a comparison of standardized test
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"Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure…”Nelson Mandela. South African Statesman , 1993 Nobel Prize for Peace, b.1918
A Comparison of Standardized Test
Methods For The Incline Plane Test
For Insulator Materials
G Heger G Heger
HJ VermeulenHJ Vermeulen
P PieterseP Pieterse
JP HoltzhausenJP Holtzhausen
WL VoslooWL Vosloo
Authors:
NamPower
Stellenbosch University
Stellenbosch University
Stellenbosch University
Eskom
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Comparison of two different test methods for theIncline Plane Test for tracking and erosion in
insulator materials, as described in IEC 60587: Constant Tracking Voltage Method
Stepwise Tracking Voltage Method
Comparison according to results for several
evaluation criteria
Goal: determining the superior test method for use
in future experiments
AIM OF PAPER
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PRESENTATION OVERVIEW
Test Setup & Apparatus
Test Methodology
Evaluation Criteria
Results
Summary of Results
Conclusion
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TEST SETUP & APPARATUS
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TEST METHODLOGY
Comparison of following methods:Comparison of following methods:
Constant Tracking Voltage: Excitation voltage kept
constant for 6 hours
Typical standardised
voltages: 2.5, 3.5, 4.5 kV
Material classification→
max. voltage withstood by all
samples
Stepwise Tracking Voltage: Voltage raised with 250 V every
hour
Series resistance & contaminant
flow rate need to be adjusted
Failure must occur on/after 3rd
voltage step (i.e. 4th hour)
Highest voltage withstood by allsamples: Stepwise tracking
voltage
→→ One test series of 5 samples per test methodOne test series of 5 samples per test method
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TEST METHODOLOGY
Test samples made from industrial grade HTV
silicone rubber
Samples cleaned with ethanol & distilled water
Surfaces abraded with P800 sandpaper
(reduces hydrophobicity)
Test voltages chosen: 3.5 kV/6 hours for constant voltage method
2.5 – 3.75 kV/6hours for stepwise voltage
method Sample designation:
Series A: Constant Voltage method
Series B: Stepwise Voltage method
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EVALUATION CRITERIA
Comparison criteria: Sample material loss [mg] Surface erosion depth [mm] RMS leakage current measurements [mA] Peak current level counts
One sample of each series selected for chemicalanalysis→ ATR-FTIR spectroscopy
Samples not cleaned after testing to prevent
interference with results Chosen samples not represented in mass loss &
erosion depth criterion!
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RESULTS: LOSS OF MATERIAL
Determined by weighing samples before & after testing
Samples cleaned after testing using distilled water
Series average & standard deviation calculated for comparison
Results show: Series A/constant voltage: higher mass loss
Series B/stepwise voltage: smaller deviation around mean
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RESULTS: EROSION DEPTH
Measured using Coordinate Measuring (CM) machine
Measurements taken after cleaning of samples
Series average & standard deviation calculated
Results show:Results show: Similar sample means (Similar sample means (± 0.03 mm difference)± 0.03 mm difference)
Similar standard deviationsSimilar standard deviations
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RESULTS: RMS CURRENTS
Current measured using an Online Leakage CurrentAnalyzer (OLCA)
RMS values calculated over 1 minute interval
Hourly series average current calculated fromsample data
First 2 hours ignored→ different series resistor &flow rate for that period
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RESULTS: RMS CURRENTS
Results show for hour 3 - 6: Similar hourly means & standard deviations
Series B slightly higher mean (± 0.5 mA)
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RESULTS: PEAK CURRENT BIN COUNTS
OLCA registers peak current values per 1 minuteinterval (+ & -)
4 Major current categories/bins for this experiment:
Results:Results: Counts in lower current bins similar for both seriesCounts in lower current bins similar for both series
Series B shows larger counts for highest peakSeries B shows larger counts for highest peak
current bincurrent bin
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RESULTS: ATR-FTIR SPECTROSCOPY
One sample per test series analysed 3 specimen per sample: lower 17 mm, middle 17
mm & upper 16 mm region Spectra of tested specimen compared to spectrum
of virgin specimen Focus areas for analysis:
Loss of alumina trihydrate (ATH) filler peak height ratio Loss of methyl groups degree of conversion, β Oxidation through carbonyl formation peak area ratio
Chemical change indicated by decrease of peakheight ratio or increase in β and peak area ratio
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RESULTS: ATR-FTIR SPECTROSCOPY
Similar results for both series
Series A reveals slightly stronger changes
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SUMMARY OF RESULTS
Test methods show similar results in most
evaluation criteria
Some slight differences:
Constant Voltage method yielded slightly larger mass loss &stronger chemical change
Stepwise Voltage method has slightly higher peak & rms currents
Results indicate that neither method is superior
when compared to the other
N.B. Small number of samples could influence results!
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CONCLUSIONS
Choice of method up to user Problems for using Stepwise Voltage method:
No standardised starting voltages time consuming todetermine by experimentation
Difficult to maintain constant arcing at ground electrode
required by this methodology Hourly rise of 250 V not representative of field conditions
difficult to relate test data to field data
Constant Tracking Voltage method preferred for future work & studies, including a comparative studyof the erosion & tracking resistance of insulator materials for both High Voltage AC & DC
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THANK YOU!