A contra-rotating axial-flow fan is prone to stalling and motor overload at partial flow rates. Moreover, its efficiency decreases sharply at a high flow rate, which is accompanied by disparity between the shaft powers of the two impellers and the light loads of their motors. It is necessary to maintain a high fan operating efficiency and a reasonable match between the powers of the two impellers. In this study, model and simulation analyses of a mine contra-rotating axial-flow fan were conducted. Different impeller rotational speeds were obtained by controlling the pole speed. The aerodynamic characteristics, namely, the total pressure rise, shaft power, and operating efficiency, were investigated with respect to the flow rate and rotational speed combination of the impellers. The pressure and velocity distributions were also determined and analyzed. The high-efficiency operating range and variation range of the total pressure rise of the fan with different speed combinations were obtained. The findings indicate that the variable speed operation of two impellers can expand the fans’ stable operating range and that impeller speed combinations can be set based on the flow rate and the resistance of the pipe network. This enables the contra-rotating axial-flow fan to operate in the high-efficiency operating range.

A method to analytically calculate the parameters of the fault area between core laminations are proposed and the dynamic trend of the fault development is predicted to comprehensively and accurately obtain the fault degree and damage level of short-circuits between the core laminations of large motors. Considering the influences of frequency and magnetic flux on the axial skin depth of the core and of the eddy current loss on the insulation resistance between the laminations and reviewing the laminations of the stator core tooth as the research object, based on the Maxwell equations and equivalent circuit theory, analytic expressions of active power and induced voltage in the fault area between the laminations are derived; the influence of the number of fault laminations on the electrical parameters in the fault area is quantitatively analyzed; the actual fault development process of the short-circuit faults between the laminations are obtained; and the correctness and effectiveness of the proposed method are verified via numerical simulations and the experiment of faults between core laminations. The sequence of induced voltage changing with the number of fault laminations is selected as the grey sequence to establish the grey prediction model (GM (1,1)). The development curve of the damage depth of the faults between core laminations along the axial direction is illustrated by calculating the sequence data. The results show that the error between the predicted value of the damage depth of the short-circuit fault herein and the experimental value is less than 7%. This method can be used in engineering practices.