Methodology of motor predictive monitoring

7/29/2019 Methodology of motor predictive monitoring

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Methodology of Motor Predictive Monitoring.

This presentation covers the methodology of Motor Predictive Monitoring, the

background to motor failure and the Instruments available to achieve correct analysis for

both on line (live) and off line motors.Whitelegg are UK and Ireland agents for Baker Inc (anSKF Company)

On-Line or Dynamic Testing

(Explorer Monitoring)

Explorer

Off-Line or Static Testing

(Advanced Winding Analyzer)

AWA


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Cost savings

Reduced unscheduled downtime through MPM

(Motor Predictive Monitoring)

Indicates root cause analysis

Save s of energy costs

VFD: Analysis

Motor Quality Assurance


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Electrical Motor Management

Programme

The Question is not if a Motor will fail electrically,

it is

(1) Dielectric Strength of a new motor is very high

(2) All Motor will see normal ageing

Thermal

Chemical Mechanical

(3)T-T Dielectric Strength falls below

level of switching surges

Arcing occurs when motor starts up


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(4) Insulation begins to deteriorate much faster

(5) T-T Dielectric Strength drops below operating voltage

The short fuses

(6) Transform action causes high induced current - high heat 16-20

time full load amps

(7) Rapid Failure (Typically Minutes)

80% of electrical motor failures start as turn-to-turn fault

Most will fail to ground but the root cause will be turn toturn failure

General Electric Paper


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Turn insulation is the weakest insulation in the motor

Chemical deposits breakdown the insulationMovement from start up rubs the turns together causing

wear source: D.E. Crawford\General Electric

The Surge Test is the only method available to find weak

insulation between the turns. Thus allowing the operatorto be predictive.


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Field Testing Can Find-

Weak insulation (PPM, QA, TS)

Turn-To-Turn

Phase-To-Phase

Coil-To-Coil

In-Shop Testing (Rotor Removed)

Can find-

Weak insulation turn to turn, phase to phase, coil to coil (QA, TS, PPM)

Reversed coils (QA)

Turn-To-Turn shorts (QA,)

Unbalanced turn count (QA)

Different size copper wire (QA)

Shorted laminations (QA)


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Scope

This insulation maintenance guide is applicable to industrial air-cooled rotating electric machines ratedfrom 5 hp to 10 000 hp. The procedures detailed herein may also be useful for other types of machines.

7.4 Interturn Insulation Tests

Film insulation usually provides high dielectric strength but, in many cases, the interturn insulation onmotor coils is porous in nature. Fibrous insulation effectively provides a physical separation of the turns ofthe order of 0.010 to 0.025 in (0.250.635 mm) for motors, and the electric strength between the turns isessentially provided by the insulating value of the gas (air, hydrogen, etc.) contained between thesebers. Micaceous insulations are commonly used in high-voltage machines.

To provide a useful service in checking the adequacy of the insulation between turns, the test levelselected must be greater than the minimum sparking potential of the air at the minimum permissiblespacing. The test potential will often, therefore, be several times normal operating volts per turn. A test ofabout 500 V rms per turn is considered average for a new machine, while for maintenance tests potentialsof one-half to two-thirds of the new coil turn test, eight to ten t imes normal operating volts per turn, areusually considered adequate to provide insurance from the possibilities of marginal insulation andcontains allowance for switching transients and for surges likely to be encountered in service.

The normal operating volts per turn are often up to about 30 V for motors, while turbine and water-wheelgenerators are substantially above that value. The test methods used include forms of surge comparisontests. A steep-front surge is applied to all or part of a winding, or by induction to individual coils within awinding. The resultant waveforms are viewed on an oscilloscope screen and interpretation of the patternsor amplitudes permits detection of short-circuited turns. The surge comparison test applied directly to thewinding terminals is limited, in the case of windings consisting of many coils in series, by the magnitude ofthe voltage that can be applied to the ground insulation without exceeding its specified test voltage. Thislimitation can be overcome by placing a surge coil in the bore over the coil to be tested and by applyingdirectly into it a voltage appropriate to the induced volts per turn required in the stator coil. For additional

information on procedures and requirements for interturn insulation tests, see IEEE Std 522-1992 [10].See [B14] for detailed information on surge comparison testing.

