Online and Offline Testing - Maintenance · 1 (C) 2006, SUCCESS by DESIGN Online and Offline Motor...

1

(C) 2006, SUCCESS by DESIGN

Online and Offline Online and Offline Motor TestingMotor Testing

Howard W Penrose, Ph.D., CMRPPresident, SUCCESS by DESIGNSUCCESS by DESIGN


Flowchart For Problem Resolution

Don’t Mess With It!

YES NO

YES

YOU IDIOT!

NO

Will it Blow UpIn Your Hands?

NO

Look The Other Way

Anyone ElseKnows? You’re SCREWED!

YESYES

NO

Hide ItCan You Blame Someone Else?

NO

NO PROBLEM!

Yes

Is It Working?

Did You Mess With It?

2


Electrical Theory


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, XL, XC,

Z

3


Atomic Structure and Electron Movement


Classic Atom

+ N -

4


Electron Movement

+ N -

Photon

Photon -


Conductors, Semi-Conductors and Insulators

5


Conductors

• Free Electrons (e)• Easily Directed• Usually metals

– Copper– Aluminum– Gold– Platinum

-

-

-

-

-

--

--

-

-

-

-

-

-

-

-

-

-

-

--

--

-

-

-

-

-

-- +


Semi-Conductors

• Dielectrics• 4 Valence Electrons• Polarize with Some

Electron Flow due to Electrical Fields

+

-

6


Insulators

• No Free Electrons• No Current Flow with

Field

+

-


Basic Electricity: Current, Voltage and Resistance

7


Current (Amperage - I)

Current is the flow of electricity, much like the flow of water in a pipe. It is measured in Amperage as opposed to gallons per minute of water.


Current

• 1 Amp = 6.28 x 1018 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!

8


Voltage (Volts - V or E)

Voltage is the electrical pressure in the system, much like water pressure. Electrical pressure is measured in Volts as opposed to Pounds per Square Inch. (ie: 110V like water from a tap, 4160 like a fire hose)


Voltage = Electrical Potential

• 1 Volt = 1 Joule/Coulomb (Q)• The Work to move the charge against a field

Ground (‘0’)

Potential 1

Potential 2

Potential 3

Energy

9


Resistance (Ohms - R or Ω)

Resistance is simply the restriction of current flow in a circuit. Smaller wire (conductors) and poor conductors have higher resistance.


Resistance

eee e

ee

ee

e

ee

ee

e

Many Collisions = Heat!

Fewer Collisions = Less Heat!

10


Ohm’s Law

Current, Voltage, and Resistance relate as follow:

I = E / R


Power

• Power (Watt) = 1 Joule per Second• Energy changing from one form to another• Watts = Voltage x Current• Watts = I2R

11


Electrical and Magnetic Fields


Magnetics

NorthSouth

Magnetic Flux

Magnet

12


Current Flow in Conductor

- +

Current Flowing in a Conductor


Generated Field Around Conductor

+

13


Magnetic Field With Coil

+

-

+

-

North Magnetic Pole

South Magnetic Pole


Interaction with Medium

NorthSouth

Magnetic Flux

MagnetMetal NS

14


Alternating Current Electricity


Electrical Properties

• Frequency• Inductance (L)

– Mutual– Inductive Reactance (XL)

• Capacitance (C)– Capacitive Reactance (XC)

• Phase Angle/Power Factor• Impedance (Z)

15


Frequency

0 90 180 270 360


Inductance

• Stores electromagnetic energy in its magnetic field

• mHdtdiLV =

∫ +=t

idvL

i0

)0()(1 ττ2

21 LiW =

I lags V

16


Mutual Inductance

• When 2 coils in close proximity, a changing current in one coil will induce a voltage in a second coil

0 90 180 270 360

N1 = 5 Turns100 Volts

N2 = 5 Turns100 Volts


Inductive Reactance XL

• Inductive Reactance is the AC Resistance of a coil

• Presented as a resistance in Ohms

• Frequency and Inductance Dependant

fLX L π2=

17


Capacitance

• Stores energy in an electric field

• Dielectric between 2 plates

• The charged condition is maintained until a discharge path is present

• Causes current to lead voltage

+

-


Capacitive Reactance XC

fCXC π2

1=

18


IV

Phase Angle / Power Factor

• In a coil or motor, current lags behind voltage

• This is represented as an angle or a fraction of ‘unity’

