Motoring and generation
Armature circuit equation for motoring and generation,
Types of field excitations - separately excited, shunt and series.
Open circuit characteristic of separately excited DC generator,
back EMF with armature reaction,
voltage build-up in a shunt generator,
critical field resistance and critical speed.
V-I characteristics and torque-speed characteristics of separately excited shunt and series motors.
Speed control through armature voltage.
Losses, load testing and back-to-back testing of DC machines
1) A DC motor works by applying a magnetic field to a coil attached to a rotor. When current flows through the coil, it experiences an electromagnetic force that causes it to rotate.
2) As the coil rotates, commutator rings switch the direction of current to ensure the torque always acts in the same direction, causing continuous rotation.
3) For smoother rotation, practical DC motors have multiple coils around the rotor connected to separate commutators. This keeps a magnetic force present at all times during rotation.
A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings. It generates torque through magnetic reluctance.
Reluctance motor sub types include synchronous, variable, switched and variable stepping.
Reluctance motors can deliver high power density at low cost, making them attractive for many applications. Disadvantages include high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and noise due to torque ripple.
The document discusses various methods for starting 3-phase induction motors. It describes five main methods: 1) direct-on-line starting, 2) stator resistance starting, 3) autotransformer starting, 4) star-delta starting, and 5) rotor resistance starting. Direct-on-line starting applies full voltage at start and is suitable for small motors. Stator resistance and autotransformer starting reduce starting voltage to limit current. Star-delta switching changes the winding configuration. Rotor resistance starting adds external resistors in the rotor circuit for slip ring motors.
This document provides an overview of stepper motors, including:
- Their working principle is that they rotate through discrete angular steps in response to input current pulses. They come in different types like permanent magnet, variable reluctance, and hybrid.
- Applications include computer peripherals, textile machines, robotics, printers, drives, machine tools, and process controls where incremental motion is required.
- Advantages are low cost, high reliability, and high torque at low speeds. Disadvantages include resonance effects at low speeds and decreasing torque with increasing speed.
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
The document discusses synchronous motors. It begins by introducing synchronous motors and explaining that their rotor rotates at the synchronous speed of the rotating magnetic field. It then describes how changing the load affects the motor's operation and discusses the motor's lack of starting torque. It proposes improvements to the starting torque using a squirrel cage rotor. Finally, it provides details on the typical construction of a synchronous machine, including laminated stator cores and projected pole rotors.
Hey i'm DIVYA SHREE NANDINI. I'm here to present my topic on INDUCTION MOTOR. An INDUCTION MOTOR is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction. Wanna know more about it then check it out. If you've any queries about it then you can ask me. Thank You! :)
An AC motor has a stationary stator with coils that produce a rotating magnetic field. The inner rotor is given torque by this field. There are two main types - induction motors which rely on induction to induce rotor currents, and synchronous motors which rotate at the exact supply frequency. Squirrel cage rotors consist of embedded conductors in steel and are widely used. Three-phase induction motors are economical and rugged for industrial drives. They work by the rotating stator field inducing currents in the rotor to generate torque and rotate it slightly slower than the field.
1) A DC motor works by applying a magnetic field to a coil attached to a rotor. When current flows through the coil, it experiences an electromagnetic force that causes it to rotate.
2) As the coil rotates, commutator rings switch the direction of current to ensure the torque always acts in the same direction, causing continuous rotation.
3) For smoother rotation, practical DC motors have multiple coils around the rotor connected to separate commutators. This keeps a magnetic force present at all times during rotation.
A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings. It generates torque through magnetic reluctance.
Reluctance motor sub types include synchronous, variable, switched and variable stepping.
Reluctance motors can deliver high power density at low cost, making them attractive for many applications. Disadvantages include high torque ripple (the difference between maximum and minimum torque during one revolution) when operated at low speed, and noise due to torque ripple.
The document discusses various methods for starting 3-phase induction motors. It describes five main methods: 1) direct-on-line starting, 2) stator resistance starting, 3) autotransformer starting, 4) star-delta starting, and 5) rotor resistance starting. Direct-on-line starting applies full voltage at start and is suitable for small motors. Stator resistance and autotransformer starting reduce starting voltage to limit current. Star-delta switching changes the winding configuration. Rotor resistance starting adds external resistors in the rotor circuit for slip ring motors.
This document provides an overview of stepper motors, including:
- Their working principle is that they rotate through discrete angular steps in response to input current pulses. They come in different types like permanent magnet, variable reluctance, and hybrid.
- Applications include computer peripherals, textile machines, robotics, printers, drives, machine tools, and process controls where incremental motion is required.
- Advantages are low cost, high reliability, and high torque at low speeds. Disadvantages include resonance effects at low speeds and decreasing torque with increasing speed.
A synchronous motor is electrically identical with an alternator or AC generator.
A given alternator ( or synchronous machine) can be used as a motor, when driven electrically.
Some characteristic features of a synchronous motor are as follows:
1. It runs either at synchronous speed or not at all i.e. while running it maintains a constant speed. The only way to change its speed is to vary the supply frequency (because NS=120f/P).
2. It is not inherently self-starting. It has to be run up to synchronous (or near synchronous) speed by some means, before it can be synchronized to the supply.
3. It is capable of being operated under a wide range of power factors, both lagging and leading. Hence, it can be used for power correction purposes, in addition to supplying torque to drive loads.
The document discusses synchronous motors. It begins by introducing synchronous motors and explaining that their rotor rotates at the synchronous speed of the rotating magnetic field. It then describes how changing the load affects the motor's operation and discusses the motor's lack of starting torque. It proposes improvements to the starting torque using a squirrel cage rotor. Finally, it provides details on the typical construction of a synchronous machine, including laminated stator cores and projected pole rotors.
Hey i'm DIVYA SHREE NANDINI. I'm here to present my topic on INDUCTION MOTOR. An INDUCTION MOTOR is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction. Wanna know more about it then check it out. If you've any queries about it then you can ask me. Thank You! :)
An AC motor has a stationary stator with coils that produce a rotating magnetic field. The inner rotor is given torque by this field. There are two main types - induction motors which rely on induction to induce rotor currents, and synchronous motors which rotate at the exact supply frequency. Squirrel cage rotors consist of embedded conductors in steel and are widely used. Three-phase induction motors are economical and rugged for industrial drives. They work by the rotating stator field inducing currents in the rotor to generate torque and rotate it slightly slower than the field.
1. The document discusses DC machines and their components. It describes how a DC machine contains a stator and rotor.
2. The commutator is described as a mechanical rectifier that converts the alternating voltage generated in the armature winding into direct voltage across the brushes.
3. The brushes provide an electrical connection between the rotating commutator and the stationary external load circuit.
The universal motor can operate on either AC or DC power sources. It is modified slightly from a DC series motor to allow proper operation on AC, such as adding a compensating winding and using laminated pole pieces. Universal motors are commonly used in appliances and power tools where high speed and torque are needed. They have advantages of simple construction and cost effectiveness.
The document summarizes the synchronous machine. It describes how synchronous machines can operate as generators or motors and are used in large power applications. The rotor rotates at a constant synchronous speed and its magnetic field rotates in sync with the stator magnetic field. Common applications include power generation, pumps, timers and mills. The document then focuses on the synchronous generator, describing its construction, types of rotors and windings, voltage generation process, equivalent circuit model and phasor diagrams under different load conditions. An example problem is also included to illustrate voltage and current calculations.
This document summarizes the key aspects of three phase synchronous motors. It discusses the working principle, construction, features, principle of operation, methods of starting, excitation, phasor diagram, applications, and disadvantages. Synchronous motors operate at a constant synchronous speed determined by supply frequency. They require an external starting mechanism and DC excitation of the rotor. The motor can operate at lagging, unity, or leading power factors depending on the level of excitation. Main applications are in machine tools and industrial machinery due to their constant speed characteristic. Disadvantages include higher cost and need for auxiliary starting components compared to induction motors.
STARTING AND SPEED CONTROL OF THREE PHASE INDUCTION MOTORRagulS61
– Separation of no load losses –Need for starters – Types of starters: Stator resistance, Rotor resistance, Autotransformer, Star-delta starters and DOL starters– Soft starters – Speed control by varying voltage, frequency, poles and rotor resistance – Slip power recovery scheme.
