Download NGEE ANN POLYTECHNIC MECHANICAL ENGINEERING

DC Machines and Drives .
Books
Principle Of Electrical Machines (V.K. Mehta, Rohit Mehta)
Electric Machinery Fundamentals (CHAPMAN J STEPHEN)
Electrical Technology Volume II (B.L.Theraja)
Basic Concepts
Lecture # 01
Basic Quantities and Definitions
Energy? Types of Energy?
Conversation of Energy
What is electricity /electrical Energy?
- flow of electric charge.
Charge . (atom, Electrons Protons, Neutrons)
1- Current
2- Voltage
3-Resistance
Electric Machines
“Electromechanical device that converts electrical
energy into mechanical energy is called motor ”
while
“A device that converts mechanical energy into
electrical energy is called generator”
We need electric machines in almost every field of
our life today.
From transportation to construction.
Cars, Clocks, Drills, Fans, Fridges, Vacuum Cleaners,
Water pumps, Washing Machines, Computers,
Lifts, lathes, robots etc.
Machines are categorized or classified on the basis of
input supply, construction and operation principles.
Input supply ?
In electrical system there are two kinds of supply
systems means power source are provided.
1. AC system.
2. DC system.
Alternating Current (AC).
An electric current that reverses direction
sinusoidally. Concept of phases and frequency.
Direct Current (DC).
Current flow is unidirectional and of constant magnitude .
Negative and positive terminals (battery, cells)
Type of Electric Machines
Classification of Machines
Electric machines
Alternating Current (AC)
Machines
Synchronous
Induction
Single-Phase
Three-Phase
Direct Current (DC)
Machines
Separately
Excited
Series
Self Excited
Compound
Shunt
Construction and working of Electric machines
An electric motor consists of many parts.
Stator : The stationary part of an electric motor is called the
stator. The stator will be provided with permanent magnets
or windings.
Rotor: The rotor is the part that actually converts electrical
energy into mechanical energy. The rotor is connected to the
mechanical load through the shaft. These come in various
designs.
For Example if we are talking about Induction or
asynchronous motor,
(a) Squirrel cage rotor,
(b) Slip ring rotor or wound rotor or phase wound rotor.
Or if we are talking about synchronous motors
(a) Salient pole (100 to 1500rpm.) (b) non salient
pole(>1500rpm).
Field windings: conductors used to produce electromagnetic
field.
Armature windings: conductors in which output voltage is
produced (or input is provided)
Electromagnetic Induction
It is the fundamental operating principle of transformers, inductors,
and many types of electrical motors, generators and solenoids.
Faraday (1831):
An emf is induced in a conductor if a
magnetic field passes by a conductor
Whenever in a conductor if change
in current occurs it
"induces”a voltage (electromotive
force) in both the conductor itself
(self-inductance) and in any nearby
conductors (mutual inductance).
Electromagnetic Induction
• Magnitude of induced current can be increased
by:
– Increasing strength of magnetic field
– Increasing speed of relative motion
– Positioning of field & conductor to increase number
of magnetic lines of flux cut
• Magnetic field usually produced by
electromagnet
How motors work
• Electricity supplied to stator
• Magnetic field generated that moves
around rotor
• Current induced in rotor
• Rotor produces second
magnetic field that opposes
stator magnetic field
Electromagnetics
• Rotor begins to rotate
Rotor
Stator
Overview of Direct Current Machines
Direct-current (DC) machines are divided into dc generators and dc motors.
Most DC machines are similar to AC machines: i.e. they have AC voltages and current
within them.
DC machines have DC outputs just because they have a mechanism converting AC
voltages to DC voltages at their terminals.
This mechanism is called a commutator; therefore, DC machines are also called
commutating machines.
DC generators are not as common as they used to be, because direct current, when
required, is mainly produced by electronic rectifiers.
While dc motors are widely used, such automobile, aircraft, and portable electronics,
in speed control applications…