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1 Electrical Theory

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    (c)2005 Penrose

    Electrical Theory

    Howard W Penrose, Ph.D., CMRPInstructor

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    Overview of Electrical Theory

    Atomic Structure and Electron Movement

    Conductors, Semi-Conductors, Insulators Basic Electricity: Current, Voltage and

    Resistance

    Electrical and Magnetic Fields Alternating Current Electricity: L, C, X L, XC, Z

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    Atomic Structure andElectron Movement

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    Classic Atom

    + N -

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    Electron Movement

    + N -

    Photon

    Photon -

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    Conductors, Semi-Conductors and

    Insulators

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    Conductors

    Free Electrons (e) Easily Directed Usually metals

    Copper Aluminum

    Gold Platinum

    -

    -

    -

    -

    -

    --

    --

    -

    -

    -

    -

    -

    -

    --

    -

    -

    -

    --

    - -

    -

    -

    --

    -

    -

    - +

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    Semi-Conductors

    Dielectrics

    4 Valence Electrons Polarize with Some

    Electron Flow due toElectrical Fields

    +

    -

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    Insulators

    No Free Electrons

    No Current Flow withField

    +

    -

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    Basic Electricity:Current, Voltage and

    Resistance

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    Current (Amperage - I)

    Current is the flow ofelectricity, much like

    the flow of water in apipe. It is measured in Amperage as opposedto gallons per minute of

    water.

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    Current

    1 Amp = 6.28 x 10 18 electrons per second

    1 Amp = 1 Coulomb per second Electron charge = 1.60219 x 10 -19 Coulombs Flows Negative Charge to Positive Charge

    Electron! Electron!Electron!

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    Voltage (Volts - V or E)Voltage is the electrical

    pressure in the system,much like water pressure.

    Electrical pressure ismeasured in Volts asopposed to Pounds perSquare Inch. (ie: 110V likewater from a tap, 4160 likea fire hose)

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    Resistance (Ohms - R or )

    Resistance is simply therestriction of current

    flow in a circuit.Smaller wire(conductors) and poorconductors have higherresistance.

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    Resistance

    eee e

    ee

    ee

    e

    ee

    ee

    e

    Many Collisions = Heat!

    Fewer Collisions = Less Heat!

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    Ohms Law Current, Voltage, and Resistance relate as

    follow:

    I = E / R

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    Electrical andMagnetic Fields

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    Magnetics

    NorthSouth

    Magnetic Flux

    Magnet

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    Current Flow in Conductor

    - +

    Current Flowing in a Conductor

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    Generated Field Around

    Conductor

    +

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    Magnetic Field With Coil+

    -

    +

    -

    North Magnetic Pole

    South Magnetic Pole

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    Interaction with Medium

    NorthSouth

    Magnetic Flux

    MagnetMetal NS

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    Alternating CurrentElectricity

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    Electrical Properties Frequency Inductance (L)

    Mutual Inductive Reactance (X L)

    Capacitance (C)

    Capacitive Reactance (X C) Phase Angle/Power Factor Impedance (Z)

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    Frequency

    0 90 180 270 360

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    Inductance Stores electromagnetic

    energy in its magneticfield

    mH

    dt di LV

    t id v L

    i0

    )0()(1 2

    21

    LiW

    I lags V

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    Mutual Inductance When 2 coils in close

    proximity, a changingcurrent in one coil will

    induce a voltage in asecond coil

    0 90 180 270 360

    N1 = 5 Turns100 Volts

    N2 = 5 Turns100 Volts

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    Inductive Reactance X L

    Inductive Reactance isthe AC Resistance of a

    coil Presented as a

    resistance in Ohms Frequency and

    Inductance Dependant

    fL X L 2

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    Capacitance

    Stores energy in anelectric field

    Dielectric between 2plates

    The charged conditionis maintained until a

    discharge path ispresent Causes current to lead

    voltage

    +

    -

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    Capacitive Reactance X C

    fC X C 21

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    IV

    Phase Angle / Power Factor

    In a coil or motor,current lags behindvoltage

    This is represented asan angle or a fraction

    of unity Adding C can improve

    PF

    0 90 180 270 360

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    fC X C

    21 fL X L 2

    DCResistance

    Complex AC

    Resistance

    Impedance Z

    22 )( C L X X R Z

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    Summary

    Atomic Structure and Electron Movement Conductors, Semi-Conductors, Insulators

    Basic Electricity: Current, Voltage andResistance

    Electrical and Magnetic Fields Alternating Current Electricity: L, C, X L, XC, Z

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    AC Induction Motor

    TheoryHoward W Penrose, Ph.D.Instructor

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    Basic Motor Circuit

    Resistance Inductance Capacitance Phase Angle Inductive Reactance X L Capacitive Reactance X C Impedance

