Previously, we looked at the "why" for ventilating motors and saw that thermal imaging lets you avoid guesswork. We also looked more closely at the "how,” with a focus on using thermography to properly map out a correct route for cooling ducts.
Unless you’re using a totally enclosed motor, all this assumes that the cooling air can actually get inside the motor. Dirt, dust, chemicals, snow, oil, vegetation, and process waste can clog the ventilation ducts of an open-frame motor. So can insect nests, rodent nests, and associated droppings. All of this nasty stuff also may help form a thermally insulating coating on the windings.
But isn’t the solution just to use a ventilation filter? You definitely should have a ventilation filter, but understand that this nasty stuff can clog the filter and therefore defeat the ventilation. This problem is quite common, partly because these filters often are installed in a way that makes inspection and replacement difficult.
The solution to a clogged ventilation filter is often to remove the filter, and that puts you back where you started — motor windings coated with nasty stuff. But at least that prevents overheating because of a clogged filter, right?
If it’s a critical motor, put a differential pressure (DP) alarm across that filter. This should trigger a local alarm light, at the very least. Preferably one that blinks annoyingly.
If it’s not a critical motor (or even if it is), you could redesign the filter system to make inspection and replacement easy. Here’s how a maintenance department at a plastic extrusion plant in Kentucky solved that issue.
A sheet metal contractor came in and built rectangular extension ducts that were attached (and sealed) to the original filter location. These extended the filter location from under the machine, where they were difficult to access.
With these in place, anyone walking by could glance at the filter and see its condition. And instead of a screw and nut assembly as the original filters had, these ducts were outfitted with hook and loop fastener strips. The filter medium was a material that these strips readily latched onto.
All of the filter openings were the same size, so that one size filter could be used plant-wide. The maintenance department ordered these precut to that size. A maintenance helper could walk through the production floor and change all the filters in less than one hour. Previously, it took two technicians that long to change a single filter.