Brushless DC motors have magnets inside the rotor and coils outside in the stator. They use electronic commutation rather than brushes to switch the current through the coils to rotate the motor. They have advantages over brushed DC motors like increased reliability, efficiency, and lifespan due to eliminating sparks from the commutator. However, they require more complex drive circuitry and position sensors. Applications include consumer goods like fans, tools, and toys as well as medical devices like artificial hearts and surgical tools.
This document discusses different types of DC generators, including permanent magnet, separately excited, and self-excited generators. It focuses on self-excited DC generators, which can be series wound, shunt wound, or compound wound. The document provides details on the magnetic or open circuit characteristic curve, which shows the relationship between field current and generated voltage without a load. It also discusses the internal and external characteristic curves when the generator is loaded, accounting for voltage drops due to armature reaction and ohmic losses. Characteristics of series wound and shunt wound generators are covered as well.
The document discusses different types of AC motors including induction motors and synchronous motors. It provides details on their construction, working principles, starting methods, torque characteristics and applications. Some key points covered are:
- Induction motors are the most commonly used AC motors due to their simple and rugged construction. They operate at a slightly lower speed than synchronous speed.
- Synchronous motors rotate exactly at the synchronous speed of the rotating magnetic field. They cannot be started directly and require an external prime mover to start.
- Both induction and synchronous motors require maintenance like cleaning electrical connections and checking for overheating to ensure safe and efficient operation.
This document outlines and compares two types of synchronous machines - cylindrical rotor type and salient pole rotor type generators. It describes their construction, working principles, types, and applications. The key differences are that cylindrical rotor type generators have a smooth cylindrical rotor, uniform air gap, operate at high speeds of 1000-3000 RPM, and are used in thermal and gas turbine power plants. Salient pole rotor type generators have projecting poles, non-uniform air gap, larger diameter and operate at lower speeds of 100-500 RPM, often driven by engines.
This document discusses electromagnetic induction and Faraday's law. It explains that magnetic fields have flux lines that run from the North to South pole of a magnet. The flux Φ is calculated as BA sinθ and represents the strength of the magnetic field times the area it passes through. Faraday's law states that an electromotive force (EMF) is induced in a conductor when it passes through a changing magnetic flux. The EMF is directly proportional to the rate of change of flux linkage over time. For a coil of N turns, the EMF induced is equal to -N * (change in flux linkage over time).
This document discusses special electrical machines, specifically permanent magnet synchronous motors (PMSM). It describes PMSM as a brushless DC motor with permanent magnets on the rotor that create magnetic poles instead of a field winding. The document outlines the basic construction and working principle of PMSM, noting that a rotating magnetic field from the stator interacts with the permanent rotor magnets to produce torque. Applications mentioned include servo drives, robotics, traction systems, and railway transportation.
This is a presentation about linear induction motor. here I had explained LIM clearly like effects, construction, working, application and many more. most of people don't know much about this type of motor. I hope this will be usefull to you
This document provides information about AC generators. It begins by defining a generator as a device that converts mechanical energy to electrical energy. It then discusses Faraday's law of electromagnetic induction, which explains how a generator works. The key components of an AC generator are described as the field, armature, and prime mover. The construction and operation of a three-phase synchronous generator is explained, including its stator, rotor, and how speed and frequency relate. Advantages of AC generators include ease of voltage transformation while disadvantages include potential hazards from heat generation.
This document discusses ultrasonic motors, which use ultrasonic vibrations from a piezoelectric transducer to generate torque. It describes how they work by establishing a traveling wave on the stator that causes elliptical motion to propel the rotor. Ultrasonic motors are classified based on their mode of operation, type of motion, and shape. Their advantages include compact size, high accuracy, and resistance to electromagnetic fields. Applications include camera autofocus systems, medical equipment, and small robotics. Future work may include using ultrasonic motors in miniature surgical robots.
The document discusses a thermal management approach for fault-resilient design of three-level IGCT-based NPC converters. It analyzes the power device thermal stresses during overcurrent conditions when the firing mode protection is activated. Adding resilience impedances to the clamping diode branches helps restrict short circuit current through the internal IGCTs and limits their thermal stress, protecting the IGCTs even if the circuit breaker fails to operate properly during a fault. This allows damage to be confined to the freewheeling diodes instead of the more expensive IGCTs, reducing repair costs and downtime for the converter.
This presentation describes the per-phase equivalent circuit of induction motor - Power flow diagram - Ratio of air gap power, rotor copper loss and mechanical power developed.
- A DC motor converts electrical energy into mechanical energy through electromagnetic principles. It has a rotor that rotates when current passes through the motor's armature winding within a magnetic field.
- The key components of a DC motor are the armature winding, field winding, commutator, and brushes. The field winding generates a magnetic field and the armature winding cuts this field to produce torque when powered.
- DC motors can be shunt wound, series wound, or compound wound depending on how the field winding is connected in relation to the armature winding. This determines the speed and torque characteristics of the motor.
1) There are several types of losses that reduce the efficiency of DC machines, including electrical or copper losses, core losses, brush losses, mechanical losses, and stray load losses.
2) Electrical losses include losses from the armature winding resistance, shunt field winding resistance, series field winding resistance, and interpole winding resistance.
3) Core losses are hysteresis and eddy current losses and account for around 20% of full load losses.
4) Brush losses are due to the voltage drop and current at the brush contact with the commutator.
1) A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It works on the principle that a changing magnetic field in one coil induces a voltage in a nearby coil.
2) A DC machine can operate as a motor or generator. As a motor, it converts electrical energy into mechanical energy. As a generator, it converts mechanical energy into electrical energy.
3) The key components of a DC machine are the stator, rotor, commutator, and brushes. The stator contains field windings that generate a magnetic field. The rotor contains armature windings. The commutator and brushes convert alternating current from the rotor into direct current.
1. The document discusses DC machines and their components. It describes how a DC machine contains a stator and rotor.
2. The commutator is described as a mechanical rectifier that converts the alternating voltage generated in the armature winding into direct voltage across the brushes.
3. The brushes provide an electrical connection between the rotating commutator and the stationary external load circuit.
The universal motor can operate on either AC or DC power sources. It is modified slightly from a DC series motor to allow proper operation on AC, such as adding a compensating winding and using laminated pole pieces. Universal motors are commonly used in appliances and power tools where high speed and torque are needed. They have advantages of simple construction and cost effectiveness.
The document summarizes the synchronous machine. It describes how synchronous machines can operate as generators or motors and are used in large power applications. The rotor rotates at a constant synchronous speed and its magnetic field rotates in sync with the stator magnetic field. Common applications include power generation, pumps, timers and mills. The document then focuses on the synchronous generator, describing its construction, types of rotors and windings, voltage generation process, equivalent circuit model and phasor diagrams under different load conditions. An example problem is also included to illustrate voltage and current calculations.
This document summarizes the key aspects of three phase synchronous motors. It discusses the working principle, construction, features, principle of operation, methods of starting, excitation, phasor diagram, applications, and disadvantages. Synchronous motors operate at a constant synchronous speed determined by supply frequency. They require an external starting mechanism and DC excitation of the rotor. The motor can operate at lagging, unity, or leading power factors depending on the level of excitation. Main applications are in machine tools and industrial machinery due to their constant speed characteristic. Disadvantages include higher cost and need for auxiliary starting components compared to induction motors.
STARTING AND SPEED CONTROL OF THREE PHASE INDUCTION MOTORRagulS61
– Separation of no load losses –Need for starters – Types of starters: Stator resistance, Rotor resistance, Autotransformer, Star-delta starters and DOL starters– Soft starters – Speed control by varying voltage, frequency, poles and rotor resistance – Slip power recovery scheme.
Brushless DC motors have magnets inside the rotor and coils outside in the stator. They use electronic commutation rather than brushes to switch the current through the coils to rotate the motor. They have advantages over brushed DC motors like increased reliability, efficiency, and lifespan due to eliminating sparks from the commutator. However, they require more complex drive circuitry and position sensors. Applications include consumer goods like fans, tools, and toys as well as medical devices like artificial hearts and surgical tools.
