A DC generator converts mechanical energy to DC electrical energy using electromagnetic induction. It has two main parts - a rotor that rotates within a stator. As the rotor cuts the magnetic field in the stator, an alternating voltage is induced in the rotor windings. A commutator is used to convert the alternating voltage to direct voltage that can be used to power loads. The characteristics of a DC generator include its open circuit characteristic showing the relationship between generated voltage and field current, and its external characteristic showing the relationship between terminal voltage and load current.
This document discusses different types of armature windings used in DC motors and generators including lap, wave, simplex, duplex, and triplex windings. It explains the characteristics of each type of winding such as the number of parallel paths through the armature, the relationship between back and front pitch, and how they are connected to the commutator segments. The document also covers closed winding configurations and how they provide multiple parallel paths while maintaining a zero resultant EMF around the complete armature circuit.
A DC generator converts mechanical energy into electrical energy using electromagnetic induction. It consists of a magnetic frame, field poles, an armature, and a commutator. The armature rotates under the poles, cutting the magnetic flux and inducing an EMF. The commutator converts the alternating EMF into a pulsating DC voltage. DC generators are classified as separately excited, self-excited (series, shunt, compound), depending on how the field is connected. A DC motor operates on the principle that a current-carrying conductor in a magnetic field experiences a torque. It consists of an armature, field poles, a commutator, and brushes. The back EMF opposes the applied voltage
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.
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
This document discusses different types of DC generators, including separately excited, self-excited, series, shunt, and compound generators. It provides details on how each type works, including the positioning of field coils and how current flows. Compound generators are described as having both series and shunt field windings to overcome disadvantages of series and shunt generators. Short shunt and long shunt compound generators are also explained in terms of how armature and field currents are calculated.
The document summarizes the operating principles and key components of an alternator. It operates on the principle of electromagnetic induction, with a stationary armature and rotating magnetic field. As the rotor rotates, voltage is induced in the stationary conductors. The induced emf is alternating current. Advantages of the stationary armature include reduced voltage drop from fixed terminals and easier insulation of windings. Key components include the stator frame, armature core, cylindrical or salient pole rotor, and damper windings. Ratings specified include voltage, KVA, power factor, and winding resistances. Regulation refers to the drop in terminal voltage from no load to full load conditions.
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.
Armature reaction is the effect of current flowing in the armature windings on the main field flux in a DC machine. It causes two undesirable effects: 1) a reduction in the main field flux per pole, and 2) distortion of the main field flux wave along the air gap. Armature current produces cross-flux that either aids or weakens the main flux depending on its location. This results in a non-uniform flux distribution and a shift in the magnetic neutral axis in the direction of rotation for a generator and against rotation for a motor. It also causes demagnetization due to magnetic saturation, further reducing the main field flux from its no-load value.
This document discusses different types of armature windings used in DC motors and generators including lap, wave, simplex, duplex, and triplex windings. It explains the characteristics of each type of winding such as the number of parallel paths through the armature, the relationship between back and front pitch, and how they are connected to the commutator segments. The document also covers closed winding configurations and how they provide multiple parallel paths while maintaining a zero resultant EMF around the complete armature circuit.
A DC generator converts mechanical energy into electrical energy using electromagnetic induction. It consists of a magnetic frame, field poles, an armature, and a commutator. The armature rotates under the poles, cutting the magnetic flux and inducing an EMF. The commutator converts the alternating EMF into a pulsating DC voltage. DC generators are classified as separately excited, self-excited (series, shunt, compound), depending on how the field is connected. A DC motor operates on the principle that a current-carrying conductor in a magnetic field experiences a torque. It consists of an armature, field poles, a commutator, and brushes. The back EMF opposes the applied voltage
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.
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
This document discusses different types of DC generators, including separately excited, self-excited, series, shunt, and compound generators. It provides details on how each type works, including the positioning of field coils and how current flows. Compound generators are described as having both series and shunt field windings to overcome disadvantages of series and shunt generators. Short shunt and long shunt compound generators are also explained in terms of how armature and field currents are calculated.
The document summarizes the operating principles and key components of an alternator. It operates on the principle of electromagnetic induction, with a stationary armature and rotating magnetic field. As the rotor rotates, voltage is induced in the stationary conductors. The induced emf is alternating current. Advantages of the stationary armature include reduced voltage drop from fixed terminals and easier insulation of windings. Key components include the stator frame, armature core, cylindrical or salient pole rotor, and damper windings. Ratings specified include voltage, KVA, power factor, and winding resistances. Regulation refers to the drop in terminal voltage from no load to full load conditions.
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.
Armature reaction is the effect of current flowing in the armature windings on the main field flux in a DC machine. It causes two undesirable effects: 1) a reduction in the main field flux per pole, and 2) distortion of the main field flux wave along the air gap. Armature current produces cross-flux that either aids or weakens the main flux depending on its location. This results in a non-uniform flux distribution and a shift in the magnetic neutral axis in the direction of rotation for a generator and against rotation for a motor. It also causes demagnetization due to magnetic saturation, further reducing the main field flux from its no-load value.
Synchronous machines include synchronous generators and motors. Synchronous generators are the primary source of electrical power and rely on synchronous motors for industrial drives. There are two main types - salient-pole and cylindrical rotor machines. Synchronous generator operation is based on synchronizing the electrical frequency to the mechanical speed of rotation. The parameters of synchronous machines can be determined from open-circuit, short-circuit, and DC tests. Synchronous generators must be synchronized before connecting in parallel by matching their voltages, phase sequences, and frequencies.
The document discusses various braking methods for induction motors, including regenerative braking, plugging, and different types of dynamic braking. Regenerative braking occurs when the rotor speed exceeds synchronous speed, causing power to flow in the reverse direction. Plugging involves reversing the phase sequence of the supply to change operation from motoring to braking. Dynamic braking disconnects one phase of the supply or connects the motor to a DC supply, causing the motor to act as a generator and dissipate energy as heat.
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.
Principles of Electromechanical Energy ConversionYimam Alemu
This document is the first chapter of a textbook on electromechanical energy conversion. It introduces key concepts such as electrical energy conversion to mechanical energy using magnetic fields. It discusses different types of electromechanical devices and the principle of energy conservation. It also covers energy balance analysis in conversion systems and determining forces and torques from the energy and coenergy of magnetic systems, including those with permanent magnets. The chapter objectives are to understand electromechanical conversion analysis and components, and how to determine forces and torques from energy considerations.
This document provides an overview of symmetrical components for analyzing three-phase power systems. It introduces symmetrical components and how they can be used to simplify fault calculations. The key symmetrical components are defined as the positive, negative, and zero sequence components. Equations are presented to express the original unbalanced phase voltages and currents in terms of these symmetrical components. The significance of each component is described. Methods for calculating faults using symmetrical components are also outlined.
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.
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.
A transformer is a device that changes alternating current (ac) electric power at one voltage level to ac electric power at another voltage level through the action of a magnetic field. An ideal transformer is a lossless device that transfers power efficiently between its two windings. A real transformer is modeled using an equivalent circuit that accounts for power losses, including copper losses, eddy current losses, hysteresis losses, and leakage fluxes. The parameters of the equivalent circuit can be determined experimentally using open-circuit and short-circuit tests.
