The document summarizes the key aspects of polyphase induction motors, including:
1) Nikola Tesla conceived the induction motor in 1883 and sold the rights to George Westinghouse. Most large industrial motors are polyphase induction motors with multiple stator windings driven by time-shifted sine waves, usually two or three phases.
2) An induction motor has a rotor and stator, with the stator windings connected to a polyphase power source. The rotating magnetic field produced by the stator induces current in the rotor, causing it to turn.
3) The induction motor is simple and reliable compared to DC motors as the rotor has no commutator or brushes. Torque is
The document discusses induction motors, which are asynchronous AC motors that operate below synchronous speed. It describes the two main types - single phase and three phase induction motors. Three phase induction motors are commonly used in industry due to their ability to provide bulk power conversion from electrical to mechanical power. The document then discusses the construction and working principles of three phase induction motors in detail, including their stator, rotor, and how rotational motion is induced in the rotor via electromagnetic induction from the rotating stator magnetic field.
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.
1. Three phase induction motors have a rotating magnetic field produced by a three phase stator winding that causes the rotor to turn.
2. The rotor can be either a squirrel cage (copper or aluminum bars short circuited by end rings) or wound construction.
3. Starters are used to reduce the starting current by lowering the supply voltage and improve starting torque by increasing rotor resistance during start up. Common starting methods include direct-on-line, star-delta, and auto transformer starters.
This document discusses different types of AC motors. It describes induction motors, including single-phase and three-phase induction motors. Three-phase induction motors can have either a squirrel cage or wound rotor. Synchronous motors are also discussed, which rotate at a constant synchronous speed. While synchronous motors have high efficiency, they require auxiliary equipment to allow for self-starting. The document compares different AC motor types and provides examples of their common applications.
This document discusses the synchronous motor, including its introduction, construction, and operating principle. A synchronous motor runs at a constant synchronous speed determined by the supply frequency. It consists of a stator winding and a rotor with salient poles. The rotor is excited by direct current to synchronize with the rotating stator field. A synchronous motor is not self-starting and requires an auxiliary method like an induction motor principle or separate starting motor.
An alternator is an electrical generator that converts mechanical energy to electrical energy. It uses a rotating magnetic field with a stationary armature. The working principle relies on Faraday's law of electromagnetic induction. As the armature rotates within the magnetic field, an alternating current is produced. The main components are the stator with stationary armature windings and the rotor with a rotating magnetic field supplied by a DC current. Armature reaction causes the magnetic field to be distorted by the armature current. Alternators have various applications including in automobiles, power plants, and for providing regenerative braking in induction motors. Induction generators can also be used to convert the rotational energy of windmills into electrical energy.
The document discusses different types of AC motors, including induction motors and synchronous motors. Induction motors operate slightly slower than the supply frequency, while synchronous motors rotate exactly at the supply frequency. Common types of AC motors include squirrel cage motors and wound rotor motors. Squirrel cage motors have conductors in the rotor that produce torque from induced currents, while wound rotor motors have insulated windings in the rotor that allow external resistance to control starting torque and speed.
The document discusses induction motors, which are asynchronous AC motors that operate below synchronous speed. It describes the two main types - single phase and three phase induction motors. Three phase induction motors are commonly used in industry due to their ability to provide bulk power conversion from electrical to mechanical power. The document then discusses the construction and working principles of three phase induction motors in detail, including their stator, rotor, and how rotational motion is induced in the rotor via electromagnetic induction from the rotating stator magnetic field.
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.
1. Three phase induction motors have a rotating magnetic field produced by a three phase stator winding that causes the rotor to turn.
2. The rotor can be either a squirrel cage (copper or aluminum bars short circuited by end rings) or wound construction.
3. Starters are used to reduce the starting current by lowering the supply voltage and improve starting torque by increasing rotor resistance during start up. Common starting methods include direct-on-line, star-delta, and auto transformer starters.
This document discusses different types of AC motors. It describes induction motors, including single-phase and three-phase induction motors. Three-phase induction motors can have either a squirrel cage or wound rotor. Synchronous motors are also discussed, which rotate at a constant synchronous speed. While synchronous motors have high efficiency, they require auxiliary equipment to allow for self-starting. The document compares different AC motor types and provides examples of their common applications.
This document discusses the synchronous motor, including its introduction, construction, and operating principle. A synchronous motor runs at a constant synchronous speed determined by the supply frequency. It consists of a stator winding and a rotor with salient poles. The rotor is excited by direct current to synchronize with the rotating stator field. A synchronous motor is not self-starting and requires an auxiliary method like an induction motor principle or separate starting motor.
An alternator is an electrical generator that converts mechanical energy to electrical energy. It uses a rotating magnetic field with a stationary armature. The working principle relies on Faraday's law of electromagnetic induction. As the armature rotates within the magnetic field, an alternating current is produced. The main components are the stator with stationary armature windings and the rotor with a rotating magnetic field supplied by a DC current. Armature reaction causes the magnetic field to be distorted by the armature current. Alternators have various applications including in automobiles, power plants, and for providing regenerative braking in induction motors. Induction generators can also be used to convert the rotational energy of windmills into electrical energy.
The document discusses different types of AC motors, including induction motors and synchronous motors. Induction motors operate slightly slower than the supply frequency, while synchronous motors rotate exactly at the supply frequency. Common types of AC motors include squirrel cage motors and wound rotor motors. Squirrel cage motors have conductors in the rotor that produce torque from induced currents, while wound rotor motors have insulated windings in the rotor that allow external resistance to control starting torque and speed.
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three phase alternators in power plants generate most of the world's electric power, which is distributed by electric power grids.
An induction motor is described with the following specifications:
- 480-V, 60 Hz, 50-hp, 3-phase
- Drawing 60A at 0.85 PF lagging
- Stator copper losses of 2 kW
- Rotor copper losses of 700 W
To determine the rotor frequency at full load, the slip is calculated using the given power rating, current, and power factor. The slip is then used to calculate the rotor frequency.
The document provides information on various types of electric motors, including DC motors, AC motors, and stepper motors. It discusses the fundamental characteristics and classifications of different motor types. For DC motors specifically, it describes the basic functions, types, wiring topologies, and modeling of series, shunt, compound, and permanent magnet DC motors. It also covers motor control using an H-bridge and brushless DC motor designs. For AC motors, it summarizes fractional horsepower designs as well as induction motors, synchronous motors, squirrel cage rotors, torque/speed characteristics, and NEMA standards.
An AC motor operates using the interaction between a rotating magnetic field in the stator created by AC current and a magnetic field in the rotor. The stator is the stationary part containing windings that generate the magnetic field, while the rotor is the rotating part. Induction motors are the most common type and have a wound stator and rotor. In an induction motor, currents induced in the rotor by the stator create rotation, while in a synchronous motor the rotor carries its own magnetic field from a separate DC source and locks to the rotating magnetic field frequency. Synchronous motors have constant synchronous speed regardless of load but require an external starting mechanism, while induction motors have self-starting torque but a speed that decreases slightly with increasing load
1. A DC motor runs on direct current electricity. It has a field winding that produces a magnetic field when energized, and an armature winding that rotates when placed in this magnetic field.
2. The key parts of a DC motor include the yoke, poles, field winding, armature core, armature winding, commutator, and brushes. The field winding produces flux, and the rotation of the armature winding within this flux induces voltage that is used to power the load.
3. DC motors can be shunt wound, series wound, or compound wound depending on how the field and armature windings are connected. Shunt and series motors have different torque-speed characteristics due
DC motors
Torque & Speed Equations
Torque -Armature current Characteristics
Speed - Armature current Characteristics
Torque-speed characteristics
Applications
Speed Control
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.
