Through analysis of abnormal operation parameters under different output capacity of centrifugal fans

it has been believed that the cause to be backward rotation of the inlet guide blades.Based on this

the inlet guide blades have been repaired and adjusted

and the fault being eliminated.At the same time

comparison of the fans' electric current when the inlet air flow to be backward prerotation and forward prerotation has been carried out under same open degree

and causes resulting in said phenomenon have been briefly analysed by using velocity triangle and Oular equation.