Variable speed electric drive with increased human protection for unearthed neutral systems

For human safety, electrical systems are required to have neutral wire connected to earth. In some applications (ships, aircrafts, and underground operations) neutral cannot be earthed, causing problems of undetected faults and dangerous potentials. This research has developed a high quality variable speed drive for electric motors, which also provides increased safety and instant fault detection in unearthed neutral systems.

Competitive advantage

Typical land-based variable speed drive offer speed control and high energy efficiency. However, they:

  • produce distortion of power supply and acoustic noise
  • create high-level high-frequency voltage at the motor star point, causing electromagnetic interference, protection, safety and service problems

The developed drive provides the top-level control accuracy and energy efficiency.

At the same time, it offers:

  • very low input harmonics, complete power factor correction and reduced acoustic noise
  • the unique feature of zero volts at the motor star point, eliminating the associated problems and providing a mechanism for enhanced fault protection

Successful applications of research

  • Electrically safe variable speed drive for shuttle cars in underground mining


  • Australian Coal Association Research Program
  • Restech
  • Komatsu Mining


  • Increased human safety
  • Reduced acoustic noise and electromagnetic interference
  • Long service life due to elimination of shaft and bearing currents
  • Fast reliable fault detection (< 1 millisecond) and local disconnection of only faulty equipment
  • Service continuity of the rest of the electrical system

Capabilities and Facilities

  • Working prototype drive for a 10kW/415VAC electric motor
  • Industrial quality drive controller
  • Laboratory model of Unearthed Neutral System environment
  • Capability to adapt to specific application requirements
  • Ongoing collaboration with drive manufacturer

Further reading on: Material Sciences and Manufacturing

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