• Adding C can improve PF

0 90 180 270 360


fCXC π2

1=fLX L π2=

DC Resistance

Complex AC

Resistance

Impedance Z

22 )( CL XXRZ −+=

19


Summary

• Atomic Structure and Electron Movement• Conductors, Semi-Conductors, Insulators• Basic Electricity: Current, Voltage and

Resistance• Electrical and Magnetic Fields• Alternating Current Electricity: L, C, XL, XC, Z


AC Induction Motor Theory

20


Basic Motor Circuit

• Resistance• Inductance• Capacitance• Phase Angle• Inductive Reactance XL

• Capacitive Reactance XC

• Impedance 22 )( CL XXR −+


The Polyphase Induction Motor

StatorWindings

Stator Laminations

RotorBearing

Fan

21


Interaction of Rotor Field and Stator Field

Interaction of Two Magnetic Fields

Stator FieldRotor Field

N

S

NS

Electrical Energyto

Mechanical Torque


Rotating Fields

22


Rotating Field and Rotor Cage


Rotor Cage

23


Output Torque


Operating Motor

24


Locked Rotor Coil Movement


Torque• The movement of the rotor field

causes a shaft to rotate • This force, called torque, produces

useful work

25


Motor Size

– Horsepower– Torque


Horsepower

• 1 hp = 33,000 foot-pounds per minute

26


Torque


Motor Speed

– The approximate speed in revolutions per minute (rpm) of a motor is a function of:

• electrical supply frequency

• number of poles for which the motor is wound

27


Electric Motors

hp lb ft RPM=

−τ( ) *5250

RPM fofpoles

=120*

#

• Converts electrical energy to mechanical• The horsepower depends on the torque and

RPM• The RPM depends on the frequency and

winding configuration


Available Motor Speeds

2468

1012

3600 rpm1800 rpm1200 rpm900 rpm720 rpm600 rpm

No. of PolesSynchronous

Speed at 60 Hz

28


SlipSlip: Difference between a motor’s synchronousspeed and its full-load

speed

Percent slip = synchronous speed _ actual speed

x 100synchronous speed


STANDARD AC INDUCTION MOTORS

SPEED GOVERNED BY: SPEED = f x 120P

f = supply frequency

P = number of poles

typically: SPEED = 60 x 120 = 1800RPM4

LESS 3% SLIP = 1750 rpm

29


Motor Slip

– Rated speed is on the motor nameplate

– Caveat: When motors driving centrifugal loads are replaced, actual motor speed should remain the same -- higher motor speeds can increase energy use


Voltage

– Most three-phase motors operate at 460 Volts

– Some motors run on 230V, 200V, or are dual voltage, such as 230/460V

30


Enclosure Types

– Open Drip-Proof (ODP)

– Totally-Enclosed Fan-Cooled (TEFC)

– Explosion Proof (EXP)

– Totally-Enclosed Non-ventilated (TENV)

– New standards for designating cooling and environmental protection are included in NEMA (MG1-1993 rev.1)


Open Drip-Proof

– Open Drip-Proof (ODP)

– Ventilation openings are positioned to keep out liquid or solid particles falling at any angle from 00 to 150

from the vertical

31


Totally-Enclosed Fan-Cooled

– Totally-Enclosed Fan-Cooled (TEFC)

– Equipped with a fan for external cooling


• Defines the shape and size of the motor

– No standardization until 1952

– U-frame standardized in 1952

– T-frame standardized in 1964

– Replacing U-frame with T-framewill require modifications

Frame Size

32


NEMA Design

– Designs “A,” “B,” “C,” “D,” and “E”

– Type of load determines the NEMA design standard to use

– Design B is most common


Motor Torque Curves

33


Service Factor

– Specifies the capacity of the motor to withstand prolonged overload conditions

• 1.0 or 1.15 is typical

• Can be as high as 1.3


Service Factor

– Don’t size a motor to operate continuously within the service factor

– For every 10oC increase in motor temperature, the insulation life is cut in half

34


Summary• Transformer changes voltage and current from

one value to another across an air-gap using magnetic theory

• An electric motor converts electrical energy to mechanical torque using an interaction of magnetic fields.

