DIELECTRICS AND ELECTRICAL INSULATION Robert Hebner, Ph.D. Center for Electromechanics University of Texas at Austin

Background - Personal • Decades of research experience •  50+ publications in the field •  Twice selected president of the IEEE Dielectrics and

Electrical Insulation Society

Simulating Mode Transitions during Breakdown in Liquids Brian T. Murphy, Robert E. Hebner, Edward F. Kelley

Longer free path

Background - CEM

Stress Grading

A. Roberts, Electrical Insulation Magazine, 1995

Semiconductive Coating

Stress Grading Coating

Endwinding Insulation

Copper Conductors

Two conference papers

Forensic investigation Failure due to rubbing and flow

(Okabe, et al. IEEE Trans. Diel. Elec. Insulation, 2006)

Basic materials properties

Experience in application environment*

Electrical environment*

*CEM Focus

VG 12968k

Key Takeaways Vendor knows material – user knows environment

Failures are due to environment

Published NAVAIR Data on Wiring Failure

5

Chafed wire insulation leading to short circuit and/or arcing 37%

Short circuit, unspecified cause (includes arcing incidents)18%

Broken wires11%

Connector failure 9%

Unspecified failure 6%

Failure due to corrosion 5%

Loose connection 4%

Insulation failure

3%

Circuit breaker failure 2%

Crossmating 2%

Short due to corrosion 1%

Miswire 1%

Other 1%

Failure primarily due to environment, not poor insulation

Current CEM Research - Cables • Cable plant is too large in electrified

•  Ships •  Aircraft •  Automobiles

• Analysis for existing and emerging materials is that they can be significantly smaller thermally and electrically.

•  Focus is developing environmental tests that predict life. •  Multiphysics challenge

•  Electrical •  Thermal •  Mechanical •  Chemical

Technical Approach •  Focus on dc cables

•  Much less physics-of-failure data for dc •  Worldwide interest growing

•  Cable plant can be smaller if loads are also dc

• Accelerate electrical/mechanical/thermal aging

• Use partial discharge measurements to gauge health

PD initiated

Space charge impact after polarity reversal – a unique dc

challenge

Strategic Partnership • Gian Carlo Montanari, University of Bologna

•  Globally recognized expert in relating partial discharge to life •  Partnership mired in legal issues at present, but expect success

• Access to EU-funded program data and materials •  Joint paper

•  Trying to explore a Bayesian, rather than strictly measurements based approach, to life estimation.

Anticipated Next Focus • Wide Band Gap semiconductors

enable higher voltage operation. •  Packaging problems occurring

•  Partial discharges •  Surface discharges •  EMI •  Thermal failure

• CEM, ME, ECE collaborative research

Polyimide Damage

Temperature measurement using UT’s thermal imaging microscope system

Needed R&D •  3-d, multiphysics model

of semiconductor package

•  Integrated cooling •  Functionally graded

materials •  Possibly via additive

package manufacturing

EW-enhanced heat pipe evaporator

EW voltage

Heat flux

Nucleate boiling

EW-­‐enhanced  evaporator  Higher  heat  transfer  via  EW-­‐stabilized  nucleate

boiling  (dryout  prevention)

Heat  transfer  mechanism:  Nucleate  boiling

Heat pipe evaporator

Heat flux

Evaporation

Traditional  heat  pipe  evaporator

Heat  transfer  mechanism:  Conduction  &  evaporation

Conduction

Hot  surface

Vapor  layer Liquid

Proximity  electrode

Surface   dryout Hot  surface

Liquid 100   V  applied

Dryout   preven=on   (sustained  nucleate  boiling)

Demonstra*on  of   nucleate  boiling and  dryout  preven*on  using  electrowe8ng  (EW)

Summary • UT research aims

•  Improved asset management via better life prediction •  Characterizing use environment

•  Modeling and manufacturing technologies that lead to longer service life

•  Team with others for access to emerging materials