    22 )( C L X X R

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    The Polyphase Induction Motor

    StatorWindings

    StatorLaminations

    RotorBearing

    Fan

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    Interaction of Rotor Fieldand Stator FieldInteraction of Two Magnetic Fields

    Stator Field Rotor Field

    N

    S

    Electrical Energyto

    Mechanical Torque

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    Rotating Fields

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    Rotating Field and Rotor Cage

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    Rotor Cage

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    Output Torque

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    Operating Motor

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    (C)2004, Howard W Penrose,Ph.D., All rights reserved

    Insulation System

    Considerations for MCAand Motor ConnectionsQuantum Mechanics and Motor Diagnostics

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    STATOR LAMINATIONS

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    Stator Failure Modes Turn to Turn Coil to Coil Open Circuit

    Phase to Phase Coil to Ground

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    Insulation Diagram of Motor

    Ground

    Phase A

    Phase B

    Phase C

    Circuit CapacitanceChanges due to chargeEffects of atoms inInsulation medium.Dipoles are created

    As electric field crosses Atoms. As they alignCapacitance increases.

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    - -

    The Dipole

    +Neg Potential Pos Potential

    Di l M ti i O ti

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    Dipolar Motion in Operation

    GRND

    Wire

    Wire

    Voltage

    Capacitance

    High

    Low

    MegOhms

    High

    Low

    High

    High

    Ground Insulation

    Di l M i i DC T

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    Dipolar Motion in DC Tests

    GRND

    Neg

    Neg

    Capacitance

    Low

    MegOhms

    Low

    High

    High

    MegOhms

    Time

    Pos

    Dipolar Motion in Surge Test

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    Dipolar Motion in Surge Test

    Conductor 1 Conductor 2

    Voltage

    Time

    Impulse

    Overcomes DipolarSpin and CircuitCapacitance

    Requires Higher Voltage as a ResultIn order to cross air gap (Paschen)Potentially Destructive!!!

    Accelerated Insulation Degradation

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    Accelerated Insulation Degradation

    Arc during fault detection using surge test.

    The separated insulation is the result of the arc (burned). The grey area on thecopper is carbonized insulation.

    Dipolar Motion in MCA 1

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    Dipolar Motion in MCA - 1

    wire

    wire

    wire

    wire

    wire

    wire

    Good PhasePhase Angle: 77 degreesCurrent/Frequency: -44%

    Dipolar Motion in MCA 2

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    Dipolar Motion in MCA - 2

    wire

    wire

    wire

    wire

    wire

    wire

    Bad PhasePhase Angle: 73 degreesCurrent/Frequency: -40%

    CapacitiveDefect

    Before and After Defect

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    Before and After Defect

    1-2 1-3 2-3

    Resistance 0.6821 0.6798 0.6865

    Impedance 21 21 39

    Inductance 8 8 7

    Phase Angle 77 76 76

    I/F -47 -45 -47

    Ins Resist >99

    1-2 1-3 2-3

    Resistance 0.6786 0.6797 0.6819

    Impedance 21 21 39

    Inductance 8 8 7

    Phase Angle 77 77 76

    I/F -47 -43 -47

    Ins Resist >99

    MCA Result on20 hp with contamination and slight

    phase to phase defect. Still running.

    MCA test results following surge testfrom previous example. Trips on start.

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    Time to Failure

    Estimation Techniques Howard W Penrose, Ph.D.

    T-Solutions, Inc.

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    Concept of TTFE Setting test frequencies such that faults can

    be detected in advance Setting alarms at a point where fault

    detection is effective Knowing that failures are random

    Know that the resistance to failure decreasesfollowing detection of a CBM alarm

    C di i Di d E l

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    Source: reliability-centered maintenance, Nowlan and Heap

    Condition-Directed Example

    Operating age (time T)

    Inspection Interval

    R e s

    i s t a n c e

    t o f a i l u r e B (Insulation begins to degrade between turns)

    P (Interturn insulation degradation detection)

    F (Winding fails)T

    ( F-P)

    A (New Motor Installed)100%

    0%

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    Example of TTFE in

    MCA

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    This Presentation Stages of Winding Failure Causes and Effects Trending Time to Failure Discussion

    < 600 Vac Standard, integral, three phase motors,

    operating an average of 4000 hours 50% load, balanced voltage, good power quality,

    constant load

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    Insulation Breakdown Contamination

    Moisture and electric fieldexpansion

    Gasses, vapors, dust, etc.