1) Single phase induction motors use a split phase winding or capacitor start method to generate a rotating magnetic field for starting.
2) Synchronous motors operate at a constant synchronous speed and use a damper winding, pony motor, or DC motor method to reach synchronous speed before loading.
3) V curves show the relationship between armature current, field current, and excitation voltage in synchronous motors.
This document outlines and describes the key components and operating principles of three-phase induction motors, which are widely used in industrial applications due to their continuous operation. It discusses the main types of electrical machines and induction motors, including squirrel cage and slip ring induction motors. The document explains the basic working principle of three-phase induction motors, involving the generation of a rotating magnetic field in the stator that induces current in the rotor. It also describes the main components of three-phase induction motors such as the frame, stator, rotor, and windings.
CONTENT
Starting Of Induction Motor
Starters
Types Of Starter For 3-ph Induction Motors
Starting Of Slip Ring Induction Motor
D.O.L.(Direct On Line) starter
Star-delta Starter
Auto Transformer Starter
Difference Between DOL/Star Delta/ Autotransformer
This document summarizes different types of stepper motors, including variable reluctance, permanent magnet, and hybrid stepper motors. It describes their construction, working principles, modes of operation like single phase ON, two phase ON, and half step modes. It also discusses static characteristics like torque vs step angle/current and dynamic characteristics like pull in and pull out. Finally, it lists some common industrial applications of stepper motors such as in printers, disk drives, machine tools, robotics, and tape drives.
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
The induction motor operates on the principle of electromagnetic induction. It consists of two main parts - the stator and the rotor. The stator contains windings that generate a rotating magnetic field, acting as the primary. This rotating field induces currents in the rotor windings, which acts as the secondary. The rotor is then pushed to rotate at a slightly lower speed than the rotating field due to "slip."
A stepper motor converts electrical pulses into discrete mechanical movements of its shaft. The shaft rotates in discrete step increments that correspond directly to the sequence and frequency of input pulses. There are three main types of stepper motors: variable-reluctance, permanent magnet, and hybrid. Stepper motors provide controlled movement and are well-suited for applications that require control of rotation angle, speed, position, and synchronization. They have advantages like full torque at standstill and excellent response to starting, stopping, and reversing.
Winding
What is Armature winding?
Terms related to armature winding.
Single layer and double layer windings.
Comparison between closed and open windings.
Types of DC armature winding.
Types of AC armature winding.
The document discusses permanent magnet brushless DC motors, including their construction with a permanent magnet rotor, electronic commutation instead of a mechanical commutator, and applications in automotive, industrial, computer and small appliance uses. It provides details on the operation, classifications based on pole arc and waveform, and common controller circuits used for permanent magnet brushless DC motors.
Universal motors can operate on either AC or DC power. They have high starting torque because the armature and field windings are connected in series. Speed control of a universal motor is achieved by varying the terminal voltage, which changes the current and electromagnetic torque. The motor's angular velocity is determined by solving the differential equation for the electrical system, which depends on the induced back EMF. Back EMF is produced by the motion of the rotor in the magnetic field and opposes the applied voltage, with its magnitude proportional to speed. Varying the applied voltage allows control of the motor's speed and torque.
The document discusses DC motors. It describes 3 types of DC motors - shunt motors, series motors, and compound motors. It explains the construction and working principles of each type. Speed control methods for DC motors are also discussed, including flux control, armature control, and voltage control. Various applications of each DC motor type are provided.
The document provides an overview of induction motors, including:
1. It describes the basic operating principle of induction motors, which induce a current in the rotor via electromagnetic induction from a rotating magnetic field in the stator.
2. It discusses different types of induction motors including single phase, three phase, squirrel cage, and slip ring rotors.
3. It provides some key formulas for induction motors relating supply frequency, pole pairs, synchronous speed, rotor speed, and slip.
The polyphase induction motor is commonly used in industry due to its simplicity and reliability. It works by inducing currents in the rotor windings via a rotating magnetic field produced by the stator windings. This induces a torque on the rotor causing it to rotate at a slightly lower speed than the rotating field. There are two main types: squirrel-cage motors which have shorted rotor windings, and wound-rotor motors which have external connections to the rotor windings allowing control of starting torque. An equivalent circuit model is used to analyze induction motor performance characteristics such as torque-speed curves.
Rotating magnetic fields are produced by supplying a three-phase winding with alternating current such that the current in each phase is 120 degrees out of phase. This produces three magnetic fluxes that are 120 degrees out of phase. The vector sum of these three fluxes results in a single magnetic flux vector that rotates in space. This rotating magnetic field can be used to drive an electric motor or generator. The speed of rotation is proportional to the supply frequency and number of poles, such that for a 2-pole winding, the magnetic field rotates at half the frequency of the alternating current supply.
An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature. Occasionally, a linear alternator or a rotating armature with a stationary magnetic field is used. In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto. Alternators in power stations driven by steam turbines are called turbo-alternators. Large 50 or 60 Hz three phase alternators in power plants generate most of the world's electric power, which is distributed by electric power grids.
An induction motor is described with the following specifications:
- 480-V, 60 Hz, 50-hp, 3-phase
- Drawing 60A at 0.85 PF lagging
- Stator copper losses of 2 kW
- Rotor copper losses of 700 W
To determine the rotor frequency at full load, the slip is calculated using the given power rating, current, and power factor. The slip is then used to calculate the rotor frequency.
The document provides information on various types of electric motors, including DC motors, AC motors, and stepper motors. It discusses the fundamental characteristics and classifications of different motor types. For DC motors specifically, it describes the basic functions, types, wiring topologies, and modeling of series, shunt, compound, and permanent magnet DC motors. It also covers motor control using an H-bridge and brushless DC motor designs. For AC motors, it summarizes fractional horsepower designs as well as induction motors, synchronous motors, squirrel cage rotors, torque/speed characteristics, and NEMA standards.
An AC motor operates using the interaction between a rotating magnetic field in the stator created by AC current and a magnetic field in the rotor. The stator is the stationary part containing windings that generate the magnetic field, while the rotor is the rotating part. Induction motors are the most common type and have a wound stator and rotor. In an induction motor, currents induced in the rotor by the stator create rotation, while in a synchronous motor the rotor carries its own magnetic field from a separate DC source and locks to the rotating magnetic field frequency. Synchronous motors have constant synchronous speed regardless of load but require an external starting mechanism, while induction motors have self-starting torque but a speed that decreases slightly with increasing load
1. A DC motor runs on direct current electricity. It has a field winding that produces a magnetic field when energized, and an armature winding that rotates when placed in this magnetic field.
2. The key parts of a DC motor include the yoke, poles, field winding, armature core, armature winding, commutator, and brushes. The field winding produces flux, and the rotation of the armature winding within this flux induces voltage that is used to power the load.
3. DC motors can be shunt wound, series wound, or compound wound depending on how the field and armature windings are connected. Shunt and series motors have different torque-speed characteristics due
DC motors
Torque & Speed Equations
Torque -Armature current Characteristics
Speed - Armature current Characteristics
Torque-speed characteristics
Applications
Speed Control
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.
1) Single phase induction motors use a split phase winding or capacitor start method to generate a rotating magnetic field for starting.
2) Synchronous motors operate at a constant synchronous speed and use a damper winding, pony motor, or DC motor method to reach synchronous speed before loading.
3) V curves show the relationship between armature current, field current, and excitation voltage in synchronous motors.
This document outlines and describes the key components and operating principles of three-phase induction motors, which are widely used in industrial applications due to their continuous operation. It discusses the main types of electrical machines and induction motors, including squirrel cage and slip ring induction motors. The document explains the basic working principle of three-phase induction motors, involving the generation of a rotating magnetic field in the stator that induces current in the rotor. It also describes the main components of three-phase induction motors such as the frame, stator, rotor, and windings.
