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Selection criteria for alternating-current variable speed drives.

Author(s) : MCMAHON G.

Type of article: Article

Summary

Speed control of standard three-phase motors is by varying the frequency of the electrical supply. Such a constant torque application requires that the voltage varies in the same proportion as the frequency. Centrifugal pumps and fans however have a quadratic torque requirement. At half speed the torque falls to a quarter of full speed value. To match this, the motor need not be fully magnetised and can run quieter and at reduced energy. Variable drive control for such machines must involve this factor. Other problems arise, but can be solved (harmonic currents, radio interference). Motor insulation damage due to the switching speed of the inverter transistors, should be countered by inductors in the motor leads. In certain cases, the motor may need to be derated to avoid a rise in temperature. The article expands on these problems and advises good selection. D.W.H.

Details

  • Original title: Selection criteria for alternating-current variable speed drives.
  • Record ID : 1995-0188
  • Languages: English
  • Source: AIRAH J. - vol. 48 - n. 2
  • Publication date: 1994/02
  • Document available for consultation in the library of the IIR headquarters only.

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