What causes unstable speeds in medium-to-high pressure centrifugal fans?

What causes unstable speeds in medium-to-high pressure centrifugal fans?

During operation, medium-to-high pressure centrifugal fans may experience excessive speeds due to control system issues. However, some users encounter this problem: the fan's speed fluctuates between high and low during operation, causing adverse effects on work processes. So why does this occur? Let us analyse the issue. In practice, the root cause typically lies with the motor of the medium-to-high pressure centrifugal fan. Generally, four primary reasons exist: Firstly, a faulty rectifier diode within the fan's four-diode rectifier assembly may cause erratic speed fluctuations, disrupting normal operation. The second potential cause involves poor carbon powder or faulty carbon brushes between the motor rotor and rectifier, which may induce such behaviour. Diagnostic procedures can identify the issue. First, measure the adjustable resistor. If resistance is normal, check the trigger for abnormalities. If all readings are satisfactory, verify the connections on the medium-high pressure centrifugal fan circuit board. Positive and negative terminals may have become loose. A third potential cause involves abnormal conditions within the medium-high pressure centrifugal fan itself, such as faults including short circuits, open circuits, trigger failures, or internal contact issues. These problems can destabilise the fan's rotational speed, causing it to fluctuate between accelerated and decelerated states. The issue lies with the well-known adjustable resistor, which presents several problems. Positioned on the control panel within the installation structure and subject to frequent use, this adjustable resistor is prone to developing poor contact over time, leading to unstable rotation of the medium-high pressure centrifugal fan.