded DC motor
The Kirchhoff’s voltage law equation for a compounded DC motor is
T A A A S
V E I R R
The currents in a compounded DC motor are
A L F
T
F
F
I I I
V
I
R
The mmf of a compounded DC motor:
net F SE AR
F F F F
Cumulatively compounded
Differentially compounded
The effective shunt field current in a compounded DC motor:
* SE AR
F F A
F F
N
I I I
N N
F
Number of turns
(5.85.1)
(5.85.2)
(5.85.3)
(5.85.4)
(5.85.5)
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Cumulatively compounded motors:
torque-speed characteristic
In a cumulatively compounded motor, there is a constant component of flux and a
component proportional to the armature current (and thus to the load). These motors
have a higher starting torque than shunt motors (whose flux is constant) but lower
than series motors (whose flux is proportional to the armature current).
The series field has a small effect at light loads – the motor behaves as a shunt
motor. The series flux becomes quite large at large loads – the motor acts like a
series motor.
Similar (to the previously discussed)
approach is used for nonlinear analysis of
compounded motors.
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Differentially compounded motors:
torque-speed characteristic
Since the shunt mmf and series mmf subtract from each other in a differentially
compounded motor, increasing load increases the armature current IA and
decreases the flux. When flux decreases, the motor speed increases further
increasing the load. This results in an instability (much worse than one of a shunt
motor) making differentially compounded motors unusable for any applications.
In addition to that, these motors are not
easy to start… The motor typically
remains still or turns very slowly
consuming enormously high armature
current.
Stability problems and huge starting
armature current lead to these motors
being never used intentionally.
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Compounded DC motor: Example
Example 5.5: A 100 hp, 250 V compounded DC motor with compensating windings
has an internal resistance, including the series winding of 0.04 . There are 1000
turns per pole on the shunt field and 3 turns per pole on the series windings. The
magnetization curve is shown below.
The field resistor has been adjusted for the
motor speed of 1200 rpm. The mechanical,
core, and stray losses may be neglected.
a) Find the no-load shunt field current.
Find the speed at IA = 200 A if the motor is b)
cumulatively; c) differentially compounded
89. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Compounded DC motor: Example
a) At no load, the armature current is zero; therefore, the internal generated voltage
equals VT = 250 V. From the magnetization curve, a field current of 5 A will produce
a voltage EA = 250 V at 1200 rpm. Therefore, the shunt field current is 5 A.
b) When the armature current is 200 A, the internal generated voltage is
( ) 250 200 0.04 242
A T A A S
E V I R R V
The effective field current of a cumulatively compounded motor will be
* 3
5 200 5.6
1000
SE AR
F F A
F F
N
I I I A
N N
F
From the magnetization curve, EA0 = 262 V at speed n0 = 1200 rpm. The actual
motor speed is
0
0
242
1200 1108
262
A
A
E
n n rpm
E
90. ELEN 3441 Fundamentals of Power Engineering Spring 2008
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Compounded DC motor: Example
c) The effective field current of a differentially compounded motor will be
* 3
5 200 4.4
1000
SE AR
F F A
F F
N
I I I A
N N
F
From the magnetization curve, EA0 = 236 V at speed n0 = 1200 rpm. The actual
motor speed is
0
0
242
1200 1230
236
A
A
E
n n rpm
E
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Cumulatively compounded
motors: speed control
The same two techniques that have been discussed for a shunt motor
are also available for speed control of a cumulatively compounded
motor.
1. Adjusting the field resistance RF;
2. Adjusting the armature voltage VA.
The details of these methods are very similar to already discussed for
shunt DC motors.
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DC motor starters
In order for DC motors to function properly, they must have some
special control and protection equipment associated with them. The
purposes of this equipment are:
1. To protect the motor against damage due to short
circuits in the equipment;
2. To protect the motor against damage from long-term
overloads;
3. To protect the motor against damage from excessive
starting currents;
4. To provide a convenient manner in which to control the
operating speed of the motor.
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DC motor problems on starting
At starting conditions, the motor is not turning, therefore the internal
generated voltage EA = 0V. Since the internal resistance of a normal DC
motor is very low (3-6 % pu), a very high current flows.
