monitoring of shaft voltage and shaft grounding current - beth galano (mps)

8/10/2019 Monitoring of Shaft Voltage and Shaft Grounding Current - Beth Galano (MPS)

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Copyr ight 2007 Magnet ic Products and Serv ices www.gaussbusters.com

MPS Gaussbusters are proud to be

Safeguarding Mach inery Worldw ide

Magnetic Products and Services, 2135 Highway 35, Holmdel, NJ 07733 USA

Introduction to MPSand

Monitoring of Shaft Voltage

and Shaft Grounding Currentin

Rotating Machinery

By

Paul Nippes, P. E. and Beth Galano


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Founder and President, Mr. Paul Nippes,

P.E. has been consulting to

Petrochemical, Power Utilities and

Industry since 1965.

IEEE C50 Chairman for many years,

Cigre, ASNT and ASTM Contributor.

A Motor and Generator designer with Allis

Chalmers and Elliott Company, Electro

Dynamic Division of General Dynamics, a

Penn State Graduate and a Professor at

the University of Wisconsin.

In Pauls Electrical Engineering consulting capacity, due to the frequency

of bearing failures in his consulting practice, Mr. Nippes championed this

research and developed products to provide solutions.


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Areas of specialization

Magnetism and the problems it can cause in Rotating

Machinery, Industrial Processes, or in any application.

Shaft Condition Monitoring - CBM using Stray Shaft

Currents and Shaft Voltages in Rotating Machinery for

Early Warning of Developing Faults.

Field Services Degaussing, Magnetizing and Shaft

Voltage Testing


4/46Copyr ight 2007 Magnet ic Products and Serv ices www.gaussbusters.com



SHAFT CURRENT FROSTINGShaft Journal Bearing Pad





SHAFT CURRENT EFFECTS

Spark tracks Gear Pitting





Electric Current Erosion of Thrust Bearing Pads

from a Turbine Driven Natural Gas Compressor

Spark Tracks

on the Active Pad FacePad Steel Backing Erosion

on Two Adjacent Pads





Spark tracks Developing into Heavy Current Discharge Melting into the Babbitt





Degaussing Turbine Diaphragms Degaussing Blower Casing





Demagnetizing Screw Compressor





Auto Degauss

Auto Down-Cycle

Demagnetizing is SystematicRemoval of Magnetism





Measuring Magnetism MPS Gaussometer

Avoid Field Indicators (Magnetometer)


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Red No Weld, Yellow Maybe?, Green Good to Weld


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South China Sea

On Barge Vertical Pipe Welding Magnetic Field Stabilization


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Portable Magnetic Particle InspectionsApplied to Military Impellors

Procedures Developed by an ASNT Level III (MPS Customer)


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Military Applications Degaussing Solutions


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Grounding Brush Performance ChecksShaft Voltage Surveys


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Failure Analysis and Solution Recommendations


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Carbon brush contact surface comparison

Normal Glazed

Figure #4

G


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1. Ground the Shaft

2. Check Grounding

Devices Often via

Local or Remote

Monitoring

MP G b b


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Grounding Brush Reliability is Critical

MPS G b d b


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SHAFT CONDITION MONITORING (SCM) a Patented TechnologyA continuous monitoring technology that uses shaft current and voltage profiles in

operating units for early diagnostics and prognostics to identify developing problems in

electrical and non-electrical rotating machinery.

Sensors = Grounding Brushes

Permanent Mount Monitors, Rack

Mount, Din-Rail Modules or

Hand-Held Monitors

MPS G b d b


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VCM-E disposes of numerous and varyingfrequencies and amplitudes for the purpose of

sensing only the important signal changes in

waveform fundamental frequency, peaks and

averages.

At the earliest changes and/or an excess in

these quantities, action can be taken to identify

and confirm possible problems.

Confirmation may include collection and

analysis of other unit operating parameters.

MPS Signal Conditioning

MPS G b t d t b


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Shaft Grounding And Voltage Sensing

Applied To Industrial Class Rotating Machinery

MPS G b t p d t b


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HP TURB. IP TURB. LP TURB.

GENERATOR

EXCITER

NO BRUSHES NO MONITORS AND NO PROTECTION

Shaft currents are not confined nor controlled.

Shaft current damage to bearings and seals is not prevented.

Bearing and seal oil films insulate against stray currents.

Stray voltages can damage unit or impair efficiency .

Events or oil impurities can establish electrical circuits.

MPS Ga ssb st s a p d t b


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HP TURB. IP TURB.LP TURB.

GENERATOR

EXCITER

A quality grounding brush should discharge static electrical charge before damage occurs.

A quality grounding brush should establish good shaft contact protecting the nearby bearings.

The grounding brush could provide a return path for magnetically-generated current.

The brush may require maintenance, with loss of shaft grounding without warning

Damage can occur to bearings and/or seals if the generator outboard bearing insulation fails!

Shaft current damage to bearings and seals is first indicated by excessive vibration/temperature.

SHAFT GROUNDING BRUSH

GROUNDING BRUSH, NO MONITOR, POSSIBLE PROTECTION



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Shaft Voltage Decrease And Current Increase Indicates Shaft Rub.

High Voltage At Sb#1, Inversely Proportional To Steam Temperature Indicates Wet Steam In Turbine.

High Current In Grounding Brushes And Low Voltage At Brush Sb#2 Indicates Loss Of Bearing Or Seal Insulation .