• The electric motor is part of a larger system called the ‘motor system’ which consists of the power, distribution, controls, motor, coupling, load and process.

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

Insulation System Considerations for MCA

Quantum Mechanics and Motor Diagnostics

35


STATOR LAMINATIONS


Stator Failure Modes• Turn to Turn• Coil to Coil• Open Circuit• Phase to Phase• Coil to Ground

36


Insulation Diagram of Motor

Ground

Phase A

Phase B

Phase C

Circuit CapacitanceChanges due to chargeEffects of atoms inInsulation medium.Dipoles are createdAs electric field crossesAtoms. As they alignCapacitance increases.


- -

The Dipole

+Neg Potential Pos Potential

37


Dipolar Motion in Operation

GRND

Wire

Wire

Voltage

Capacitance

High

Low

MegOhms

High

Low

High

High

Ground Insulation


Dipolar Motion in DC Tests

GRND

Neg

Neg

Capacitance

Low

MegOhms

Low

High

High

MegOhms

Time

Pos

38


Dipolar Motion in Surge Test

Conductor 1 Conductor 2

Voltage

Time

ImpulseOvercomes DipolarSpin and CircuitCapacitance

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


Accelerated Insulation Degradation

Arc during fault detection using surge test.

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

39


Dipolar Motion in MCA - 1

wire

wire

wire

wire

wire

wire

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


Dipolar Motion in MCA - 2

wire

wire

wire

wire

wire

wire

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

CapacitiveDefect

40


Maximum Temperatures

Insulation Class Temperature (C)

A 105

B 130

F 155

H 180


Temperature Limitations

ServiceFactor

InsulationTemp.

Class B Class F

1.0/1.15 Ambient 40C/104F 40C/104F

1.0 Allowable Rise 80C/176F 105C/221F

1.0 OperatingLimit

120C/248F 145C/293F

1.15 Allowable Rise 90C/194F 115C/239F

1.15 OperatingLimit

130C/266F 155C/311F

41


Insulation Test Method Overview

• Electrical Insulation is a dielectric• Electric fields cause atoms to polarize with a change to capacitance

as they polarize• DC Insulation tests measure change to capacitance as charge

crosses in one direction• Surge test uses a high voltage impulse in order to detect defects by

causing an arc. Voltages too high to detect small changes in capacitive reactance defects in insulation systems. Requires over-stress.

• MCA causes full excitation of the insulation system with low voltage. Small changes will effect circuit capacitance which will not be ‘masked’ by high voltage.

• MCA method also allows early detection of faults and, as a result, can trend winding faults over time.


Considerations for Testing

42


Safety ConsiderationsPPE LOTO

Test for Power


Safety Considerations: Flash Protection

43


Motor Testing (Motor Only)


Overview

• IEEE P1415: “Draft Guide for Induction Machinery Maintenance Testing and Failure Analysis”

• Key to Understanding Condition-Based Monitoring and Troubleshooting is to understand the capabilities and limitations of testing technology

44


Overview

• Focus of This Presentation– Stator Winding and Core– Rotor Winding and Core– Vibration and Noise– Bearings and Shafts– Structure and Frame– Ventillation– Accessories


Condition-Based Technologies

• AC High Potential– 2Ev + 1,000V for new– 125-135% of nameplate for existing– Pass/Fail

• Acceleration Time– Changes may indicate power supply problems– Trending if conditions are identical

• Bearing Insulation– Evaluate for reduced shaft currents– Follow IEEE Std 43-2000 (up for re-affirmation in

October, 2005)– Pass/Fail

45



• Bearing Temperature by RTD– Thermocouple or Bulb-Type– Temperature limits vary but generally fall in the range

of 90-100C for alarm and 105-120C for shutdown– Higher temp limits for synthetics– Trendable with temp correction

