Electric Motor...

GROUP INTRODUCTION

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?

PRINCIPLE OF HOW MOTORS WORK

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

Alternating Current (AC)

Motors

Synchronous Induction

Three-PhaseSingle-Phase

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.