For instance, for a 50 hp, 250 V DC motor with armature resistance RA of 0.06
and a full-load current about 200 A, the starting current is
250 0
4167
0.06
T A
A
A
V E
I A
R
This current is over 20 times the motor’s rated full-load current and may severely
damage the motor.
A solution to the problem of excessive starting current is to insert a starting
resistor in series with the armature to limit the current until EA can build up to limit
the armature current. However, this resistor must be removed from the circuit as
the motor speed is high since otherwise such resistor would cause losses and
would decrease the motor’s torque-speed characteristic.
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DC motor problems on starting
In practice, a starting resistor is made up of a series of resistors that can be
successively removed from the circuit as the motor speeds up.
A shunt motor with an extra
starting resistor that can be cut out
of the circuit in segments by
closing the 1A, 2A, and 3A
contacts.
Therefore, two considerations are
needed to be taken into account:
Select the values and the number
of resistor segments needed to
limit the starting current to desired
ranges; Design a control circuit shutting the resistor bypass contacts at the proper
time to remove particular parts of the resistor from the circuit.
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DC motor problems on starting: Ex
Example 5.6: A 100 hp, 250 V 350 A shunt DC motor with an armature resistance of
0.05 needs a starter circuit that will limit the max starting current to twice its rated
value and which will switch out sections of resistor once the armature current
decreases to its rated value.
a. How many stages of starting
resistance will be required to limit
the current to the specified
range?
b. What must the value of each
segment of the resistor to be? At
what voltage should each stage
of the starting resistance be cut
out?
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DC motor problems on starting: Ex
a. The starting resistor must be selected such that the current flow at the start
equals twice the rated current. As the motor speeds up, an internal voltage EA
(which opposes the terminal voltage of the motor and, therefore, limits the current)
is generated. When the current falls to the rated value, a section of the starting
resistor needs to be taken out to increase the current twice. This process (of
taking out sections of the starting resistor) repeats until the entire starting
resistance is removed. At this point, the motor’s armature resistance will limit the
current to safe values by itself.
The original resistance in the starting circuit is
1 2
max
... T
tot A
V
R R R R
I
After the stages 1 through i are shorted out, the total resistance left in the starting
circuit is
, 1 ...
tot i i A
R R R
97. ELEN 3441 Fundamentals of Power Engineering Spring 2008
97
DC motor problems on starting: Ex
The resistance R1 must be switched out of the circuit when the armature current
falls to
,1
,min min 350
T A
A
tot
V E
I I A
R
After the resistance R1 is out of the circuit, the armature current must increase to
,2
,max max
,1
700
T A
A
tot
V E
I I A
R
Since EA = K, the quantity VT – EA must be constant when the resistance is
switched out. Therefore
min max ,1
tot T A tot
I R V E I R
The resistance left in the circuit is
min min
,
max
,1
max
tot t
n
tot n t
t o
o t
I
R R
I
I
R R
I
98. ELEN 3441 Fundamentals of Power Engineering Spring 2008
98
DC motor problems on starting: Ex
The starting process is completed when Rtot,n is not greater than the internal
armature resistance RA. At the boundary:
min
,
max
n
A tot n tot
I
R R R
I
Solving for n:
min max
log
log
A tot
R R
n
I I
Notice that the number of stages n must be rounded up to the next integer.
