The effect of salt fog test _on_insulator

The effect of Salt fog test The effect of Salt fog test on insulator flashover on insulator flashover

characteristicscharacteristics

Written byWritten byAlexander AganyanAlexander Aganyan

March 2012March 2012

Factors involved in aging of Factors involved in aging of silicon rubbersilicon rubber

Real Pollution ProcessReal Pollution Process Dust, micro organism, bird secretions, Dust, micro organism, bird secretions,

fliesflies Desert pollutionDesert pollution sand and dry windsand and dry wind Ice & Fog deposits at high altitudesIce & Fog deposits at high altitudes Coastal pollution Coastal pollution

• corrosive and hygroscopic salt corrosive and hygroscopic salt layers are deposited on the layers are deposited on the insulator surfacesinsulator surfaces

Industrial pollution Industrial pollution • smoke, petroleum vapours, dustsmoke, petroleum vapours, dust

POPULAR CONTAMINATION POPULAR CONTAMINATION TESTSTESTS

(1) Salt fog (1) Salt fog

(2) Wet-contaminant(2) Wet-contaminant

(3) Clean fog test(3) Clean fog test

In the method, the insulator is In the method, the insulator is energized at the service voltage energized at the service voltage which is held constant through the which is held constant through the test, and subjected to a salt fog test, and subjected to a salt fog whose salinity, ranged from 2.5 to whose salinity, ranged from 2.5 to 160 g/m3.160 g/m3.

The Salt fog testThe Salt fog test

The basic principle The basic principle of long-term Salt fog testof long-term Salt fog test

The generation of continuous The generation of continuous discharges by exposing the energized discharges by exposing the energized insulator to a salt water spray.insulator to a salt water spray.

Salt fog reference to real Salt fog reference to real contamination 1contamination 1

Salt fog test is just particular and rare case Salt fog test is just particular and rare case of pollution which is really important and has of pollution which is really important and has more or less correlation with real pollution more or less correlation with real pollution process only for Marine coast disposition.process only for Marine coast disposition.

The conditions described in ……allow vitiate The conditions described in ……allow vitiate severity of conditions in rather wide range. severity of conditions in rather wide range. As result the repeatability of test results is As result the repeatability of test results is unsolved problem.unsolved problem.

The aim of this presentation to get analytic The aim of this presentation to get analytic and to obtain the answer to the questions and to obtain the answer to the questions “How increase the probability to pass the “How increase the probability to pass the test?”test?”

Salt fog reference to real Salt fog reference to real contamination 2contamination 2

Four stages of degradation of Four stages of degradation of silicone rubber compounds to silicone rubber compounds to

flashover at Salt fog testflashover at Salt fog test

Leakage current surging with associated dry band formation Leakage current surging with associated dry band formation and partial arc development along the insulator surface and partial arc development along the insulator surface eventually spanning the whole insulator eventually spanning the whole insulator

Silicone rubber may fail as an insulator Silicone rubber may fail as an insulator due to the formation of a thick silica due to the formation of a thick silica layer which could lead to trapped layer which could lead to trapped moisture and high leakage currents. A moisture and high leakage currents. A silicone rubber insulator may also fail silicone rubber insulator may also fail due to material erosion exposing the due to material erosion exposing the fiberglass rod.fiberglass rod.

1. loss of hydrophobicity1. loss of hydrophobicity 2. 2. dry band arcingdry band arcing 3. 3. formation of silica layerformation of silica layer 4. 4. erosionerosion

Some more details about Some more details about degradation at Salt fog testdegradation at Salt fog test

Hydrophobicity is the Hydrophobicity is the property that property that prevents water from prevents water from forming a sheet on forming a sheet on the surface of a the surface of a polymerpolymer..

Hydrophobicity – the main Hydrophobicity – the main advantage of SRadvantage of SR

Contact angle measurements showing Contact angle measurements showing hydrophilic surface (A), minimum hydrophobic hydrophilic surface (A), minimum hydrophobic surface (B), typical hydrophobicity for silicone surface (B), typical hydrophobicity for silicone rubber (C) and ideal superhydrophobic surface rubber (C) and ideal superhydrophobic surface (D).(D).

Main problem of SR degradation Main problem of SR degradation during Salt fog testduring Salt fog test

The tracking and erosion test is an accelerated The tracking and erosion test is an accelerated test because the hydrophobicity is removed in the test because the hydrophobicity is removed in the first few cycles, and the test sample is not given first few cycles, and the test sample is not given an opportunity to recover the hydrophobicity.an opportunity to recover the hydrophobicity. Recovery takes days to weeks, depending first on Recovery takes days to weeks, depending first on the absence of electrical activity, and then on the the absence of electrical activity, and then on the silicone compound, environmental conditions, silicone compound, environmental conditions, thickness of the silica layer, and the presence of thickness of the silica layer, and the presence of cracks in the silica layer.cracks in the silica layer.

