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

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

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

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 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


Material TypeCore LossSaturation Flux DensityPermeabilityEase of ProcessingRaw Material Relative Cost
CRML SteelFairGoodGoodBest0.5
Non-Oriented Silcon SteelGoodGoodFairGood1.0
Grain-Oriented Silcon SteelBetterGoodBetterFair1.25
Amorphous Alloy-Iron basedBetterFairHighMuch Care Required1.25
Thin-Gauge Silicon SteelBetterGoodGoodFair10
6-1/2% Nickel-Iron AlloyBetterGoodGoodCare Required12
49% Nickel-Iron AlloyBetterFairHighCare Required12
80% Nickel-Iron AlloyBestLowHighCare Required15
Cobalt-Iron AlloyGoodBestBetterCare Required45
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


  • 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

Commonly Used Magnet Materials

MaterialMagnetic PropertiesMagnetic CharacteristicsCurie TemperatureTemperature Coefficient of InductionCost $ / lb.
Cast AlnicoBr – 5,500 – 13,500 Hc – 475 – 1,900 MGOe 1.4 – 10.5Cast to Shape, Hard, Crystal Structure – Grind or EDM840°C0.02% / °C$40
Sintered AlnicoBr – 6,000 – 10,800 Hc – 550 – 1,900 MGOe 1.4 – 5.0Powder Pressed to Shape, Hard Structure – Grind or EDM840°C0.02% / °C$23
Ceramic (Hard Ferrite)Br – 3,450 – 4,100 Hci – 3,000 – 4,800 MGOe 2.7 – 4.0Simple Shapes: Arcs, Rect., Plugs, Rings – Hard-Grind450°C0.02% / °C$2
Samarium CobaltBr – 8,800 – 11,000 Hci – 11,000 – 21,000 MGOe – 18 – 32Very Brittle – Grind or EDM750°C / 825°C0.035% / °C$125
Neodymium Iron BoronBr – 10,500 – 14,000 Hci – – 14,000 MGOe 27 – 50Requires Coating to Prevent Oxidization Grind or EDM310°C0.13% / °C$95
Iron-Chrome CobaltBr – 9,000 – 13,500 Hc – 50 – 600 MGOe – 4.25 – 5.25Can be Formed, Stamped, Thin Rolled Mat’l 0.050″- .0005″600°C0.02% / °C$30
Bonded Flexible (Callenered or ExtrudedBr – 2,500 – 5,600 Hci – 3,500 – 16,000 Ferrite 450°C 0.18% / °C $3 MGOe 1.4 – 6.2Flexible, Thermal Shock Resistant, Low-tono Tooling Charge, Available In Wide Range of SizesFerrite 450°C Neo 310°C0.18% / °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 – 10.5Complex Shapes, Thin Walls, Tight Dimensions without Machining, Good StrengthFerrite 450°C Neo 310°C0.18% / °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 – 15.0Simple Geometry, Close Tolerancing W.O Machining Higher BhMax Than Inj. Molded With Lower Tooling CostNeo 310°C0.07 to 0.13% / °C$60

Commonly Used Epoxy

Temp classProduct no.DescriptionSpecific gravityCut-through resistanceEdge coverageImapct resistanceGel time @193°C (380°F) hot plateDielectric strengthVolume resisitivityColor
B260 260CGSpray and fluid bed drip application1.43215°C (410°F)35-45100 (11.3)12-16 s1000 (12-15 mil coating)1015Green
B262Spray and fluid bed drip application1.34130°C (266°F)38-48100 (11.3)12-16 s1000 (10-mil coating)1013Red
B263Spray and fluid bed drip applications in high-temperature cut-through resistance1.47290°C (554°F)40-50100 (11.3)8-14 s1000 (12-15 mil coating)1015Green
B270Spray and fluid bed drip applications for high-temperature cut-through and bridging gaps1.48250°C (482°F)35-40120 (13.8)12-16 s1000 (10-mil coating)1013Green
B5555Cold electrostatic fluid bed, hot venturi spray, or hot fluid be dip for fractional horsepower motor stators and armatures1.7>340°C (644°F) 160 (18.1)8-12 s1300 (V/ml2) Green
B5388Electrostatic fluid bed process, superior cut-through resistance and well heat, chemical and moisture resistance1.57>340°C (644°F)35 (11.3)10025-35 s1100 (V/mil) Blue
B5133Electrostatic coating for cold as well as heated parts1.45160°C (320°F)15 (13.8)120 500 (V/mil)5×1014Light 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.MethodStandardsInsulation Tested and Diagnostic Value
1Insulation ResistanceIEEE 43. NEMA MG 1Find contaminations and defects in phase-to-ground insulation
2Polarization IndexIEEE 43Find contaminations and defects in phase-to-ground insulation
3DC High Potential Test (Dielectric Withstand Test)IEEE 95, IEC 34.1, NEMA MG 1Find contaminations and defects in phase-to-ground insulation
4AC High Potential Test (Dielectric Withstand Test)IEC 60034 NEMA MG 1Find contaminations and defects in phase-to-ground insulation
5Surge TestIEEE 522 NEMA MG 1Detects deterioration of the turn-to-turn insulation
6Partial Discharge TestIEEE 1434Detects deterioration of the phase-to-ground and turn-to turn insulation
7Dissipation-FactorIEEE 286 IEC 60894Detects 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.


  • 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
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