A Comparison of Standardized Test

8/3/2019 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



Eskom



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



PRESENTATION OVERVIEW

Test Setup & Apparatus

Test Methodology

Evaluation Criteria

Results

Summary of Results

Conclusion



TEST SETUP & APPARATUS



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



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



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!



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



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



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



RESULTS: RMS CURRENTS

Results show for hour 3 - 6: Similar hourly means & standard deviations

Series B slightly higher mean (± 0.5 mA)



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



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



RESULTS: ATR-FTIR SPECTROSCOPY

Similar results for both series

Series A reveals slightly stronger changes



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!



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



THANK YOU!

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A Comparison of Standardized Test