Electric MotorsElectric Motors

ESM 288ESM 288Betty SetoBetty Seto

Kat WuelfingKat Wuelfing

Electric MotorElectric Motor

•• Converts electricity into mechanical motionConverts electricity into mechanical motion•• Works by electromagnetismWorks by electromagnetism•• Lorentz Force LawLorentz Force Law

Current flowing through a Current flowing through a wire produces a magnetic wire produces a magnetic field (labeled M here) around field (labeled M here) around the wire. the wire.

Simple DC MotorSimple DC Motor

•• Armature or rotor Armature or rotor •• CommutatorCommutator•• Brushes Brushes •• Axle Axle •• Field magnet Field magnet •• DC power supply DC power supply

Simple DC MotorSimple DC Motor•• A magnetic field is generated A magnetic field is generated

around the armature. around the armature. •• The left side of the armature is The left side of the armature is

pushed away from the left pushed away from the left magnet and drawn toward the magnet and drawn toward the right, causing rotation. right, causing rotation.

•• When the armature becomes When the armature becomes horizontally aligned, the horizontally aligned, the commutatorcommutator reverses the reverses the direction of current through the direction of current through the coil, reversing the magnetic coil, reversing the magnetic field. field.

•• Momentum keeps the motor Momentum keeps the motor moving the right direction.moving the right direction.

•• The process then repeats. The process then repeats.

3 Pole Motor3 Pole Motor•• A motor can have any A motor can have any

number of polesnumber of poles•• Most common formMost common form•• DoesnDoesn’’t get stuck in t get stuck in

horizontal positionhorizontal position•• In 2 pole, always In 2 pole, always

shorts out the battery shorts out the battery when the when the commutatorcommutator flips the fieldflips 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 mattersMotor 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). www.pumps.org/public/member_services/presentations/2005_spring/electric_motor_efficiency.pps

• 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 (I2R) 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). www.pumps.org/public/member_services/presentations/2005_spring/electric_motor_efficiency.pps

U.S. standard for determination U.S. standard for determination of motor efficiency: IEEE 112of motor efficiency: IEEE 112--BB•• 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 Efficiency changes as grease ““breaks inbreaks in””–– Output and input power can varyOutput and input power can vary–– Readings of speed, torque, volts, amperes, watts are Readings of speed, torque, volts, amperes, watts are

not steady of constant valuesnot steady of constant values

Source: Source: http://www.iprocessmart.com/leeson/leeson_epact_motor_testing.hthttp://www.iprocessmart.com/leeson/leeson_epact_motor_testing.htmm

Overview of motor efficiencies

• The following table of results from three different testing standards:

Test Method 15 HP 75 HP 800 HP 1500 HPIEEE 112 B (U.S.) 87.4 90.0 95.9 95.9IEC 34-2 (International) 89.2 92.7 95.6 96.0JEC 37 (Japanese) 90.1 93.1 95.9 96.8

Improving motor efficienciesImproving 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® motorsExample One 50 hp, 1800 rpm,

460 V

Example Two 25 hp, 1800 rpm,

460 V

EPAct Standard NEMA Premium EPAct Standard NEMA Premium

Full Load Efficiency 93.1* 94.5 92.4 93.6Efficiency (at 75%

load) 93.6 95.1 93.1 94.1

Demand Reduction (at 75% load) - 0.47 kW - 0.16 kW

Meets EPAct? yes yes yes 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…

http://www.spacemart.com/reports/Nano_World_First_Solar_Powered_http://www.spacemart.com/reports/Nano_World_First_Solar_Powered_Nano_Motor.htmlNano_Motor.html

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, 1888Inventor Nikola Tesla

1894 InductionMotor. World’s largest when new. 65 HP

How is efficiency determined?How is efficiency determined?

•• IEEE 112IEEE 112--B (United States)B (United States)

•• IEC IEC60034.2 (International IEC IEC60034.2 (International ElectrotechnicalElectrotechnical Commission)Commission)

•• JECJEC--37 (Japanese 37 (Japanese ElectrotechnicalElectrotechnical Committee)Committee)

•• CC--390 (Canadian Standards Association)390 (Canadian Standards Association)

There are different standards in use There are different standards in use around the world for the around the world for the determination of motor efficiency. determination of motor efficiency. They yield slightly different results.They yield slightly different results.

Source: U.S. DOE. Energy Efficiency and Renewable Energy (EERE). www.pumps.org/public/member_services/presentations/2005_spring/electric_motor_efficiency.pps

What’s in an efficient motor?Same components; just more and better materials and closer tolerances.

Larger wire gage – Lower stator winding lossLonger rotor and stator – Lower core lossLower rotor bar resistance – Lower rotor lossSmaller fan – Lower windage lossOptimized air gap size – Lower stray load lossBetter steel with thinner laminations --Lower core lossOptimum bearing seal/shield – Lower friction loss

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