    Arc Tracking High Current Between

    Conductors

    Thermal Aging (10 oC)

    Partially Assembled 125 horsepowerMotor in repair shop

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    Insulation Breakdown VFD Applications

    Partial Discharge

    Mechanical Faults Stress cracking Parts Faults

    Stators awaiting assembly after rewind

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    Stages of Winding Failure Time to Failure

    Severity of the Fault Potential Between Conductors

    Type and Amount of Insulation Cause of the Fault Cycling and Load

    Contamination, Thermal, MoistureIncursion, Corona, Transients, Overloads,etc. may initiate fault.

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    Stage 1 Insulation between conductors stressed Changes to R and C between conductors

    High temps and reactive faults Carbonization begins to occur MCA values of Fi and I/F begin to change

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    Stage 2

    Fault becomes more Resistive Mutual Inductance between good and bad I2R losses increase at point of fault Motor may start tripping although may run

    after short cooling period (ins res increasesas insulation cools)

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    Stage 3 Insulation breaks down Possible explosive rupture Vaporization of windings

    Inductance and sometimes resistance maychange

    Stage 3 winding failure

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    Review

    MCA Requirement: Resistance Loose connections, Broken Wires (~5%) Impedance and Inductance Rotor position or contaminated

    windings. Also, used for rotor test in assembled equipment. (Parallelgood, Unparallel bad)

    I/F and Fi Early winding shorts (I/F: +/-2; Fi: +/-1) Insulation Resistance Ground Faults (5 MOhm/100 MOhm)

    Combination used for troubleshooting or trending

    Comparative tests: Assumes that phases do not fail at samerate

    How Trended

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    How Trended

    AC Motors % unbalance: R, Z and L Phase Diff: I/F and Fi

    Reading: Insulation Resistance

    Induction Rotors: Neednumerical method (RotorGrading System RGS)

    MCABeing used to confirm the

    Winding voltage connection

    in a submersiblePump.

    AC Rotating Machine Testing

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    AC Rotating Machine Testing

    Reading Change fromBaseline

    Severity

    R, Z, L < 3% Green

    R, Z, L >3 and 5% Red

    Fi, I/F 1 and 3 Red

    Trended Reading

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    Trended Reading

    AC Motor 2

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    AC Motor 2

    PdM Testing Frequency

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    PdM Testing Frequency

    Motor Type Clean/DryEnvironment

    ModerateEnvironment

    Dirty/WetEnvironment

    3-PhaseNon-Critical

    12 Mo 9 Mo 6 Mo

    3-PhaseProduction

    6 Mo 6 Mo 3 Mo

    3-PhaseCritical

    3 Mo 2 Mo 1 Mo

    DC Motors 6 Mo 6 Mo 3 MoTransformer 12 Mo 9 Mo 6 Mo

    Estimating Time To Failure!

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    g

    What To Do Once A Fault IsDetected

    Motor ready for test in motor repair shop

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    What Makes Fault

    Detection Difficult? Time To Failure

    Application Type of Fault Severity of Fault

    Based upon Stages of Failure, Insulation failsover time

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    Winding Contamination

    0

    1

    2

    3

    45

    6

    7

    Annual 9Months Semi Quarterly Monthly

    Test Frequency

    T i m e

    t o A c

    t i o n

    ( M o

    n t h s

    )

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    Turn to Turn Shorts

    0

    2

    4

    6

    8

    10

    Annual 9 Months Semi Quarterly Monthly

    Test Frequency

    T i m e

    t o A c

    t i o n

    ( M o n

    t h s

    )

    1pt2pt3pt>3

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    Phase to Phase or Coil to Coil

    -1

    01

    2

    3

    45

    6

    7

    Annual 9 Months Semi Quarterly Monthly

    Test Frequency

    T i m e t o

    A c

    t i o n

    ( M o

    n t h s

    )

    1pt

    2pt

    3pt

    >3

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    TTFE Software

    Final Comments

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    When is TTFE effective? Technology can detect developing faults

    (Condition-Based) Optimized testing frequency or continuous

    monitoring A history exists or can be obtained Multiple-Technology approach to confirm

    condition and stage of failure

    Understanding that the functional failure is notinstantaneous and some forcing function drivesthe failure

    Action is taken on findings: Risk-based decision

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    SUCCESS by DESI GN

    5 Dogwood LnOld Saybrook, CT 06475

    Ph: 860 575-3087 Fax: 860 577-8537http://www.motordoc.nethoward@motordoc net


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