Three phase Induction Motor (Construction and working Principle)Sharmitha Dhanabalan
The three phase induction motor consists of a stationary stator and a rotating rotor. The stator contains three-phase windings that generate a rotating magnetic field. This rotating field induces currents in the rotor windings, causing the rotor to turn. There are two common types of rotors - squirrel cage and wound rotor. A squirrel cage rotor has embedded conductors inside its core that are permanently short-circuited. A wound rotor has three insulated windings connected to slip rings to allow external resistance control. Due to slight differences in speed, the rotor always rotates at a slightly slower synchronous speed than the stator's magnetic field.
This document provides an overview of DC machines and motors. It discusses:
1) The fundamentals of DC generators and motors, including how voltage is induced in a conductor moving through a magnetic field and how a force is induced on a current-carrying conductor in a magnetic field.
2) The construction of DC machines, including the stationary stator with field poles and rotating armature/rotor with windings.
3) Different types of DC motors like shunt, series, and compound motors and how their field and armature windings are connected. Speed control methods for DC motors are also discussed.
4) Workings of DC motors are explained through equivalent circuits and equations for induced voltage
1) Synchronous machines have a rotor supplied by an external DC source that produces a rotating magnetic field. This induces a voltage in the stator windings.
2) The rotor can have either salient or non-salient poles and is laminated to reduce eddy currents. DC power is supplied to the rotor via slip rings and brushes or a brushless exciter.
3) An equivalent circuit model represents the internal generated voltage and accounts for armature reaction, inductance, and resistance effects on the terminal voltage.
This document provides an overview of DC machines including generators and motors. It discusses the working principles, construction details, types of DC motors including shunt, series and compound motors. It covers key concepts such as EMF equation, back EMF, torque equation and characteristics of DC motors. It also discusses starters for DC shunt motors and speed control methods including flux and armature voltage control. Finally, it briefly mentions some industrial applications of DC motors.
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.
This document discusses electrical measurements and various types of measuring instruments. It covers topics like indicating instruments, wattmeters, energy meters, bridges, potentiometers and instrument transformers. Specifically, it describes the principles and components of instruments like permanent magnet moving coil meters, moving iron meters, dynamometer wattmeters and single phase induction energy meters. It also discusses bridges like Wheatstone bridge and potentiometers for electrical measurements. Measurement of parameters like frequency, power factor using different types of meters is presented.
Synchronous generators operate on the principle of electromagnetic induction. They have a stationary armature winding and a rotating field winding supplied by a direct current source. It is advantageous to have the field winding on the rotor and armature winding on the stator because it allows for easier insulation of the high voltage winding and direct connection to the load. The frequency of the induced voltage depends on the number of rotor poles and its rotational speed. Armature reaction is the effect of the armature magnetic field on the main rotor field, distorting or strengthening it depending on the load power factor.
This document provides information about various types of electrical machines and transformers. It discusses direct current machines and alternating current machines. It also describes different types of motors like induction motors, synchronous motors, and transformers. Key components of these machines like the rotor, stator, windings and magnetic core are explained. Different speed control methods for induction motors are also summarized.
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."
This document discusses the measurement of power and energy in electrical circuits. It begins by defining power in DC and AC circuits, and how it can be measured using a voltmeter and ammeter. It then describes the operating principle of an electrodynamometer wattmeter, which uses two coils to measure power consumed by a load. The moving coil is proportional to voltage, while the fixed coil carries the load current. Errors in wattmeter measurements are also discussed, such as those caused by the pressure coil's inductance and how compensation can be achieved by adding capacitance.
A DC generator converts mechanical energy into electrical energy using the principles of electromagnetic induction. It has two main parts - a stationary stator that produces a magnetic field and a rotating armature.
The stator contains pole cores, pole shoes, and field coils that create the magnetic field when current is passed through the coils. The armature is made of laminated steel and contains conductors that rotate through the magnetic field. This cutting of magnetic flux by the conductors induces an electromotive force (emf) based on Faraday's law of induction.
The induced emf alternates as the conductors pass through different parts of the magnetic field. A commutator is used to rectify the alternating emf
A DC motor converts electrical energy into mechanical energy by using the principle of electromagnetic induction. When a current carrying conductor is placed in a magnetic field, it experiences a force that causes it to rotate. In a DC motor, current is passed through stationary conductors located between poles of a magnetic field. This sets up opposing magnetic fields that produce a torque causing the rotor to rotate within the stator. The direction of current flow determines the direction of rotation. By reversing the current direction, the direction of torque and rotation is also reversed, allowing DC motors to run in both forward and reverse directions.
Synchronous machines include synchronous generators and motors. Synchronous generators are the primary source of electrical power and rely on synchronous motors for industrial drives. There are two main types - salient-pole and cylindrical rotor machines. Synchronous generator operation is based on synchronizing the electrical frequency to the mechanical speed of rotation. The parameters of synchronous machines can be determined from open-circuit, short-circuit, and DC tests. Synchronous generators must be synchronized before connecting in parallel by matching their voltages, phase sequences, and frequencies.
The document discusses various braking methods for induction motors, including regenerative braking, plugging, and different types of dynamic braking. Regenerative braking occurs when the rotor speed exceeds synchronous speed, causing power to flow in the reverse direction. Plugging involves reversing the phase sequence of the supply to change operation from motoring to braking. Dynamic braking disconnects one phase of the supply or connects the motor to a DC supply, causing the motor to act as a generator and dissipate energy as heat.
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.
Principles of Electromechanical Energy ConversionYimam Alemu
This document is the first chapter of a textbook on electromechanical energy conversion. It introduces key concepts such as electrical energy conversion to mechanical energy using magnetic fields. It discusses different types of electromechanical devices and the principle of energy conservation. It also covers energy balance analysis in conversion systems and determining forces and torques from the energy and coenergy of magnetic systems, including those with permanent magnets. The chapter objectives are to understand electromechanical conversion analysis and components, and how to determine forces and torques from energy considerations.
This document provides an overview of symmetrical components for analyzing three-phase power systems. It introduces symmetrical components and how they can be used to simplify fault calculations. The key symmetrical components are defined as the positive, negative, and zero sequence components. Equations are presented to express the original unbalanced phase voltages and currents in terms of these symmetrical components. The significance of each component is described. Methods for calculating faults using symmetrical components are also outlined.
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.
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.
A transformer is a device that changes alternating current (ac) electric power at one voltage level to ac electric power at another voltage level through the action of a magnetic field. An ideal transformer is a lossless device that transfers power efficiently between its two windings. A real transformer is modeled using an equivalent circuit that accounts for power losses, including copper losses, eddy current losses, hysteresis losses, and leakage fluxes. The parameters of the equivalent circuit can be determined experimentally using open-circuit and short-circuit tests.
Three phase Induction Motor (Construction and working Principle)Sharmitha Dhanabalan
The three phase induction motor consists of a stationary stator and a rotating rotor. The stator contains three-phase windings that generate a rotating magnetic field. This rotating field induces currents in the rotor windings, causing the rotor to turn. There are two common types of rotors - squirrel cage and wound rotor. A squirrel cage rotor has embedded conductors inside its core that are permanently short-circuited. A wound rotor has three insulated windings connected to slip rings to allow external resistance control. Due to slight differences in speed, the rotor always rotates at a slightly slower synchronous speed than the stator's magnetic field.
