New Diagnostics Concepts for Better Assessment Management 2002 Las Vegas... · New Diagnostics Concepts for Better Assessment Management ... Doble Clients > 100 MVA ... Block Diagram

Weidmann Weidmann -- ACTI Inc.ACTI Inc.ConferenceConference

New Diagnostics Concepts forNew Diagnostics Concepts forBetter Assessment ManagementBetter Assessment Management

OnOn--Line Insulation Condition Assessment forLine Insulation Condition Assessment for

Large Power TransformersLarge Power Transformers

When Does Equipment Fail?When Does Equipment Fail?

bb 77% 77% -- 93% of Failures are Random93% of Failures are Randombb 7% 7% -- 23% are Age Related23% are Age Related

This means that 80% of the failures This means that 80% of the failures have not been predicted with our have not been predicted with our current maintenance practices.current maintenance practices.

Causes of Power Transformer FailuresCauses of Power Transformer Failures

Defect Element % of Failure CauseBushings 35LTC 16Major Insulation 9Winding (turn/coil) aging 16Winding Distortion 12Core 7Leads 5

Doble Clients > 100 MVA

1996-1997

Additional ObservationsAdditional Observations

bbCauses of Decrease of Dielectric StrengthCauses of Decrease of Dielectric Strength•• Moisture in CelluloseMoisture in Cellulose•• Oil contamination with water, particles and oil Oil contamination with water, particles and oil

deterioration productsdeterioration products•• Surface contamination of celluloseSurface contamination of cellulose•• PD in weakened insulation and PD in weakened insulation and •• Creeping discharges on barriersCreeping discharges on barriers

Additional ObservationsAdditional Observations

bb80% of the defects can be predicted and 80% of the defects can be predicted and prevented is effective diagnostics systems prevented is effective diagnostics systems are used.are used.

bb52% of all Bushing Failures are violent52% of all Bushing Failures are violent•• SafetySafety•• Environmental ContaminationEnvironmental Contamination

Results of Bushing FailureResults of Bushing Failure

Why Bushings Taken Out of ServiceWhy Bushings Taken Out of Service

Increase in C1 Power Factor 53.6%Change in C1 Capacitance 1.8%Partial Discharge 1.3%Cap Tap Problems 3.8%Moisture Ingress 2.9%Increase in C2 Power Factor 7.9%Other 28.5%

Method of Detection - Off Line Tests

Deficiencies of Periodic MeasurementsDeficiencies of Periodic Measurements

bb Periodic testsPeriodic tests•• Time between tests (Months to Years)Time between tests (Months to Years)

–– Many problems manifest themselves in shorter periods Many problems manifest themselves in shorter periods of timeof time

–– If caught early on, remedial action can usually be taken If caught early on, remedial action can usually be taken to mitigate the causeto mitigate the cause


bb If a Problem is Found, One starts to ask these If a Problem is Found, One starts to ask these questionsquestions•• When did it start?When did it start?•• How fast is it changing?How fast is it changing?•• How fast will it continue to degrade?How fast will it continue to degrade?


AnswerAnswerbb You really do not KnowYou really do not Know

•• Lack bothLack both–– Qualitative DataQualitative Data–– Quantitative DataQuantitative Data

bb You really just end up guessing and making You really just end up guessing and making arbitrary decisionsarbitrary decisions

When to Test Again?

Repair Now?

Repair Later?

Leave in service

Replace?

When to Test Again?

Repair Now?

Repair Later?

Leave in service

Replace?


bb Time consumingTime consuming•• Labor intensiveLabor intensive•• Usually requires an expertUsually requires an expert

bbOrganizations are being driven to do more with Organizations are being driven to do more with lessless•• Need to take the “work” out of it = LaborNeed to take the “work” out of it = Labor•• Essence of condition based maintenanceEssence of condition based maintenance

Continuous Monitoring Will Save $Continuous Monitoring Will Save $

bb Finding a problem is not left to chance.Finding a problem is not left to chance.•• Find a problem early in the development stageFind a problem early in the development stage•• Make better decisions since you have recent dataMake better decisions since you have recent data•• Repairs are less expensiveRepairs are less expensive

bb Provide info as to type of defect and locationProvide info as to type of defect and location


bbNo labor required to perform the testNo labor required to perform the testbbUnnecessary maintenance is reducedUnnecessary maintenance is reducedbb Accurate data since tests are done under Accurate data since tests are done under

actual operating conditionsactual operating conditionsbbNo outage to perform testsNo outage to perform testsbbNo introduction of infant mortality failure No introduction of infant mortality failure

