ACCELERATED MULTISTRESS AGING OF

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ACCELERATED MULTISTRESS AGING OF POLYMERIC
INSULATORS UNDER SAN FRANCISCO COASTAL
ENVIRONMENT
NOPPORN CHAIPANIT CHAIWAT R. RAJI SUNDARARAJAN
ELECTRONICS COMPUTER ENGINEERING TECHNLOGY ASU
EAST MESA AZ-85212 raji_at_asu.edu
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ELECTRICAL DATA
3RD Year Readings mA Insr 1 Insr
2 0.75 103896 72800 1 84532 93968 2 4934 874 5 87
72 10 32 30 20 0 0 30 0 0 35 0 0 40 0 0 45 0 0
Number of Leakage Current Pulses in Bins 1 to 10
4th Year Readings mA Insr 1 Insr
2 0.75 109073 80577 1 95816 140569 2 13354 11830
5 1948 1969 10 40 31 20 0 0 30 0 0 35 0 0 40 0 0 4
5 0 0
Cumulative Surface Charge
Watts Loss (p(t)v(t)I(t))
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ELECTRICAL DATA ANALYSIS

• Leakage current pulses, cumulative charge and
  watts loss in-line with previous researchers
  data
• Large number of low current (0.75 mA and 1 mA)
  pulses
• High current pulses (gt10 mA) are virtually nil
• Insulator 2 had more Q and W than Insulator 1
• Charge change from year 3 to 4 was
  dramatically high while from
• year 2 to 3 was Comparatively low for insulator
  2
• Power loss change from year 3 to 4 was much
  less than the change from year 2 to 3
• Insulator 1 experienced relatively less change
  in Q and W compared to insulator 2

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SEM MICROGRAPHS FOR 1-4 YEARS AGING
300x
300x
Virgin
1st Year
2nd Year
3rd Year
4th Year
1000x
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ACKNOWLEDGMENTS
NSF DEIS RESEARCH FELLOWSHIP DR. ED
CHERNEY K-LINE INSULATORS DAVID WRIGHT DR. LIU,
ASU SEM FACILITY
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CONCLUSIONS

• Monthly weather cycles simulate environmental
  stresses more closely than
• summer and winter cycles
• Monthly weather cycles have been designed and
  developed for coastal San Francisco
• 4 year lab aging had been performed on 28 kV
  distribution class silicone rubber
• Insulators
• No major degradation, such as cracking has been
  observed
• The 3rd year sample had the highest porosity and
  roughness of all the 4 year samples
• The surface seemed to be in the process of
  recovery in the 4th year.
• This was corroborated from the findings of SEM,
  FTIR, hydrophobicity classification

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Si/Al Ratio using various EDX Results
Sample EDX Weight Atomic Virgin 1.2151 1.152
8 1.1070 1 year 1.5365 1.4570 1.4230 2
Years 1.1688 1.1088 1.0648 3 Years 1.1819 1.1213 1
.0768 4 Years 1.6600 1.5759 1.5138

• Virgin sample has a smoother, more homogeneous,
  and less porous surface than aged samples
• Phase difference is the least for virgin sample
• For 1-3 years, roughness and porosity increases
  with aging
• Year 3 sample is more porous of all
• Year 4 sample has less porosity than year 3
• Also looks smoother than year 3
• This was supported by other data from EDX and XRM
  attachments of SEM
• Si/Al calculation shows highest value for year-4
  than other years
• Si/Al ratio calculated by 3 different ways
  correlate very well in both magnitude and in
  trend of variation
• This indicated that the sample was trying to
  recover
• This may be due to diffusion of LMW species from
  bulk/curing of polymer due to heat/reorientation
• This is in line with other observations, such as
  FTIR and hydrophobicity classification and visual

Overall, no major degradation, such as
cracking Aged samples have different
microstructures Surface roughness and porosity
increased with increase in years of aging Third
year has more porosity than other year 4th year
sample seems to be in the recovery phase
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RESULTS DISCUSSION
Visual Observation No color change No
cracking STRI Hydrophobicity Classification 1
Year HC 2-3 2 Years HC 3-4 3 Years HC 4-5 4
Years HC 4-5
ESDD/NSDD Aging Insulator ESDD NSDD Time mg/cm2
mg/cm2 Year 1 1 0.0042 0.0000 2 0.0027 0.0000 Y
ear 2 1 0.0044 0.0330 2 0.0029 0.0322 Year
3 1 0.0058 0.0118 2 0.0033 0.0118 Year
4 1 0.0032 0.0589 2 0.0029 0.0574
Virgin
2 Years
3 Years
4 Years
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MULTISTRESS LAB AGING
 
UVA Heat/Temperature Cold Rain Mist Salt Fog
0-100 kV, 400 mA Test Transformer IEEE STD 4
Salt Nozzles UVA Intensity - 1 mW/cm2 4000 ?s/cm
Salt Fog
 
Leakage Distance 600 mm Shed Diameter 96.1
mm Sheath Diameter 25.3 mm Dry Arc Distance 283
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SAN FRANCISCO WEATHER CYCLES
Month Days Temp UVA Rain Salt Fog Clear
Fog oC h/Day h/Day h/Day h/Day January 1.65
13 0-4.24 0.32hx5 0 0.5hx8 May 3.46 17 0-18 0 0
.5hx4 0.5hx6 September 6.03 21 0-12.75 0
0.5hx4 0.5hx8
RAF Relative Aging Factor for Each Month
Unique Bay Area Weather Sea-Fog and Sun Shine
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INTRODUCTION

• Multistress aging simulating service conditions
  more desirable
• They enable to obtain realistic performance
  index of long term performance of polymeric
  insulators
• Conventional aging tests, such as salt fog
  test, tracking wheel test, inclined plane test,
  and IEC 1109 1000 h test served well during the
  initial period t0 screen various polymeric
  material performance
• Do not simulate the service environment and the
  synergy of various stresses
• Stress associated are often unrealistic
• Multistress tests simulate Environmental
  Electrical Stresses
• UV, Heat, Rain, Clear mist, salt Contamination
• Lab aging correlate with Field Aging
• Coastal San Francisco 4 year aging using
  monthly weather cycles

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WEATHERING

• Weathering Photo degradation of polymer
  materials cause billions of dollars product
  damage and power outages
• The damages include color change, strength loss,
  cracking, chalking, erosion arcing
• To make an informed choice of insulators, know
  the weathering of polymers in their actual
  service environment or field conditions
• USA is the fourth largest country
• Positioned in the belt of disturbed westerly
  winds
• Weather in most regions of US, for most part of
  the year, affected by Cyclonic storms, or
  depressions, with their associated warm and cold
  fronts
• Most of these depressions move across the
  country from west to southwest to east to
  northeast clouds, precipitation, disturbed
  changeable weather

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FTIR ANALYSIS
Nicolet AVATAR 360 FTIR Golden Gate Single
Reflection Diamond Year 1 to 4 samples after 24
h of test completion These spectra different from
those of immediately after test

• For year 2, absorption of CH in CH3 (2962-2920
  cm-1) and CH in Si-CH3 (1270-1255 cm-1)
• decreased
• this means there is reduction in number of CH
  bonds
• However, year 3 and 4 show increased absorption
  compared to year 2
• Absorption of Si(CH3)2 (840-790 cm-1) changed
  just a little
• There was virtually no change in Si-O-Si
• This is in-line with SEM data, showing no major
  degradation or cracking
• Year 4 is closer to virgin than year 3 and 2
• Year 1 seems to be better than virgin