The lack of recovery time is the reason The lack of recovery time is the reason silicone rubber compounds were not silicone rubber compounds were not originally expected to perform as well as originally expected to perform as well as porcelain glaze on the tracking and erosion porcelain glaze on the tracking and erosion test.test.

Typical test results for silicon Typical test results for silicon rubberrubber

A fast reduction of the hydrophobicity is A fast reduction of the hydrophobicity is observed within 200-400 h of the test.observed within 200-400 h of the test.

Later on, currents of typically more than Later on, currents of typically more than 100 mA arise, corresponding to unstable, 100 mA arise, corresponding to unstable, rather long discharges.rather long discharges.

Salt fog test results on hydrophobic and hSalt fog test results on hydrophobic and hydrophilic surfacesydrophilic surfaces

The gap between hydrophobic and hydrophilic performance of silicone is The gap between hydrophobic and hydrophilic performance of silicone is in the range of 20 % to 30%in the range of 20 % to 30%

Three possible ways of Salt fog Three possible ways of Salt fog Test performance improvementTest performance improvement

Reducing stress at the test by the Reducing stress at the test by the right choice of laboratory right choice of laboratory

Shape optimizationShape optimization Material improvementMaterial improvement

Technology

Main condition to pass Salt fog Main condition to pass Salt fog Test!Test!

Materials without an inherent resistance to tracking and erosion do not perform well in this test because the formation of the silica layer occurs very early in the test.

In this test, the insulators are In this test, the insulators are contaminated by spraying the contaminated by spraying the contaminant mixture. Voltage is contaminant mixture. Voltage is applied 3 to 5 minutes after the end applied 3 to 5 minutes after the end of the contamination procedure while of the contamination procedure while the insulator still wet. The test the insulator still wet. The test voltage is raised until flashover voltage is raised until flashover occurs.occurs.

Wet-contaminant test methodWet-contaminant test method

This test method can be separated This test method can be separated into two types:into two types:

1) In some fog test, insulators are 1) In some fog test, insulators are contaminated, dried, and then wetted by contaminated, dried, and then wetted by clean-fog. Test voltage is applied to the clean-fog. Test voltage is applied to the insulators when the leakage resistance has insulators when the leakage resistance has reached its lowest value. This method has reached its lowest value. This method has been mainly developed in Germany, under been mainly developed in Germany, under the name “pre-deposit method”. the name “pre-deposit method”.

Clean fog test methodClean fog test method

2) In the second type of test : 2) In the second type of test :

voltage is applied to dry contaminated voltage is applied to dry contaminated insulators and then a wetting condition is insulators and then a wetting condition is applied. This can be regarded as a applied. This can be regarded as a reasonable simulation of natural reasonable simulation of natural conditions; however, it is more conditions; however, it is more complicated than other methods.complicated than other methods.

Clean fog test methodClean fog test method

Process of pollution at Salt Process of pollution at Salt fog and start of flashoverfog and start of flashover

1) Deposit of pollution on the 1) Deposit of pollution on the insulator surface as the surface layer insulator surface as the surface layer is moistened.is moistened.

3) The surface layer is heated and 3) The surface layer is heated and causes an increase in the causes an increase in the conductivity and the leakage current.conductivity and the leakage current.

4) The heating results in local drying 4) The heating results in local drying of the surface layer and so-called dry of the surface layer and so-called dry bands occur.bands occur.

5) Partial arcs occur across the dry 5) Partial arcs occur across the dry bands on such contaminated bands on such contaminated insulators.insulators.

6) The partial discharges increase6) The partial discharges increase 7) Finally the partial streamer 7) Finally the partial streamer

discharges (partial flashovers) are discharges (partial flashovers) are “connected” in serious and a “connected” in serious and a complete flashover occurs.complete flashover occurs.

These figures show insulator These figures show insulator flashoverflashover 1 1

These figures show insulator flashoverThese figures show insulator flashover 2 2

Salt fog withstand characteristics of different profiles and materials

The results are shown in terms of withstand unified specific creepage distance (USCD)

How improve the Salt Fog How improve the Salt Fog test resultstest results ? ?

(1) To reduce the stress of the test (1) To reduce the stress of the test procedure procedure

(2) To improve the shape of the (2) To improve the shape of the insulatorinsulator

(3) To improve the material.(3) To improve the material.

Some words about siliconeSome words about silicone

Influence of Surface Material 1

ALUMINA TRIHYDRATE ( ATH )ALUMINA TRIHYDRATE ( ATH )

Of the Common fillers used in Plastics, Of the Common fillers used in Plastics, Rubber, FRP, SMC, DMC moulding and Rubber, FRP, SMC, DMC moulding and other polymers only Alumina Trihydrate other polymers only Alumina Trihydrate has flame retarding and smoke has flame retarding and smoke suppressing properties as well as being suppressing properties as well as being an economical resin extender. an economical resin extender.

Alumina Trihydrate ATH - 800 gradeAlumina Trihydrate ATH - 800 grade:-:-

This is finely ground grades consisting This is finely ground grades consisting entirely of superfine pass through 800 entirely of superfine pass through 800 mesh. Average particle size 1.5 - 5 mesh. Average particle size 1.5 - 5 microns.microns.