patterns (common to preventive type of patterns (common to preventive type of inspection and testing)inspection and testing)


bbNo surprises, reduction in forced outages, No surprises, reduction in forced outages, increased safety to personnelincreased safety to personnel

bbMonitoring of dynamics and correlation of PD Monitoring of dynamics and correlation of PD activity to these dynamicsactivity to these dynamics

bb Provides opportunity for remote diagnosticsProvides opportunity for remote diagnostics•• No need for expert to be in the field on a consistent No need for expert to be in the field on a consistent

basisbasis


bbBase evaluation on the equipment’s own Base evaluation on the equipment’s own history and not a comparison to other history and not a comparison to other equipmentequipment•• Makes detecting subtle problems easierMakes detecting subtle problems easier

bbMonitor worsening conditionsMonitor worsening conditions•• Defer RepairsDefer Repairs•• Plan an outagePlan an outage

bb Universal Bushing Sensor is Connected to Universal Bushing Sensor is Connected to Capacitance Tap of a BushingCapacitance Tap of a Bushing

Bushing MonitoringBushing MonitoringChange in Power

Factor & Capacitance

SensorSensor

bbUniversal SensorUniversal Sensor•• Used for Gamma Used for Gamma -- Bushing Tan Bushing Tan δδ and Capacitance and Capacitance

Continuous MonitorContinuous Monitor•• PD Measurements PD Measurements -- PeriodicPeriodic

bb Protection is built into the sensorProtection is built into the sensor•• Designs up to 800 kVDesigns up to 800 kV•• Will limit voltage at tap to about 135 v if open Will limit voltage at tap to about 135 v if open

circuitedcircuited

Change in Power Factor &

Capacitance



( ) ( )γ δ= = +∆

∆ ∆II

CCo o

tan 22

• Thus the current flowing through the Tap is directly proportional to capacitance C1, and a change in that capacitance results in a proportional change in the current.

• Another failure mode is the increase in the dielectric losses of the bushing. Changes in the dielectric losses will also cause a proportional change in the current.

KK ΣΣ

UUCC

UUBB

UUAA

CC1A1A CC1c1cCC1B1B

IIAA IIBB IICC

∆ ∆ II

K - Current Balancing UnitK - Current Balancing Unit ΣΣ - Current Summer - Current Summer

PD Sensors

Block Diagram of On-Line Monitor



InsulGard InsulGard -- G2G2

bb Microprocessor basedMicroprocessor basedbb Gamma & PhaseGamma & Phasebb 1 1 -- Dry Contact AlarmDry Contact Alarmbb 4 4 -- 20 ma Isolated 20 ma Isolated bb 0 0 -- 5vdc non5vdc non--isolatedisolatedbb RS232RS232bb RS485 optionRS485 optionbb Temperature InputTemperature Inputbb On Board MemoryOn Board Memory


Capacitance

InsulGard InsulGard -- G2G2

bb Self TestSelf Testbb Self CalibrationSelf Calibrationbb Time of Day or IntervalTime of Day or Intervalbb Continuous Watch Continuous Watch

FeatureFeaturebb Auto Auto -- Learn of Temp. Learn of Temp.

DependenciesDependenciesbb Auto TrendingAuto Trending


Capacitance

Gamma VariationsGamma Variations

bb Temperature can be an important diagnostics Temperature can be an important diagnostics factorfactor

Defective Bushing

Good Bushing

Temperature

Gamma

1%

0.1%

Tan Tan δδ Behavior on a Defective BushingBehavior on a Defective Bushing

Comparison of Tan δ - 110 kV Bushing

02468

101214161820

0 50 100 150 200 250

Time - Hours

% t

an

δ

% Tan δ @ 10 kV

% Tan δ @ 70 kV

Sokolov, V. V. and Vanin, B. V. “On-Line Monitoring of High Voltage Bushings”,

Proceedings of the Sixty-Second Annual International Conference of Doble Clients, 1995

Developing Defect in a 500 kV, 1600 amp Developing Defect in a 500 kV, 1600 amp BushingBushing

Change in Imbalance Current - 500 kV bushing

0

2

4

6

8

0 20 40 60

Time - Days

% Im

bal

ance

Cu

rren

t

Failure

Failure in 57 days

Sokolov, V. V. and Vanin, B. V. “On-Line Monitoring of High Voltage Bushings”,

Proceedings of the Sixty-Second Annual International Conference of Doble Clients, 1995

Gamma Gamma -- TrendingTrending

Gamma TrendGamma Trend

Phase ShiftPhase Shift

•• PD is a localized electrical discharge in an PD is a localized electrical discharge in an insulation system that does not completely insulation system that does not completely bridge the electrodesbridge the electrodes

What is Partial Discharge?

