Post-mortem on a VFD failure: a compound fault of dust plus blocked cooling duct

Three VFDs reported over-temperature and over-current in turn, and the IGBTs eventually failed. The workshop does stone processing with heavy dust; the VFD cabinets had enclosure air conditioning, but the filters had not been changed in six months.

One detail is worth noting: all three failures happened on summer afternoons, when the ambient-temperature peak coincided with blocked airflow and ate up the entire cooling margin.

Strip-down confirmed that dust in the air path was the main cause: the gaps between heatsink fins were packed solid, and the fans running at full speed could not carry the heat away. Infrared measurement showed the heatsinks running 41°C above ambient at full load, far beyond the design margin.

Three remedial actions: convert the VFD cabinets to positive-pressure ventilation with two-stage filtration; add a visual filter differential-pressure strip to the weekly inspection; and fit a cabinet temperature sensor wired to an alarm. The cabinets then went through a full summer with no over-temperature on any unit.

In a dusty environment, check cooling before you check the circuit on an electrical fault. Heat is the silent killer.

Consumables such as filters have to be put on the inspection list and made visible. A blockage you cannot see will eventually make itself known by blowing the drive.

In a dusty workshop, a blown VFD is not an accident but a certainty - the only question is which day. The value of this case lies in the word "post-mortem": the destroyed module was worth a few thousand yuan, but without pinning down the trigger, a new module would have died the same way. Infrared thermography gave hard evidence: at full load the heatsink ran 41°C above ambient, far beyond the design margin, with dust sealing off the airflow as the main cause. All three corrective actions were environmental - no "better" hardware was fitted - and faults of this kind dropped to zero from then on.

If your electrical cabinets are also in a dusty workshop, check three things: open the door and look at the heatsinks and airflow - can a layer of dust be scraped off? Measure the heatsink temperature once at full load - a rise above 30°C should be taken seriously. Check whether the filters have a cleaning record - how often they are changed and who is responsible. All three take one morning. Before a blow-out, the equipment has been sending signals all along; the question is whether anyone is reading them.