This document provides an overview of DC machines and motors. It discusses:
1) The fundamentals of DC generators and motors, including how voltage is induced in a conductor moving through a magnetic field and how a force is induced on a current-carrying conductor in a magnetic field.
2) The construction of DC machines, including the stationary stator with field poles and rotating armature/rotor with windings.
3) Different types of DC motors like shunt, series, and compound motors and how their field and armature windings are connected. Speed control methods for DC motors are also discussed.
4) Workings of DC motors are explained through equivalent circuits and equations for induced voltage
1) Synchronous machines have a rotor supplied by an external DC source that produces a rotating magnetic field. This induces a voltage in the stator windings.
2) The rotor can have either salient or non-salient poles and is laminated to reduce eddy currents. DC power is supplied to the rotor via slip rings and brushes or a brushless exciter.
3) An equivalent circuit model represents the internal generated voltage and accounts for armature reaction, inductance, and resistance effects on the terminal voltage.
This document provides an overview of DC machines including generators and motors. It discusses the working principles, construction details, types of DC motors including shunt, series and compound motors. It covers key concepts such as EMF equation, back EMF, torque equation and characteristics of DC motors. It also discusses starters for DC shunt motors and speed control methods including flux and armature voltage control. Finally, it briefly mentions some industrial applications of DC motors.
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.
This document discusses electrical measurements and various types of measuring instruments. It covers topics like indicating instruments, wattmeters, energy meters, bridges, potentiometers and instrument transformers. Specifically, it describes the principles and components of instruments like permanent magnet moving coil meters, moving iron meters, dynamometer wattmeters and single phase induction energy meters. It also discusses bridges like Wheatstone bridge and potentiometers for electrical measurements. Measurement of parameters like frequency, power factor using different types of meters is presented.
Synchronous generators operate on the principle of electromagnetic induction. They have a stationary armature winding and a rotating field winding supplied by a direct current source. It is advantageous to have the field winding on the rotor and armature winding on the stator because it allows for easier insulation of the high voltage winding and direct connection to the load. The frequency of the induced voltage depends on the number of rotor poles and its rotational speed. Armature reaction is the effect of the armature magnetic field on the main rotor field, distorting or strengthening it depending on the load power factor.
This document provides information about various types of electrical machines and transformers. It discusses direct current machines and alternating current machines. It also describes different types of motors like induction motors, synchronous motors, and transformers. Key components of these machines like the rotor, stator, windings and magnetic core are explained. Different speed control methods for induction motors are also summarized.
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."
This document discusses the measurement of power and energy in electrical circuits. It begins by defining power in DC and AC circuits, and how it can be measured using a voltmeter and ammeter. It then describes the operating principle of an electrodynamometer wattmeter, which uses two coils to measure power consumed by a load. The moving coil is proportional to voltage, while the fixed coil carries the load current. Errors in wattmeter measurements are also discussed, such as those caused by the pressure coil's inductance and how compensation can be achieved by adding capacitance.
A DC generator converts mechanical energy into electrical energy using the principles of electromagnetic induction. It has two main parts - a stationary stator that produces a magnetic field and a rotating armature.
The stator contains pole cores, pole shoes, and field coils that create the magnetic field when current is passed through the coils. The armature is made of laminated steel and contains conductors that rotate through the magnetic field. This cutting of magnetic flux by the conductors induces an electromotive force (emf) based on Faraday's law of induction.
The induced emf alternates as the conductors pass through different parts of the magnetic field. A commutator is used to rectify the alternating emf
A DC motor converts electrical energy into mechanical energy by using the principle of electromagnetic induction. When a current carrying conductor is placed in a magnetic field, it experiences a force that causes it to rotate. In a DC motor, current is passed through stationary conductors located between poles of a magnetic field. This sets up opposing magnetic fields that produce a torque causing the rotor to rotate within the stator. The direction of current flow determines the direction of rotation. By reversing the current direction, the direction of torque and rotation is also reversed, allowing DC motors to run in both forward and reverse directions.
This document describes the components and working principle of a DC generator. It contains the following key points:
1. A DC generator converts mechanical energy to electrical energy through electromagnetic induction. It consists of a magnetic field and a conductor that can move to cut the magnetic flux.
2. The basic components are a magnetic frame, field coils, armature shaft, armature core and windings, commutator, and brushes. The rotating armature windings cut the magnetic flux from the stationary field coils to induce an alternating current.
3. The commutator rectifies the alternating current from the armature to produce a unidirectional current that is collected by the brushes and supplied to the external
1. The document discusses the objectives, working principles, and types of DC motors. It describes brushed and brushless DC motors.
2. Key components of DC motors are described in detail, including the field structure, armature, commutator, brushes, yoke, poles, field and armature windings.
3. The document explains how electrical energy is converted to mechanical energy in a DC motor through electromagnetic interactions between the magnetic fields set up in the stationary and rotating components by currents.
1. A DC generator converts mechanical energy into direct current electricity through electromagnetic induction. It consists of a rotor with field windings that produce a magnetic field and an armature with conductors that spin within this field.
2. Key components include a yoke, poles with pole shoes that carry the field windings, an armature core with slots for conductors, armature windings using lap or wave windings, and a commutator with brushes to collect the generated current.
3. In operation, the rotation of the armature conductors within the magnetic field produced by the stationary field windings induces an electromotive force according to Faraday's law of induction, generating a flow of direct current
The document discusses DC motors, providing definitions, working principles, and components. It describes:
1) The key components of a DC motor include a DC supply, conductor/coil, and magnetic field. The magnetic field acts as a medium to convert electrical input into mechanical output.
2) Fleming's left hand rule describes how the direction of generated force is determined based on the direction of current flow and magnetic flux.
3) DC motors have several parts like magnetic poles, armature winding, commutator, and brushes that work together to convert electrical energy to rotational motion.
4) Speed can be controlled through methods like armature control using a rheostat, and field control using
1) A DC generator produces direct current through electromagnetic induction. When a conductor moves through a magnetic field, an electromotive force (EMF) is induced in the conductor.
2) The basic components of a DC generator are magnetic poles and conductors that rotate within the magnetic field.
3) In a single loop DC generator, an EMF is induced in the sides of a rotating rectangular conductor loop as it cuts through the magnetic flux lines. The loop is connected to brushes to output a direct current.
- DC generators and motors operate using the principle of electromagnetic induction. When a conductor moves through a magnetic field, an electromotive force (emf) is induced in the conductor.
- The basic components of a DC generator are a magnetic field (produced by poles and field windings) and a conductor (armature) that rotates within the magnetic field. This motion induces an emf in the armature.
- A commutator is used to convert the alternating current from the armature into direct current that can be supplied to a load. Brushes make contact with the commutator segments to carry the output current.
