electric motor
TRANSCRIPT
TOPIC INTRODUCTION
Electromechanical device that converts electrical
energy to mechanical energy.
Mechanical energy used to e.g.
Rotate pump impeller, fan, blower
Drive compressors
Lift materials
Motors in industry: 70% of electrical load.
What is an Electric
Motor?
STRUCTURAL DESIGN
An electric motor is all about magnets andmagnetism: A motor uses magnets to create
motion. A motor is consist of two magnets.
SPINNING ARMATURE IN A MOTOR
CLASSIFICATION OF MOTORS
Electric Motors
Alternating Current (AC)
Motors
Direct Current (DC)
Motors
Synchronous Induction
Three-PhaseSingle-Phase
Self ExcitedSeparately
Excited
Series ShuntCompound
AC MOTORS
Electrical current reverses direction
Two parts: stator and rotor
Stator: stationary electrical component
Rotor: rotates the motor shaft
Speed difficult to control
Two types
• Synchronous motor
• Induction motor
stator
rotor
Synchronous Motors
Ns = 120 f / PWHERE,
F = supply frequency
P = number of poles
A synchronous motor is an AC
motor,which runs at constant speed fixed by
frequency of the sysem.
This motor rotates at a synchronous
speed, which is given by the following
equation
INDUCTION MOTORS
•Induction motors are the most common motors used for
various equipments in industry.
Components
Rotor
• Squirrel cage
• Wound rotor
Stator
INDUCTION MOTORS
Induction motors can be classified into two main groups:
single-phase induction motors
three-phase induction motors
Single-phase induction motors:
These only have one stator winding, operate
with a single-phase power supply...
Three –phase induction motors:
They use three sets of stator coils the rotating
magnetic field drags the rotor around with it.
DC MOTORS
DC motors,as the name implies,use a direct unidirectional current sources of electricity :-◦ Batteries◦ DC Power supply
When power is applied, DC motors turn in one direction at a fixed speed.
They are optimized to run at a fixed, usually high RPM.
Torque is highest at the rated speed and lowest at low speeds.
Almost all can be reversed.
Inexpensive and commonly available.
DC MOTOR
DC Motors – Components
• Field pole
• North pole and south pole
• Receive electricity to form
magnetic field
• Armature
• Cylinder between the poles
• Electromagnet when current goes through
• Linked to drive shaft to drive the load
• Commutator
• Overturns current direction in armature
(Direct Industry, 1995)
DC MOTOR
Speed control without impact power supply quality
• Changing armature voltage
• Changing field current
Suitable for turning, spinning, etc.
• Main Advantage of DC Motor is-
• Restricted use
• Few low/medium speed applications
• Clean, non-hazardous areas
• Expensive compared to AC motors
DC MOTOR
• Relationship between speed, field flux and
armature voltage
Back electromagnetic force: E = KN
Torque: T = KIa
E = electromagnetic force developed at armature terminal (volt)
= field flux which is directly proportional to field current
N = speed in RPM (revolutions per minute)
T = electromagnetic torque
Ia = armature current
K = an equation constant
TYPES OF DC MOTOR
• Separately excited DC motor: field current supplied from
a separate force
• Self-excited DC motor:
1. Shunt motor : the field winding (shunt field) is connected in
parallel with the armature winding.
2. Series motor : the field winding (shunt field) is connected in
series with the armature winding.
3. Compound motor : compound motor is a combination of
shunt and series motor.
UNIVERSAL MOTORS
While most motors operate from either AC or DC, some
can operate from either
These are universal motors and resemble series-wound
DC motors, but are designed for both AC and DC
operation
– typically operate at high speed (usually > 10,000 rpm)
– offer high power-to-weight ratio
– ideal for portable equipment such as hand drills and
vacuum cleaners
UNIVERSAL MOTORS
Both DC and AC motors are used
– high-power motors are usually AC, three-phase
– domestic applications often use single-phase induction
motors
– DC motors are useful in control applications
– Either an AC or DC electrical energy source serves as
the input to the motor.
Another two useful motor’s name are :-
◦ DC servo motors
◦ Stepper motors
EFFICIENCY OF ELECTRIC MOTORS
•The efficiency of a motor can be defined as “the
ratio of a motor’s useful power output to its total
power output.”
•Motors convert electrical energy to mechanical
energy to serve a certain load. In this process,
energy is lost as shown in the figure.
EFFICIENCY OF ELECTRIC MOTORS
Factors that influence efficiency
• Age
• Capacity
• Speed
• Type
• Temperature
• Rewinding
• Load
Motor Load
• Motor load is indicator of efficiency
• Equation to determine load:
Load = Pi x HP x 0.7457
= Motor operating efficiency in %
HP = Nameplate rated horse power
Load = Output power as a % of rated power
Pi = Three phase power in kW
APLICATION
There are numerous ways to design a motor, thus there are many different types of motors.
The type of motor chosen for an application depends on the characteristics needed in that application.
These include:◦ How fast you want the object to move,
◦ The weight, size of the object to be moved,
◦ The cost and size of the motor,
◦ The accuracy of position or speed control needed.
APPLICATION
The different types of motors possess different operating characteristics.
◦ Heavy Industrial applications: AC motors.
◦ Mobile robotics & hobby robots: DC motor, DC servo motor and stepper motors.