Motors vs Engines
• Motors convert electrical energy to mechanical energy.
• Engines convert chemical energy to mechanical energy.
Magnetic Induction
• Simple Electromagnet
• Like Poles Repel
• Opposite Poles Attract
Operating Principle
Motor Parts
• Enclosure
• Stator
• Rotor
• Bearings
• Conduit Box
• Eye Bolt
Enclosure
• Holds parts together
• Helps with heat dissipation
• In some cases, protects internal components
from the environment.
Stator (Windings)
• “Stationary” part of the motor sometimes referred to as “the windings”.
• Slotted cores made of thin sections of soft iron are wound with insulated copper wire to form one or more pairs of magnetic poles.
Rotor
• “Rotating” part of the motor.
• Magnetic field from the stator induces an opposing magnetic field onto the rotor causing the rotor to“push” away from the stator field.
Wound Rotor Motors
• Older motor designed to operate at “variable speed”
• Advantages
– Speed Control, High Starting Torque, Low Starting Current
• Disadvantages
– Expensive, High Maintenance, Low Efficiency
Bearings
• Sleeve Bearings
– Standard on most motors
– Quiet
– Horizontal shafts only
– Oil lubricated
• Ball (Roller) Bearings
– Support shaft in any position
– Grease lubricated
– Many come sealed requiring no maintain
Other Parts
• Conduit Box
– Point of connection of electrical power to the motor’s stator windings
• Eye Bolt
– Used to lift heavy motors
with a hoist or crane to
prevent motor damage.
Motor Speed
• Synchronous Speed
– Speed the motor’s magnetic field rotates.
– Theoretical speed with not torque or friction.
• Theoretical Speed
• A well built motor may approach synchronous speed when it has no load.
• Factors
– Electrical Frequency (cycles/second)
– NO of poles in motor
Synchronous Speed = 120 X Frequency
NO. of poles
• Rated Speed
– Speed the motor operates when fully loaded.
– Actual speed at full load when supplied rated voltage.
• Speed the motor runs at when fully loaded and supplied rated nameplate voltage.
Motor Slip
• Percent difference between a motor’s synchronous speed and rated speed.
• The rotor in an induction motor lags slightly behind the synchronous speed of the changing
polarity of the magnetic field.
– Low Slip Motors
• “Stiff”….High Efficiency motors
– High Slip Motors
• Used for applications where load varies significantly…oil pump jacks.
Torque
• Measure of force producing a rotation
– Turning Effort
– Measured in pound-feet
(foot-pounds)
Torque-Speed Curve
• Amount of Torque produced by motors varies with Speed.
• Torque Speed Curves
– Starting Torque
– Pull Up Torque
– Breakdown Torque
Motor Power
• Output Power
– Horsepower
– Amount of power motor can produce at shaft and not reduce life of motor.
• Input Power
– Kilowatts
– Amount of power the motor consumes to produce the output power.
Calculating Horsepower
HP=RPM X Torque/5252
• Need Speed and Torque
• Speed is easy
– Tachometer
• Torque is difficult
– Dynamo meter
– Prony Brake
Watt’s Law
• Input Power
• Single Phase
– Watts = Volts X Amps X p.f.
• Three Phase
– Watts = Avg Volts X Avg Amps X p.f. X 1.74
Motor Types (CLASSIFICATION OF MOTORS)
• Motors convert electrical energy to mechanical energy.
• Engines convert chemical energy to mechanical energy.
Magnetic Induction
• Simple Electromagnet
• Like Poles Repel
• Opposite Poles Attract
Operating Principle
Motor Parts
• Enclosure
• Stator
• Rotor
• Bearings
• Conduit Box
• Eye Bolt
Enclosure
• Holds parts together
• Helps with heat dissipation
• In some cases, protects internal components
from the environment.
Stator (Windings)• “Stationary” part of the motor sometimes referred to as “the windings”.
• Slotted cores made of thin sections of soft iron are wound with insulated copper wire to form one or more pairs of magnetic poles.
Rotor
• “Rotating” part of the motor.• Magnetic field from the stator induces an opposing magnetic field onto the rotor causing the rotor to“push” away from the stator field.
Wound Rotor Motors
• Older motor designed to operate at “variable speed”
• Advantages
– Speed Control, High Starting Torque, Low Starting Current
• Disadvantages
– Expensive, High Maintenance, Low Efficiency
Bearings
• Sleeve Bearings– Standard on most motors
– Quiet
– Horizontal shafts only
– Oil lubricated
• Ball (Roller) Bearings
– Support shaft in any position
– Grease lubricated
– Many come sealed requiring no maintain
Other Parts
• Conduit Box
– Point of connection of electrical power to the motor’s stator windings
• Eye Bolt
– Used to lift heavy motors
with a hoist or crane to
prevent motor damage.
Motor Speed
• Synchronous Speed
– Speed the motor’s magnetic field rotates.– Theoretical speed with not torque or friction.
• Theoretical Speed
• A well built motor may approach synchronous speed when it has no load.
• Factors
– Electrical Frequency (cycles/second)
– NO of poles in motor
Synchronous Speed = 120 X Frequency
NO. of poles
• Rated Speed
– Speed the motor operates when fully loaded.
– Actual speed at full load when supplied rated voltage.
• Speed the motor runs at when fully loaded and supplied rated nameplate voltage.
Motor Slip
• Percent difference between a motor’s synchronous speed and rated speed.
• The rotor in an induction motor lags slightly behind the synchronous speed of the changing
polarity of the magnetic field.
– Low Slip Motors
• “Stiff”….High Efficiency motors
– High Slip Motors
• Used for applications where load varies significantly…oil pump jacks.
Torque• Measure of force producing a rotation
– Turning Effort
– Measured in pound-feet
(foot-pounds)
Torque-Speed Curve
• Amount of Torque produced by motors varies with Speed.
• Torque Speed Curves
– Starting Torque
– Pull Up Torque
– Breakdown Torque
Motor Power
• Output Power
– Horsepower
– Amount of power motor can produce at shaft and not reduce life of motor.
• Input Power
– Kilowatts
– Amount of power the motor consumes to produce the output power.
Calculating Horsepower
HP=RPM X Torque/5252
• Need Speed and Torque
• Speed is easy
– Tachometer
• Torque is difficult
– Dynamo meter
– Prony Brake
Watt’s Law
• Input Power
• Single Phase
– Watts = Volts X Amps X p.f.
• Three Phase
– Watts = Avg Volts X Avg Amps X p.f. X 1.74
Motor Types (CLASSIFICATION OF MOTORS)
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