Technical World – Electrical Machines Energy Efficiency & Power Generation

The overall efficiency of any electrical power generation system is fundamentally important to reducing both the life cycle costs and environmental impact of operating the equipment.

Electricity accounts for around 33% of all global energy consumption and over 40% of energy related CO2 emissions. Fossil fuels account for 66% of all electricity generation, at an average of 36% efficiency. Significant potential exists to improve this efficiency with the use of new technology. Given the relatively low efficiency of the fuel to mechanical power conversion process, primarily governed by thermodynamic laws, very high electrical equipment efficiencies are needed to preserve the useful energy available.

Where gas turbine engines are used for electrical generation, it is common to use a gearbox to reduce the output speed of the turbine to a ‘standard’ speed suitable for conventional electrical machines. In decreasing the working speed of any rotating machinery, there is an inversely proportional increase in the transmitted torque and an unavoidable loss of efficiency that occurs. Torque rating is a very good measure of the physical size of a piece of rotating equipment, so the net result is a much larger and heavier generator than if the machine could operate at the same speed as the gas turbine. This would of course also avoid the weight and inefficiency of the gearbox, so the net result is a much smaller and more efficient engine/generator combination. At this point it is necessary to consider that the characteristics of the high-speed generator do not allow direct connection to the grid, so a power converter is required, essentially meaning we have replaced the mechanical gearbox with an electrical one.

 Turbo Power Systems High-Speed 1.2MW Generator

In our experience, the use of a Permanent Magnet high-speed generator and a specially design power converter will exceed the efficiency achievable when using the conventional approach. For example, our 23,000 rpm 1.2 MW system, will operate at a net 96% efficiency, including both the generator and its power converter. To put a value on this, we should consider that at an average cost of electricity of 10 c/kWh, each efficiency point is worth $1.20 per hour. If the equipment operates continuously, then the annual benefit would be around $10,000. At 5% improvement, the benefit would be $50,000 per year.  A simple payback assessment of replacing the conventional approach with a high-speed approach, particularly for new equipment, usually results in the high-speed approach prevailing, especially when combined with the following benefits:

  • Much smaller and lighter generator combined with the flexibility in installation, relative location and cooling of the power converter
  • No gearbox maintenance, vibration, lubrication or troubleshooting issues
  • Very high output power quality
  • Excellent transient response
  • Variable-speed capability
  • Far superior part-load performance
  • Engine starting capability, dependent on engine type

 

For larger power applications, these benefits remain, and over the next ten years we expect to see widespread adoption of high-speed direct-drive machines up to 10MW and potentially above.

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