This document discusses different types of DC generators, including permanent magnet, separately excited, and self-excited generators. It focuses on self-excited DC generators, which can be series wound, shunt wound, or compound wound. The document provides details on the magnetic or open circuit characteristic curve, which shows the relationship between field current and generated voltage without a load. It also discusses the internal and external characteristic curves when the generator is loaded, accounting for voltage drops due to armature reaction and ohmic losses. Characteristics of series wound and shunt wound generators are covered as well.
The document discusses different types of AC motors including induction motors and synchronous motors. It provides details on their construction, working principles, starting methods, torque characteristics and applications. Some key points covered are:
- Induction motors are the most commonly used AC motors due to their simple and rugged construction. They operate at a slightly lower speed than synchronous speed.
- Synchronous motors rotate exactly at the synchronous speed of the rotating magnetic field. They cannot be started directly and require an external prime mover to start.
- Both induction and synchronous motors require maintenance like cleaning electrical connections and checking for overheating to ensure safe and efficient operation.
This document outlines and compares two types of synchronous machines - cylindrical rotor type and salient pole rotor type generators. It describes their construction, working principles, types, and applications. The key differences are that cylindrical rotor type generators have a smooth cylindrical rotor, uniform air gap, operate at high speeds of 1000-3000 RPM, and are used in thermal and gas turbine power plants. Salient pole rotor type generators have projecting poles, non-uniform air gap, larger diameter and operate at lower speeds of 100-500 RPM, often driven by engines.
This document discusses electromagnetic induction and Faraday's law. It explains that magnetic fields have flux lines that run from the North to South pole of a magnet. The flux Φ is calculated as BA sinθ and represents the strength of the magnetic field times the area it passes through. Faraday's law states that an electromotive force (EMF) is induced in a conductor when it passes through a changing magnetic flux. The EMF is directly proportional to the rate of change of flux linkage over time. For a coil of N turns, the EMF induced is equal to -N * (change in flux linkage over time).
This document discusses special electrical machines, specifically permanent magnet synchronous motors (PMSM). It describes PMSM as a brushless DC motor with permanent magnets on the rotor that create magnetic poles instead of a field winding. The document outlines the basic construction and working principle of PMSM, noting that a rotating magnetic field from the stator interacts with the permanent rotor magnets to produce torque. Applications mentioned include servo drives, robotics, traction systems, and railway transportation.
This is a presentation about linear induction motor. here I had explained LIM clearly like effects, construction, working, application and many more. most of people don't know much about this type of motor. I hope this will be usefull to you
This document provides information about AC generators. It begins by defining a generator as a device that converts mechanical energy to electrical energy. It then discusses Faraday's law of electromagnetic induction, which explains how a generator works. The key components of an AC generator are described as the field, armature, and prime mover. The construction and operation of a three-phase synchronous generator is explained, including its stator, rotor, and how speed and frequency relate. Advantages of AC generators include ease of voltage transformation while disadvantages include potential hazards from heat generation.
This document discusses ultrasonic motors, which use ultrasonic vibrations from a piezoelectric transducer to generate torque. It describes how they work by establishing a traveling wave on the stator that causes elliptical motion to propel the rotor. Ultrasonic motors are classified based on their mode of operation, type of motion, and shape. Their advantages include compact size, high accuracy, and resistance to electromagnetic fields. Applications include camera autofocus systems, medical equipment, and small robotics. Future work may include using ultrasonic motors in miniature surgical robots.
The document discusses a thermal management approach for fault-resilient design of three-level IGCT-based NPC converters. It analyzes the power device thermal stresses during overcurrent conditions when the firing mode protection is activated. Adding resilience impedances to the clamping diode branches helps restrict short circuit current through the internal IGCTs and limits their thermal stress, protecting the IGCTs even if the circuit breaker fails to operate properly during a fault. This allows damage to be confined to the freewheeling diodes instead of the more expensive IGCTs, reducing repair costs and downtime for the converter.
This presentation describes the per-phase equivalent circuit of induction motor - Power flow diagram - Ratio of air gap power, rotor copper loss and mechanical power developed.
- A DC motor converts electrical energy into mechanical energy through electromagnetic principles. It has a rotor that rotates when current passes through the motor's armature winding within a magnetic field.
- The key components of a DC motor are the armature winding, field winding, commutator, and brushes. The field winding generates a magnetic field and the armature winding cuts this field to produce torque when powered.
- DC motors can be shunt wound, series wound, or compound wound depending on how the field winding is connected in relation to the armature winding. This determines the speed and torque characteristics of the motor.
1) There are several types of losses that reduce the efficiency of DC machines, including electrical or copper losses, core losses, brush losses, mechanical losses, and stray load losses.
2) Electrical losses include losses from the armature winding resistance, shunt field winding resistance, series field winding resistance, and interpole winding resistance.
3) Core losses are hysteresis and eddy current losses and account for around 20% of full load losses.
4) Brush losses are due to the voltage drop and current at the brush contact with the commutator.
1) A transformer is a static electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It works on the principle that a changing magnetic field in one coil induces a voltage in a nearby coil.
2) A DC machine can operate as a motor or generator. As a motor, it converts electrical energy into mechanical energy. As a generator, it converts mechanical energy into electrical energy.
3) The key components of a DC machine are the stator, rotor, commutator, and brushes. The stator contains field windings that generate a magnetic field. The rotor contains armature windings. The commutator and brushes convert alternating current from the rotor into direct current.
Slides of DC Machines with detailed explanationOmer292805
This document provides an overview of DC machines, including DC motors and generators. It discusses the basic components and principles of operation for DC machines. Some key points:
- DC machines convert mechanical energy to electrical energy (generators) or vice versa (motors). They are commonly used to drive industrial loads.
- The main parts are the stator, rotor/armature, commutator, and brushes. The commutator converts the AC voltage in the rotor to DC.
- DC motors operate by applying a DC current to the armature in a magnetic field, producing a torque via the Lorentz force. Speed and torque can be regulated by controlling field and armature circuits.
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This document discusses different types of electric motors. It begins by defining an electric motor as a device that converts electrical energy to mechanical energy. There are two main types of motors - alternating current (AC) motors and direct current (DC) motors. AC motors include synchronous and induction motors, while DC motors can be separately excited, self-excited, or universal motors. The document provides details on the basic design and operation of these different motor types. It also discusses motor efficiency and applications.
Direct-current (DC) machines can operate as motors or generators. They have stationary and rotating parts, with the rotor containing windings connected to a commutator. In a DC motor, current in the rotor windings interacts with the magnetic field from stationary field windings to produce torque. Generators operate on the same principles but convert mechanical power to electrical power by inducing current in the rotor windings. The key characteristics of DC machines include their use of commutation to produce unidirectional current and the orthogonality of magnetic fields from the rotor and field windings.
1. The document discusses DC generators and DC motors, including their operating principles, different types (shunt, series, compound), and methods of speed and torque control.
2. Some key topics covered include separately excited DC generators, armature reaction, back EMF in motors, starting and braking methods for DC motors, and the differences between shunt, series, and compound motor characteristics.
3. The document provides information on DC machines that would be useful for understanding their design and applications.
The document describes a wire rod mill roller table that has three sections, each driven by a separate DC motor powered by a common thyristor converter. It provides details on the roller table components, control equipment, power scheme, motor specifications, and discusses DC motors in general including their construction, principles of operation, classifications, speed control methods, and torque-speed characteristics.
The document describes the roller table of a wire rod mill. It has 3 sections each driven by a separate DC motor powered by a common thyristor converter. Provision is made to run each section independently. The roller table experiences kinks forming in the last few coils of wire rod, negatively impacting production. DC motors are then described as consisting of a stator and rotor that use electromagnetic forces to convert electrical energy into rotational motion.
The document provides an introduction to electrical machines, including their basic structure and operation. It discusses different types of electrical machines such as DC machines, synchronous machines, and induction machines. For DC machines, it describes their construction including the armature, field windings, and commutator. It also discusses the working principles of DC generators and DC motors. For AC machines, it summarizes the working of synchronous generators and induction motors.
This presentation is about the whole pricipal about DC machine. It explain the various important parts of dc machine.It tells about how many types of losses are present in DC machine.
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.