Arc or Spark

Phase to Phase or

Phase to Ground

Equivalent Circuit of a PD SiteEquivalent Circuit of a PD SiteAC High Voltage

VOID

AC High Voltage

Ct

Ca

Cv


•• Phenomena that only occurs at higher AC Phenomena that only occurs at higher AC voltages (> 2,000 V). Prefer 4 kV and higher.voltages (> 2,000 V). Prefer 4 kV and higher.

•• The higher the voltage the more destructive the The higher the voltage the more destructive the activity.activity.

bb PD is a leading indicator of insulation PD is a leading indicator of insulation breakdown.breakdown.


PD Measurement Matrix

15 Degree Windows

Pu

lse

Mag

nit

ud

e

-11-10

-9-8-7-6-5-4-3-2-10123456789

1011

0 15 30 45 60 75 90 105

120

135

150

165

180

195

210

225

240

255

270

285

300

315

330

345

360

Partial Discharge Pulses

Negative Polarity

- PositivePolarity

+

Cycle 1

Cycle 2

To N samples

PD Stops a 90 degrees PD Stops at 270 degrees

Phase Resolved DistributionPhase Resolved Distribution

PD PD -- TransformersTransformers

bb Periodic Only at this timePeriodic Only at this timebbMain issue is noiseMain issue is noise

•• Severe Corona exists at these higher voltagesSevere Corona exists at these higher voltages•• Specialized Analyzer is requiredSpecialized Analyzer is required•• The UPDA is the only known Analyzer that exists The UPDA is the only known Analyzer that exists

that can perform the necessary noise rejectionthat can perform the necessary noise rejection

UPDA “Twins” processes up to 8 UPDA “Twins” processes up to 8 channels of PD data.channels of PD data.

Universal Partial Discharge Analyzer Universal Partial Discharge Analyzer -- UPDAUPDA

IEEE 488 Bus

Yokogawa DL1540LOscilloscopes

Signal Conditioning Modules

Set of SensorsPC Controller

Test Report

IEEE 488 Bus

UPDA “Twins” processes up to 8 UPDA “Twins” processes up to 8 channels of PD data channels of PD data -- SimultaneouslySimultaneously

UPDAUPDA

bbMain sources of noise: Main sources of noise: •• Thyristor’s firing Thyristor’s firing •• Digital noise from control electronicsDigital noise from control electronics•• Radio station operation Radio station operation •• Arcing or sparking originating at the facility Arcing or sparking originating at the facility

Signal Processing: Signal Processing: Noise Cancellation TechniquesNoise Cancellation Techniques

An analyzer must detect PD signal in presence of external pulse noises with 10 times greater amplitude

Problems SolutionsLow LevelBackground Noise

• Noise identification and cancellation based on statisticaldigital waveform analysis.

Synchronous Noise • Detection of thyristor firing power frequency phaseintervals using superposition of series of acquisitions.

PulseCrosscouplingNoise

• Comparison of pulse magnitudes occurring simultaneouslyin different channels to determine signal origination.

Special Situations • Any of the channels can be designated as a “noise” sourceto discard simultaneous pulses in other channels.

• Full control of pulse parameters to filter out all noisepulses.

Signal Processing: Signal Processing: Noise Cancellation TechniquesNoise Cancellation Techniques

UPDA As an Effective ToolUPDA As an Effective Tool

bb After effective noise elimination techniques were After effective noise elimination techniques were confirmed. The residual noise level did not exceed 50pC.confirmed. The residual noise level did not exceed 50pC.

Signal Processing: Noise Rejection

Noise Rejection Effectiveness

Before

After

750 kV 750 kV -- Location of FaultLocation of Fault

C r e e p i n gd i scharge

B u s h i n g

W i n d i n g

Bar r i e r

Par t ia lDi scharges

Shield

Discharges caused by Water leaking in due to a bad gasket

750 kV Auto Transformer750 kV Auto Transformer

Creeping Discharge within Pressboard Barrier

Discharge in excess of

10,000 pC

Case StudyCase Study

bb ArgentinaArgentina•• Tested 21 Transformers Tested 21 Transformers -- GSUGSU

–– 13.8 kV generator side13.8 kV generator side–– 500 kV connected directly to SF6 Bus500 kV connected directly to SF6 Bus