This document discusses electrical machines and DC machines. It begins by defining different types of electrical machines including stationary transformers and rotating machines like DC motors, generators, induction motors, and synchronous motors/generators. It then discusses Faraday's law of electromagnetic induction and features that are common to all rotating machines like field and armature windings. DC generators and motors are defined as converting mechanical to electrical energy and vice versa. The construction, working principles, characteristics and commutation process of DC machines are then explained in detail through diagrams and equations.
The document provides information about DC generators, including:
1) It describes the basic principles and components of a DC generator, including the field magnet, armature, commutator, and brushes.
2) It discusses armature winding types, the EMF equation, armature reaction, and methods to improve commutation like interpoles and compensating windings.
3) It outlines the characteristics of DC generators like open-circuit characteristics, load characteristics, and efficiency considerations including various loss components.
1. A DC machine can operate as either a generator or motor. It converts mechanical power to electrical power as a generator and converts electrical power to mechanical power as a motor.
2. The main components of a DC machine are the stator, rotor, field windings, armature windings, commutator, and brushes. The field windings produce flux and the armature windings, which rotate, cut this flux to generate voltage or consume current depending on if it is operating as a generator or motor.
3. Armature reaction causes the magnetic neutral axis to shift from its ideal position, requiring careful brush placement. Commutation is the process that converts the alternating currents induced in the armature to
DC Machines can be either generators or motors. A DC generator converts mechanical power into electrical power, while a DC motor converts electrical power into mechanical power. Both have similar constructions with a stator and rotor separated by an air gap. The rotor contains field windings to produce a magnetic field, while the stator contains armature windings. A commutator and brushes allow current to flow in one direction from the armature to an external circuit. The direction of current induced in the armature windings changes as it rotates, but the commutator switches the connections to maintain unidirectional current output.
1. An electrical machine that converts mechanical energy to electrical energy is called a generator, while one that converts electrical to mechanical is called a motor.
2. Generators operate based on Faraday's law of induction - a changing magnetic flux induces an electromotive force (emf) in any conductor within it. In a DC generator, the armature coils rotate within a stationary magnetic field, inducing an AC emf that is rectified into DC via the commutator.
3. The document then discusses the components, construction, winding types, EMF equation and excitation methods of DC generators. Key components include the yoke, poles, field winding, armature and commutator. Generators can be separately or self
1. An electrical machine that converts mechanical energy to electrical energy is called a generator, while one that converts electrical to mechanical is called a motor.
2. Generators operate based on Faraday's law of induction - a changing magnetic flux induces an electromotive force (emf) in any conductor within it. In a DC generator, the armature coils cut the magnetic flux from stationary field poles to generate an alternating emf that is rectified into direct current using a commutator.
3. The speed of the armature rotation determines the frequency of the induced alternating emf, while the number of field poles and magnetic flux strength set the output voltage level according to the generator equation. Proper excitation of the field
The document summarizes key aspects of DC machines, including:
1) DC machines convert mechanical energy to DC electric energy (generators) or convert DC electric energy to mechanical energy (motors).
2) They contain a commutator that converts internally generated AC to DC at the terminals.
3) Construction includes a yoke, poles, field windings, armature, commutator, and brushes.
4) Armature reaction distorts the magnetic field and weakens it as load increases. Commutation reverses current in coils as they pass the magnetic neutral axis.
- The document discusses electric generators, specifically DC generators. It describes the key components of a DC generator including the yoke, pole cores, pole shoes, pole coils, armature core, armature winding, commutator, bearings, and brushes.
- It explains the working principle of a DC generator, including how rotation of the armature in a magnetic field generates an induced electromotive force (emf) via Faraday's law of induction. The commutator is described as collecting the current from the armature coils and delivering DC power to an external load.
- Equations for calculating the generated emf are provided, and different types of DC generator circuits are summarized including separately excited,
This document provides reading material for electrical and electronics engineering students studying electrical machines II at RGPV affiliated colleges. It covers the syllabus for the unit on DC machines, including the basic construction of DC machines, types of excitation, armature and field windings, EMF equations, armature reaction and methods to limit it, commutation processes, performance of DC generators, and different types of DC motors like metadyne, amplidyne, permanent magnet, and brushless motors. The topics are explained over several pages with diagrams and examples. Key concepts covered are the magnetic circuits, armature and commutator construction, separately excited and self-excited machines, wave and lap windings, EMF equations, ar
Poles carry field windings and pole shoes, which support the coils and spread flux uniformly in the air gap. The commutator rectifies alternating current to direct current in a generator and inverts direct current to alternating current in a motor, reversing the current through the armature conductors to produce unidirectional torque. Brushes conduct current between stationary wires and the rotating shaft, charging the commutator to cause the armature to rotate in a particular direction by reversing the brush polarity. Field windings are wound copper coils that form north and south poles when energized. Armature windings are wound on a laminated steel core with slots and can use lap or wave winding configurations.
Synchronous machines have two sets of windings - a three-phase armature winding on the stationary stator and a DC field winding on the rotating rotor. The rotor can have either a salient pole or cylindrical structure. Large generators use brushless excitation systems to avoid maintenance issues associated with slip rings and brushes. Excitation is provided by a small AC generator (brushless exciter) mounted on the stator whose output is rectified to supply DC current to the main field winding. Proper cooling is required to dissipate heat generated in the windings.
Alternators operate using the same principles of electromagnetic induction as DC generators but produce an AC output. They have a stationary armature winding (stator) and rotating field windings (rotor). As the rotor spins, the magnetic field cuts the stator conductors, inducing an alternating voltage. This voltage alternates in magnitude and direction as the north and south poles of the rotor pass by. Alternators can have either a rotating field and stationary armature or vice versa. Rotating field designs are commonly used as they allow for simpler construction, higher speeds of operation, and easier insulation of the high voltage stator windings.
Fuzzy logic was used to improve induction motor control by developing alternative control methods to field oriented control. A fuzzy flux controller was developed using two fuzzy logic blocks, one to describe the nonlinear relationship between slip frequency and current, and another fuzzy PI controller for the outer control loop. Simulation results showed the fuzzy flux controller had almost as good performance as field oriented control, but required less development time. The fuzzy flux controller was further improved by replacing the linear PI controller with a nonlinear fuzzy PI controller, achieving even better dynamic performance while maintaining robustness.
This document discusses using fuzzy logic control for voltage stability in a power system. It proposes calculating a fuzzy-based voltage stability index at each step of load flow simulation to identify critical buses. The method is tested on the 18-bus IEEE test system under different disturbances and load models. A fuzzy controller with 7 predicates is applied to maintain voltage stability. Simulation results show the terminal voltage response at bus 7 for a short circuit at bus 12 lasting 300ms under different load models.
This document discusses several applications of fuzzy logic in electrical systems, including induction motor control, switched reluctance motor control, excitation control in automatic voltage regulators, and fuzzy logic control in an 18 bus power system. It focuses on using fuzzy logic for automatic voltage regulation, describing the typical components of a power system, challenges with conventional controllers, and presenting simulation results that demonstrate how a fuzzy logic controller can effectively regulate the voltage of a synchronous generator.
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This document provides an overview of artificial neural networks. It defines ANNs as highly interconnected networks of neurons inspired by the human brain. The document then discusses key aspects of ANNs like biological neurons, network architecture, learning rules, activation functions, and specific ANN models including perceptrons, backpropagation networks, associative memories, and Hopfield networks. It provides details on the basic building blocks and functioning of various ANN concepts.