A DC motor converts electrical energy into mechanical energy through electromagnetic induction. When a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force. In a DC motor, this force causes the armature conductors to rotate, producing torque. The motor's magnetic field is produced by a field winding and direct current is supplied by an external DC power source. A three-point starter is used to gradually reduce armature current and limit sparking during startup as motor speed increases and back EMF rises.
Construction DC motor and it applicationMahesh840753
This document provides information about direct current (DC) motors, including their construction, principle of operation, and different types. It will discuss DC motor torque-speed characteristics for shunt wound, series wound, and separately excited motors. The key components of a DC motor like the armature, commutator, and different winding configurations for shunt, series, and separately excited motors will be examined. Calculations of torque, armature voltage, and the performance of different DC motor types will also be covered.
DC machines can operate as motors or generators. They have a commutator that converts the internal alternating current to direct current at the terminals. This allows for easy speed and torque control of DC motors. While DC is no longer widely used by consumers, DC machines were commonly used in industry and transportation due to their versatility and controllability. Advances in solid-state AC drive systems have replaced DC machines in many applications. However, DC machines remain useful due to their simple drive systems and versatility in operating characteristics.
DC machines can operate as motors or generators. They have a commutator that converts the internal alternating current to direct current at the terminals. This allows for easy speed and torque control of DC motors. While DC is no longer widely used by consumers, DC machines were commonly used in industry and transportation due to their versatility and controllability. Advances in solid-state AC drive systems have replaced DC machines in many applications.
A presentation on Electric Motor and its working principle, components, it's classification, types of AC & DC motor, special types of motors & its application.
DC machines can operate from a DC source and either generate mechanical energy (DC generator) or convert mechanical energy to DC electricity (DC motor). A DC machine consists of a yoke, poles, field winding, armature core and winding, and commutator. In a DC motor, current flowing through the armature winding inside the magnetic field generated by the field winding experiences a rotational force, causing the armature to rotate. DC machines can be separately excited, self-excited, or series/compound excited. Common applications include DC motors used in industrial equipment and vehicles.
The document discusses different types of DC generators and alternators used in aircraft. It describes the key components of DC generators including the armature, field coils, commutator, and brushes. It explains how terminal voltage is produced and factors it depends on. It also summarizes different types of DC generators such as shunt-wound, series-wound, and compound generators as well as how they regulate voltage. Finally, it provides an overview of alternators, describing how they work and how rectifiers are used to convert the AC output to DC.
1) A DC generator converts mechanical energy to electrical energy through electromagnetic induction. It produces direct current and is used on light aircraft to power electrical loads and charge batteries.
2) The major components are a frame, rotating armature, and brush assembly. The frame supports the magnetic field windings and other parts. The armature has wire coils wound around an iron core and a commutator to transfer voltage.
3) Generators operate by transforming mechanical energy from rotation into electrical energy via magnets and the rotating armature. Slip rings and brushes transfer this energy from the rotating part to stationary aircraft loads. Proper maintenance is required to ensure security, clean connections and components, and check for issues like worn br
DC Machines with explanation in detail of everythingOmer292805
A DC motor chapter is summarized in 3 sentences:
DC machines can operate as motors or generators and include DC motors which use a DC power source and have a stationary field coil and rotating armature. The speed of a DC motor is proportional to its back EMF and inversely proportional to the armature current. Examples show how to calculate the speed of DC motors under different load conditions by determining the back EMF using the motor's equivalent circuit.
Similaire à DC MACHINE-Motoring and generation, Armature circuit equation (20)
Null Bangalore | Pentesters Approach to AWS IAMDivyanshu
#Abstract:
- Learn more about the real-world methods for auditing AWS IAM (Identity and Access Management) as a pentester. So let us proceed with a brief discussion of IAM as well as some typical misconfigurations and their potential exploits in order to reinforce the understanding of IAM security best practices.
- Gain actionable insights into AWS IAM policies and roles, using hands on approach.
#Prerequisites:
- Basic understanding of AWS services and architecture
- Familiarity with cloud security concepts
- Experience using the AWS Management Console or AWS CLI.
- For hands on lab create account on [killercoda.com](https://killercoda.com/cloudsecurity-scenario/)
# Scenario Covered:
- Basics of IAM in AWS
- Implementing IAM Policies with Least Privilege to Manage S3 Bucket
- Objective: Create an S3 bucket with least privilege IAM policy and validate access.
- Steps:
- Create S3 bucket.
- Attach least privilege policy to IAM user.
- Validate access.
- Exploiting IAM PassRole Misconfiguration
-Allows a user to pass a specific IAM role to an AWS service (ec2), typically used for service access delegation. Then exploit PassRole Misconfiguration granting unauthorized access to sensitive resources.
- Objective: Demonstrate how a PassRole misconfiguration can grant unauthorized access.
- Steps:
- Allow user to pass IAM role to EC2.
- Exploit misconfiguration for unauthorized access.
- Access sensitive resources.
- Exploiting IAM AssumeRole Misconfiguration with Overly Permissive Role
- An overly permissive IAM role configuration can lead to privilege escalation by creating a role with administrative privileges and allow a user to assume this role.
- Objective: Show how overly permissive IAM roles can lead to privilege escalation.
- Steps:
- Create role with administrative privileges.
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- Perform administrative actions.
- Differentiation between PassRole vs AssumeRole
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DC MACHINE-Motoring and generation, Armature circuit equation
1. DC Machines –II
• Motoring and generation
• Armature circuit equation for motoring and generation,
• Types of field excitations - separately excited, shunt and series.
• Open circuit characteristic of separately excited DC generator,
• back EMF with armature reaction,
• voltage build-up in a shunt generator,
• critical field resistance and critical speed.
• V-I characteristics and torque-speed characteristics of separately
excited shunt and series motors.
• Speed control through armature voltage.
• Losses, load testing and back-to-back testing of DC machines..
2. Motoring and Generation -
• Motoring and generation are two fundamental concepts
associated with the operation of DC (Direct Current) machines,
such as DC motors and DC generators.
• These concepts describe how these machines function when
they are either consuming electrical power to produce
mechanical work (motoring) or converting mechanical work
into electrical power (generation).
3. Motoring:
•Motoring refers to the operation of a DC machine as an electric motor. In
this mode, electrical power is supplied to the machine to produce
mechanical output or work.
•When voltage is applied to the armature of the DC motor, it generates a
magnetic field due to the flow of current in the coils (windings).
•The magnetic field interacts with the field produced by the stator's field
winding (either permanent magnets or separate field windings) to create a
mechanical torque.
4. •This torque causes the motor's shaft to rotate, which is used to drive a
load or perform some mechanical task.
•The motor operates until an opposing force, such as friction or the load,
is balanced by the motor's torque.
•The speed and direction of rotation can often be controlled by
adjusting the applied voltage and the field winding current.
5. Generation:
•Generation refers to the operation of a DC machine as an electric
generator. In this mode, mechanical work is applied to the machine,
causing it to generate electrical power.
•When the shaft of the DC generator is mechanically rotated (e.g., by a
prime mover like a steam turbine, waterwheel, or engine), it induces an
electromotive force (EMF) in the armature coils.
•This EMF creates an electrical current, which can be used to power
external electrical loads or charge batteries.
6. • The generated voltage is proportional to the speed at which
the machine is rotated (N) and the strength of the magnetic
field (Φ) produced by the field winding or permanent
magnets.
• DC generators are commonly used in applications where a
steady and controllable DC power source is required, such as
in portable generators and backup power systems.
7. In summary, the key difference between motoring and generation in DC
machines is the direction of energy flow.
In motoring, electrical energy is supplied to the machine to produce
mechanical work, while in generation, mechanical work is applied to the
machine to produce electrical energy.
The operation mode (motor or generator) depends on the direction of
the current flow and the relative relationship between the applied
voltage and the machine's generated voltage.
8. Difference between motoring and generation in DC machines
Motor Generator
Input and
Output
Motor has dc current as an input
and mechanical energy as an
output.
Generator has dc current as an
output and mechanical energy
as an input.
EMF
(Electromotive
Force)
EMF is used to energize the coil
to rotate the armature.
EMF is generated around the
coil and transmitted to the
load or another section of the
circuit.
