Electric Machine

  • Electric machine – transducer for converting electrical energy to mechanical energy or mechanical energy to electrical energy
  • electric machine
  • Types of Electric machines
    • Motors
    • Generators
    • Sensors
    • Electromagnets
    • Electromagnetic Amplifiers, etc.

Common Electric Motor Types

  • AC Induction Motor
    • Squirrel Cage
    • Wound Field
  • Brushed DC Motor
  • AC Synchronous Motor
    • Permanent magnets
    • Wound field
  • Brushless AC/DC Motor
  • Switched reluctance Motor
  • Linear Motor
    • Flat
    • Tubular
  • Stepper Motor
    • Permanent Magnet (PM)
    • Variable Reluctance (VR)
    • Hybrid Stepper
    • Linear

Brushed DC Motor Construction and Performance

brushless dc motor

brushed dc motor performance

  • Easy to predict motor performance
  • Simple, inexpensive control electronics
  • Use of a feedback device is optional
  • Difficult to design brush system
  • Limited availability of the brush system components
  • Very difficult to predict brush life
  • Not a motor of choice for high-performance application
  • Manufacturing cost very low for mass production, when fully tooled

Typical applications for Brushed DC Motor

applications for brushed dc motors

  • Appliances
  • Hand Tools
  • Automotive Manufacturing
  • Military and Commercial Aerospace Manufacturing
  • Autopilot/Auto-throttles
  • Fin Controls
  • Gimbals
  • Optics & Radars

AC Induction Motor Construction and Performance

  • Easy to predict motor performance for a three-phase motor windings, notoriously difficult for a single-phase designs
  • Limited availability for copper fabricated rotors
  • Still a popular choice for a new 400 Hz military and commercial aerospace applications
  • Low manufacturing costs low for mass production, when fully tooled

typical induction motor construction

Typical applications for AC Induction Motors

  • Fans & Blowers
  • Military and Commercial, rotary or fixed wing aircraft
  • Industrial Automation
  • Flight Controls
  • Radar Drives
  • Environmental Control Systems
  • Throttle/Pilot Interface Devices
  • Oil & Gas Downhole Tooling
  • Pumps & Valves

applications for ac induction motor

Hybrid Stepper Motor Construction and Performance

  • Difficult to predict motor performance, based on design experience
  • Attractive for some space applications when feedback device not required
  • Can require precision lamination stamping
  • Motor winding similar to a brushless DC design
  • Manufacturing cost very low for mass production, when fully tooled

hybrid stepper motor construction

Typical applications for Stepper Motors

  • Low Precision Positioning without Feedback Device
  • Positioning Optical Filter/Lenses with Feedback Device
  • Robotic Joint Positioning
  • Pan & Tilt Assemblies
  • Low Power, Low Speed Scanners
  • Radar Drives (limited rotation, low inertia or power)
  • 3D Printers
  • Proportional Valves — Hydraulic, Fuel Control etc.

applications for stepper motor

Brushless DC Motor Construction and Performance

  • Easy to predict motor performance, however extremely drive/controller dependent
  • Motor of choice for new and/or high-performance applications
  • Very high power density
  • Very high speeds
  • Very high efficiency
  • Requires a feedback device

brushless dc motor construction

brushless dc motor construction
Read about how magnet selection and implementation affect the overall performance of a BLDC motor

Typical applications for Brushless Motors

  • Highest Performance Applications
    • Fin Controls
    • TVC Controls
    • Multi-Mode Radar Drives
    • Weapons Gimbals
    • Turret Drives
    • Primary & Secondary Flight Controls
    • High speed / High Power Pumps & Fans
    • Vehicle Traction Drives
    • High Reliability and Storage Life

applications for brushless motor

Switched Reluctance Motor Construction and Performance

  • Electronically Commutated
  • No permanent magnets
  • High torque ripple
  • Difficult to predict motor performance
  • Once was a major alternative to induction and brushless DC designs
  • Manufacturing cost low for mass production, when fully tooled

switched reluctance motor construction

Typical applications for Switched Reluctance Motor

  • Appliances
  • Hand Tools
  • Automotive Manufacturing
  • Locomotive Traction

applications for switched reluctance motors

Linear Motor Construction and Performance

  • Easy to predict motor performance
  • Very high speeds
  • Very high precision
  • Best for light/low inertial loads
  • Limited travel lengths
  • Motor of choice for new and/or high-performance applications
  • Manufacturing cost high

linear motor construction

motor construction and performance

Typical applications for Linear Induction Motors

  • Small Linear Motors
    • Semiconductor Manufacturing
    • Flat Panel Manufacturing
    • Conveyor Systems
    • Airport Baggage Handling
    • Accelerators and Launchers
    • Pumping of Liquid Metal
  • Large Linear Motors
    • Transportation (Low & Medium Speed Trains)
    • Sliding Doors Closure (Malls, Metros)
    • People Movers
    • Material Handling and Storage