• Capacitance– Trended value– Surface contamination, high humidity, high

temperature or general insulation breakdown– Effective for trending



• Core Loss (Loop Test)– During motor repair to detect inter-laminar insulation

damage– No hot spots greater than 10C from ambient core

temperature– If value shown: <6 Watts/lb and no change from

before and after winding removal– Pass/Fail

• Coupling Insulation– Ensure no shaft currents into driven equipment– IEEE Std 43-2000– Pass/Fail

46



• Current, Demodulation– Used in ESA and MCSA as a method of removing the

fundamental frequency from current FFT spectra– Trendable

• Current, Running– Indication of load– Pulsating current, measured with an analog probe will indicate

rotor faults– Not trendable

• Current, Signature Analysis– Provides analysis of electro-mechanical condition and driven

equipment condition– Analysis of current FFT spectra– Trendable



• Current, Starting– Inrush and starting current is evaluated for anomalies– Trendable

• DC High Potential– Trendable when leakage recorded– (2Ev + 1000V) x 1.7 new insulation– Value x 0.65-0.75 for used insulation– A sudden increase in leakage current indicates a fault– Trendable

47



• Dissipation Factor and Power Factor– Utilize AC at the rated voltage of motor– Trended value should not exceed a change of 2%

• Grease Analysis– Used to trend and evaluate deterioration of lubrication

properties– Trendable

• Growler (explain where name from)– Used to evaluate the condition of rotor bars when the

rotor is removed from the electric motor– Pass/Fail



• Insulation Resistance– Measures insulation value (leakage converted to MegOhms)– IEEE Std 43-2000– Trendable

• Oil Analysis– Used to evaluate the degradation of the lubricating properties of

oil– Detect excessive mechanical wear– Trendable

• Partial Discharge– Measurement of capacitive discharges– Generally trended on machines over 6kV– Trendable

48



• Phase Angle– The timed measurement between the peak voltage

and current at about 7Vac applied to a coil– Compare two coils +/-1 digit from average– Trendable

• Phase Balance (Z and L)– Used to detect severe winding unbalances– Detect inter-turn winding contamination– Compare phase to phase patterns between

impedance and inductance– Trendable



• Polarization Index– Ratio of 10 minute and 1 minute insulation resistance

tests– A ratio of 2 or more is required on pre-1970 insulation

systems– Trending required on newer insulation

• Single-Phase Rotor Test– 10% of motor nameplate voltage applied across one

phase of motor– Rotor is turned and current values taken– Variations of 3% or more over 360 degrees of rotation

indicate rotor bar fault– Not trendable

49



• Shaft Grounding Current– Measurement of shaft current– Trendable

• Shaft Testing– Magnetic particle, liquid penetrant and ultrasonic

examination used to evaluate condition of shaft material

– Pass/fail• Shaft Voltage

– Measurements taken from shaft of motor– Variations may indicate problems with the motor– Trendable



• Speed– Uses measurements of motor RPM in order to

determine if potential motor or load problems exist– Trendable

• Surge Test– High frequency, high voltage impedance-based test to

check turn-to-turn dielectric strength– Comparison of waveforms– Not trendable

50



• Surge PD– Variation of the surge test, evaluates partial

discharges that result from the high voltage, fast rise-time test

– Trendable• Thermography

– Utilizes an infrared camera to compare the ambient to test component

– Defects can cause a high temperature rise at the point of fault

– Trendable



• Torque Analysis– Uses three phases of voltage and current in order to calculate torque– Value is displayed and analyzed as torque FFT spectra– Trendable

• Ultrasound/Ultrasonics– Used to detect bearing and other electro-mechanical defects in motors– Trendable

• Variable Frequency (I/F)– Using about 7Vac, the motor current is measured then applied

frequency doubled and the resulting current compared to the first current

– Displayed as a percentage, which should be no more than one or two digits from average

– Trendable

51



• Vibration– FFT spectra of vibration information is used to trend

and detect mechanical and some electrical faults– Trendable

• Voltage Unbalance– Voltage measurements detect voltage unbalance

defects in supply– Less than 2% recommended, no more than 5%– Trendable

• Voltage Distortion– Harmonic content of voltage– If value too high, rotor and stator heating occurs– Trendable



