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Questions and Answers
What is the function of a pole in a DC generator?
The pole provides a path for the magnetic flux and supports the field coils.
Explain the role of the yoke in an electromagnetic machine.
The yoke acts as an outer cylindrical frame that supports the main poles and inter poles, providing structural integrity and a path for the magnetic flux.
Differentiate between static and rotating electric machines.
Static electric machines include transformers, while rotating electric machines consist of electric generators and electric motors.
How does a DC generator convert energy?
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What are the major parts of a DC generator?
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Describe the composition of a yoke in terms of material used.
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What is the function of pole coils in a DC generator?
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Explain the difference between lap windings and wave windings in armature windings.
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What is the purpose of the commutator in a DC machine?
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What is the significance of field excitation in a DC generator?
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Why are bearings frequently employed in electric machines?
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What is the key difference between a Separately Excited DC Generator and a Self-Excited DC Generator?
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What is the study of how energy gets converted from one form to another?
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What law states that energy can neither be created nor destroyed?
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Who discovered electromagnetism in 1820?
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What is the space surrounding a magnet, in which magnetic force is exerted?
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What is the unit of magnetic flux equal to one line of force?
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What is the term for the flux passing per unit area through a plane at right angles to the flux?
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Study Notes
Fleming's Hand Rules
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Fleming's Left Hand Rule is used to find the direction of motion in an electric motor
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Thumb represents the direction of thrust on the conductor
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Index finger represents the direction of the magnetic field
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Middle finger represents the direction of the current
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Fleming's Right Hand Rule is used to find the direction of induced current in a generator
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Thumb represents the direction of motion of the conductor
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Index finger represents the direction of the magnetic field
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Middle finger represents the direction of the induced current
Electromagnetic Machine
- It is a device that links an electrical energy system to another energy system
- It provides a reversible means of energy conversion
Electric Machines
- It is a general term for machines using electromagnetic forces
- Examples include electric motors, electric generators, and others
- Classified into two types: static electric machines and rotating electric machines
Static Electric Machines
- Examples include transformers
Rotating Electric Machines
- Examples include electric generators and electric motors
DC Generator
- It converts mechanical energy into DC form of electrical energy
- Consists of two major parts: stator and rotor
- Yoke is the outer cylindrical frame that fixes the main poles and inter poles
- Yoke helps to fix the machine on the foundation
Stator
- The stationary part of the machine
Rotor
- The moving part of the machine
Pole
- Consists of the pole core and pole shoes
- Produces magnetic flux when the field winding is excited
Armature Core
- Houses the armature conductors
- Provides a path of very low reluctance to the flux through the armature
Commutator
- Facilitates the collection of current from the armature windings
- Passes the current to the external load via brush
Brushes
- Collect current from the commutator
Bearings
- Frequently employed in DC machines due to their reliability
Armature Windings
- Divided into two types: lap windings and wave windings
- Lap windings are suitable for high current, low voltage machines
- Wave windings are suitable for high voltage, low current machines
Field Excitation
- When a DC voltage is applied to the field windings of a DC generator
- Current flows through the windings and sets up a steady magnetic field
Separately Excited DC Generator
- External DC source is used to energize the field magnets
Energy Conversion
- Also known as energy transformation
- The process of changing from one form of energy to another
Thermodynamics
- The study of how energy gets converted from one form to another
- 1st Law of Thermodynamics states that energy can neither be created nor destroyed
Magnetism
- A natural phenomenon whereby attraction takes place
- Possessed by iron, steel, nickel, cobalt, and certain other magnetic materials
Types of Magnets
- Natural magnets: always permanent
- Artificial magnets: can either be temporary or permanent
Electromagnetism
- A magnetism produced by an electric current
- Discovered by Hans Christian Oersted in 1820
Magnetic Field
- The space surrounding a magnet, in which magnetic force is exerted
Magnetic Flux
- The number of magnetic lines of forces in a magnetic field
- Unit of magnetic flux: Maxwell (1 line of force) or Weber (10^8 Maxwell)
Flux Density
- Given by the flux passing per unit area through a plane at right angles to the flux
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Description
Test your knowledge on Fleming's Left Hand Rule and Fleming's Right Hand Rule used in electric motors and generators to determine the direction of motion and induced current respectively. Practice identifying which hand represents the direction of thrust, magnetic field, and current in different scenarios.