Commonly Used Sensors

  • Resolvers/Synchros
    • Industrial Servo motors
    • Aerospace and Military
    • Down hole oil and gas exploration
    • Applications with high temperature and mechanical vibration requirements
    • Difficult to predict performance
    • Difficult to achieve high accuracy due to manufacturing variances
    • Manufacturing cost can be low in mass production, when fully tooled
    • No new development, mainly second source by matching resolver performance

commonly used sensors

Electromagnets/Solenoids

  • Industrial
  • Magnetic mechanical support
  • Automotive

electromagnets and solenoids

Commonly Used Materials

Magnetic Materials

  • Carbon steels
  • Stainless steel
  • Silicon steels
  • High saturation alloys
  • Amorphous ferromagnetic alloys
  • Soft magnetic powder composites
  • Nanostructured materials
  • Ceramic
  • Alnico
  • Rare Earth

Dielectric Materials

  • Paper
  • Epoxy
  • Plastic

Magnet Wire

  • Copper
  • Aluminum
  • Litz

Commonly Used Materials in Our History

Carbon steels/Stainless steels /Silicon steels/High saturation alloys

commonly used materials in history

Examples

Material Type Core Loss Saturation Flux Density Permeability Ease of Processing Raw Material Relative Cost
CRML Steel Fair Good Good Best 0.5
Non-Oriented Silcon Steel Good Good Fair Good 1.0
Grain-Oriented Silcon Steel Better Good Better Fair 1.25
Amorphous Alloy-Iron based Better Fair High Much Care Required 1.25
Thin-Gauge Silicon Steel Better Good Good Fair 10
6-1/2% Nickel-Iron Alloy Better Good Good Care Required 12
49% Nickel-Iron Alloy Better Fair High Care Required 12
80% Nickel-Iron Alloy Best Low High Care Required 15
Cobalt-Iron Alloy Good Best Better Care Required 45
Powdered Alloys-SMC * * * * *

* The ultimate properties and cost of SMC materials are determined in large measure by the design of the machine and thus are not referenced in this table

Examples

  • Deterioration of Magnetic Properties due to Punching
  • Fully processed material is simply material which has been annealed to optimum properties at the steel mill. Even though annealed at the mill, fully processed material may require further stress relief anneal after stamping. The stresses introduced during punching degrade the material properties around the edges of the lamination, and must be removed to obtain maximum performance. This is particularly true for parts with narrow sections, or where very high flux density is required

examples

Commonly Used Magnet Materials

Material Magnetic Properties Magnetic Characteristics Curie Temperature Temperature Coefficient of Induction Cost $ / lb.
Cast Alnico Br – 5,500 – 13,500 Hc – 475 – 1,900 MGOe 1.4 – 10.5 Cast to Shape, Hard, Crystal Structure – Grind or EDM 840°C 0.02% / °C $40
Sintered Alnico Br – 6,000 – 10,800 Hc – 550 – 1,900 MGOe 1.4 – 5.0 Powder Pressed to Shape, Hard Structure – Grind or EDM 840°C 0.02% / °C $23
Ceramic (Hard Ferrite) Br – 3,450 – 4,100 Hci – 3,000 – 4,800 MGOe 2.7 – 4.0 Simple Shapes: Arcs, Rect., Plugs, Rings – Hard-Grind 450°C 0.02% / °C $2
Samarium Cobalt Br – 8,800 – 11,000 Hci – 11,000 – 21,000 MGOe – 18 – 32 Very Brittle – Grind or EDM 750°C / 825°C 0.035% / °C $125
Neodymium Iron Boron Br – 10,500 – 14,000 Hci – – 14,000 MGOe 27 – 50 Requires Coating to Prevent Oxidization Grind or EDM 310°C 0.13% / °C $95
Iron-Chrome Cobalt Br – 9,000 – 13,500 Hc – 50 – 600 MGOe – 4.25 – 5.25 Can be Formed, Stamped, Thin Rolled Mat'l 0.050″- .0005″ 600°C 0.02% / °C $30
Bonded Flexible (Callenered or Extruded Br – 2,500 – 5,600 Hci – 3,500 – 16,000 Ferrite 450°C 0.18% / °C $3 MGOe 1.4 – 6.2 Flexible, Thermal Shock Resistant, Low-tono Tooling Charge, Available In Wide Range of Sizes Ferrite 450°C Neo 310°C 0.18% / °C 0.07 to 0.13% / °C $3 $30 – $50
Bonded Plastic (Molded) Br – 2,500 – 6,900 Hci – 3,000 – 16,000 Ferrite 450°C 0.18% / °C $3 MGOe – 1.5 – 10.5 Complex Shapes, Thin Walls, Tight Dimensions without Machining, Good Strength Ferrite 450°C Neo 310°C 0.18% / °C 0.07 to 0.13% / °C $3 $60
Compression Bonded Neo (Epoxy) Br – 6,200 – 8,200 Hci – 4,300 – 18,000 MGOe – 7.5 – 15.0 Simple Geometry, Close Tolerancing W.O Machining Higher BhMax Than Inj. Molded With Lower Tooling Cost Neo 310°C 0.07 to 0.13% / °C $60