Artificial intelligence techniques like artificial neural networks, fuzzy logic, and expert systems can help address complex problems in power systems that were previously difficult to solve. They have applications in areas like economic load dispatch, load forecasting, transmission capacity and optimal power flow, generator limits, and system protections. By using environmental sensors and AI techniques together, the performance of transmission lines can be improved by changing line parameters based on conditions and diagnosing and addressing any faults. AI provides benefits like increased reliability, efficiency, and cost savings within power systems.
This document provides an introduction to artificial intelligence including definitions, intelligence, the need for AI, applications of AI, and motivation. It defines AI as the study and design of machines that can perform tasks requiring human intelligence. Intelligence involves abilities like reasoning, learning, problem solving and perception. The need for AI is to create expert systems that exhibit intelligent behavior and solve complex problems like humans. Applications of AI include expert systems, game playing, natural language processing, computer vision, speech recognition and intelligent robots. The motivation for researchers is to develop systems that can match or exceed human intelligence.
This document discusses fuzzy rule-based classification systems. There are three types of rules that can be formed: assignment statements, conditional statements, and unconditional statements. A fuzzy inference system uses a rule base of fuzzy rules to perform fuzzy reasoning and mapping of fuzzy inputs to outputs. The key components of a fuzzy inference system are fuzzification of inputs, a rule base, an inference engine, and defuzzification of outputs. Fuzzy rule-based systems find application in decision making problems.
This document discusses fuzzy logic controller design. It describes open and closed loop control systems, as well as regulatory and tracking controllers. It then provides an overview of the basic components of a simple fuzzy logic controller, including fuzzification, rule base, inference mechanism, and defuzzification. Next, it discusses the principal design elements of general fuzzy logic controllers. Finally, it outlines two common models for representing fuzzy logic control systems: fuzzy rule-based structures and fuzzy relational equations.
Fuzzification transforms crisp quantities into fuzzy quantities by identifying deterministic values as uncertain and represented by membership functions, such as describing a temperature of 45°C as "favorable", "hot", or "cold". Defuzzification is the inverse process, converting fuzzy results back into crisp results by mapping a possibility distribution of an inferred fuzzy control action into a nonfuzzy control action.
This document discusses various methods for defuzzification, which is the process of converting a fuzzy quantity into a crisp quantity. It describes seven common defuzzification methods: 1) max membership principle, 2) centroid method, 3) weighted average method, 4) mean max membership, 5) center of sums, 6) centre of largest area, and 7) first of maxima, last of maxima. For each method, it provides details on the calculation approach and formulas used to determine the defuzzified crisp value. The centroid method is noted as the most commonly used defuzzification technique.
This document discusses D.C. motors. It begins by explaining that D.C. motors are advantageous for special applications that require converting alternating current to direct current, as D.C. motors have superior speed/torque characteristics compared to A.C. motors. It then discusses the three types of D.C. motors - series-wound, shunt-wound, and compound-wound - and their characteristics, applications, and speed control methods. The document also covers topics such as back EMF, torque, speed regulation, and testing of D.C. motors.
The document discusses lighting instruments used for energy audits. It covers key concepts in lighting including illuminance, luminance, lighting quantity units (watts, lumens, foot-candles), efficacy, IES recommended light levels, and aspects of lighting quality such as uniformity, glare, color rendering index, and coordinated color temperature. Good lighting design aims to provide the right quantity and quality of light to suit the visual task and create the desired mood or atmosphere in a space. Lighting quality factors like uniformity and minimizing glare are important for occupant comfort and productivity.
This document discusses energy efficient motors and power factor improvement. It provides details on the construction, operation, and benefits of energy efficient motors. Key points include:
1. Energy efficient motors have efficiencies 3-7% higher than standard motors due to design improvements that reduce losses. This includes using lower loss materials and improving the magnetic circuit.
2. The higher upfront cost of efficient motors is often paid back quickly through energy savings. Life cycle cost is lower despite the higher initial price.
3. Applications that benefit most are those with continuous heavy loads, like pumps and fans. Variable speed controls provide additional savings by matching motor speed to load.
4. Proper motor sizing and power factor
The document discusses energy auditing and provides definitions and concepts related to energy auditing. It describes that the goal of an energy audit is to characterize and quantify energy use within an organization to identify opportunities for reduced consumption. There are two main types of energy audits: preliminary audits which involve basic data collection and analysis to identify low-cost savings opportunities, and detailed audits which use instruments to comprehensively analyze each energy consuming system and determine specific savings recommendations along with cost analyses. The overall purpose is to establish a baseline understanding of energy usage to inform conservation efforts.
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The root locus technique is a graphical method used in control systems to adjust the locations of closed loop poles by varying system parameters to achieve desired performance. The root locus represents the possible locations of closed loop poles for different values of a parameter in the s-domain, forming a symmetrical plot about the real axis. It has advantages over other methods by being easy to implement and allowing prediction of system performance by indicating important parameters. Construction of the root locus involves 7 steps including finding pole and zero locations, the real axis path, asymptotes, and breakpoints.
1) The document discusses DC and AC circuits, defining key concepts like voltage, current, resistance, inductance, and capacitance.
2) It describes different types of circuit elements and how they are connected in series, parallel and series-parallel configurations.
3) Kirchhoff's laws and theorems like superposition, phasor representation, and analysis of RL, RC, and RLC circuits under alternating current are explained.
International Conference on NLP, Artificial Intelligence, Machine Learning an...gerogepatton
International Conference on NLP, Artificial Intelligence, Machine Learning and Applications (NLAIM 2024) offers a premier global platform for exchanging insights and findings in the theory, methodology, and applications of NLP, Artificial Intelligence, Machine Learning, and their applications. The conference seeks substantial contributions across all key domains of NLP, Artificial Intelligence, Machine Learning, and their practical applications, aiming to foster both theoretical advancements and real-world implementations. With a focus on facilitating collaboration between researchers and practitioners from academia and industry, the conference serves as a nexus for sharing the latest developments in the field.
A SYSTEMATIC RISK ASSESSMENT APPROACH FOR SECURING THE SMART IRRIGATION SYSTEMSIJNSA Journal
The smart irrigation system represents an innovative approach to optimize water usage in agricultural and landscaping practices. The integration of cutting-edge technologies, including sensors, actuators, and data analysis, empowers this system to provide accurate monitoring and control of irrigation processes by leveraging real-time environmental conditions. The main objective of a smart irrigation system is to optimize water efficiency, minimize expenses, and foster the adoption of sustainable water management methods. This paper conducts a systematic risk assessment by exploring the key components/assets and their functionalities in the smart irrigation system. The crucial role of sensors in gathering data on soil moisture, weather patterns, and plant well-being is emphasized in this system. These sensors enable intelligent decision-making in irrigation scheduling and water distribution, leading to enhanced water efficiency and sustainable water management practices. Actuators enable automated control of irrigation devices, ensuring precise and targeted water delivery to plants. Additionally, the paper addresses the potential threat and vulnerabilities associated with smart irrigation systems. It discusses limitations of the system, such as power constraints and computational capabilities, and calculates the potential security risks. The paper suggests possible risk treatment methods for effective secure system operation. In conclusion, the paper emphasizes the significant benefits of implementing smart irrigation systems, including improved water conservation, increased crop yield, and reduced environmental impact. Additionally, based on the security analysis conducted, the paper recommends the implementation of countermeasures and security approaches to address vulnerabilities and ensure the integrity and reliability of the system. By incorporating these measures, smart irrigation technology can revolutionize water management practices in agriculture, promoting sustainability, resource efficiency, and safeguarding against potential security threats.