CONTENT
Starting Of Induction Motor
Starters
Types Of Starter For 3-ph Induction Motors
Starting Of Slip Ring Induction Motor
D.O.L.(Direct On Line) starter
Star-delta Starter
Auto Transformer Starter
Difference Between DOL/Star Delta/ Autotransformer
This document summarizes different types of stepper motors, including variable reluctance, permanent magnet, and hybrid stepper motors. It describes their construction, working principles, modes of operation like single phase ON, two phase ON, and half step modes. It also discusses static characteristics like torque vs step angle/current and dynamic characteristics like pull in and pull out. Finally, it lists some common industrial applications of stepper motors such as in printers, disk drives, machine tools, robotics, and tape drives.
1) DC generators convert mechanical energy to electrical energy through Faraday's law of electromagnetic induction. When a conductor moves through a magnetic field, an EMF is induced in the conductor.
2) The main components of a DC generator are the yoke, field electromagnets, armature, commutator, and brushes. The armature is wound with coils and rotates within the magnetic field produced by the field electromagnets to generate an EMF.
3) As the armature rotates, the commutator and brushes are used to periodically reverse the direction of current in the external circuit, thereby producing direct current. Losses in the generator arise from copper, iron, and mechanical components
The induction motor operates on the principle of electromagnetic induction. It consists of two main parts - the stator and the rotor. The stator contains windings that generate a rotating magnetic field, acting as the primary. This rotating field induces currents in the rotor windings, which acts as the secondary. The rotor is then pushed to rotate at a slightly lower speed than the rotating field due to "slip."
A stepper motor converts electrical pulses into discrete mechanical movements of its shaft. The shaft rotates in discrete step increments that correspond directly to the sequence and frequency of input pulses. There are three main types of stepper motors: variable-reluctance, permanent magnet, and hybrid. Stepper motors provide controlled movement and are well-suited for applications that require control of rotation angle, speed, position, and synchronization. They have advantages like full torque at standstill and excellent response to starting, stopping, and reversing.
Winding
What is Armature winding?
Terms related to armature winding.
Single layer and double layer windings.
Comparison between closed and open windings.
Types of DC armature winding.
Types of AC armature winding.
The document discusses permanent magnet brushless DC motors, including their construction with a permanent magnet rotor, electronic commutation instead of a mechanical commutator, and applications in automotive, industrial, computer and small appliance uses. It provides details on the operation, classifications based on pole arc and waveform, and common controller circuits used for permanent magnet brushless DC motors.
Universal motors can operate on either AC or DC power. They have high starting torque because the armature and field windings are connected in series. Speed control of a universal motor is achieved by varying the terminal voltage, which changes the current and electromagnetic torque. The motor's angular velocity is determined by solving the differential equation for the electrical system, which depends on the induced back EMF. Back EMF is produced by the motion of the rotor in the magnetic field and opposes the applied voltage, with its magnitude proportional to speed. Varying the applied voltage allows control of the motor's speed and torque.
The document discusses DC motors. It describes 3 types of DC motors - shunt motors, series motors, and compound motors. It explains the construction and working principles of each type. Speed control methods for DC motors are also discussed, including flux control, armature control, and voltage control. Various applications of each DC motor type are provided.
The document provides an overview of induction motors, including:
1. It describes the basic operating principle of induction motors, which induce a current in the rotor via electromagnetic induction from a rotating magnetic field in the stator.
2. It discusses different types of induction motors including single phase, three phase, squirrel cage, and slip ring rotors.
3. It provides some key formulas for induction motors relating supply frequency, pole pairs, synchronous speed, rotor speed, and slip.
The polyphase induction motor is commonly used in industry due to its simplicity and reliability. It works by inducing currents in the rotor windings via a rotating magnetic field produced by the stator windings. This induces a torque on the rotor causing it to rotate at a slightly lower speed than the rotating field. There are two main types: squirrel-cage motors which have shorted rotor windings, and wound-rotor motors which have external connections to the rotor windings allowing control of starting torque. An equivalent circuit model is used to analyze induction motor performance characteristics such as torque-speed curves.
Rotating magnetic fields are produced by supplying a three-phase winding with alternating current such that the current in each phase is 120 degrees out of phase. This produces three magnetic fluxes that are 120 degrees out of phase. The vector sum of these three fluxes results in a single magnetic flux vector that rotates in space. This rotating magnetic field can be used to drive an electric motor or generator. The speed of rotation is proportional to the supply frequency and number of poles, such that for a 2-pole winding, the magnetic field rotates at half the frequency of the alternating current supply.
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.
1) The document discusses Nikola Tesla's discovery of the rotating magnetic field, which allows production of rotary force without commutators.
2) It explains that arranging coils connected to alternating electromagnetic forces (EMFs) out of phase by 90 degrees produces a traveling magnetic pole that rotates and causes the field magnet to rotate as well.
3) This rotating magnetic field principle underlies all periodic electric waves and enabled many later inventions beyond just electric motors.
This presentation provides an overview of induction motors, including:
1. It discusses the history and invention of induction motors by Tesla and Dobrovolsky.
2. It explains the principle of operation of induction motors, how they generate torque via electromagnetic induction without direct electrical connection to the rotor.
3. It covers the construction of common induction motors, including squirrel cage and slip ring rotors, and describes speed control techniques like PWM.
This document provides information about induction motors. It describes the basic construction of an induction motor, including its stator and squirrel cage or wound rotor. It explains how a rotating magnetic field is produced from the three-phase stator windings and how this induces a voltage and current in the rotor. It defines key terms like synchronous speed and slip. It also presents the equivalent circuit model of an induction motor and discusses speed control methods and power losses in induction machines.
1. The document discusses single phase transformers on load and no load conditions with vector diagrams and approximate equivalent circuits.
2. It explains that under no load conditions, the primary current lags the voltage by an angle less than 90 degrees due to iron and copper losses.
3. Under load conditions, the secondary current induces an opposing magnetic field, reducing the primary current increase until the core's magnetic field is restored to its original strength.
This document outlines a lecture on induction machines. It begins with an agenda and objectives. It then discusses the basic structure of induction machines, including the stator, rotor, and additional components. A key point is that the stator produces a rotating magnetic field when powered by a three-phase AC supply, which induces current in the rotor. Diagrams and animations are provided to illustrate this rotating magnetic field. The document also discusses topics like rotor windings and the relationship between electrical frequency and magnetic field rotational speed.
Autotransformer and three phase transformerRitu Rajan
This document discusses three phase transformers and auto transformers. It begins by explaining the construction of three phase transformers, including forced oil and air cooling systems. It then reviews the star and delta configurations for three phase circuits. Star connections have a neutral point while delta connections do not. The document also discusses typical three phase transformer connections like Y-zigzag and delta-zigzag. It explains that auto transformers have only one winding and are used for small voltage changes, with diagrams of step-up and step-down configurations. Finally, it notes that three phase transformers can be made from single phase transformers connected in banks or from coils on a single core with multiple limbs.
SSD - Solid State Drive PPT by Shyam jos Shyam Jos
Solid State Drive (SSD)
In 1995, M-Systems introduced the first flash-based solid-state drives. SSDs use non-volatile solid state memory like NAND flash or DRAM to store data without moving parts, distinguishing them from traditional hard disk drives. SSDs have significant performance advantages over HDDs with faster access times and read/write speeds, higher reliability since there are no moving parts, lower power consumption, and silent operation. However, SSDs currently have higher costs and offer less storage capacity than HDDs.