d) The 2300 V and 4000 V designs shall use vacuum-pressure-

impregnated form windings, capable of withstanding a voltage surge

of 3.5 per unit at a rise time of 0.1 s to 0.2 s and of 5 per unit at a

rise time of 1.2 s or longer. (One per unit equals 0.8165 V L -L .)The

test method and instrumentation used shall be per IEEE Std 522-

1992. When specified by the purchaser, this requirement shall also

apply to form windings supplied for voltages 575 V and below on

motors rated above 150 kW (200 hp).


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Winding Resistance (PPM, QA, TS)

Meg-ohm test (PPM, TS)PI (polarization test) (PPM, QA)

Step Voltage Test (PPM, QA, TS)

Surge Test (PPM, QA, TS)

Balance between phases (PPM, QA, TS)

# of Turns per phase (QA)

Diameter copper (QA)

High resistance connections (PPM, TS, QA)

Turn-To-Turn shorts (TS, QA, PPM)

Turn-To-Turn Opens (TS, QA,)

Trending


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Meg-Ohm-Meter

It Can:

Determine if the motor has failed to ground. (TS)

Dirty motor (Surface leakage) (PPM)

Trending (PPM)

Meg-Ohm-Meter

It Can Not

Determine if a motor is good

Determine a Turn-to-Turn Fault

Determine a Open Phase

Determine a Phase-to-Phase Fault


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Can find-

Deteriorated ground wall insulation (PPM, QA)

Dry-rotted, hard, brittle ground wall insulation (PPM, QA)

Moisture and Contamination

Can find-

Weak Ground wall insulation (PPM, QA, TS)

Cable insulation (PPM, QA, TS)


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Low Voltage Tests Show all good

Low Voltage Tests Show all good


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Surge test is the only test capable of finding weak

insulation turn to turn

Phase 1 & 2 are good

Phase 3 shows weak insulation TurnTurn at about 1,000 volts.

This is not a TurnTurn Short

If it was the winding resistance would be unbalanced and it is not

No other technology can find this fault


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480 Volt

60 Hp1760 RPM

Low voltage Tests show good


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White wave form shows the frequency shift when the

weak insulation occurred

1490 volts is where the weak insulation occurred on this

phase

Motor

7200 volt

1000 Hp

3600 RPM Motor


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Results after the J-Box was cleaned


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Only by elevating the voltage above operating voltage did

we see a problem

Voltage spikes could track and cause a failure

4160 Volt Motor

300 HP

1770 speedTested 4 identical motors at a power plant


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Last step at 8,960 Volts shows unstable ground wall

insulation

The step test allows the operator to see and trend the

current leakage

Dynamic Motor Monitoring


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Standard Connection

Install PPE

Open cabinet Connect CTs and Voltage Clips

Less Than 600 V connect to bottom of starter

Greater Then 600 Volts Connect into Secondary PTs and CTs

Time for connection 4 Min

Testing Time

1 Sample 1560 Seconds

Depends on rates and acquisition time

See next slide

Standard Connection

Install PPE

Open cabinet

Connect CTs and Voltage Clips

Less Than 600 V connect to bottom of starter

Greater Then 600 Volts Connect into Secondary PTs and CTs

Time for connection 4 Min

Testing Time

1 Sample 1560 Seconds

Depends on rates and acquisition time

See next slide


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Motor

MCC

LoadBreaker

Step one: Running motor

Step two: STOP motor

Step three: Connect MPM

Step four: Run and test

Step five: STOP motor

Step six: Disconnect MPM

Exp

Motor

CTs

Breaker

PTs

EP

Explorer

First EnergyRC Pump

1 of 700+ EPs at one customer


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PQ Capabilities

Voltage and Current level, unbalance distortions

Kvars, KVA, KWs, Power factor, Crest factor, Harmonic bar chart ect.


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Eff. s.f.