Literature Review Basics and Understanding Reference Management.pptxDr Ramhari Poudyal
Three-day training on academic research focuses on analytical tools at United Technical College, supported by the University Grant Commission, Nepal. 24-26 May 2024
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As digital technology becomes more deeply embedded in power systems, protecting the communication
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Robust Intrusion Detection Systems (IDS) are necessary for early threat detection and mitigation because
of the interconnection of these networks, which makes them vulnerable to a variety of cyberattacks. To
solve this issue, this paper develops a hybrid Deep Learning (DL) model specifically designed for intrusion
detection in smart grids. The proposed approach is a combination of the Convolutional Neural Network
(CNN) and the Long-Short-Term Memory algorithms (LSTM). We employed a recent intrusion detection
dataset (DNP3), which focuses on unauthorized commands and Denial of Service (DoS) cyberattacks, to
train and test our model. The results of our experiments show that our CNN-LSTM method is much better
at finding smart grid intrusions than other deep learning algorithms used for classification. In addition,
our proposed approach improves accuracy, precision, recall, and F1 score, achieving a high detection
accuracy rate of 99.50%.
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geopolitical, geostrategic, and geoeconomic variables. Topics including trade, political hegemony, oil
politics, and conventional and nontraditional security are all explored and explained by the researcher.
Using Mackinder's Heartland, Spykman Rimland, and Hegemonic Stability theories, examines China's role
in Central Asia. This study adheres to the empirical epistemological method and has taken care of
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Introduction- e - waste – definition - sources of e-waste– hazardous substances in e-waste - effects of e-waste on environment and human health- need for e-waste management– e-waste handling rules - waste minimization techniques for managing e-waste – recycling of e-waste - disposal treatment methods of e- waste – mechanism of extraction of precious metal from leaching solution-global Scenario of E-waste – E-waste in India- case studies.
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The proper function of the integrated circuit (IC) in an inhibiting electromagnetic environment has always been a serious concern throughout the decades of revolution in the world of electronics, from disjunct devices to today’s integrated circuit technology, where billions of transistors are combined on a single chip. The automotive industry and smart vehicles in particular, are confronting design issues such as being prone to electromagnetic interference (EMI). Electronic control devices calculate incorrect outputs because of EMI and sensors give misleading values which can prove fatal in case of automotives. In this paper, the authors have non exhaustively tried to review research work concerned with the investigation of EMI in ICs and prediction of this EMI using various modelling methodologies and measurement setups.
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2. What is a DC Generator?
A DC generator is an Electrical Machine which converts Mechanical
Energy into DC Electrical Energy.
GENERATOR PRINCIPLE:
The energy conversion is based on the principle of the production of
dynamically (or motionally) induced e.m.f.
Whenever a conductor cuts magnetic flux, dynamically induced e.m.f. is
produced in it according to Faraday’s Laws of Electromagnetic Induction.
This e.m.f. causes a current to flow if the conductor circuit is closed.
Hence, two basic essential parts of an electrical generator are
(i) a magnetic field and
(ii) a conductor or conductors which can so move as to cut the flux.
4. Consider a single turn loop ABCD rotating clockwise in a uniform magnetic field
with a constant speed as shown in Fig.(a).
As the loop rotates, the flux linking the coil sides AB and CD changes
continuously.
Hence the e.m.f. induced in these coil sides also changes but the e.m.f. induced in
one coil side adds to that induced in the other.
(i) When the loop is in position no. 1 [See Fig. a], the generated e.m.f. is
zero because the coil sides (AB and CD) are cutting no flux but are moving parallel
to it.
(ii) When the loop is in position no. 2, the coil sides are moving at an angle
to the flux and, therefore, a low e.m.f. is generated as indicated by point 2 in Fig.
(b).
(iii) When the loop is in position no. 3, the coil sides (AB and CD) are at
right angle to the flux and are, therefore, cutting the flux at a maximum rate. Hence
at this instant, the generated e.m.f. is maximum as indicated by point 3 in Fig. (b).
(iv) At position 4, the generated e.m.f. is less because the coil sides are
cutting the flux at an angle.
5. (v) At position 5, no magnetic lines are cut and hence induced e.m.f. is
zero as indicated by point 5 in Fig. (b).
(vi) At position 6, the coil sides move under a pole of opposite polarity
and hence the direction of generated e.m.f. is reversed. The maximum e.m.f. in this
direction (i.e., reverse direction, See Fig. b) will be when the loop is at position 7
and zero when at position 1. This cycle repeats with each revolution of the coil.
Note that e.m.f. generated in the loop is alternating one.
It is because any coil side, say AB has e.m.f. in one direction when under the
influence of N-pole and in the other direction when under the influence of S-pole.
If a load is connected across the ends of the loop, then alternating current will
flow through the load.
The alternating voltage generated in the loop can be converted into direct voltage
by a device called commutator.
We then have the d.c. generator. In fact, a commutator is a mechanical rectifier.
7. A d.c. machine consists of two parts:
i) the stator (the stationary part)
ii) the rotor (the rotating part)
A. Frame (or) Yoke:
The outer frame or yoke serves double purpose:
(i) It provides mechanical support for the poles and acts as a protecting
cover for the whole machine
(ii) It carries the magnetic flux produced by the poles.
In small generators where cheapness rather than weight is the main consideration,
yokes are made of cast iron.
But for large machines usually cast steel or rolled steel is employed.
The modern process of forming the yoke consists of rolling a steel slab round a
cylindrical mandrel and then welding it at the bottom.
The feet and the terminal box etc. are welded to the frame afterwards. Such
yokes possess sufficient mechanical strength and have high permeability.
8. B. Pole Cores and Pole Shoes:
The field magnets consist of pole cores and pole shoes.
The pole shoes serve two purposes,
(i) they spread out the flux in the air gap and also, being of larger cross-
section, reduce the reluctance of the magnetic path
(ii) they support the exciting coils (or field coils).
9. There are two main types of pole construction.
(a) The pole core itself may be a solid piece made out of either cast iron or
cast steel but the pole shoe is laminated and is fastened to the pole face by means of
counter sunk screws.
(b) In modern design, the complete pole cores and pole shoes are built of
thin laminations of annealed steel which are riveted together under hydraulic
pressure. The thickness of laminations varies from 1 mm to 0.25 mm.
The laminated poles may be secured to the yoke of the following two ways :
(i) Either the pole is secured to the yoke by means of screws bolted through
the yoke and into the pole body
(ii) The holding screws are bolted into a steel bar which passes through the
pole across the plane of laminations.