This document discusses different types of starters for 3-phase induction motors, including their operation and advantages/disadvantages. It describes stator resistance, auto-transformer, star-delta, rotor resistance, and direct online starters. The star-delta starter connects the motor in a star configuration at start to reduce voltage and current by 1/3, then switches to delta for run. The direct online starter connects the motor directly to full voltage, providing maximum torque but also maximum starting current of 6-8 times full load current. Variable frequency drives control motor speed by varying supply frequency and voltage.
This document discusses the design of a wound rotor induction motor. It defines key terms like slip, slip rings, and brushes. It describes the basic requirements of variable speed and high starting torque. The rotor contains three-phase windings connected in a star configuration with open ends connected to slip rings. Rotor resistance can be adjusted to control torque and speed characteristics. The wound rotor design provides benefits like low starting current and high starting torque compared to a squirrel cage motor.
This document provides an overview of direct current (DC) machines, including DC generators and DC motors. It discusses key components such as the armature, commutator, field windings, and how they work together to convert mechanical energy to electrical energy in a DC generator or convert electrical energy to mechanical energy in a DC motor. Diagrams are included to illustrate the construction and operating principles of DC machines.
Description of Auto-Transformer working principle,Constructional features of Auto transformer,Advantages of Auto transformer,Inductional law in Auto transformer,copper saving advantage in Auto transformer,Types of Auto transformer,Conversion of two-winding transformet to Auto transformer,Disadvantages of Auto transformer,Applications of Auto transformer,Limitations of Auto transformer.
Tap changers are devices fitted to power transformers that allow for regulation of the output voltage. Voltage regulation is achieved by altering the number of turns in one winding of the transformer, which changes the transformer ratios. Tap changers offer variable control to keep the supply voltage within limits. They can be on load or off load tap changers. On load tap changers consist of a diverter switch and selector switch to transfer current between taps without interruption.
The document discusses electrical drive systems and power electronic converters used in drives. It begins by explaining what power electronics are and their applications. Modern electrical drive systems often use power electronic converters to efficiently control electric motors and improve performance over traditional fixed speed drives. Power electronic converters can be configured in different ways depending on the drive application and whether an AC or DC motor is used. Common converter configurations for DC drives include AC-DC, AC-DC-DC, and various DC-DC converter topologies.
This document discusses power system stability and microgrids. It defines power system stability and classifies it into several types including rotor angle stability, voltage stability, and frequency stability. It also discusses microgrids, their interconnection to main grids for availability and economic benefits, and methods for connecting microgrids using switchgear or static switches. In conclusion, it states that power system stability is important for normal operation and can be improved through devices like capacitors and FACTS controllers, and that microgrids satisfy local loads while reducing transmission losses through local renewable generation.
AC motors are commonly used on aircraft and are classified by output power. Large motors have over 3KW output and are three-phase, while medium and small motors range from 3KW to 50W and are mostly single-phase. Miniature motors are under 50W. The document then describes various types of AC motors used on aircraft, including induction motors, which are the most widely used type and operate using a rotating magnetic field to induce current in the rotor. Two-phase induction motors can control rotation direction and speed, while split-phase motors use a capacitive winding to phase split the current. Synchronous motors maintain a constant speed set by the rotating magnetic field frequency.
This presentation provides an overview of induction motors. It begins by defining an electric motor as a device that converts electrical energy to mechanical energy. It then classifies motors as either alternating current (AC) or direct current (DC). The presentation focuses on AC induction motors, which are the most common type used in industry due to their simple design, low cost, and ease of maintenance. It describes the basic components and operation of an induction motor, including its stator, rotor, and how rotational motion is produced through electromagnetic induction. It also discusses two common rotor types - squirrel cage and wound rotor - and defines the concept of slip in induction motors.
An induction motor starter is necessary to control the starting current and torque of the motor. There are different types of starters that can be used depending on the size of the motor, including DOL, star-delta, primary resistance, and auto transformer starters. A soft starter uses electronics to gradually increase the voltage applied to the motor during starting and stopping, reducing mechanical and electrical stresses on the system.
An AC motor operates using a rotating magnetic field produced by an alternating current to generate torque and turn the rotor shaft. There are two main types - synchronous motors where the rotor rotates at the exact supply frequency, and induction motors where the rotor rotates slightly slower. Induction motors are the most common and operate using electromagnetic induction to induce currents in the rotor and generate torque. Squirrel cage rotors are the most widely used type and consist of conductive bars in the rotor that induce currents to generate a magnetic field and turn the shaft.
1. The document discusses the principle of operation of 3-phase induction motors and their applications. It explains how a rotating magnetic field is generated using a 3-phase supply, which causes the rotor to turn.
2. Key aspects covered include induction motor construction, torque-speed characteristics, multi-pole motors, and applications of variable frequency drives.
3. The document compares DC and AC machines, and explains why AC induction motors are more commonly used due to the availability of single or multi-phase AC power.
The document discusses the principles of operation of 3-phase induction motors. It explains that a 3-phase induction motor operates using a rotating magnetic field produced by a 3-phase AC current in the stator windings which causes the rotor to turn. As the rotor turns slightly slower than the rotating field, a slip is produced which generates an induced current in the rotor and produces torque. The torque causes the rotor to accelerate until the motor reaches its operating speed where the torque equals the load.
This document discusses the principle of operation of 3-phase induction motors. It explains that a 3-phase induction motor operates using a rotating magnetic field produced by a 3-phase AC current in the stator windings which causes the rotor to turn. As the rotor turns slightly slower than the rotating magnetic field, a slip is produced which induces currents in the rotor windings to generate torque. The torque causes the rotor to accelerate until the motor reaches its operating speed where the torque exactly balances the mechanical load on the shaft.
The document discusses the principles of operation of 3-phase induction motors. It explains that a 3-phase induction motor operates using a rotating magnetic field produced by a 3-phase AC current in the stator windings which causes the rotor to turn. The speed of the rotor is slightly less than the synchronous speed of the rotating magnetic field due to slip. The difference between the rotor speed and synchronous speed is used to produce torque. Torque-speed characteristics and power output equations for 3-phase induction motors are also presented.
The document summarizes the construction and working of alternators and synchronous motors. It describes the main components of an alternator including the stator, which contains three-phase windings, and the rotor, which carries a field winding supplied by a DC source. It discusses two types of rotors: salient pole for low speeds and cylindrical for high speeds. It also explains the working principle of synchronous motors, including how they develop torque through magnetic locking between the stator and rotor fields rotating at the same speed.
The document discusses the asynchronous or induction motor, specifically focusing on its construction and working principles. It describes the main components of an asynchronous motor including the stator and rotor, and explains how different types of rotors like squirrel cage and slip ring function through electromagnetic induction to generate torque without a direct electrical connection. The working principle is demonstrated through diagrams showing how a rotating magnetic field is produced in the stator to induce currents in the rotor and make it rotate at a slightly lower synchronous speed.
The document describes the construction and operating principles of induction motors. It discusses:
- The key components of induction motors including the stator, rotor, and rotating magnetic field generated by the stator windings.
- The two main types of rotors: squirrel cage and wound rotor. Squirrel cage rotors are simpler and more rugged while wound rotors can be used to adjust torque-speed characteristics.
- Concepts like synchronous speed, slip, and rotor frequency. Slip is defined as the difference between synchronous and actual rotor speed.
- The per-phase equivalent circuit model of induction motors and how it is used to analyze power flow and calculate performance parameters like torque.