• Voltage Drop– Trended measurement of voltage drop when starting a large

motor– Changes may indicate defects– Trendable

• Voltage Level– Measurements used to ensure that the supply voltage remains

+/-10% of nameplate– Trendable

• Voltage Spikes– Monitoring spikes allows the ability to evaluate supply and

control conditions– Trendable

52



• Winding Resistance– Used to detect broken wires and loose

connections.– Trendable unbalance

• Winding Temperature– Trended over time in order to determine if

overload conditions or insulation failure may occur

– Trendable


Use of Technologies: Combining for Effect

53


Motor System Diagnostic Technology Comparison

LXXX-LXXL-LXXMCSA

-------LL-LLLVolt/Amp

-L---X--L--L-Ultrasonics

-LL--L--LLXXXInfrared

-XXX-XLLL----Vibration Analysis

On-Line Testing

----X-XXXXXX-MCA Test

----X--------PI Testing

--------L-L--Ohm Meter

----X--------Insulation Tester

--------X----Surge Test

----X--------High Potential Testing

Off-Line Testing

VFDLoadAlignVibeInsBrgsAir Gap

Rotor StatorCableConnCntrlPQ

X = Yes; L = Late stage faults/Limited detection; - = No


Voltage Testing

Volt Ohm

A B C

Vab = 460Vac = 458Vbc = 466

460458466

Standard Tolerance = 0.1 V

54


Ohm Testing

Volt Ohm

A B C

OHMab = 10.2OHMac = 10.5OHMbc = 10.7

10.210.510.7

Standard Tolerance = 0.2 OhmsMilli-Ohm Meters = 0.001 or betterMicro-Ohm Meters = 0.0001 or better


Temperature Correction

234.5Copper

225Aluminum

KKMaterialMaterial

H

CHC TK

TKxRR++

=

C

HCH TK

TKxRR++

=

RC = Resistance at Temperature TC (Ohms)

RH = Resistance at Temperature TH (Ohms)

TC = Temperature of Cold Winding (C)

TH = Temperature of Hot Winding (C)

55


Current Testing

A B C

5.1 6.2 4.8

Ia = 5.1 AmpsIb = 6.2 AmpsIc = 4.8 Amps


Insulation to Ground

A B C

93.6 M

56


Insulation Resistance Testing Results

5000-10000120012500-50005001-120001000-25002501-5000500-10001001-2500

500<1000

IR DC VoltageWinding Voltage

Random wound stators under 1,000 V after 19705 MegOhms

Form wound stators after 1970100 MegOhms

Most windings made before 1970kV + 1 MegOhms

Winding Being TestedMin Insulation Resistance at 1 min

Correct TemperaturesTo 40 C


Dielectric AbsorptionRatio of 1 Minute to 30 Second IR Testing

> 1.6Excellent1.4 – 1.6Good1.0 – 1.4Questionable

< 1Dangerous

DA RatioInsulation Condition

Only accurate in insulation systems less than 5,000 MegOhms

57


Polarization IndexRatio of 10 Minute to 1 Minute IR Testing

> 4Excellent2.0 – 4.0Good1.0 – 2.0Questionable

< 1Dangerous

PIInsulation Condition

Only accurate in insulation systems less than 5,000 MegOhms


Motor Diagnostics

Motor Circuit Analysis (MCA)

58


Definitions• Motor Circuit Analysis (MCA)

– A series of low voltage tests performed while an electric motor or other winding system is de-energized. Fault detection includes: Cables, Contacts, Connections, Winding shorts, Winding grounds, Winding contamination, Air gap and rotor faults.

• Electrical Signature Analysis (ESA)– Test results of voltage and current while the

equipment is running under load. Uses FFT analysis of voltage, current and demodulated voltage and current. Fault detection includes: Incoming power, Connections, Windings, Air gap and rotor, Mechanical condition, Coupling and Load.