10. C. Pole Coils:
The field coils or pole coils, which consist of copper wire or strip, are former-
wound for the correct dimension.
Then, the former is removed and wound coil is put into place over the core.
When current is passed through these coils, they electro magnetize the poles which
produce the necessary flux that is cut by revolving armature conductors.
D. Armature Core:
It houses the armature conductors or coils and causes them to rotate and hence cut
the magnetic flux of the field magnets.
In addition to this, its most important function is to provide a path of very low
reluctance to the flux through the armature from a N-pole to a S-pole.
It is cylindrical or drum-shaped and is built up of usually circular sheet steel discs
or laminations approximately 0.5 mm thick.
It is keyed to the shaft. The slots are either die-cut or punched on the outer
periphery of the disc and the keyway is located on the inner diameter as shown.
11. Such ventilating channels are clearly visible in the laminations.
Up to armature diameters of about one metre, the circular stampings are cut out in
one piece.
But above this size, these circles, especially of such thin sections, are difficult to
handle because they tend to distort and become wavy when assembled together.
In small machines, the armature stampings are keyed directly to the shaft.
Usually, these laminations are perforated for air ducts which permits axial flow of
air through the armature for cooling purposes.
12. Hence, the circular laminations, instead of being cut out in one piece, are cut in a
number of suitable sections or segments which form part of a complete ring.
A complete circular lamination is made up of four or six or even eight segmental
laminations.
Usually, two keyways are notched in each segment and are dove-tailed or wedge-
shaped to make the laminations self-locking in position.
The purpose of using laminations is to reduce the loss due to eddy currents.
Thinner the laminations, greater is the resistance offered to the induced e.m.f.,
smaller the current and hence lesser the iron loss in the core.
E. Armature Windings:
The armature windings are usually former-wound.
These are first wound in the form of flat rectangular coils and are then pulled into
their proper shape in a coil puller.
Various conductors of the coils are insulated from each other.
13. The conductors are placed in the armature slots which are lined with tough
insulating material.
This slot insulation is folded over above the armature conductors placed in the
slot and is secured in place by special hard wooden or fibre wedges.
F. Commutator:
The function of the commutator is to facilitate collection of current from the
armature conductors.
As it rectified i.e. converts the alternating current induced in the armature
conductors into unidirectional current in the external load circuit.
It is of cylindrical structure and is built up of wedge-shaped segments of high-
conductivity hard-drawn or drop forged copper.
These segments are insulated from each other by thin layers of mica.
The number of segments is equal to the number of armature coils.
14. Each commutator segment is connected to the armature conductor by means of a
copper lug or strip (or riser).
To prevent them from flying out under the action of centrifugal forces, the
segments have V-grooves, these grooves being insulated by conical micanite rings.
G. Brushes and Bearings:
The brushes whose function is to collect current from commutator, are usually
made of carbon or graphite and are in the shape of a rectangular block.
These brushes are housed in brush-holders usually of the box-type variety.
The brush-holder is mounted on a spindle and the brushes can slide in the
rectangular box open at both ends.
The brushes are made to bear down on the commutator by a spring whose
tension can be adjusted by changing the position of lever in the notches.
A flexible copper pigtail mounted at the top of the brush conveys current from
the brushes to the holder.
15. The number of brushes per spindle depends on the magnitude of the current to be
collected from the commutator.
Because of their reliability, ball-bearings are frequently employed, though for
heavy duties, roller bearings are preferable.
The ball and rollers are generally packed in hard oil for quieter operation and for
reduced bearing wear, sleeve bearings are used which are lubricated by ring oilers
fed from oil reservoir in the bearing bracket.
16. E.M.F. EQUATION OF A D.C. GENERATOR
Let Φ = flux/pole in Wb
Z = total number of armature conductors
P = number of poles
A = number of parallel paths = 2 ... for wave winding
= P ... for lap winding
N = speed of armature in r.p.m.
Eg = e.m.f. of the generator = e.m.f./parallel path
Flux cut by one conductor in one revolution of the armature,
df = PΦ webers
Time taken to complete one revolution, dt = 60/N second
17. e.m.f. of generator, Eg = e.m.f. per parallel path
= (e.m.f/conductor) × No. of conductors in series per
parallel path
18. METHODS OF EXCITATION OF DC MACHINES
(OR)
TYPES OF GENERATOS
The magnetic field in a d.c. generator is normally produced by electromagnets
rather than permanent magnets.
Generators are generally classified according to their methods of field excitation.
19. D.C. generators are divided into the following two classes:
(i) Separately excited d.c. generators
(ii) Self-excited d.c. generators
A. Separately Excited D.C. Generators:
20. A d.c. generator whose field magnet winding is supplied from an independent
external d.c. source (e.g., a battery etc.) is called a separately excited generator.
Figure shows the connections of a separately excited generator.
The voltage output depends upon the speed of rotation of armature and the field
current (Eg = PΦZN/60 A).
The greater the speed and field current, greater is the generated e.m.f.
It may be noted that separately excited d.c. generators are rarely used in
practice.
The d.c. generators are normally of self-excited type.
21. B. Self-Excited D.C. Generators:
A d.c. generator whose field magnet winding is supplied current from the output
of the generator itself is called a self-excited generator.
There are three types of self-excited generators depending upon the manner in
which the field winding is connected to the armature, namely;
(i) Series generator;
(ii) Shunt generator;
(iii) Compound generator
22. (i) Series generator-
In a series wound generator, the field winding is connected in series with
armature winding so that whole armature current flows through the field winding
as well as the load.
Figure shows the connections of a series wound generator.
Since the field winding carries the whole of load current, it has a few turns of
thick wire having low resistance.
Series generators are rarely used except for special purposes e.g., as boosters.
24. In a shunt generator, the field winding is connected in parallel with the armature
winding so that terminal voltage of the generator is applied across it.
The shunt field winding has many turns of fine wire having high resistance.
Therefore, only a part of armature current flows through shunt field winding and
the rest flows through the load.
Figure shows the connections of a shunt-wound generator.
25. (iii) Compound generator:
In a compound-wound generator, there are two sets of field windings on each
pole—one is in series and the other in parallel with the armature.
A compound wound generator may be:
(a) Short Shunt in which only shunt field winding is in parallel with the
armature winding [See Fig.(i)].
(b) Long Shunt in which shunt field winding is in parallel with both series
field and armature winding [See Fig.(ii)].
28. CHARACTERISTICS OF D.C. GENERATORS
Following are the three most important characteristics or curves of a d.c.
generator :
1. Open Circuit Characteristic (O.C.C.):-
This curve shows the relation between the generated e.m.f. at no-load (E0) and
the field current (If) at constant speed.
It is also known as magnetic characteristic or no-load saturation curve.
Its shape is practically the same for all generators whether separately or self-
excited.
The data for O.C.C. curve are obtained experimentally by operating the
generator at no load and constant speed and recording the change in terminal
voltage as the field current is varied.
29. 2. Internal or Total characteristic (E/Ia):-
This curve shows the relation between the generated e.m.f. on load (E) and the
armature current (Ia).
The e.m.f. E is less than E0 due to the demagnetizing effect of armature reaction.