The document discusses induction motors, also known as asynchronous motors. It describes their construction, including the stator, rotor, and rotating magnetic field produced. Squirrel cage and wound rotors are covered. Formulas for synchronous speed, slip, and rotor frequency are provided. Examples calculations are given to demonstrate determining speeds and frequencies under different operating conditions. The per-phase equivalent circuit of an induction motor is also mentioned.
The document discusses synchronous motors, including their definition, construction, working principle, types, advantages, and applications. Synchronous motors run at a constant synchronous speed determined by the supply frequency, and consist of a stationary stator and rotating rotor. The stator contains three-phase windings powered by AC, while the rotor is excited by DC. The rotor synchronizes with the rotating stator magnetic field. Synchronous motors provide constant speed operation and are used for applications requiring precise speed control or power factor correction.
DC and AC motors convert electrical energy to mechanical energy through electromagnetic interaction between a magnetic field and electric current. DC motors use direct current and have commutators, while AC motors use alternating current and have either induction or synchronous designs. Induction motors generate torque through electromagnetic induction, and synchronous motors synchronize the rotor speed to the supply frequency to maintain a constant speed under varying loads. Both motor types have various applications depending on their torque, speed, and load characteristics.
This document discusses three-phase induction motors. It describes their common use in industry due to their simple and rugged design. It explains that induction motors run at a constant speed from no-load to full-load. Variable speed control requires an adjustable frequency power supply. The motor has a stationary stator and a revolving rotor, which can have either wound or squirrel cage windings. A rotating magnetic field from the stator induces currents in the rotor to generate torque. Induction motors always run slightly slower than synchronous speed due to slip.
Three Phase Induction Motor consists of a stator and rotor. The stator contains three-phase windings that produce a rotating magnetic field when powered. This rotating magnetic field induces currents in the rotor conductors, causing the rotor to rotate at a synchronous speed proportional to the power frequency and inversely proportional to the number of poles. As the rotor rotates, its speed is slower than the rotating magnetic field due to induction principles that generate torque to keep the rotor spinning even after the magnetic field has passed by.
The document discusses induction motors. It explains that an induction motor works by electromagnetic induction, where the alternating current in the stator produces a rotating magnetic field that induces current in the rotor and causes it to turn. It describes the basic components of induction motors including the stator, rotor, and housing. It also discusses how varying the frequency of the alternating current supply can be used to control the motor's speed.
Induction motors work by using a rotating magnetic field in the stator to induce currents in the rotor. This produces a torque on the rotor causing it to rotate slightly slower than the synchronous speed of the magnetic field. The induction motor has no direct electrical connection between the stator and rotor; instead, current is induced in the rotor by electromagnetic induction from the stator's magnetic field. This self-starting property makes induction motors well-suited for many applications.
The document provides an overview of induction motors, including:
1. It describes the basic operating principle of induction motors, which induce a current in the rotor via electromagnetic induction from a rotating magnetic field in the stator.
2. It discusses different types of induction motors including single phase, three phase, squirrel cage, and slip ring rotors. Speed control methods like PWM are also covered.
3. Formulas relating supply frequency, pole pairs, synchronous speed, slip, and rotor speed are presented.
The document provides an overview of induction motors, including:
1. It describes the basic operating principle of induction motors, which induce a current in the rotor via electromagnetic induction from a rotating magnetic field in the stator, rather than supplying current directly to the rotor like a synchronous motor.
2. It discusses the different types of induction motors, including single phase, three phase, squirrel cage, and slip ring rotor designs.
3. It provides some key formulas for relating supply frequency, pole pairs, synchronous speed, slip speed, and rotor speed in induction motors.
The document discusses the key concepts of induction motors. It explains that an induction motor operates by using a rotating magnetic field in the stator to induce currents in the rotor that generate torque. It describes the different components of an induction motor including the squirrel cage and wound rotors. It also discusses important concepts like slip speed, synchronous speed, rotor frequency, equivalent circuits, power flow, and how torque is developed based on the interaction between stator and rotor magnetic fields.
This document discusses different types of motors, including DC motors, AC motors, and servo motors. It describes the key components and characteristics of series, shunt, and compound DC motors. It also explains induction motors, synchronous motors, and the differences between squirrel cage and wound rotors. AC motors are divided into synchronous and induction types. Servo motors are described as incorporating a DC motor, gear train, potentiometer, and control circuit to enable precise angular positioning. Common applications of different motor types are also mentioned.
Diodes are semiconductor components that allow current to flow in only one direction. They have two terminals called the anode and cathode. Current can flow from the anode to the cathode but not in the reverse direction. When a forward bias is applied, the depletion region collapses and current can flow through the diode. When a reverse bias is applied, the depletion region expands and blocks current flow. Diodes are used in applications such as rectifiers, reverse current protection, logic gates, and voltage spike suppression.
This document provides an introduction to basic electronic components. It discusses two types of components - passive components (resistors, capacitors, inductors) and active components (tube devices, semiconductor devices). Resistors oppose current flow, capacitors store electrical energy, and inductors produce inductance. Semiconductor devices like chips are now replacing tube devices due to their smaller size, lower power needs, and longer life. The document provides details on interpreting color codes for resistors and markings for other components.
There are 5 active volcanoes, 5 inactive volcanoes, and 5 dormant volcanoes in the Philippines. The active volcanoes include Musuan Peak, Smith Volcano, Kanlaon Volcano, Matutum, and Mount Ragang. The inactive volcanoes include Mount Alu, Mount Binaca, Mount Guinsiliban, Mount Kitanglad, and Tadlac Lake. The dormant volcanoes include Mount Isarog, Mount Apo, Mount Banahaw, Mount Cagua, and the Leonard Range volcanic complex.
Electronics deals with electrical circuits involving active components like transistors and diodes. Vacuum tubes were early electronic components and drove technological advances in the early 20th century. By the 1950s, transistors replaced vacuum tubes and allowed for smaller, faster, and more reliable electronics. Key branches of electronics include digital, analog, microelectronics, and optoelectronics. Electronics is widely used today for entertainment, communication, defense applications, industrial control, medical devices, and instrumentation.
This document provides an introduction to statistics. It defines statistics as techniques used to collect, organize, analyze and interpret quantitative data. There are two main kinds of statistics: descriptive statistics, which summarizes and describes data through graphical or computational methods; and inferential statistics, which makes inferences about populations based on samples. Key statistical concepts introduced include populations, samples, data types (continuous and discrete), methods of data presentation (graphs), and measures of central tendency (mean, median, mode) and dispersion (range).
This document provides an overview of different types of probability concepts including:
- History of probability originating from a gambler's dispute in 1654.
- Definitions of probability, complementary probability, joint probability, conditional probability, independent probability, and repeated trials probability.
- Formulas and examples are given for each type of probability concept to illustrate their calculation and applications involving events such as dice rolls, card draws, and blood types.
- Key individuals in the development of probability theory are mentioned like Pascal, Fermat, and Bernoulli.
This document provides an overview of different types of probability, including:
- Complementary probability, which is the probability of an event not occurring.
- Joint probability, including mutually exclusive events where outcomes do not overlap and non-mutually exclusive events where outcomes can overlap.
- Conditional probability, where the probability of one event is dependent on another event occurring, including dependent and independent probabilities.
- Repeated trial probability, which calculates the probability of an event occurring a specific number of times over multiple trials.
Formulas and examples are provided for each type of probability.
The document provides an overview of different types of probability, including:
- Complementary probability, which is the probability of an event not occurring and sums to 1 with the original probability.
- Joint probability, which measures the probability of two events occurring together, including mutually exclusive events where the probability of both occurring is 0.
- Conditional probability, where the probability of one event is dependent on another occurring, such as the probability of answering a question correctly given it was guessed.