Generated EMF
Motor has a generated EMF less
than the voltage across the
source terminal (EMF<V).
Generator has a generated
EMF more than the voltage
across the source terminal
(EMF>V).
EMF
Calculation
Eb = V – IaRa Eg = V + IaRa
9. Motor Generator
Electric
current
Electric current is used to
energize the armature winding
through the commutator.
Electric current is generated
from the armature winding to
the commutator.
Rule Fleming Left Hand Rule Fleming Right Hand Rule
Work
principle
Operated by a current-
carrying conductor in a
magnetic field and generates
forces.
Operated by mechanical force
that rotates the armature in a
magnetic field and generates
induced current.
Armature
shaft
The armature is supplied by
an electrical current in a
magnetic field.
The armature is rotated by a
mechanical energy in a
magnetic field.
10. Motor Generator
Energy
conversion
The motor will rotate faster
when supplied with higher
power up to its maximum
power rating.
The generator will likely
produce fixed voltage with
rated rpm.
Examples
Robotic motors, production
and manufacturing tools
and machines, printers, and
many more.
Wind turbines, hydro power
plants, dynamos, alternators,
and many more.
11. Motoring and generation Armature circuit equation for motoring
and generation-
The armature circuit equation for both motoring (electric motor
operation) and generation (electric generator operation) in a direct current
(DC) machine can be expressed using the following equation:
Ea = V - Ia * Ra ± (Φ * N)
Where:
Ea is the back electromotive force (EMF) generated in the armature coil.
V is the applied voltage to the armature.
Ia is the armature current.
Ra is the armature resistance.
Φ is the magnetic flux in the machine's magnetic field.
N is the speed of the machine (rotational speed in revolutions per minute, RPM).
12. In the above equation:
When the machine is operating as a motor (motoring), the armature
current Ia flows in the direction of the applied voltage V, and the back
EMF Ea opposes the applied voltage. Therefore, the equation becomes:
Ea = V - Ia * Ra - Φ * N
When the machine is operating as a generator (generation), the armature
current Ia flows in the opposite direction of the applied voltage V, and the
back EMF Ea aids the applied voltage. Therefore, the equation becomes:
Ea = V - Ia * Ra + Φ * N
Ea = V - Ia * Ra ± (Φ * N)
13. • In both cases, the armature current Ia and the armature resistance Ra
cause a voltage drop, and the term Φ * N represents the voltage
generated due to the machine's magnetic field interacting with the
armature coils as they rotate.
• The polarity of the generated voltage (Ea) depends on whether the
machine is operating as a motor or a generator.ta
14. Types of field excitations –
separately excited, shunt and series.
15. The magnetic flux in a d.c machine is produced by field coils
carrying current. The production of magnetic flux in the device
by circulating current in the field winding is called excitation.
Excitation -
What is the main purpose of excitation in dc machine ??
16. The main purpose of excitation in a DC machine is
- to establish and control the magnetic field, which is fundamental for
converting electrical energy to mechanical energy (in the case of a motor)
or mechanical energy to electrical energy (in the case of a generator)
while providing control, stability, and adaptability to different operating
conditions.
17. • Creation of Magnetic Field
• Conversion of Electrical Energy to Mechanical Energy (Motor Mode)
• Conversion of Mechanical Energy to Electrical Energy
(Generator Mode)
• Control of Machine Operation
• Reversibility
• Stability and Regulation
• Starting
19. There are two types of excitation in D.C machine.
• Separate excitation, and
• Self-excitation.
Self-excitation –
The current flowing through the field winding is supplied by
the machine itself.
Separate excitation –
The field coils are energized by a separate D.C. Source.
20. Separately Excited DC Motor -
In separately excited DC motors, the supply is given to the field
and armature windings separately.
The main feature of this type of DC motor is that the current
through the armature doesn’t flow through the field windings
because the field winding is energized by a separate DC source.
This can be understood in a better way through the diagram given
below.
21. Separately excited DC machines are commonly used in applications
requiring fine control of speed and torque, such as in industrial drives
and some types of electric vehicles.
22. Self Excited DC Motor -
• As the name implies self-excited, hence, in this type of motor, the
current in the windings is supplied by the machine or motor itself to
establish the magnetic field in the field winding.
• This type of excitation is based on the feedback of the generated
electromotive force (EMF) to the field winding.
There are three subtypes of self-excited DC machines:
23. a. Shunt-Wound DC Machine:
•In a shunt-wound DC machine, the field winding (shunt field)
is connected in parallel with the armature winding. They
both receive the same supply voltage.
•Shunt-wound machines have relatively constant speed
characteristics and are commonly used in applications where
stable speed is required, such as in small generators and certain
types of industrial applications.
24. • The parallel connection means that the current is split between the
two components.
• A DC shunt motor has a constant speed that doesn’t change with
varying mechanical loads.
25. b. Series-Wound DC Machine:
In series-wound DC motors, the field winding and the
armature coil are connected in series to the power
supply. This means the same current flows through the
coil and armature. Since these types of motors can work
both with DC and AC, they are also called universal
motors.
Series motors always rotate in the same direction, and
their speed depends on the mechanical load.
26. Series-wound machines provide high starting torque but tend to have
poor speed regulation, making them suitable for applications like
electric traction (e.g., locomotives).
27. c. Compound-Wound DC Machine:
•Compound-wound DC machines combine elements of both
shunt and series winding.
•They have two sets of field windings: one connected in
parallel (shunt) and another in series with the armature.
•Compound-wound machines offer a compromise between the
characteristics of shunt and series machines, providing good
torque and speed regulation.
28. •They are used in various industrial applications, including
machine tools and rolling mills.
29. These motors are further divided into
• Short shunt and
• Long shunt and
• Cumulative Compound
• Differential Compound motors.
30. Relation Between Back EMF and Load Current -
• When the armature of the DC motor rotates under the influence of
the driving force, the armature of the conductors moves through the
magnetic field and generates an electromotive force(emf) in them.
• The induced emf is in opposite direction to the externally applied
voltage and this induced voltage is known as back emf and denoted
by E. Emf induced in any DC motor is given by the formula
31. Where
N = Speed of DC motor
P = Number of pole
φ = magnetic flux
Z = Number of Conductor
A = Number of Parallel Path
• for a dc motor Number of Pole(P), Number of conductors (Z), and
Number Of Parallel Path (A) is constant hence we can replace this
emf equation in a general form By Removing all Constant By a new
Constant K then
32. If this motor is connected with a DC Source of terminal voltage V
and a load Current I start to flow in the motor then due to internal
armature resistance(R), a voltage will drop then We can write the
KVL equation for this motor like this
V = E+IR
E=V - IR
k𝜙N =V - IR
33. Torque Equation of Separately Excited DC motor
It is a mathematical equation that provides the torque value produced by
the motor at its shaft. it is given as
Power Developed In armature = Mechanical Power Developed at the
shaft of DC motor
Above equation shows torque equation of a separately excited DC motor.
34. PARAMET
ER
Series
Wound DC
Motor
Shunt
Wound DC
Motor
Compound
Wound DC
Motor
Permanent
Magnet
DC(PMDC)
Constructio
n
Rotor, Field
windings in
series
Rotor, Field
windings in
parallel
Rotor,
Combined
series and
shunt
windings
Rotor with
permanent
magnets,
Stator with
windings
Advantages High
starting
torque,
Suitable for
heavy loads
Good speed
regulation,
Precise
control,
Stable
operation
Compromise
between
torque and
speed
regulation
Simple
construction
, High
efficiency,
Responsive
35. PARAMET
ER
Series
Wound DC
Motor
Shunt
Wound DC
Motor
Compound
Wound DC
Motor
Permanent
Magnet
DC(PMDC)
Disadvanta
ges
Limited
speed
control,
Inefficient at
high speeds,
Prone to
overheating
Lower
starting
torque,
Efficiency
may not be
as high
Complex
control,
Efficiency
may not be
optimal
Limited to
low to
moderate
power,
Limited
speed
control
Application Electric
vehicles,
Winches,
Elevators
Conveyor
belts,
Printing
presses
Rolling
mills,
Industrial
equipment
Toys, Small
appliances,
Fans
36. Applications of DC Motors
The applications of a dc motor depend on the requirement of the
electrical equipment and the characteristics of the DC motor.