Therefore, this curve will lie below the open circuit characteristic (O.C.C.).
The internal characteristic is of interest chiefly to the designer.
It cannot be obtained directly by experiment.
It is because a voltmeter cannot read the e.m.f. generated on load due to the
voltage drop in armature resistance.
The internal characteristic can be obtained from external characteristic if
winding resistances are known because armature reaction effect is included in both
characteristics.
30. 3. External characteristic (V/IL):-
This curve shows the relation between the terminal voltage (V) and load current
(IL).
The terminal voltage V will be less than E due to voltage drop in the armature
circuit.
Therefore, this curve will lie below the internal characteristic.
This characteristic is very important in determining the suitability of a generator
for a given purpose.
It can be obtained by making simultaneous measurements of terminal voltage
and load current (with voltmeter and ammeter) of a loaded generator.
31. CHARACTERISTICS OF A SEPARATELY EXCITED D.C. GENERATOR
(i) Open circuit characteristic.
The O.C.C. of a separately excited generator is determined in a manner.
Figure shows the variation of generated e.m.f. on no load with field current for
various fixed speeds.
Note that if the value of constant speed is increased, the steepness of the curve
also increases.
When the field current is zero, the residual magnetism in the poles will give rise
to the small initial e.m.f. as shown.
32. (ii) Internal and External Characteristics
The external characteristic of a separately excited generator is the curve between
the terminal voltage (V) and the load current IL (which is the same as armature
current in this case).
In order to determine the external characteristic, the circuit set up is as shown in
Fig. (i).
As the load current increases, the terminal voltage falls due to two reasons:
(a) The armature reaction weakens the main flux so that actual e.m.f.
generated E on load is less than that generated (E0) on no load.
(b) There is voltage drop across armature resistance (= ILRa = IaRa).
33. Due to these reasons, the external characteristic is a drooping curve [curve 3 in
Fig. (ii)].
Note that in the absence of armature reaction and armature drop, the generated
e.m.f. would have been E0 (curve 1).
The internal characteristic can be determined from external characteristic by
adding ILRa drop to the external characteristic.
34. It is because armature reaction drop is included in the external characteristic.
Curve 2 is the internal characteristic of the generator and should obviously lie
above the external characteristic.
35. CHARACTERISTICS OF SERIES GENERATOR
Fig. (i) shows the connections of a series wound generator.
Since there is only one current (that which flows through the whole machine),
the load current is the same as the exciting current.
36. (i) O.C.C.
Curve 1 shows the open circuit characteristic (O.C.C.) of a series generator.
It can be obtained experimentally by disconnecting the field winding from the
machine and exciting it from a separate d.c. source.
(ii) Internal characteristic
Curve 2 shows the total or internal characteristic of a series generator.
It gives the relation between the generated e.m.f. E on load and armature current.
Due to armature reaction, the flux in the machine will be less than the flux at no
load.
Hence, e.m.f. E generated under load conditions will be less than the e.m.f.
E0 generated under no load conditions.
Consequently, internal characteristic curve lies below the O.C.C. curve; the
difference between them representing the effect of armature reaction [See Fig. (ii)].
37. (iii) External characteristic
Curve 3 shows the external characteristic of a series generator.
It gives the relation between terminal voltage and load current IL.
V = E - Ia (Ra + Rse )
Therefore, external characteristic curve will lie below internal characteristic
curve by an amount equal to ohmic drop [i.e., Ia(Ra + Rse)] in the machine as
shown in Fig. (ii).
38. CHARACTERISTICS OF A SHUNT GENERATOR
Fig (i) shows the connections of a shunt wound generator.
The armature current Ia splits up into two parts; a small fraction Ish flowing
through shunt field winding while the major part IL goes to the external load.
39. (i) O.C.C.
The O.C.C. of a shunt generator is similar in shape to that of a series generator as
shown in Fig. (ii).
The line OA represents the shunt field circuit resistance.
When the generator is run at normal speed, it will build up a voltage OM.
At no-load, the terminal voltage of the generator will be constant (= OM)
represented by the horizontal dotted line MC.
(ii) Internal characteristic
When the generator is loaded, flux per pole is reduced due to armature reaction.
Therefore, e.m.f. E generated on load is less than the e.m.f. generated at no load.
As a result, the internal characteristic (E/Ia) drops down slightly as shown in
Fig.(ii).
40. (iii) External characteristic
Curve 2 shows the external characteristic of a shunt generator.
It gives the relation between terminal voltage V and load current IL.
V = E - IaRa = E - IL + Ish R
Therefore, external characteristic curve will lie below the internal characteristic
curve by an amount equal to drop in the armature circuit [i.e., (IL + Ish)Ra] as
shown in Fig.(ii).
41. COMPOUND GENERATOR CHARACTERISTICS
In a compound generator, both series and shunt excitation are combined as shown
in Fig. (i).
The shunt winding can be connected either across the armature only (short-shunt
connection S) or across armature plus series field (long-shunt connection G).
The compound generator can be cumulatively compounded or differentially
compounded generator.
Therefore, we shall discuss the characteristics of cumulatively compounded
generator.
It may be noted that external characteristics of long and short shunt compound
generators are almost identical.
42. External characteristic
Fig. (ii) shows the external characteristics of a cumulatively compounded
generator.
The series excitation aids the shunt excitation.
The degree of compounding depends upon the increase in series excitation with
the increase in load current.
43. (i) If series winding turns are so adjusted that with the increase in load
current the terminal voltage increases, it is called over-compounded generator. In
such a case, as the load current increases, the series field m.m.f. increases and tends
to increase the flux and hence the generated voltage. The increase in generated
voltage is greater than the IaRa drop so that instead of decreasing, the terminal
voltage increases as shown by curve A in Fig. (ii).
(ii) If series winding turns are so adjusted that with the increase in load
current, the terminal voltage substantially remains constant, it is called flat-
compounded generator. The series winding of such a machine has lesser number of
turns than the one in over-compounded machine and, therefore, does not increase
the flux as much for a given load current. Consequently, the full-load voltage is
nearly equal to the no-load voltage as indicated by curve B in Fig (ii).
(iii) If series field winding has lesser number of turns than for a flat
compounded machine, the terminal voltage falls with increase in load current as
indicated by curve C m Fig. (ii). Such a machine is called under-compounded
generator.
44. CRITICAL SPEED (NC):-
The speed for which the given filed resistance acts as critical resistance
is called the critical speed. It is denoted as Nc.
CRITICAL FIELD RESISTANCE:-
The maximum field circuit resistance (for a given speed) with which
the shunt generator would just excite is known as its critical field resistance. s
45. CONDITIONS FOR BUILD UP OF EMF IN A DC GENERATOR:-
The necessary conditions for building up of emf in a dc generator are,
1) There must be some residual magnetism in the generator poles.
2) The field winding should be connected with the armature such that the filed
current should strengthen the residual magnetism.
3) In case of shunt generator, if excited on open circuit, its shunt field resistance
should be less than the critical resistance.
4) If excited on load, its shunt filed resistance should be more than a certain
minimum value of resistance which is given by internal characteristic.
5) For a series generator, the resistance of the external circuit should be less than
the critical resistance.