Bachelor’s Thesis - Electrostatic Bearing Discharge

TU Brunswick/Tesla Feb 2015 - May 2015

I had the opportunity to write a thesis on an issue that was not well understood and quite pressing for Tesla at the time. The work offered many challenges and a lot of opportunity for growth.

 
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Grade: 4.0 (US)

Corporation with Tesla

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Bearing Currents

  • Use of variable frequency drive to operate three phase motors can cause parasitic current from motor rotor to case ground, through bearings

  • Current significantly damages the bearing race, which leads to bearing failure over time

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Modeling

  • High frequency equivalent circuit modeling

  • Model indicates, that a low-enough impedance ground path can significantly reduce the current flow through the bearing

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Measurements

  • Self-built Rogowski coil used for rotor shaft measurements

  • Measurements must be conducted in full transmission system to get accurate results, special sensor was needed due to space constraints

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Testing

  • Designed and built test stand to:

    • Characterize impedance of all bearings used in transmission

    • Measure impedance of different shaft grounding solutions

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The grounding solution developed. prevents damage to bearings over the vehicle lifetime.

As a Mechanical Engineer by training, I was able to understand and address a problem with a deep electrical root cause.