Commonly Used Epoxy

Temp class Product no. Description Specific gravity Cut-through resistance Edge coverage Imapct resistance Gel time @193°C (380°F) hot plate Dielectric strength Volume resisitivity Color
B 260 260CG Spray and fluid bed drip application 1.43 215°C (410°F) 35-45 100 (11.3) 12-16 s 1000 (12-15 mil coating) 1015 Green
B 262 Spray and fluid bed drip application 1.34 130°C (266°F) 38-48 100 (11.3) 12-16 s 1000 (10-mil coating) 1013 Red
B 263 Spray and fluid bed drip applications in high-temperature cut-through resistance 1.47 290°C (554°F) 40-50 100 (11.3) 8-14 s 1000 (12-15 mil coating) 1015 Green
B 270 Spray and fluid bed drip applications for high-temperature cut-through and bridging gaps 1.48 250°C (482°F) 35-40 120 (13.8) 12-16 s 1000 (10-mil coating) 1013 Green
B 5555 Cold electrostatic fluid bed, hot venturi spray, or hot fluid be dip for fractional horsepower motor stators and armatures 1.7 >340°C (644°F) 160 (18.1) 8-12 s 1300 (V/ml2) Green
B 5388 Electrostatic fluid bed process, superior cut-through resistance and well heat, chemical and moisture resistance 1.57 >340°C (644°F) 35 (11.3) 100 25-35 s 1100 (V/mil) Blue
B 5133 Electrostatic coating for cold as well as heated parts 1.45 160°C (320°F) 15 (13.8) 120 500 (V/mil) 5×1014 Light blue

Commonly Used Magnet Wire

  • Conductor
    • The most suitable materials for magnet wire applications are unalloyed pure metals, particularly copper
    • High-purity oxygen-free copper grades are used for high-temperature applications
    • Aluminum magnet wire is sometimes used as an alternative for transformers and motors. Because of its lower electrical conductivity, aluminum wire requires a 1.6-times larger cross sectional area than a copper wire to achieve comparable DC resistance.
  • Insulation
    • Modern magnet wire typically uses one to four layers of polymer film insulation, often of two different compositions, to provide a tough, continuous insulating layer.
  • Classification
    • Magnet wire is classified by diameter (AWG /SWG or millimeters) or area (square millimeters), temperature class, and insulation class

commonly used magnet wire

Stator's Most Common Constructions

stator constructions stator constructions

Rotor's Constructions

rotor constructions

Electric Machine Parameter and Testing — Part 1

  • Mechanical Dimensions
    • Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part.
  • GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.
  • ASME standards ASME Y14.5 – Dimensioning and Tolerancing
  • ISO TC 10 Technical product documentation
  • ISO/TC 213 Dimensional and geometrical product specifications and verification

Electric Machine Parameter and Testing — Part 2

  • Electrical parameters
    • Example:
      • Measure and record A-B, B-C, C-A line-line resistances and inductances.
      • Hipot and surge test the stator after varnish at 1800VAC, max current leakage 5mA Before and after varnish, perform corona test(partial discharge) with pulse up to but not exceeding 3000V.
    • Resistance
      • The electrical resistance of an electrical conductor is the opposition to the passage of an electric current through that conductor. Electrical resistance shares some conceptual parallels with the mechanical notion of friction. The SI unit of electrical resistance is the ohm (Ω)
    • Inductance
      • Inductance is a property of an electrical conductor which opposes a change in current. The Henry (symbol: H) is the SI derived unit of electrical inductance

Electric Machine Parameter and Testing — Part 3

Different Methods of Tests in the Stator Insulation of Electric Machine

S.No. Method Standards Insulation Tested and Diagnostic Value
1 Insulation Resistance IEEE 43. NEMA MG 1 Find contaminations and defects in phase-to-ground insulation
2 Polarization Index IEEE 43 Find contaminations and defects in phase-to-ground insulation
3 DC High Potential Test (Dielectric Withstand Test) IEEE 95, IEC 34.1, NEMA MG 1 Find contaminations and defects in phase-to-ground insulation
4 AC High Potential Test (Dielectric Withstand Test) IEC 60034 NEMA MG 1 Find contaminations and defects in phase-to-ground insulation
5 Surge Test IEEE 522 NEMA MG 1 Detects deterioration of the turn-to-turn insulation
6 Partial Discharge Test IEEE 1434 Detects deterioration of the phase-to-ground and turn-to turn insulation
7 Dissipation-Factor IEEE 286 IEC 60894 Detects deterioration of the phase-to-ground and phase-to phase insulation