DC Series Motor Applications
•Cranes
•Lifts and elevators
•Winching systems
•Hair driers
•Power tools
37. DC Shunt Motor
Applications
•Windscreen wiper drives
•Drills
•Conveyers
•Fans
•Centrifugal pumps
•Blowers
Compound DC Motor
Applications
•Conveyers
•Stamping machines
•Compressors
•Heavy planners
•Rolling mills
•Presses
38. Permanent Magnet
DC Motors
•Toys
•Starter motors
•Disc drivers
•Wheels chairs
Brushless DC Motor Applications
•Computer cooling fans
•Heating and ventilation
•Cooling systems in aircraft and vehicles
•Handheld power tools
Separately Excited DC Motor
Applications
•Actuators in industrial machinery
•Traction motors in trains
•Steel rolling mills
40. What is open circuit characteristics of separately excited DC
generator???
41. • The curve which gives the relation between field current (If) and
the generated voltage (E0) in the armature on no load is called
magnetic or open circuit characteristic of a DC generator.
• The plot of this curve is practically same for all types of
generators, whether they are separately excited or self-excited
42.
43.
44.
45. • It is also known as magnetic characteristics or no-load
saturation characteristics.
• It shows the relation between the induced emf E0 at the no-load
condition and the field current If at a constant speed.
• For separately excited DC generator, the open circuit
characteristics is obtained by conducting an experiment
under no-load conditions.
46. • An ammeter is connected to the field winding and a voltmeter
is connected to the generator to measure the induced voltage.
47. • The circuit is connected as shown in the above diagram.
• The field current is varied by connecting an additional
resistance(Rheostat) and is measured by an ammeter.
48. • At a constant speed, when the field current
is increased from zero, the flux and hence
the induced emf increases.
• The values of induced emf corresponding
to the field current is measured and
tabulated. From the tabulation, a graph is
drawn with field current as the x-axis and
generated emf as the y-axis.
• The graph shows the open circuit characteristics of a separately excited
DC generator
49. • From the above graph, it is observed that the increase in field
current increases the emf induced.
• When the poles get saturated, the increase in field current does not
increase the flux and thus the emf induced also remains constant.
• Different curves can be obtained for different speeds.
• From graph it is observed that, for higher speeds, the emf induced
will be more.
50. voltage build-up in a shunt generator, critical field resistance and
critical speed.
51. Conditions to build up voltage in shunt generator:
1.The shunt winding should have residual magnetic field.
2.The direction of shunt winding and armature winding should be in
such a way that flux generated by them should aid together.
3. The shunt winding should have critical winding resistance.
52. Process of voltage build up:
• When the armature is rotated, the residual flux in field winding
will induce small voltage in armature.
• The induced voltage in armature generates a flux and it will
aid(add) with field flux and the net flux will increase further.
This process will be repeating until the actual treminal voltage is
reached.
• Once the terminal voltage is reached then the winding will get
saturated and hence there won't be any further increase in flux,
also the voltage gets constant.
53.
54. • Consider a DC Shunt Generator at no load as shown in
figure below. The switch in the field circuit is supposed
open and the armature of DC Shunt Generator is driven at
rated speed.
• Because of presence of small residual flux in the field
poles, DC Shunt Generator will have a small voltage at its
terminal even though the switch S is open when driven at
rated speed.
• Now suppose the switch S is closed.
55. • As there is small voltage is there across the terminals of DC
Shunt Generator and Switch S is closed, therefore a small
current will start flowing through the field circuit of DC
Shunt Generator which in turn will produce magnetic flux
and if the produced magnetic flux adds the residual magnetic
flux then net flux will increase and the generated voltage
(Ea = KaØωm) will increase corresponding to point J on the
Magnetization curve as shown in figure below.
56.
57. • Since the generated voltage has increased,
therefore the field current will also increase to
OK corresponding to which the Generated
Voltage across the Terminals of DC Shunt
Generator will increase to point L.
• In the same manner the voltage will continue to
build up till the point of intersection of Field
Resistance Line and Magnetization curve /
Open Circuit Characteristics of DC Shunt
Generator.
58. Beyond point of intersection of Field Resistance Line and
Magnetization curve / Open Circuit Characteristics the voltage won’t
build up as in that case the generated voltage Ea will not be able to
drive the required field current. Thus the stable point at which the
voltage will remain fix is the voltage Ea corresponding to point of
intersection of Field Resistance Line and Magnetization curve / Open
Circuit Characteristics.
59. Effect of variation of field resistance of DC Shunt Generator in its
Voltage Build up:
60.
61. If the field resistance is increased to OA, then Field Resistance
line intersect the OCC curve at point p, and hence there will not be
voltage build up beyond point p.
Now, if shunt field resistance is such that OB represents the Field
resistance line then as clear from the figure above, the lone is
intersecting the OCC curve at many points between q and r,
therefore the field current will fluctuate between s and t and hence
the voltage generated at the terminals of DC Shunt Generator will
vary from qs to rt resulting in unstable condition.
62. If we find the slope (tanƟ) of the Field Resistance Line then we will
get Field Resistance value which is known as Critical Filed
Resistance.
63. What is the significance of Critical Field Resistance?
As clear from the figure above, if the field resistance is more than
the Critical Field Resistance then there will not be voltage build up
in DC Shunt Generator.
See in the figure OA is shunt field resistance which is more than
Critical Field Resistance OB (check by slope, slope of OA is more
than slope of OB), hence there is no voltage build up in DC Shunt
Generator.
64. Effect of variation of speed of rotation of DC Shunt
Generator in its Voltage Build up:
65.
66. Suppose the field resistance is OC and DC Shunt Generator is
running at a speed of n1 for which the stable point of its terminal
voltage is C.
Now the speed of DC Shunt Generator is reduced to n2 therefore the
OCC curev will also move downward as shown in figure.
It should be noted here that the same field resistance line OC is now
tangent to the new OCC curve and therefore will create an unstable
condition of operaton of DC Shunt Generator.
67. This speed n2 is hence called Critical Speed.
Thus Critical Speed is that speed at which the DC Shunt Generator
just fails to built up voltage with no external resistance in the field
circuit.
68. V-I characteristics and torque-speed characteristics of
separately excited shunt and series motors.
70. There are generally three most important characteristic of DC
motor
1. Magnetic or Open Circuit Characteristic of Separately Excited
DC Motor.
2. Internal or Total Characteristic of Separately Excited DC Motor.
3. External Characteristic of Separately Excited DC Motor.
71. • The curve which gives the relation between field current
(If) and the generated voltage (E0) in the armature on no
load is called magnetic or open circuit characteristic of
a DC Motor.
• The plot of this curve is practically same for all types of
motors, whether they are separately excited or self-
excited. This curve is also known as no load saturation
characteristic curve of DC motor.
Magnetic or Open Circuit Characteristic of Separately
Excited DC motor
72.
73. • From the above graph, we can see the variation of generated
emf on no load with field current for different fixed speeds of
the armature.
• For higher value of constant speed, the steepness of the curve is
more.
• When the field current is zero, for the effect residual magnetism
in the poles, there will be a small initial emf (OA) as show in
figure.
74. • Let us consider a separately excited DC motor giving its no load
voltage E0 for a constant field current.
• If there is no armature reaction and armature voltage drop in the
machine then the voltage will remain constant.
• Therefore, if we plot the rated voltage on the Y axis and load
current on the X axis then the curve will be a straight line and
parallel to X-axis as shown in figure below.
75. • Here, AB line indicating the no load voltage (E0).
When the motor is loaded then the voltage drops due to two
main reasons-
• Due to armature reaction,
• Due to ohmic drop (IaRa).
76. Internal or Total Characteristic of Separately Excited DC motor
The internal characteristic of the separately excited DC motor
is obtained by subtracting the drops due to armature reaction from no
load voltage.
This curve of actually generated voltage (Eg) will be slightly
dropping.
Here, AC line in the diagram indicating the actually generated voltage
(Eg) with respect to load current.
This curve is also called total characteristic of separately excited
DC motor.
77.
