Methods of electric drive reliability calculation at introduction of frequency converters

The paper lists main application areas for variable frequency electric drives (VFD) at the iron and steel works. Their introduction at pump and ventilation equipment ensures a significant reserve of power saving. The paper provides evidence to the fact that the main obstruction for wide-range introduction of the frequency control systems is reduction of the facility reliability indexes. As a rule, personnel of the enterprises is not supplied with exact information on actual reliability indexes of the VFDs. The study proposes main provisions of the developed methods for calculation of electric drive reliability at the introduction of frequency converters. The methods are based on the application of the logical-and-probabilistic method accompanied by the expert estimation of the facility conditions. VFD decomposition has been performed with the sophistication enabling expert estimations. The trees reflecting faults of Siemens electric drive and frequency converter have been elaborated. Expert estimations of times to failure of frequency converter elements are provided. An average time to failure has been calculated. It has been proved that switching to frequency control may result in reduction of reliability indexes of the electric drive by 3-4 times. In connection with the above, it is practicable to consider the issue of power saving and reliability improvement of the power facilities at VFD introduction as a complex. The paper supplies references to the accomplished studies and developments in this area.