Unipolar and RF surface flashover under atmospheric conditions

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Unipolar and RF surface flashover under
atmospheric conditions

• Advisor A. Neuber
• Project28
• Member Brian Palmer

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Project Statement
Study of flashover on dielectric surface under
atmospheric conditions.
Motivation To provide experimental data to
develop/verify numerical models for lightning
propagation across a surface sponsored by Sandia
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causes of BD

• Electron emission
• Avalanche effect
• Photon excitation (Ei)

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Test Setup
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Spice
3ns
75ns
25pF
40ns
20ns
.671pF
117nF
100pF
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Comparison
18kV peak
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Data PlotBreak Down current (volume)
Rise time90ns Setup does not limit Tr.
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Data Plots Prebreakdown(volume)
1012 e- take part in this
3us
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Data Plotscurrent wave form
Switching spike Dielectric displacement current
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Breakdown in N2 w Lexan
Breakdown Delay time
Breakdown in N2 w/o Lexan
1 atm
1 atm
Air looks similar
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Photo of setup
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Triple point
Test modes T1 Triplepoint illuminated for 1 min,
30 sec dark time, voltage applied T2 Continuous
illumination, voltage applied during illumination.
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T1
T2 no significant change to without UV.
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Setup
T3 1min illuminate, 30 sec dark time, voltage
applied. T4 5J, 5us pulse Xe flashlamp, vary
time delay.
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T3
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Setup
Master Trigger
Pulsed
To
To 20us8usx
To30us
Push Button
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Surface shots in nitrogen
reference
nitrogen
T2 UV Pulsed, 20us after Long expos
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Damage

• Breakdown was occurring between the outer and
  inner conductor before reaching the chamber.

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Conclusions

• Photoemission must be modeled as a major part in
  flashover, and causes the breakdown to stick to
  the surface more readily.
• Surface decreases the breakdown delay time
• Nitrogen causes Breakdown to occur off the
  surface except when in the presence of UV
  radiation.

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Gantt Chart
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Gantt Chart cont.
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Budget
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Future plans

• Take data on Breakdown in nitrogen with UV vary
  the dark time.

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Gather Data Varying dark time
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Damaged area Diagram
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Damaged area Animation