Rapid Escalation In Both Sb#2 Voltage And Grounding Currents Indicates Developing Stator Winding Fault.

Erratic And Pulsing Voltage And Current Indicate Stator Lamination Shorting And Melting .

Long Term Gradual Increases In Voltage And Current Indicate Shift In Air Gap.

Pulsing, Then Gradual Increase In Shaft Voltage And Current Indicate Rotor Winding Faulting.

Shaft Voltage Changes As Excitation Changes May Indicate The Need For A Shaft Voltage Harmonic Filter.

Trending Of Each Brush Grounding Current, With Maximum Current Alarm On Each Brush.

Each Brush Will Alarm On Low Brush Grounding Current Indicating Brush Or Grounding Maintenance Required.



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Oscilloscope recordings

taken from the identical

shaft grounding currentbut with different voltage

and time scaling.

Upper trace =

112mV @ ~ 70MHz

Lower trace =

720mV @ ~ 80Hz



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Ungrounded OB end similar to IB end

OB trace, IB end Ground brush skip

Ungrounded IB end similar to OB end

Grounded IB end skip not apparent

Erratic grounding on shaft (Voltage source = The blower motor)



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Oscilloscope trace ofshaft grounding current

composed of a 60Hz

fundamental plus a strong

common mode buckingthird harmonic.

Characteristic of

magnetic saturation



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Ungrounded (40 Volts)

1k Ohm (40 Volts)

100 Ohm (25 Volts)

10 Ohm (5 Volts)

Effect on shaft of Electromagnetic

Voltages, determined from different

resistances in the shaft grounding cable.



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Effect on shaft of electrostatic

voltages determined from different

resistances in the shaft grounding cable.

Ungrounded (30 Volts)

10k Ohm (4 Volts)

1k Ohm (0.5 Volts)



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750MW GENERATOR VCM OUTPUT INDICATING A

UNIT OR SYSTEM RECURRING CONDITION

CHART SCALES - ZERO TO 1.0 VOLTS AND 10.0 AMPERES

ONE HOUR BRUSH CURRENT

Figure #11



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MPS G p




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P G p


Ground Fault Condition at a Nuclear Power Plant and Root Cause



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G p


Root

Cause



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G p


Unit 1 Shaft Peak

Currents and

Voltages for Six

Days

Grounding brush

Currents = 3.1 and

8.7 Amperes

Generator OB End

Shaft Voltage = 23.4

Volts

Turbine Shaft

Voltage = 0.2 Volts



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G


Unit 2 Shaft Peak

Currents and Voltages

over a Day

Grounding brush

Currents = 2.2 and 6.7

Amperes

Generator OB End

Shaft Voltage = 14.0

Volts

Turbine Shaft Voltage

= 4.8 Volts



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500 MW

Turbine

generator

Recorded Field

Voltage and

Peak ShaftGrounding

Current

During a Field

Ground Fault

Figure #14



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MPS Family of Shaft Condition MonitorsforEarly Detect ion of Rotat ing Machinery Faul ts

VCMVCM--ENEN--SIISII Single

Enclosure Housing TwoSeparate VCM-E

Boards/Circuits For

Large Or Critical Units.

SCModulesSCModules ,, Either Voltage or Current, Battery orAC Power, Local Alarm Indications; Remote Analysis

HandHand--Held VCM orHeld VCM or SCMeterSCMeter

or use with SCModules, Displays

Voltage or Current Peaks and Averages

Also Avai lable

(Explosion-proof

Models)

VCMVCM--CC,, Battery Power,Local Display, Ungrounded

Peak-Voltage And Grounded Peak and Average

Ground Current, Max I = 3 Amps. Industrial Type

Applications.

VCMVCM--EE,,AC Powered, Local

Display, Alarm LEDs of Shaft

Grounding Current And Shaft Voltage.

Continuous Signals via 4-20 mAfor

use in Control Room, via wired or

wireless connections.

VCMVCM--ENEN--RMRMRack Mount Modelconfigurable with 1 to 4

VCM-E units.



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Grounding Brush or Ground has lost continuity.

Wet steam conditions at the exhaust end of the turbine

causing charge separation with possible blade erosionand cavitation.

Dry Steam conditions at the inlet of the turbine with partial

admission, caused charge separation and spark

discharge.

Self Excitation or compounding of shaft voltages and

grounding currents from shorted rotor coil.

SHAFT MONITORS provide Early Warning



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Shaft Rubs at bearings, seals due to oil whip, coupling

misalignment, thermal growth, loss of lubrication, impurities in

the oil, etc.

Diode Failure in Generator Excitation.

Intermittent Rotor Winding Ground Fault

Loss of or Shorting of Insulation at Bearings, Seals, Gear Teeth

and Coupling, etc.

Excessive transients in pulse width modulated rotor and/or

stator electrical supply.

Stator core lamination shorting in an electrical generator.

SHAFT MONITORS provide Early Warning



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Simplicity and Value - SCM reduces data to basic terms (a fractionof the digital data), while still preserving critical data events

Supported by technology and performance of units installed inthe Utility and Petrochemical Industries.

Offers significant enhancement to PDM and Prognostic programs

of Utilities, Industry and the Military.

It could be an important input to the decision-making processas to whether a rotating machine is Operational or Service

Ready.

Alerts at earliest possible problem development requiring confirmation,

investigation

and possible parts replacement


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monitoring of shaft voltage and shaft grounding current - beth galano (mps)

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