max
250
0.357
700
T
tot
V
R
I
min max
log log 0.05 0.357
2.84
log log 350 700
3
A tot
R R
n
I I
99. ELEN 3441 Fundamentals of Power Engineering Spring 2008
99
DC motor problems on starting: Ex
b. The armature circuit will contain the armature resistance RA and three starting
resistors. At first, EA = 0, IA = 700 A, and the total resistance is 0.357 . The total
resistance will be in the circuit until the current drops to 350 A. This occurs when
,1 ,min 250 350 0.357 125
A T A tot
E V I R V
At this time, the starting resistor R1 will be taken out making
,1
,1 2 3
max
250 125
0.1786
700
T A
tot A
V E
R R R R
I
This (new) total resistance will be in the circuit until the current drops again to 350
A. This occurs when
,2 ,min ,1 250 350 0.1786 187.5
A T A tot
E V I R V
At this time, the starting resistor R2 will be taken out leaving
,2
,2 3
max
250 187.5
0.0893
700
T A
tot A
V E
R R R
I
100. ELEN 3441 Fundamentals of Power Engineering Spring 2008
100
DC motor problems on starting: Ex
This total resistance will be in the circuit until the current drops again to 350 A. This
occurs when
,3 ,min ,2 250 350 0.0893 218.75
A T A tot
E V I R V
At this time, the starting resistor R3 will be taken out leaving only RA in the circuit.
The motor’s current at that moment will increase to
,3
,3
250 218.75
625
0.05
T A
A
A
V E
I A
R
which is less than the allowed value. Therefore, the resistances are
3 ,3
2 ,2 3
1 ,1 2 3
0.0893 0.05 0.0393
0.1786 0.0393 0.05 0.0893
0.357 0.1786 0.0393 0.05 0.1786
tot A
tot A
tot A
R R R
R R R R
R R R R R
The resistors R1, R2, and R3 are cut out when EA reaches 125 V, 187.5 V, and
218.75 V, respectively.
101. ELEN 3441 Fundamentals of Power Engineering Spring 2008
101
DC motor starting circuits
Several different schemes can be used to short contacts and cut out the sections
of a starting resistor. Some devices commonly used in motor-control circuits are
Fuses:
protects
against short
circuits
Spring-type push button switches
Relay: a
main coil
and a
number of
contacts
Time delay
relay similar to
ordinary relay
except for
having
adjustable
time delay.
Overload: a
heater coil
and normally
closed
contacts
102. ELEN 3441 Fundamentals of Power Engineering Spring 2008
102
DC motor starting circuits
A common DC motor starting circuit:
A series of time delay relays shut contacts
removing each section of the starting resistor at
approximately correct times.
Notice that the relay 1TD is energized at the
same time as the motor starts – contacts of 1TD
will shut a part of the starting resistor after some
time. At the same instance, relay 2TD is
energized and so on…
Observe also 4 fuses protecting different parts of
the circuit and the overload in series with the
armature winding.
103. ELEN 3441 Fundamentals of Power Engineering Spring 2008
103
DC motor starting circuits
Armature
current in a
DC motor
during
starting.
Another type of motor starter:
A series of relays sense the value of armature
voltage EA and cut out the starting resistors as it
riches certain values.
This starter type is more robust to different loads.
FL is the field loss relay: if the field is lost for any
reason, power to the M relay will be turned off.
104. ELEN 3441 Fundamentals of Power Engineering Spring 2008
104
DC motor efficiency calculations
To estimate the efficiency of a DC motor, the following losses must be determined:
1. Copper losses;
2. Brush drop losses;
3. Mechanical losses;
4. Core losses;
5. Stray losses.
To find the copper losses, we need to know the currents in the motor and two
resistances. In practice, the armature resistance can be found by blocking the rotor
and a small DC voltage to the armature terminals: such that the armature current
will equal to its rated value. The ratio of the applied voltage to the armature current
is approximately RA.
The field resistance is determined by supplying the full-rated field voltage to the
field circuit and measuring the resulting field current. The field voltage to field
current ratio equals to the field resistance.
105. ELEN 3441 Fundamentals of Power Engineering Spring 2008
105
DC motor efficiency calculations
Brush drop losses are frequently lumped together with copper losses. If treated
separately, brush drop losses are a product of the brush voltage drop VBD and the
armature current IA.
The core and mechanical losses are usually determined together. If a motor is
running freely at no load and at the rated speed, the current IA is very small and the
armature copper losses are negligible. Therefore, if the field copper losses are
subtracted from the input power of the motor, the remainder will be the mechanical
and core losses. These two losses are also called the no-load rotational losses. As
long as the motor’s speed remains approximately the same, the no-load rotational
losses are a good estimate of mechanical and core losses in the machine under
load.