- Repeated trial probability uses the binomial distribution to calculate the probability of outcomes over multiple independent yes/no trials, such as getting a certain number of questions right on a multiple choice test.
The document provides a history of the development of probability theory from its origins in the 16th century to modern applications. Some of the key contributors and advances mentioned include:
- Cardan wrote one of the earliest works on probability in dice rolls and games of chance in 1550.
- Pascal and Fermat laid the foundations of probability theory in correspondence solving gambling problems in 1654.
- Graunt analyzed mortality data and made predictions, gaining access to the Royal Society of London.
- Huygens published the first text on probability theory in 1657 introducing mathematical expectation.
- Laplace's 1812 work outlined the evolution of probability theory and presented key theorems, establishing it as a rigorous
- Inductance is the property of an electrical conductor by which a change in current induces an electromotive force (emf) in both the conductor itself and any nearby conductors.
- Inductors oppose changes in current by inducing a voltage proportional to the rate of change of current in accordance with Lenz's law.
- Inductors can be connected in series or parallel. When in series, their inductances add together to find the total inductance. When in parallel, the reciprocal of their inductances are added together to find the total inductance.
- Mutual inductance is the induction of an emf in one coil due to a changing current in another nearby coil due to their
Group 1: BSME IV
Gutierrez, Eduardo Jr. H.
Cabanag, Cleo C.
The document discusses capacitors, including their definition as a passive two-terminal electrical component used to temporarily store electrical energy in an electric field. It describes how capacitance is measured in Farads and depends on the physical properties of the capacitor such as plate area and separation. It also discusses how dielectrics can increase a capacitor's capacitance and the formulas used to calculate capacitance and energy storage for different capacitor configurations including parallel plate, spherical, and cylindrical capacitors.
The human body contains multiple systems that work together to sustain life. These systems include the digestive, circulatory, nervous, respiratory, muscular, skeletal, urinary, reproductive, lymphatic, integumentary, and endocrine systems. Each system is comprised of organs and tissues that perform specialized functions to keep the body functioning properly.
El documento lista los principales grupos étnicos de las tres grandes islas de Filipinas: Luzón (Ilocano, Kapampangan, Tagalog, Bicolano, Ifugao, Ivatan), Visayas (Ilonggo, Cebuano) y Mindanao (Maranao, Yakan, Subanen, Bagobo). El documento parece ser parte de un proyecto escolar de estudios sociales sobre los grupos étnicos de Filipinas.
This document discusses Bernoulli trials and the binomial probability distribution formula. It defines a Bernoulli trial as a random experiment with two possible outcomes, success and failure, where the probability of success is the same for each trial. Examples given of Bernoulli trials include flipping a coin, rolling a die, and conducting an opinion poll. The binomial probability formula is presented as P(X=x) = nCx(p)x(q)n-x, where n is the number of trials, x is the number of successes, p is the probability of success on each trial, and q is the probability of failure. Three examples applying this formula to problems involving coin tosses, dice rolls, and multiple choice tests are shown.
Conditional probability is the probability of an event occurring given that another event has occurred. It is calculated as the probability of both events occurring divided by the probability of the first event. An example is given of calculating the probability of drawing two white balls in succession from an urn without replacement. The formula for conditional probability is derived as the probability of events A and B occurring divided by the probability of A. This is demonstrated using an example of finding the percentage of friends who like chocolate that also like strawberry.
This document describes how to transform resistor networks between wye (Y) and delta (Δ) configurations. It states that wye networks are sometimes called T networks, while delta networks can be called Π networks. The document provides equations to transform between the two configurations when the resistances are equal or unequal. It gives an example of transforming a wye network into an equivalent delta network.
Cells convert stored chemical energy into electrical energy and are the basic electrochemical unit that produces voltage. Batteries are formed by connecting multiple cells electrically in either series or parallel configurations. Connecting cells in series increases the overall voltage while keeping the current the same, whereas connecting cells in parallel increases the total current while maintaining the same voltage.
Power is measured in watts and represents the rate at which work is done or energy is used. It can be calculated using current, voltage, and resistance based on Ohm's law. Energy represents the ability to do work and is the amount of power consumed over a period of time. It is measured in joules which is equal to watt-seconds. Power indicates how much work can be done in a specific amount of time and represents the rate of doing work.
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2. • Nikola Tesla conceived the basic principals of the polyphase
induction motor in 1883, and had a half horsepower (400
watt) model by 1888. Tesla sold the manufacturing rights to
George Westinghouse for $65,000
• Most large ( > 1 hp or 1 kW) industrial motors are poly-
phase induction motors. By poly-phase, we mean that the
stator contains multiple distinct windings per motor pole,
driven by corresponding time shifted sine waves. In practice,
this is two or three phases. Large industrial motors are 3-
phase. By induction motor, we mean that the stator
windings induce a current flow in the rotor conductors, like a
transformer, unlike a brushed DC commutator motor.
3. Construction
• An induction motor is composed of a rotor, known as an
armature, and a stator containing windings connected to a poly-
phase energy source . The simple 2-phase induction motor
below is similar to the 1/2 horsepower motor which Nikola
Tesla introduced in 1888.
4. • The stator is wound with pairs of coils corresponding to the
phases of electrical energy available. The 2-phase induction
motor stator has 2-pairs of coils, one pair for each of the two
phases of AC. The individual coils of a pair are connected in
series and correspond to the opposite poles of an
electromagnet. That is, one coil corresponds to a N-pole, the
other to a S-pole until the phase of AC changes polarity. The
other pair of coils is oriented 90o in space to the first pair. This
pair of coils is connected to AC shifted in time by 90o in the case
of a 2-phase motor. In Tesla's time, the source of the two
phases of AC was a 2-phase alternator.
• The stator has salient, obvious protruding poles, as used on
Tesla's early induction motor. This design is used to this day for
sub-fractional horsepower motors (<50 watts).
5. • For larger motors less torque pulsation and higher efficiency results if
the coils are embedded into slots cut into the stator laminations
• Stator frame showing slots for windings.
• The stator laminations are thin insulated rings with slots
punched from sheets of electrical grade steel. A stack of
these is secured by end screws, which may also hold the
end housings.
6. Stator with (a) 2-φ and (b) 3-φ windings.
• the windings for both a two-phase motor and a three-
phase motor have been installed in the stator slots. The
coils are wound on an external fixture, then worked into
the slots. Insulation wedged between the coil periphery
and the slot protects against abrasion.
• Actual stator windings are more complex than the
single windings per pole in Figure above.
Comparing the 2-φ motor to Tesla's 2-φ motor with
salient poles, the number of coils is the same.
7. • In actual large motors, a pole winding, is divided into identical
coils inserted into many smaller slots than above. This group is
called a phase belt. . The distributed coils of the phase belt
cancel some of the odd harmonics, producing a more sinusoidal
magnetic field distribution across the pole. This is shown in the
synchronous motor section. The slots at the edge of the pole
may have fewer turns than the other slots. Edge slots may
contain windings from two phases. That is, the phase belts
overlap.
8. • The key to the popularity of the AC induction motor is simplicity as
evidenced by the simple rotor. The rotor consists of a shaft, a steel
laminated rotor, and an embedded copper or aluminum squirrel cage,
shown at (b) removed from the rotor. As compared to a DC motor
armature, there is no commutator. This eliminates the brushes, arcing,
sparking, graphite dust, brush adjustment and replacement, and re-
machining of the commutator
• Laminated rotor with (a) embedded squirrel cage, (b)
conductive cage removed from rotor
9. Theory of operation
• A short explanation of operation is that the stator creates a
rotating magnetic field which drags the rotor around.
