Causes of Unstable Speed in Environmental Dust Removal and Purification Industrial Fans

Causes of Unstable Speed in Environmental Dust Removal and Purification Industrial Fans

Troubleshooting: Environmental dust removal and purification industrial fans are DC speed-controlled motors. Speed is adjusted via a variable resistor, which in turn controls the voltage across the motor terminals via thyristors to regulate the speed. “The motor speed is unstable. Based on an analysis of the operating principles, the following four scenarios are possible. (1) The variable resistor of the industrial fan for environmental dust removal and purification. As the variable resistor is mounted on the control panel, frequent use and prolonged operation often lead to poor contact. (2) Thyristors can also present various issues, such as short circuits, open circuits, failure to trip, or internal contact faults. (3) Only one of the four rectifier diodes is faulty. (4) There is coal dust or a defect in the coal brush between the motor rotor and the manifold of the environmental dust removal and purification industrial fan.” Following the principle of addressing the simplest issues first, the variable resistor was measured; the pattern of resistance change with adjustment confirmed that the potentiometer was functioning correctly. “No issues were found upon re-measuring the thyristors.” When measuring the four rectifier diodes on the environmental dust removal and purification industrial fan, it was found that one of the diodes was intact. As the diodes are high-current gold-sealed tubes, one end of each diode is secured to the circuit board with a screw. “The other end is soldered to the printed circuit board with a wire.” When removed from the printed circuit board, both the positive and negative terminals became loose. During the measurement process, it was confirmed that the diode was both conducting and open-circuited. As the type of diode could not be clearly identified, a diode of the same specification was installed, and the response was very rapid. I believed the diode had just broken, yet the measurement results indicated it was intact. “The measurements for the other three pairs of tubes were normal.” However, upon comparing the readings, it was found that the polarities of two pairs of tubes were completely reversed (i.e., one positive and one negative at the end of the upper screw). “Therefore, during installation, we must take care to ensure that parts of the same model and specification are used. “After replacing the components with those of the same specification and model, we commenced commissioning, and everything returned to normal.”