Learning & Development - Technical Training Engineering
Development & Skills-Based Training Team
AC Machines (Alternators, Synchronous
Motors, Induction Motors & Single-Phase
AC Motors)
October 1, 2011
Matatag Room, Lineman’s Training Camp
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AC Machines: Alternators, Synchronous Motors, Induction Motors & Single-Phase AC Motors, Slides of Electrical Engineering
A comprehensive overview of ac machines, focusing on alternators, synchronous motors, induction motors, and single-phase ac motors. It covers the principles of operation, types, advantages, and applications of each type of machine. The document also includes important basic formulas and a summary of losses in induction motors. It is a valuable resource for students and professionals in electrical engineering.
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Learning & Development - Technical Training Engineering Development & Skills-Based Training Team
AC Machines (Alternators, Synchronous
Motors, Induction Motors & Single-Phase
AC Motors)
October 1, 2011 Matatag Room, Lineman’s Training Camp
Alternators
- (^) A machine designed to generate alternating current and major electrical unit in power plants
- Converts the mechanical energy of a prime mover, such as diesel engine, steam turbine to electrical energy.
Two Main Parts of Alternators
1. Stator – the stationary part. Housed in a frame which is fabricated from electrically welded steel plates. 2. Rotor – has the rotating magnetic poles. It provides the magnetism needed to induce voltage into the stator windings. Two Types of Rotor: a. Salient-pole type or projecting pole type b. Non-salient pole type or smooth cylinder pole type
Alternators
Revolving Armature Type Alternators
Revolving Field Type Alternators
Alternators
Revolving Field Type Alternators
Alternators
Principle of Operation
- (^) Operate on the same principle of electromagnetic induction as direct current generators, but they have no commutator to change the alternating current produced in the armature into the direct current.
- In the DC generator, it is essential for armature to rotate in the magnetic field produced by stationary field give the unidirectional votlage, but in alternator it is not essential for the armature to rotate for either the armature or the field can be made to rotate while other is kept is constant.
- Nowadays, armature is kept constant and the field rotates under it.
Summary (Alternators)
- There are two basic types of three-phase alternators: rotating armature type and rotating field type.
- The rotating armature type is the least used because of its limited voltage and power rating
- The rotor of the rotating field type alternator contains electromagnets
- Direct current must be supplied to the field to the field before the alternator can produce an output voltage.
- The direct current supplied to the field is called excitation current.
- The output frequency of an alternator is determined by the number of stator poles and the speed of rotation.
Three-Phase Motors
These motors convert the three-phase alternating current into mechanical energy to operate all types of machinery. Three-phase motors are smaller in size, lighter in weight and have higher efficiencies per horsepower than single-phase motors.
Three Basic Types of Three-Phase Motors
- Squirrel-cage induction motor
- Wound rotor induction motor
- Synchronous motor
Induction Motor
- Operate on the principle of electromagnetic induction in a manner similar to transformers
- Were patented as rotating transformers by Nikola tesla
- The stator winding of a motor is often referred to as the motor primary and the rotor is referred to as the motor secondary
- The magnetic field in the rotor is induced by current flowing in the stator windings. The rotor has no connection whatsoever to the line.
Induction Motors
- Is the speed at which the magnetic field rotates. Two factors that determine the speed of the rotating magnetic field:
- Number of stator poles (per phase)
- Frequency of the applied voltage
Synchronous Speed
S – speed F – frequency P – number of stator poles (per phase)
Induction Motors
Stator of a Three-Phase Motor
Induction Motors
Measure of the Rotor Winding Losses Motor Efficiency
Induction Motors
Summarize losses in the induction motors
Squirrel-Cage Induction Motors
• This type of machine is highly efficient and
about constant-speed under normal
running conditions
• It has a poor starting torque and must be
started off or very light loaded
• On starting, the current can be four or five
times the normal full load current due to
the motor acting like a transformer with
secondary short circuited
Squirrel-Cage Induction Motors
Principles of Operation
Amount of induced voltage is determined by three factors:
- Strength of the magnetic field of the stator
- Number of turns of wire cut by the magnetic field
- Speed of the cutting action