78. External Characteristic of Separately Excited DC motor
• The external characteristic of the separately excited DC motor is
obtained by subtracting the drops due to ohmic loss (Ia Ra) in
the armature from generated voltage (Eg).
• Terminal voltage(V)
(V) = Eg – Ia Ra.
• This curve gives the relation between the terminal voltage (V)
and load current.
• The external characteristic curve lies below the internal
characteristic curve.
79. • Here, AD line in the diagram is indicating the change in terminal
voltage(V) with increasing load current.
• It can be seen from figure that when load current increases then
the terminal voltage decreases slightly.
• This decrease in terminal voltage can be maintained easily by
increasing the field current and thus increasing the generated
voltage.
• Therefore, we can get constant terminal voltage.
82. The speed-torque characteristics of a dc motor is a graph of torque
on X-axis versus the speed which is plotted on Y-axis.
As the torque is proportional to the armature current , the nature of
this characteristics is same as that of the speed-armature current
characteristic shown in graph.
From graph, at no load the torque produced by the motor is Ta0 &
the motor rotates at the no load speed N0.
As the load is increased, the torque requirement also increase.
83. To generate the required amount of torque, the motor has to draw
more armature current & motor armature current can be drawn if
the more speed decreases, because
Ia =
𝑽 − 𝑬𝒃
𝑹𝒂
Therefore, as the load increases, torque will also increase & the
speed decreases.
However the reduction in speed is not significant as the load is
increased from no load to full load.
In dc shunt motor, the torque is directly proportional to armature
current. Therefore dc shunt motor is practically called as
constant speed motor.
86. Open Circuit Characteristics (O.C.C)
• The curve (A) in the plot shows the O.C.C of a series DC motor.
• It is the graph plotted between the generated EMF at no-load
and field current.
• The O.C.C can be obtained by disconnecting the field winding
from the machine and is excited separately.
87. Internal Characteristics
• The internal characteristics of a DC series motor is the graph plotted
between generated EMF (Eg) on-load and the armature current.
• Because of the effect of armature reaction, the magnetic flux on-load
will be less than the flux at no-load.
• Therefore, the generated EMF (E) under loaded condition will be less
than the EMF generated (E0) at no-load.
• As a result of this, the internal characteristics curve lies just below the
open circuit characteristics [See the curve (B)].
88. External Characteristics or Load Characteristics
• The external characteristics or load characteristics is the plot
between the terminal voltage (V) and load current (IL}).
• Since, the terminal voltage is less than the generated voltage due
to armature and series field copper losses, which is given by,
V = E − Ia ( Ra + Rse )
• Therefore, the external characteristics curve will lie below the
internal characteristics curve by an equal amount to voltage drop
due to copper losses in the machine [see the curve (C)].
90. • The speed –torque characteristics of a dc series motor is shown in
above graph.
• We know that,
T ∝ Ia
2
.
& N ∝ 1
Ia
Ia∝ T
& N ∝
1
T
• This shows that the speed decreases with increase in the value of
torque that is with increase in load.
91. Comparison of DC shunt & DC series Motors
S.
N.
parameter DC shunt motor DC series motor
01 Connection of
field winding with
armature
Field is in parallel
with armature
Field is in series with
armature
02 Type of starter Three point Four point
03 Torque developed Low High
04 Applications Machine tool,
printing, pumps,
paper machine
Electric trains, crains,
Hoists, Conveyers
92. Comparison of Speed- Torque characteristics of DC shunt & DC series Motors
S.N parameter DC shunt motor DC series motor
01 Nature of
characteristics
02 Relation between
speed & torque
As load increases, T
increases & Speed
reduces slightly
As load increases, torque
increases & speed reduces
exponentially.
03 Reduction in speed
with increased load
Slightly reduction in
Speed takes place.
Drastic reduction in speed
takes place
04 Starting torque Moderately high Very high
93. Speed control through armature voltage
• The relationship given below gives the speed of a D.C. motor
• The above equation shows that the speed depends upon the
supply voltage V, the armature circuit resistance Ra, and the
field flux Ф, which is produced by the field current.
• Thus, there are three general methods of speed control of
D.C. Motors.
94. Thus, there are three general methods of speed control of D.C.
Motors.
• Resistance variation in the armature circuit: This method is
called armature resistance control or Rheostat control.
• Variation of field flux Ф: This method is called field flux
control.
• Variation of the applied voltage.: This method is also called
armature voltage control.
95. The speed is directly proportional to the voltage applied across the
armature.
As the supply voltage is normally constant, the voltage across the
armature can be controlled by adding a variable resistance in series
with the armature as shown in the Fig.
96.
97. • Speed control of a DC shunt motor through armature voltage
involves adjusting the armature voltage to vary the motor's speed
while keeping the field current (field winding voltage) constant.
• This method is commonly used in applications where precise speed
control is required. Here's how you can control the speed of a DC
shunt motor using armature voltage:
98. Basic Principle:
• The speed of a DC shunt motor is directly proportional to
the armature voltage and inversely proportional to the field
current.
• By increasing or decreasing the armature voltage, you can
increase or decrease the motor's speed while maintaining a
constant field current.
99. Method of Control:
Increasing Speed:
• To increase the motor's speed, we need to increase the armature
voltage.
• We can achieve this by adjusting the output voltage of an adjustable
power supply connected to the motor's armature terminals. As the
armature voltage increases, the motor speeds up.
Decreasing Speed:
• To decrease the motor's speed, you reduce the armature voltage.
• This can be done by lowering the output voltage of the power supply.
As the armature voltage decreases, the motor slows down.
100. • The field winding is excited by the normal voltage hence Ish is
rated and constant in this method.
• Initially the rheostat position is minimum and rated voltage
gets applied across the armature.
• So speed is also rated.
• For a given load, armature current is fixed.
• So when extra resistance is added in the armature circuit,
Ia remains same and there is voltage drop across the resistance
added (Ia R).
101. • Hence voltage across the armature decreases, decreasing the
speed below normal value.
• By varying this extra resistance, various speeds below rated
value can be obtained.
• So far a constant load torque, the speed is directly
proportional to the voltage across the armature.
• The relationship between speed and voltage across the
armature is shown in the following graph.
102.
103. Advantages: Disadvantages:
1.Precise Speed Control. 1)Reduced Torque at Lower Speeds
2.Energy Efficiency 2) Potential Overheating
3.Smooth Operation 3) Limited Speed Range
4.Simple Control Circuitry 4) Field Weakening
5.Compatibility 5) Wasted Power
104. Speed control of a DC shunt motor through armature
voltage is an effective and precise method for regulating
motor speed in applications such as conveyor systems,
industrial machines, and fans.
It allows for smooth and continuous control over the
motor's speed while maintaining constant field current
for optimal motor performance.
105.
106. Losses in DC Machine –
In DC machine the energy loss takes place in the form of heat
energy.
The losses occurs in the armature and field of the DC machine.
There are five types of losses
1. copper loss,
2. brush loss,
3. iron loss,
4. stray loss and
5. mechanical loss takes place in a DC machine.
107. Copper Loss in DC Machine winding
• The copper loss is caused by the ohmic resistance offered by the
winding of the DC machine.
• When the current flows through the winding the heat loss takes
place in the winding.
• The heat loss is proportional to the square of the current and the
resistance of the winding.
• The copper loss in the winding is I2R.
Where, I is the current flowing through the winding and
R is the resistance of the winding.
108. • The copper loss is also known as variable loss because the
copper loss depends on the percentage loading of the machine.
• The loss increases with increase of loading on the machine.
• The DC machine has two types of winding- field and armature
winding- and losses take place in both the winding.
• The supply is fed to armature through the carbon brushes and
losses also takes place across the carbon brush due to ohmic
voltage drop.
109. Copper Loss in Armature Winding
The armature of the DC machine has very low resistance.
The resistance of the armature is denoted by Ra.
Armature copper loss = Ia2Ra
Where, Ia is the armature current and Ra is the armature winding
resistance.
The maximum copper loss occurs in the armature winding,
because the load current flows through the armature winding.
The copper loss in the armature is about 25 to 30 % of the full
load loss.
110. Copper loss in the field winding -
• DC supply is fed to the field winding for production of the flux
in the DC machine.
• The resistance of the field winding is much more than the
resistance of the armature winding.