Electric Machine Parameter and Testing

  • High Potential Test
    • Three types of High Potential Test tests are commonly used. These three tests differ in the amount of voltage applied and the amount (or nature) of acceptable current flow:
    • Insulation Resistance test measures the resistance of the electrical insulation between the copper conductors and the core of the stator. Ideally, this resistance should be infinite. In practice, is not infinitely high. Usually, lower the insulation resistance, it is more likely that there is a problem with the insulation. Dielectric Breakdown Test. The test voltage is increased until the dielectric fails, or breaks down, allowing too much current to flow. The dielectric is often destroyed by this test so this test is used on a random sample basis. This test allows designers to estimate the breakdown voltage of a product's design and to see where the breakdown occurred.
    • Dielectric Withstand Test. A standard test voltage is applied (below the established Breakdown Voltage) and the resulting leakage current is monitored. The leakage current must be below a preset limit or the test is considered to have failed. This test is non- destructive providing that it does not fail and is usually required by safety agencies to be performed as a 100% production line test on all products before they leave the factory.

IEEE Std 43-2000IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery

Electric Machine Parameter and Testing — Part 4

  • Surge Test
    • If the turn insulation fails in a form-wound stator winding, the motor will likely fail in a few minutes. Thus the turn insulation is critical to the life of a motor. Low voltage tests on form-wound stators, such as inductance or inductive impedance tests, can detect if the turn insulation is shorted, but not if it is weakened. Only the surge voltage test is able to directly find stator windings with deteriorated turn insulation. By applying a high voltage surge between the turns, this test is an overvoltage test for the turn insulation, and may fail the insulation, requiring bypassing of the failed coil, replacement or rewind.

Electric Machine Parameter and Testing — Part 5

  • Partial Discharge Test
    • IEC TS 60034-27

      • For many years, the measurement of partial discharges (PD) has been employed as a sensitive means of assessing the quality of new insulation as well as a means of detecting localized sources of PD in used electrical winding insulation arising from operational stresses in service. Compared with other dielectric tests (i.e. the measurement of dissipation factor or insulation resistance) the differentiating character of partial discharge measurements allows localized weak points of the insulation system to be identified. The PD testing of rotating machines is also used when inspecting the quality of new assembled and finished stator windings, new winding components and fully impregnated stators.

        The measurement of partial discharges can also provide information on: points of weakness in the insulation system; ageing processes; further measures and intervals between overhauls.

        Although the PD testing of rotating machines has gained widespread acceptance, it has emerged from several studies that not only are there many different methods of measurement in existence but also the criteria and methods of analyzing and finally assessing the measured data are often very different and not really comparable. Consequently, there is an urgent need to give some guidance to those users who are considering the use of PD measurements to assess the condition of their insulation systems.

Organization/Standards/Directives

  • NEMA National Electrical Manufacturers Association
    • NEMA sets standards for many electrical products, including motors. For, example, "size 11" mean the mounting face of the motor is 1.1 inches square
    • Standards Publication ICS 16 standard covers the components used in a motion/position control system providing precise positioning, speed control, torque control, or any combination thereof. Examples of these components are control motors (servo and stepping motors), feedback devices (encoders and resolvers), and controls.
  • IEC International Electro technical Commission
    • IEC 60034 is an international standard for rotating electrical machinery
    • IEC 60034-1 Rating and Performance
  • ISO International Organization for Standardization
  • ANSI American National Standards Institute
  • ASTM American Section of the International Association for Testing Materials
  • REACH Registration, Evaluation, Authorization and Restriction of Chemicals
  • RoHS Restriction of Hazardous Substances Directive
  • DO-160 Environmental Conditions and Test Procedures for Airborne Equipment is a standard for the environmental testing of avionics hardware. It is published by the Radio Technical Commission for Aeronautics (RTCA, Inc.)
  • MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests, Published by the United States Department of Defense
  • ITAR The International Traffic in Arms Regulations and the Export Administration Regulations (EAR) are two important United States export control laws that affect the manufacturing, sales and distribution of technology.
  • AS9001 Quality Management Systems – Requirements for Aviation, Space and Defense Organizations
  • AS9002 Aerospace First Article Inspection Requirement
  • ISO/TS 16949 common automotive quality system requirement based on ISO 9001 and customer specific requirements from the automotive sector
Download a PDF copy of the Basic Motor Design Tutorial page.