• The theory of operation of induction motors is based on a
rotating magnetic field. One means of creating a rotating
magnetic field is to rotate a permanent magnet as. If the moving
magnetic lines of flux cut a conductive disk, it will follow the
motion of the magnet. The lines of flux cutting the conductor will
induce a voltage, and consequent current flow, in the conductive
disk. This current flow creates an electromagnet whose polarity
opposes the motion of the permanent magnet– Lenz's Law. The
polarity of the electromagnet is such that it pulls against the
permanent magnet. The disk follows with a little less speed than
the permanent magnet.
10. Rotating magnetic field produces torque in conductive disk.
The torque developed by the disk is proportional to the number of flux
lines cutting the disk and the rate at which it cuts the disk. If the disk
were to spin at the same rate as the permanent magnet, there would
be no flux cutting the disk, no induced current flow, no electromagnet
field, no torque. Thus, the disk speed will always fall behind that of
the rotating permanent magnet, so that lines of flux cut the disk
induce a current, create an electromagnetic field in the disk, which
follows the permanent magnet. If a load is applied to the disk, slowing
it, more torque will be developed as more lines of flux cut the disk.
Torque is proportional to slip, the degree to which the disk falls behind
the rotating magnet. More slip corresponds to more flux cutting the
conductive disk, developing more torque.
11. • An analog automotive eddy current speedometer is based on the
principle illustrated above. With the disk restrained by a spring,
disk and needle deflection is proportional to magnet rotation rate.
• A rotating magnetic field is created by two coils placed at right
angles to each other, driven by currents which are 90o out of
phase. This should not be surprising if you are familiar with
oscilloscope Lissajous patterns.
• (Out of phase (90o) sine waves produce circular Lissajous
pattern.)
12. (X-axis sine and Y-axis cosine trace circle.)
the two 90o phase shifted sine waves applied to oscilloscope
deflection plates which are at right angles in space. If this were not
the case, a one dimensional line would display. The combination of
90o phased sine waves and right angle deflection, results in a two
dimensional pattern– a circle. This circle is traced out by a
counterclockwise rotating electron beam.
13. No circular motion from in-phase waveforms.
why in-phase sine waves will not produce a circular
pattern. Equal “X” and “Y” deflection moves the
illuminated spot from the origin at (a) up to right (1,1)
at (b), back down left to origin at (c),down left to (-1.-
1) at (d), and back up right to origin. The line is
produced by equal deflections along both axes; y=x
is a straight line.
14. Rotating magnetic field from 90o phased sinewaves.
If a pair of 90o out of phase sine waves produces a circular
Lissajous, a similar pair of currents should be able to produce
a circular rotating magnetic field. Such is the case for a 2-
phase motor. By analogy three windings placed 120o apart in
space, and fed with corresponding 120o phased currents will
also produce a rotating magnetic field.
15. • As the 90o phased sinewaves, progress from points (a)
through (d), the magnetic field rotates counterclockwise
(figures a-d) as follows:
• (a) φ-1 maximum, φ-2 zero
• (a') φ-1 70%, φ-2 70%
• (b) φ-1 zero, φ-2 maximum
• (c) φ-1 maximum negative, φ-2 zero
• (d) φ-1 zero, φ-2 maximum negative
16. Motor speed
The rotation rate of a stator rotating magnetic field is related to the
number of pole pairs per stator phase. The “full speed” has a total of
six poles or three pole-pairs and three phases. However,there is but
one pole pair per phase– the number we need. The magnetic field
will rotate once per sine wave cycle. In the case of 60 Hz power, the
field rotates at 60 times per second or 3600 revolutions per minute
(rpm). For 50 Hz power, it rotates at 50 rotations per second, or
3000 rpm. The 3600 and 3000 rpm, are the synchronous speed of
the motor. Though the rotor of an induction motor never achieves
this speed, it certainly is an upper limit. If we double the number of
motor poles, the synchronous speed is cut in half because the
magnetic field rotates 180o in space for 360o of electrical sine wave.
17. Doubling the stator poles halves the synchronous speed.
The synchronous speed is given by:
Ns = 120·f/P
Ns = synchronous speed in rpm
f = frequency of applied power, Hz
P = total number of poles per phase, a multiple of 2
18. The short explanation of the induction motor is that the rotating magnetic
field produced by the stator drags the rotor around with it.
The longer more correct explanation is that the stator's magnetic
field induces an alternating current into the rotor squirrel cage
conductors which constitutes a transformer secondary. This
induced rotor current in turn creates a magnetic field. The rotating
stator magnetic field interacts with this rotor field. The rotor field
attempts to align with the rotating stator field. The result is rotation
of the squirrel cage rotor. If there were no mechanical motor
torque load, no bearing, windage, or other losses, the rotor would
rotate at the synchronous speed. However, the slip between the
rotor and the synchronous speed stator field develops torque. It is
the magnetic flux cutting the rotor conductors as it slips which
develops torque. Thus, a loaded motor will slip in proportion to the
mechanical load. If the rotor were to run at synchronous speed,
there would be no stator flux cutting the rotor, no current induced
in the rotor, no torque.
19. Torque
• When power is first applied to the motor, the rotor is at rest, while
the stator magnetic field rotates at the synchronous speed Ns. The
stator field is cutting the rotor at the synchronous speed Ns. The
current induced in the rotor shorted turns is maximum, as is the
frequency of the current, the line frequency. As the rotor speeds
up, the rate at which stator flux cuts the rotor is the difference
between synchronous speed Ns and actual rotor speed N, or (Ns -
N). The ratio of actual flux cutting the rotor to synchronous speed is
defined as slip:
• s = (Ns - N)/Ns
• where: Ns = synchronous speed, N = rotor speed
• The frequency of the current induced into the rotor conductors is
only as high as the line frequency at motor start, decreasing as the
rotor approaches synchronous speed. Rotor frequency is given by:
• fr = s·f
• where: s = slip, f = stator power line frequency
20. Torque and speed vs %Slip. %Ns=%Synchronous Speed.
graph shows that starting torque known as locked rotor torque (LRT) is
higher than 100% of the full load torque (FLT), the safe continuous
torque rating. The locked rotor torque is about 175% of FLT for the
example motor graphed above. Starting current known as locked rotor
current (LRC) is 500% of full load current (FLC), the safe running
current. The current is high because this is analogous to a shorted
secondary on a transformer. As the rotor starts to rotate the torque may
decrease a bit for certain classes of motors to a value known as the pull
up torque.
21. • This is the lowest value of torque ever encountered by the starting
motor. As the rotor gains 80% of synchronous speed, torque
increases from 175% up to 300% of the full load torque. This
breakdown torque is due to the larger than normal 20% slip. The
current has decreased only slightly at this point, but will decrease
rapidly beyond this point. As the rotor accelerates to within a few
percent of synchronous speed, both torque and current will
decrease substantially. Slip will be only a few percent during
normal operation.
• For a running motor, any portion of the torque curve below 100%
rated torque is normal. The motor load determines the operating
point on the torque curve. While the motor torque and current may
exceed 100% for a few seconds during starting, continuous
operation above 100% can damage the motor. Any motor torque
load above the breakdown torque will stall the motor. The torque,
slip, and current will approach zero for a “no mechanical torque”
load condition. This condition is analogous to an open secondary
transformer.
22. Induction motor power factor and efficiency.
Power factor
• Induction motors present a lagging (inductive) power factor to the
power line.The power factor in large fully loaded high speed motors
can be as favorable as 90% for large high speed motors. At 3/4 full
load the largest high speed motor power factor can be 92%. The
power factor for small low speed motors can be as low as 50%. At
starting, the power factor can be in the range of 10% to 25%, rising
as the rotor achieves speed.
