Presentation Overview
Motor
Introduction Construction Working Selection of motors Types Applications
Introduction
Electric motor is a device that uses up electric input to make mechanical output by the virtue of magnetic field.
Basic Structure
Stator
Remains static during motor operation. Provides support to the rotor Provides magnetic field either by P.M. or by coil
ROTOR
SHAFT
STATOR
Basic Structure
Rotor
Rotates during motor operation. Provides rotation, power and torque to shaft
ROTOR
SHAFT
Shaft
Mechanical output is taken by it
STATOR
Motor Parts
Stator Assembly
Back & Front Support
Cooling Fan
Rotor Assembly Bearings
Through Bolts & nuts
Principal of Operation
An electric current in a magnetic field produces a force F= I L X B . . . (1)
Principal of Operation
If the current carrying wire is bent into a loop then the two sides of the loop (perpendicular to the magnetic field) will experience forces in opposite direction
Principal of Operation
The pair of forces create a turning influence or torque to rotate the coil
Principal of Operation
Practical Motors have several loops on an armature to provide a more uniform torque Electromagnets produce magnetic field and are called field coils
Principal of Operation
Equation (1) shows following requirements
Conductor Electric Potential for current Magnetic field
F= I L x B
Simplest Motor ( you can make in your home)
Coil / Conductor
Battery
Magnet
Support
Selecting a Motor
Motors are selected depending on
Cost Efficiency Torque-speed profile Peak torque capability Current limitations Suitability for hazardous environment Availability of spare parts
Steps of Selecting a Motor
Select a power source you are having
AC power supply
Single phase Three phase
DC power supply
Select a functionality required
Speed (in comparison with other motors)
High Low Medium
Steps of Selecting a Motor
Efficiency
Maximum Moderate Not important
Speed control
Variable speed Constant speed
Starting
High or low torque
Stopping
Steps of Selecting a Motor
Determine
Load to be handled Load variation during operation Torque requirement
At the start Load for working
Speed requirement at the load Plot the required motor torque versus speed Provide a factor of safety where the environment or service condition is not well defined
Steps of Selecting a Motor
Have a view of the working environment
Temperature Presence of the corrosive or explosive atmosphere Exposure to weather or water Availability of cooling air ( for the long working period of motors)
Working time
Continuous working Discontinuous working
Steps of Selecting a Motor
Search for a motor approving the minimum requirements but with acceptable
Size Weight Cost
Load
The horsepower required to drive a machine is typically referred to as load. The motor drives a load which has a certain characteristics torque-speed requirement. In general,
where, k may be an integer of a fraction.
Types of Motors
Following are some types of Motors: AC Motors DC Motors Modified from Basic AC DC Motors
Torque Motors Servomotors Stepper Motors Brushless Motors Linear Motors
Introduction
Motor that uses AC power input to give mechanical output Two main categories of AC motors Asynchronous synchronous motors
Synchronous Motors
Size
Sub fractional (1-40 mhp) Large horsepower (1 hp or >)
Main features
Constant-speed electric motors Operates with a DC rotor current The rotor follows the rotating magnetic field at the synchronous speed.
Synchronous Motors
Types
Nonexcited Direct-current excited
Merits
Can be used primarily where precise constant speed is required Highly efficient means of converting AC energy to mechanical power. Can operate at leading or unity power factor
Synchronous Motors
Selected for
Constant speed requirement Gearing required to deliver speeds that are significantly less than 1200 r.p.m. Handled by flywheels Available access to AC power both
Single phase Three phase
Induction Motors
Typical features
Basically an AC transformer with a rotating secondary Also called squirrel cage motor No. of poles 2-12 Rotor currents are induced by transformer action. The motor runs at less than the synchronous speed
Stepper Motor
Typical features
Works in steps Rotates on receiving a pulse Rotates in certain degree of steps 1.8 , 3.6 , 7.5 , 15 , 30 , 45 , 90 In between pulses the motor doesn't work Unable to handle large inertial loads
Stepper Motor
Types
Permanent magnet type Reluctance type
Merits
Precise control rotations
Selected for
Low cost, open-loop positioning Feedback sensors required to monitor position if max torque not exceeded Good accuracy over long motions Reasonably high torques at low speeds Energy efficiency not important
Introduction
Motor that uses DC input for the Mechanical output Winding on rotor
Selection Criteria for DC motors
Construction Working Working torque and speed Size, weight, and cost Material selection Motor winding
Winding selection
Designing with computers
Working
Working
Working
Working
Working
DC MOTOR Types
Shunt-wound Motor Series-wound Motor Compound wound Motor Permanent Magnet Motor
DC MOTOR Types (Shunt wound)
Field coils in parallel with armature coils Merits
Lower speed/load sensitivity
Demerits
Poor characteristics for overload torque
DC MOTOR Types (Series-wound Motor)
Field coils in series with armature coils Merits
High starting torque capacity Speed is very load sensitive (limits acceleration in sys)
Demerits
Speed can run-away under no-load condition
DC Motor Types (Compound Wound)
Field and armature coils connected in combination of series and parallel Compromise between series and parallel Merits
Will not run-away under no-load Good starting capabilities
Demerits
More expensive
DC Motor Types (PM)
Stationary field from permanent magnets Merits Smaller size Easier to manufacture than other DC motors Good starting torque Demerits Speed is load sensitive Expensive to produce Can't reliably control at lowest speeds Physically larger High maintenance
Size
Smallest motor in the world
Material selection
Why to choose DC Motors ?
Adjustable speed Changeable direction of rotation Automatic speed control Acceleration & Deceleration controllable Torque controllable Dynamic braking High torque speed ratio
Some Applications
Electric Propulsion Pumps, fans, compressors Plant automation Flexible manufacturing systems Spindles and servos Appliances and power tools Cement kilns Paper and pulp mills; textile mills Automotive applications Conveyors, elevators, escalators, lifts