% NEMA derating

% Load


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Temperature (C)

Full Load 1.15 SF 1.25 SF49 64 77

56 75 91

75 102 128

64 80 94

69 89 106

Horsepower10

20

50

100

200

* Courtesy U S Motors

Operating RMS values

Voltage Level 658.2 V 99.7%

Current Level 378.4 A 91.4%

Load Level 312.6 kW 78.1%

Voltage Unbalance 3.66%

Voltage Distortion 9.80%

NEMA derating % 0.6

Eff. s.f. 1.28


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Importance

Poor power quality causes increase heat

For every ten degrees rise in temperature the life of the motor is reducedin half.

Fan 1 hp 1740 rpm


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Great tool for Separating electrical and mechanical

issues (solve disputes between mechanics and

electricians) Reason the load is what causes more or less torque from the motor

If a torque signature looks out of the ordinary the problem

is most likely in the load

4160V submersible pump


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Diagnose mechanical issues from

the MCC

Bearing Outer Race

Inner Race

Cage fr.

Fan Unbalance

Ect.


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Set up short medium and long

range trip settings

Set up Soft Starts

Diagnose Pump and Fan issues

Worn impellers

Binding pumps

Power Issues

Rotor Issues


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IEEE 522

IEC 34-15NEMA MG1

NFPA 70B

EASA

Power Quality

Poorly performing Transformers

Short, medium, long, range trip settings

Connection issues (Junction Box, In motor)

Lead Line Insulation deterioration

Turn-Turn, Phase-Phase, Coil-Coil insulationweakness

Ground Wall Insulation

Weakness

Dirt

Moisture

Dry Rotted, Brittle

Cracks

Motor Circuit

TurnTurn Shorts, Opens

Reversed Coils

Phase Unbalanced (turn count)

Phase Unbalanced (wire size)

Rotor

Cracked Bars

Poor Welds

Broken Bars Eccentricity (Dynamic, Static)

Loading Issues

Over load

Process

Mechanical

Bearing faults

Miss Alignment Fan Unbalances

Belt frequencies

Worn Impellers

Gear Mesh Frequencies

VFD

Power Quality

Shorted IGBTs

Feed Back loop

Process Information

Tuning / Set up

Soft Start

Tuning / Set up

Trouble shooting

Ect.


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Power Quality

Poorly performing Transformers

Short, medium, long, range trip settings

Connection issues (Junction Box, In motor)Lead Line Insulation deterioration

Turn-Turn, Phase-Phase, Coil-Coil insulationweakness

Ground Wall Insulation

Weakness

Dirt

Moisture

Dry Rotted, Brittle

Cracks

Motor Circuit

TurnTurn Shorts, Opens

Reversed Coils

Phase Unbalanced (turn count)

Phase Unbalanced (wire size)

Rotor

Cracked Bars

Poor Welds

Broken Bars

Eccentricity (Dynamic, Static)

Loading Issues

Over load

Process

Mechanical Bearing faults

Miss Alignment

Fan Unbalances

Belt frequencies

Worn Impellers

Gear Mesh Frequencies

VFD

Power Quality

Shorted IGBTs

Feed Back loop

Process Information

Tuning / Set up

Soft Start

Tuning / Set up

Trouble shooting

Ect.


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Explorer (On-Line) testing provides information about the

power condition, the load and the motor.

AWA (Off-Line) testing measures the integrity of the

motors insulation system and motor circuit

Together they present a picture of the motors health and

provide information required to accurately diagnose and

predict imminent failures. Increasing motor quality

assurance and trouble shooting capabilities will be

realised with the utilisation of the AWA and Explorer

Questions?

For further information, please visit www.whitelegg.com

Or contact

Whitelegg Machines Ltd, 19 Crompton Way, Manor Royal, Crawley, West Sussex RH10 9QR,

UK Tel: +44 (0) 1293 526 230 | Fax: +44 (0) 1293 538 910 | Email: [email protected]
http://www.whitelegg.com/http://www.whitelegg.com/http://www.whitelegg.com/http://www.whitelegg.com/

Methodology of motor predictive monitoring

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