• Power factor (PF) varies considerably with the motor mechanical
load. An unloaded motor is analogous to a transformer with no
resistive load on the secondary. Little resistance is reflected from
the secondary (rotor) to the primary (stator). Thus the power line
sees a reactive load, as low as 10% PF. As the rotor is loaded an
increasing resistive component is reflected from rotor to stator,
increasing the power factor.
23. Efficiency
• Large three phase motors are more efficient than smaller 3-phase
motors, and most all single phase motors. Large induction motor
efficiency can be as high as 95% at full load, though 90% is more
common.
• Efficiency for a lightly load or no-loaded induction motor is poor
because most of the current is involved with maintaining
magnetizing flux. As the torque load is increased, more current is
consumed in generating torque, while current associated with
magnetizing remains fixed.
• Efficiency at 75% FLT can be slightly higher than that at 100% FLT.
Efficiency is decreased a few percent at 50% FLT, and decreased a
few more percent at 25% FLT. Efficiency only becomes poor below
25% FLT. The variation of efficiency with loading
• Induction motors are typically oversized to guarantee that their
mechanical load can be started and driven under all operating
conditions. If a polyphase motor is loaded at less than 75% of rated
torque where efficiency peaks, efficiency suffers only slightly down
to 25% FLT.
25. • An induction motor may function as an alternator if it is driven by a torque
at greater than 100% of the synchronous speed. This corresponds to a
few % of “negative” slip, say -1% slip. This means that as we are rotating
the motor faster than the synchronous speed, the rotor is advancing 1%
faster than the stator rotating magnetic field. It normally lags by 1% in a
motor. Since the rotor is cutting the stator magnetic field in the opposite
direction (leading), the rotor induces a voltage into the stator feeding
electrical energy back into the power line.
• Such an induction generator must be excited by a “live” source of 50 or 60
Hz power. No power can be generated in the event of a power company
power failure. This type of alternator appears to be unsuited as a standby
power source. As an auxiliary power wind turbine generator, it has the
advantage of not requiring an automatic power failure disconnect switch to
protect repair crews. It is fail-safe.
• Small remote (from the power grid) installations may be make self-exciting
by placing capacitors in parallel with the stator phases. If the load is
removed residual magnetism may generate a small amount of current
flow. This current is allowed to flow by the capacitors without dissipating
power. As the generator is brought up to full speed, the current flow
increases to supply a magnetizing current to the stator. The load may be
applied at this point. Voltage regulation is poor. An induction motor may be
converted to a self-excited generator by the addition of capacitors.[6]
26. Motor starting and speed control
• Some induction motors can draw over 1000% of full load current during
starting; though, a few hundred percent is more common. Small motors of
a few kilowatts or smaller can be started by direct connection to the
power line. Starting larger motors can cause line voltage sag, affecting
other loads. Motor-start rated circuit breakers (analogous to slow blow
fuses) should replace standard circuit breakers for starting motors of a
few kilowatts. This breaker accepts high over-current for the duration of
starting.
Autotransformer induction motor
starter.
27. • Motors over 50 kW use motor starters to reduce line current from
several hundred to a few hundred percent of full load current. An
intermittent duty autotarnsformer may reduce the stator voltage for a
fraction of a minute during the start interval, followed by application of
full line voltage as in Figure above. Closure of the S contacts applies
reduced voltage during the start interval. The S contacts open and the R
contacts close after starting. This reduces starting current to, say, 200%
of full load current. Since the autotransformer is only used for the short
start interval, it may be sized considerably smaller than a continuous
duty unit.
Running 3-phase motors on 1-phase
• Three-phase motors will run on single phase as readily as single phase
motors. The only problem for either motor is starting. Sometimes 3-
phase motors are purchased for use on single phase if three-phase
provisioning is anticipated. The power rating needs to be 50% larger
than for a comparable single phase motor to make up for one unused
winding. Single phase is applied to a pair of windings simultanous with a
start capacitor in series with the third winding. The start switch is
opened upon motor start. Sometimes a smaller capacitor than the start
capacitor is retained while running.
28. Starting a three-phase motor on single phase.
• The circuit for running a three-phase motor on single phase is
known as a static phase converter if the motor shaft is not
loaded. Moreover, the motor acts as a 3-phase generator. Three
phase power may be tapped off from the three stator windings
for powering other 3-phase equipment. The capacitor supplies a
synthetic phase approximately midway ∠90o between the ∠180o
single phase power source terminals for starting. While running,
the motor generates approximately standard 3-φ,
29. Multiple fields
• Induction motors may contain multiple field windings, for example a 4-
pole and an 8-pole winding corresponding to 1800 and 900 rpm
synchronous speeds. Energizing one field or the other is less complex
than rewiring the stator coils .
• Multiple fields allow speed change.
• If the field is segmented with leads brought out, it may be rewired (or
switched) from 4-pole to 2-pole as shown above for a 2-phase motor. The
22.5o segments are switchable to 45o segments. Only the wiring for one
phase is shown above for clarity. Thus, our induction motor may run at
multiple speeds. When switching the above 60 Hz motor from 4 poles to 2
poles the synchronous speed increases from 1800 rpm to 3600 rpm. If
the motor is driven by 50 Hz, what would be the corresponding 4-pole and
2-pole synchronous speeds?
• Ns = 120f/P = 120*50/4 = 1500 rpm (4-pole)
• Ns = 3000 rpm (2-pole)
30. Variable voltage
• The speed of small squirrel cage induction motors for applications such
as driving fans, may be changed by reducing the line voltage. This
reduces the torque available to the load which reduces the speed.
• Variable voltage controls induction motor speed.
31. Electronic speed control
• Modern solid state electronics increase the options for speed control. By
changing the 50 or 60 Hz line frequency to higher or lower values, the
synchronous speed of the motor may be changed. However, decreasing
the frequency of the current fed to the motor also decreases reactance XL
which increases the stator current. This may cause the stator magnetic
circuit to saturate with disastrous results. In practice, the voltage to the
motor needs to be decreased when frequency is decreased.
• Electronic variable speed drive.
32. • Conversely, the drive frequency may be increased to increase the
synchronous speed of the motor. However, the voltage needs to be
increased to overcome increasing reactance to keep current up to
a normal value and maintain torque. The inverter approximates
sinewaves to the motor with pulse width modulation outputs. This is
a chopped waveform which is either on or off, high or low, the
percentage of “on” time corresponds to the instantaneous sine
wave voltage.
• Once electronics is applied to induction motor control, many control
methods are available, varying from the simple to complex:
Summary: Speed control
Scaler Control Low cost method described above to control only
voltage and frequency, without feedback.
Vector Control Also known as vector phase control. The flux and
torque producing components of stator current are measured or
estimated on a real-time basis to enhance the motor torque-speed
curve. This is computation intensive.
Direct Torque Control An elaborate adaptive motor model allows
more direct control of flux and torque without feedback. This
method quickly responds to load changes.
33. Summary: polyphase induction motors
A polyphase induction motor consists of a polyphase winding embedded
in a laminated stator and a conductive squirrel cage embedded in a
laminated rotor.
Three phase currents flowing within the stator create a rotating magnetic
field which induces a current, and consequent magnetic field in the rotor.
Rotor torque is developed as the rotor slips a little behind the rotating
stator field.
Unlike single phase motors, polyphase induction motors are self-starting.
Motor starters minimize loading of the power line while providing a larger
starting torque than required during running. Line current reducing
starters are only required for large motors.
Three phase motors will run on single phase, if started.
A static phase converter is three phase motor running on single phase
having no shaft load, generating a 3-phase output.
Multiple field windings can be rewired for multiple discrete motor speeds
by changing the number of poles.