• That is why the substantial copper loss takes place in the field
winding even at the low field current.
• The copper loss in the field winding is expressed as;
111. • Field winding copper loss = If
2Rf
Where, If is the field current and Rf is the field winding
resistance.
• The field winding copper loss is about 20-25 % of the full load
loss of the DC machine.
• The copper loss in the field winding is a practically constant loss
because the field current and the field resistance remains almost
constant in the DC machine.
112. Brush Contact Resistance Loss
• The armature is a rotating part of the DC machine, and brushes are
used to provide DC supply to the rotating part of the DC machine.
• Ideally, the contact resistance between the brush contacting area
with commutator surface must be zero.
• However, in reality it is impossible to have zero contact resistance.
• The voltage drop takes place across the carbon brushes. The brush
power drop depends upon the voltage drop across the brush and
armature current.
113. Power Drop in Brush = PBD = VBD Ia
Where,
PBD = Power drop in Brush
VBD = Voltage Drop in Brush
Ia = Armature Current
If the brush voltage drop is not given, it is generally assumed 2
volts drop across carbon brush and the power drop in brush is
2Ia .
114. Core Losses or Iron Losses in DC Machine
• The armature winding of the DC machine is wound
around the magnetic core.
• The flux generated by the field coil gets linked to the
armature conductors through magnetic core.
• Two types of losses namely hysteresis and eddy current
loss occur in the magnetic core.
• The iron loss is almost constant therefore the iron loss or
core loss is also called constant loss.
• The total core loss is about 20-25 % of the full load losses.
115. Mechanical Loss in DC Machine
• Losses occurring due to mechanical affects like friction
etc. are called Mechanical Losses.
• In DC machine, the field is a stationary part and the
armature is a rotating part.
• The armature rotates on the bearings. The energy loss in
the form of heat occurs due to friction between the inner
cage and outer cage of the bearing.
• The other mechanical loss is the windage loss.
116. • The air surrounding to the shaft offers resistance and,
when DC machine rotates the loss caused by air
resistance is called the windage loss.
• Mechanical losses are very small in magnitude as
compared to copper loss & iron loss.
117. Stray Losses in DC Machine
• All the losses which are neighter copper, iorn, brush or
mechanical type loss are classified under stray losses.
• Stray losses are also called as miscellaneous losses which
are difficult to determine.
• The various reasons of the stray losses in DC machine are
short circuit current undergoing commutation,distortion
of flux etc.
• The stray losses in DC machine are about 1 % of the total
losses.
118. • Load testing of DC machines is a method used to assess the
performance and operational characteristics of direct current
(DC) motors or generators under specific load conditions. It
involves applying various loads to the machine to evaluate its
response, efficiency, and reliability.
• The load testing of DC machine is needed to determine the rating
of a machine.
• When we run a machine, then some energy is lost in the machine,
which converts into the heat and cause temperature rise.
The load testing of DC machine
119. • If a machine produces too much heat then it can affect the
insulation of the machine and ultimately it can cause the
breakdown of the machine.
• Therefore, the load must be set to a value that it can operate
within the temperature limit.
• The maximum value of the load that can be delivered by the
machine without any harm is called the continuous rating of
that machine.
120. • Load testing can be considered both direct and indirect,
depending on the specific objectives and methods used:
Direct Load Testing:
Direct load testing involves directly applying a known load to
the DC machine and measuring its response to that load.
This type of testing is typically more straightforward and
provides immediate and precise information about the machine's
performance.
121. In direct load testing, you apply mechanical or electrical loads to
the machine and observe parameters such as speed, current,
torque, and temperature.
This data is collected and analyzed to assess how well the
machine handles different loads, its efficiency, and whether it
operates within its specified performance range.
122. Indirect Load Testing:
Indirect load testing refers to assessing the DC machine's
performance without applying a physical load directly to it.
Instead, it involves various analytical and diagnostic
techniques to evaluate the machine's condition and
performance indirectly.
Indirect load testing may include analyzing historical data,
conducting diagnostic tests (e.g., insulation resistance tests,
vibration analysis), and performing calculations based on
the machine's specifications and operational data.
123. It can also involve simulation and modeling to predict the
machine's behavior under different load scenarios.
Direct load testing involves physically applying loads to the
machine and directly measuring its performance parameters. This
method provides real-world performance data.
Indirect load testing involves various diagnostic and analytical
methods that assess the machine's performance without the need for
applying physical loads directly. This method is often used for
predictive maintenance and condition monitoring.
124. Back-to Back testing of DC machines..
• Back-to-back testing of DC machines, also known as regenerative
testing or Hopkinson's test .
• Hopkinson's test is a method of testing the efficiency of DC
machines.
• This test requires two identical shunt machines which are
mechanically coupled and also connected electrically in parallel.
125. • It requires two identical machines that are coupled to each
other.
• One of these two machines is operated as a generator to supply
the mechanical power to the motor and the other is operated as
a motor to drive the generator.
• The motor takes its input from the supply and the mechanical
output of the motor drives the generator. The electrical output
of the generator is used in supplying the input to the motor.
Therefore, the output of each machine is fed as input to the
other.
126. • When both the machines are run at rated load, the input from the
supply is equal to the total losses of both the machines. Thus,
the power input form the supply is very small.
Connection Diagram-
The connection diagram of Hopkinson’s test is shown in the figure.
127.
128. In the connection diagram, the machine M acts as a
motor and is started from the supply with the help of
starter. The switch S is kept open.
The field current of the machine M is adjusted with
the help of field rheostat Rm to make the motor to run
at its rated speed. The machine G acts as a generator.
129. As the G is driven by the machine M, hence it runs at
rated speed of M.
The field current of the machine G is so adjusted with
the help of its field rheostat Rg that the armature
voltage of the generator G is somewhat higher than the
supply voltage.
When the voltage of the generator is equal to and of
the same polarity of the busbar voltage, the switch S is
closed and the generator is connected to the busbar.
130. Now, both the machines are connected in parallel
across the supply voltage.
Under this condition, the generator neither taking any
current from nor giving any current to the supply, thus
it is said to be float.
Now, by adjusting the excitation of the machines with
the help of the field rheostats, any load can be thrown
on the machines.
131. Advantages:
Efficiency Assessment: Back-to-back testing allows for a precise
assessment of the efficiency of DC machines. By comparing the
electrical power input to the motor and the electrical power output
from the generator, you can calculate efficiency accurately.
Dynamic Response Testing: This method is well-suited for
evaluating the dynamic response of DC machines. It enables the
testing of rapid acceleration, deceleration, and load changes,
which is crucial for applications requiring precise control, such as
electric locomotives and industrial drives.
132. High-Power Testing: Back-to-back testing is particularly
useful for testing large and high-power DC machines,
including electric locomotives, industrial motors, and large
generators.
Closed-Loop Operation: The closed-loop configuration
allows the electrical energy generated by the generator
machine to be fed back into the power supply system or
absorbed by load banks, reducing energy wastage and making
the testing process more environmentally friendly.
133. Fault Detection: Anomalies in the behavior of the machines,
such as abnormal vibrations or electrical imbalances, can be
detected during back-to-back testing, allowing for early fault
detection and preventive maintenance.
Controlled Testing Environment: Back-to-back testing
provides a controlled environment for evaluating the
machines, allowing for consistent and repeatable testing
conditions.
134. Disadvantages:
Complex Setup: The setup for back-to-back testing
can be complex and requires two compatible DC
machines, which may not be readily available or cost-
effective for smaller machines.
Space and Infrastructure: Conducting back-to-back
testing requires a dedicated testing facility with
sufficient space to accommodate the machines and
associated equipment.
135. High Initial Cost: The equipment and infrastructure
required for back-to-back testing can be expensive to
acquire and set up, making it less practical for some
organizations.
Energy Dissipation: The electrical energy generated
by the generator machine needs to be either returned to
the power supply grid or dissipated as heat using load
banks. This energy dissipation can be inefficient and
costly.
136. Complex Data Analysis: Analyzing the data collected
during back-to-back testing can be complex and may
require specialized expertise to interpret the results
accurately.
Limited Application: Back-to-back testing is most
beneficial for high-power DC machines and may not
be practical or cost-effective for smaller machines or
applications.