Presentationon

Speed Characteristic of D.C. Shunt PMDC motor drive

Contents Contents • Introduction• Classification of dc motor• Permanent magnet DC motor • Construction• Characteristics• Advantages & disadvantages• Demagnetized is due to• Speed control• Application

IntroductionIntroduction

• Electromechanical device that converts electrical energy to mechanical energy

• Mechanical energy used to:•Rotate pump impeller, fan, blower•Drive compressors•Lift materials

• Motors in industry: 70% of electrical load

What is an Electric Motor?

• Electric Machinery: - Electric Motors: convert electrical energy into

mechanical energy. - Electric Generators: convert mechanical energy to

electric energy.• The Electric machine is composed of: - Stator - Rotor

• The Stator is the stationary part of a motor.

•The Rotor is a moving component of an electromagnetic system in the electric motor

How Does an Electric Motor Work?How Does an Electric Motor Work?

Classification of DC MotorsClassification of DC Motors

Permanent magnet DC motorPermanent magnet DC motor

• Basic structure ,working principal of PMDC motor is same as that of normal dc motor.

Construction• In PMDC motor ,permanent magnets are provided on

cylindrical steel stator. These permanent magnets provides magnetic field in PMDC motor . The stator in cylindrical Nature and made from steel.

• For making permanent magnets three types of magnets are use commonly.

1) Rare earth magnets –eg. Samarium cobalt and neodymium iron cobalt

2) Ferrite or ceramic magnets- they are used in fractional KW motor.

3) Alnico magnets – they are use for making larger rating motors varied from 1KW to 150 KW.

• Commutator is made from copper while brushes are made from carbon or graphite DC supply is given to the brushes and commutator provides unidirectional torque

characteristicscharacteristics• Characteristics of PMDC motor is same as the DC

stunt motor but speed torque characteristics is more linear in nature.

Permanent magnet DC motors

AdvantageAdvantage• Smaller size

• Due to use of permanent magnets, manufacturing cost get reduced for small rating motors.

• PMDC motor is more efficient as losses are less.

• Less costly

• As on need of field excitation winding resulting into simple construction.

• Low voltage PMDC motor generates lower noise level.

• No need of field excitation arrangement.

• No input power in consumed for excitation which improve efficiency of dc motor.

• No field coil hence space for field coil is saved which reduces the overall size of the motor.

• Cheaper and economical for fractional kW rated applications.

DisadvantagesDisadvantages• Armature reaction is more in PMDC motors due to

presence of permanents magnets in stator.

• Stator field is not possible in PMDC motors for controlling speed of motor.

• Permanents magnets may get demagnetized due to armature reaction and motor get stopped.

Demagnetized is due toDemagnetized is due to1) Temperature rise 2) Improper brush design3) Improper motor design4) Excessive current flow due to fault and transient

condition

Speed control Speed control • It is achieved by varying armature voltage by using

rheostat in series with armature. It simple method. Better speed regulation can be possible.

Application Application • PMDC motor is extensively used where small dc motors

are required and also very effective control is not required, such as in automobiles starter, toys, wipers, washers, hot blowers, air conditioners, computer disc drives and in many more.