Test SetupTest Setup

U V WSensor

Bush_RSensorBush_S

SensorBush_T

SensorNeut

SensorGen

500 kV Winding 13.8 kV Winding

Noise From GeneratorNoise From Generator

1 >

2 >

3 >

4 >

1) Bush_R: 40 mVolt 500 ns 2) Bush_S: 40 mVolt 500 ns 3) Bush_T: 40 mVolt 500 ns 4) Gen_R: 200 mVolt 500 ns

1 >

2 >

3 >

4 >

1) Bush_R: 50 mVolt 2 ms 2) Bush_S: 50 mVolt 2 ms 3) Bush_T: 50 mVolt 2 ms 4) Gen_T: 2 Volt 2 ms

Noise from 500 kV LineNoise from 500 kV Line

1 >

2 >

3 >

4 >

1) Bush_R: 40 mVolt 500 ns 2) Bush_S: 40 mVolt 500 ns 3) Bush_T: 40 mVolt 500 ns 4) Gen_R: 40 mVolt 500 ns

Transformer 18 Transformer 18 -- Neutral SensorNeutral Sensor

1 >

2 >

3 >

4 >

1) Bush_R: 100 mVolt 2 ms 2) Bush_S: 100 mVolt 2 ms 3) Bush_T: 100 mVolt 2 ms 4) Neut: 100 mVolt 2 ms

4 >

5 >

6 >

4) Neut: 40 mVolt 200 ns 5) Neut: 20 mVolt 200 ns 6) Neut: 20 mVolt 200 ns

Problems with No-load Tap Changer

Transformer LP1Transformer LP1

0 0 0 1

PD - 75 pC

PD LevelsPD Levels

bb 300 300 pC pC maximum maximum •• No permanent damage to paperNo permanent damage to paper

bb > 1,000 > 1,000 pC pC •• Permanent Damage to paper occursPermanent Damage to paper occurs

PD Measurements PD Measurements -- Other EquipmentOther Equipment

bbContinuous Monitoring 4 kV Continuous Monitoring 4 kV -- 38 kV38 kV•• MotorsMotors•• GeneratorsGenerators•• SwitchgearSwitchgear•• Bus DuctBus Duct

Case StudiesCase Studies

bb Data was collected with the Data was collected with the Cutler Hammer InsulGard Cutler Hammer InsulGard Continuous PD MonitorContinuous PD Monitor

•• 15 signal channels15 signal channels•• 75 dB signal dynamic range75 dB signal dynamic range•• 1 1 -- 20 MHz Band20 MHz Band•• Two alarm contacts, RSTwo alarm contacts, RS--485 485

and 4and 4--20 ma20 ma•• On board data storageOn board data storage•• Triggers include time, event or Triggers include time, event or

requestrequest•• Records DynamicsRecords Dynamics

Examples of PDExamples of PD

Examples of PDExamples of PD

What Is PreventWhat Is Prevent

Couplers In Switchgear

SwitchgearSwitchgear

Where to Install CouplersWhere to Install Couplers

Zone of Protection

Case Study 15 cubicles of SwitchgearCase Study 15 cubicles of Switchgear

Negative Temperature Correlation

Correlation of PDI and HumidityCorrelation of PDI and Humidity

Something Happened

PT - removed ultrasonic

Positive Humidity Correlation

Something Started Here

SummarySummary

bbOnOn--Line Monitoring and Testing for large Power Line Monitoring and Testing for large Power Transformers is HereTransformers is Here•• Periodic PDPeriodic PD•• Continuous Monitoring of changes in bushing Continuous Monitoring of changes in bushing

capacitance and power factorcapacitance and power factor

bbContinuous monitoring for PD is available on Continuous monitoring for PD is available on other equipment rated less than 38 kVother equipment rated less than 38 kV

SummarySummary

bbContinuous Monitoring Can Save MoneyContinuous Monitoring Can Save Money•• No labor is required to conduct testsNo labor is required to conduct tests•• Labor is freed up for other important tasksLabor is freed up for other important tasks•• More accurate data is availableMore accurate data is available•• Finding a problem is not left to chanceFinding a problem is not left to chance•• Reduction of unnecessary maintenanceReduction of unnecessary maintenance•• Prioritize EquipmentPrioritize Equipment

Documents

New Diagnostics Concepts for Better Assessment Management 2002 Las Vegas... · New Diagnostics Concepts for Better Assessment Management ... Doble Clients > 100 MVA ... Block Diagram