This grade use specially in XLPE,PVC Cable This grade use specially in XLPE,PVC Cable & wire coatings, polymer industries, & wire coatings, polymer industries, & Paints Industries& Paints Industries

Alumina Trihydrate surface treated Alumina Trihydrate surface treated material available on request.material available on request.

http://www.aluminachem.com/products.htm#1

AI(OH)3

http://www.rjmarshall.com/sites/default/files/bayer%20tech%20sheet%20121911%20email%20version_0.pdf

Pure silicone rubber shows little tracking and erosionbase

ECE-3650 SYLGARD HVIC (SYLGARD HVIC). High Voltage Insulator Coating?

Influence of Surface Material 2

Visual Observation Results

Effect of Surface Treatment of Fillers on Deterioration of Silicone Rubber Housing Materials andRod type specimens made of HTV SiR havingdifferent amount of Alumina Trihydrate (ATH)1

Visual Observation ResultsVisual Observation Results

a) HTV SiR ATH0

Severe Erosion Slight Erosion

b) HTV SiR ATH50

Surface discharge during Salt Fog Surface discharge during Salt Fog InjectionInjection

MICRO/NANO FILLER USE TO IMPROVESILICOMICRO/NANO FILLER USE TO IMPROVESILICONE RUBBER FOR OUTDOOR INSULATORSNE RUBBER FOR OUTDOOR INSULATORS

1 1 There are two types offillers: reinforcing and extending. Common siliconerubber reinforcing fillers are fumed silica,

aerogelsilica, and carbon black Common extending fillers are ground quartz, titanium

dioxide, clay, whiting,alumina trihydrate (ATH), and zinc oxide.

I. Surface hydrophobicity enchancing

I. anti-adhesion, low surface energy and super-

hydrophobicityThe adhesion of solid contaminations could be reduced, leading to self clearned surface

Thereby, surface leakage currents and pollution flashovers due to contaminationwould also be suppressed efficiently.

Recently Gao et al[22,23]. employedplasma treatment to modify the surface of siliconerubber. In particular, they utilisedCF4 radio frequency plasma to introduce fluorine groups onto the polymer surface.

They achieved a super-hydrophobic silicone rubber with contact angle of 150 º

[22] S.H. Gao, K.S. Zhou, M.K. Lei and L.S. Wen// Plasma Chem. Plasma Process 28 (2008)715.[23] S.H. Gao, K.S. Zhou, M.K. Lei and L.S. Wen// Appl. Surf. Sci. 255 (2009) 6017.

II. Electrical conductivity

At a given amount of conductive particles, called the percolation threshold, a continuous network of filler is formed

Shape improvementShape improvement

Surface treatmentSurface treatment

Average leakage current vs. test timeAverage leakage current vs. test time

Protect bushing from Salt fog test and flashoverProtect bushing from Salt fog test and flashover

To increase quantity of Prevent And Eliminate The Expense

Of Insulator Flashovers With Si-Coat 570

Cleaning insulator Calculate & Choose Insulators Under Calculate & Choose Insulators Under

Heavy Contaminates Heavy Contaminates Improve Performance

Recovery of hydrophobicity Recovery of hydrophobicity

Silicone rubber may lose its hydrophobic property temporarily during periods of constant wetting, arcing and darkness. The time for loss of hydrophobicity during the extreme conditions of a 1000 h Salt fog tracking and erosion test according to IEC 1109 is in the order of 200 - 500 h. The insulators recover within a few days if allowed to dry, faster if exposed to UV light, heat and mechanical rubbing.A silicone rubber insulator with lost hydrophobicity is equally good as a porcelain insulator with the same design.

Analysis of leakage current using Analysis of leakage current using SSalt fog testalt fog test for SRfor SR

average leakage current the surface discharge currentas pulse magnitude FFT analysis of the leakage

Leakage current characteristicLeakage current characteristic

0 50 150 100 200 250 300 350 400 450 500 550 600 0.01

0.1

1

10

100 leaking peak current, mA

test duration, min

EAP

TP

LAP

Influence of specific stressInfluence of specific stress

100

10

1

0.1

0.01

0.001 0 50 100 150 200 250 300 350 400 450

leaking peak current, mA

0.8 kV/cm

0.4 kV/cm 25 50

0.6 kV/cm

test duration, min

RapidRapid flashoverflashover methodmethod forfor SSaltalt fogfog testingtesting

Experimental setup for tracking test based on BS EN 60587: 2007

Visible discharge activities during similar test (deep wheel test)

SuggestionSuggestion

Creation improved material samplesCreation improved material samples Their Comparison at fast preliminary Their Comparison at fast preliminary

checkcheck Detailed Salt fog test with 2 Detailed Salt fog test with 2

improved samples and 2 usualimproved samples and 2 usual

Thank you for your attention Thank you for your attention

The effect of salt fog test _on_insulator

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