Successful Applications of MCA

• AC/DC motors• Traction Motors• Hybrid Vehicle Motors• Machine tools and robots• Synchronous machines• Alternators and

Generators• T&D Transformers• Coils• Capacitor systems• PdM, Troubleshooting

and Reliability

59


Application of MCA


Example of Starter Problem

- Operation Stops- Checked motor from Starter- Discover Starter Problem

Fault: Poor Contact; Motor OK

-Fault not visible-Checked andfound motor andCable OK

60


Successful Applications of ESA

• AC/DC Motors• VFD Applications• Transformers• Generators/Alternators• Traction Motors• Machine Tool Motors• Gearboxes• Pumps and Fans• PdM, Troubleshooting and

Reliability

**Note: Not energized, notConnected to power. So, no Safety comments, please.


Electrical Signature Analysis

61


Impact of Current During Operation


Benefit of ESA

62


MCA/ESA Combined


Electrical Signature Analysis

63


Magnetic Fields

• Strength Decreases by Square of Distance from Source

• Line Frequency is provided to motor (load)• Motor converts Voltage frequency to

Current frequency. Defects in motor generate additional current frequencies.

• Line Frequency acts as Carrier Frequency


Good Airgap

64


Static Eccentricity


Dynamic Eccentricity

65


Effect on Shaft


FFT Analysis

66


Harmonic Analysis

60Hz

60 Hz w/ 300 Hz Harmonic300 Hz

60Hz 300Hz


Gears

1750 RPM

10 Teeth

20 Teeth

25 Teeth

RPMRPMxTeethTeeth 8751750

2010

=

RPMRPMxTeethTeeth 700875

2520

=

Gearbox = Torque Multiplier

67


Example

DCMotor

Shaft w/ coupling

1800 RPM, 500V Armature

Gears3.71 Ratio

Output Shaft485 RPM MaxBearings and Seals

4 Propellors


How to Walk Through an Analysis

• Determine components of the system• Basic Failure Modes and Effects Analysis• Determine Associated Fault Frequencies• Analyze data

68


Components of System

• Voltage Signature– DC Drive

• Current Signature– DC Motor– Couplings– Shaft– Gears– Bearings– Seals– Propellor


FMEA

• Determine all possible failures– Functional System– Functional Hidden

• Determine probability• Analyze for probable faults

– 20% of failures will be 80% of findings• Analyze less likely faults later

69


DC Drive Faults• Failures

– SCR Failure – Fields– SCR Failure – Armature– Firing Cards – Fields– Firing Cards – Armature– Loss of incoming phase

• Functional Issues– Loss of fields – overspeed or loss of torque– Loss of Armature – torsional pulsation or loss of

speed– Loss of incoming phase – Rectifying issues


DC Motor Faults

• Fields– Shorted fields: Overspeed/Reduced Torque– Grounded fields: Same

• Armature– Brushes– Commutator worn– Grounded– Shorted– Bearings– Unbalance

70


Driven Equipment• Coupling Misalignment• Driver (Before Gears)

– Bearings– Seals

• Gears– Backlash– Broken Teeth

• Driven (After Gears)– Bearings– Seals

• Propellor


Most Likely Faults• VSA

– Armature Drive Circuit – SCR or Firing Card• ESA

– DC Motor• Brushes and Comm• Grounded• Unbalance

– Load• Misalignment• Seals• Gears• Propellor Blades

71


Clean Signatures (DC)

• Voltage and Current High Frequency– Line Frequency with degrading harmonics– SCR Frequency with degrading harmonics

• Current Low Frequency– Running Speed – Low– Possible turbulence

• Estimated running speed:

edRunningSpeRPMxNameplateoltageNameplateVageActualVolt

=

ESAAnalysis of

System


SUCCESS by DESIGNSUCCESS by DESIGNReliability ServicesReliability Services

5 Dogwood LnOld Saybrook, CT 06475

Ph: 860 575-3087 Fax: 860 577-8537http://[email protected]

Online and Offline Testing - Maintenance · 1 (C) 2006, SUCCESS by DESIGN Online and Offline Motor...

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Transcript of Online and Offline Testing - Maintenance · 1 (C) 2006, SUCCESS by DESIGN Online and Offline Motor...