Electric Motors Dr. Ahmad Harb

Electric Motor Converts electricity into mechanical motionConverts electricity into mechanical motion Works by electromagnetismWorks by electromagnetism Lorentz Force LawLorentz Force Law Current flowing through a wire produces a magnetic field (labeled M here) around the wire.

Simple DC Motor Armature or rotorArmature or rotor CommutatorCommutator BrushesBrushes AxleAxle Field magnetField magnet DC power supplyDC power supply

Simple DC Motor A magnetic field is generated around the armature.A magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation. When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field.When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. Momentum keeps the motor moving the right direction.Momentum keeps the motor moving the right direction. The process then repeats.The process then repeats.

3 Pole Motor A motor can have any number of polesA motor can have any number of poles Most common formMost common form Doesn’t get stuck in horizontal positionDoesn’t get stuck in horizontal position In 2 pole, always shorts out the battery when the commutator flips the fieldIn 2 pole, always shorts out the battery when the commutator flips the field

Examples of everyday motors EVERYTHING!!!!! At home: The fan over the stove and in the microwave oven The dispose-all under the sink The blender The can opener The refrigerator - Two or three in fact: – –one for the compressor, – –one for the fan inside the refrigerator, – –as well as one in the icemaker The mixer The tape player in the answering machine Probably even the clock on the oven The washer The dryer The electric screwdriver The vacuum cleaner and the Dustbuster mini-vac The electric saw The electric drill The furnace blower Even in the bathroom, there's a motor in: The fan The electric toothbrush The hair dryer The electric razor Your car is loaded with electric motors: Power windows (a motor in each window) Power seats (up to seven motors per seat) Fans for the heater and the radiator Windshield wipers The starter motor Electric radio antennas Motors in all sorts of places: Your iPod Several in the VCR Several in a CD player or tape deck Many in a computer Most toys that move Electric clocks The garage door opener Aquarium pumps

Motor efficiency matters In U.S. Industry, electric motors consume: – –~680 billion kWh/year – –~63% of all industrial electricity consumption – –~23% of all U.S. consumption Source: U.S. DOE. Energy Efficiency and Renewable Energy (EERE). These percentages are typically higher in developing countries, while the motors are typically less efficient

How is power lost in a motor? Mechanical (friction and windage) losses –friction in bearings and seals and power consumed by the motor cooling fan Magnetic (core) losses –hysteresis and eddy current losses in steel laminations of the stator and rotor Electrical (I 2 R) losses –Stator winding losses –Rotor conductor bar losses Stray losses –miscellaneous losses associated mainly with electromagnetic radiation Source: U.S. DOE. Energy Efficiency and Renewable Energy (EERE).

U.S. standard for determination of motor efficiency: IEEE 112-B Based on Energy Policy Act legislationBased on Energy Policy Act legislation (The value of efficiency is then normally converted from a decimal fraction to a percent for convenience.) Need for a standard:Need for a standard: –Efficiency changes as grease “breaks in” –Output and input power can vary –Readings of speed, torque, volts, amperes, watts are not steady of constant values Source:

Overview of motor efficiencies The following table of results from three different testing standards: Test Method15 HP75 HP800 HP1500 HP IEEE 112 B (U.S.) IEC 34-2 (International) JEC 37 (Japanese)

Improving motor efficiencies According to U.S. DOE, use of only “Premium Efficiency” motors could save ~20 billion kWh/year in the U.S. – –Covers wide-range of motor specifications – –680 billion kWh/year consumption by electric motors Joint specification by: – –National Electrical Manufacturers Association (NEMA ) – –Consortium for Energy Efficiency (CEE)

NEMA Premium® motors Example One 50 hp, 1800 rpm, 460 V Example Two 25 hp, 1800 rpm, 460 V EPAct StandardNEMA PremiumEPAct Standard NEMA Premium Full Load Efficiency93.1* Efficiency (at 75% load) Demand Reduction (at 75% load) kW kW Meets EPAct?yes Incremental Motor Cost -$176-$96 Energy Savings at 75% Load (6000 hrs/year) -2,829 kWh/y -958 kWh/y

Expanding the definition of “motor” Solar powered nano motor The Future…

Thank you. The end.

Background: AC Induction Motor This is the most commonplace motor. It has a rotating stator field. The rotor has imbedded electroconductive bars resembling a pet rodent exercise wheel, which inspired the name, “squirrel cage”. The rotating stator field induces current in the cage creating a magnetic field which causes the rotor to follow the stator field. First Induction Motor, 1888 Inventor Nikola Tesla 1894 Induction Motor. World’s largest when new. 65 HP

How is efficiency determined? IEEE 112-B (United States)IEEE 112-B (United States) IEC IEC (International Electrotechnical Commission)IEC IEC (International Electrotechnical Commission) JEC-37 (Japanese Electrotechnical Committee)JEC-37 (Japanese Electrotechnical Committee) C-390 (Canadian Standards Association)C-390 (Canadian Standards Association) There are different standards in use around the world for the determination of motor efficiency. They yield slightly different results. Source: U.S. DOE. Energy Efficiency and Renewable Energy (EERE).

What’s in an efficient motor? Same components; just more and better materials and closer tolerances. è èLarger wire gage – Lower stator winding loss è èLonger rotor and stator – Lower core loss è èLower rotor bar resistance – Lower rotor loss è èSmaller fan – Lower windage loss è èOptimized air gap size – Lower stray load loss è èBetter steel with thinner laminations -- Lower core loss è èOptimum bearing seal/shield – Lower friction loss

A Useful Tool – MotorMaster+ Compare: Motors of varying eff. Repair vs. replace >25,000 motors in database Calculate energy savings Calculate LCC