Combination of a forced air open-ventilation system of an electrical machine and an air cleaner, the open-ventilation system comprising air forcing means that is a large-diameter high-pressure fan downstream of the electrical machine that creates a high-velocity outlet stream and a single outlet through which the high-velocity outlet stream is ejected from the open-ventilation system; and the air cleaner comprising: an air chamber having at least one conical inlet through which air is drawn in from the surroundings by the fan of the open-ventilation system; at least one first outlet through which air that is substantially particle free is drawn out of the air chamber by the fan of the open-ventilation system; at least one second outlet through which air is drawn out of the air chamber by the high-velocity outlet stream of the open-ventilation system; and rotating means contained within the air chamber and drivable to rotate about an axis to subject the air within the air chamber to a centrifugal force such that any particles within the air chamber and air are thrown radially outwardly towards the at least one second outlet; wherein the at least one first outlet is formed at or near the axis of the rotating means; wherein the at least one second outlet has an upstream end that is formed in the wall of the air chamber adjacent to the radially outer edge of the rotating means and a downstream end that leads to a portion of the open-ventilation system that is located after the fan but before the outlet; wherein the fan of the open-ventilation system is located at or near the outlet of the open-ventilation system and before the downstream end of the at least one second outlet such that the effect of the high-velocity outlet stream passing the downstream end of the at least one second outlet creates a pressure differential across the length of the at least one second outlet which results in air and any particles within the air chamber that have been thrown radially outwardly towards the at least one second outlet by the rotating means being drawn out of the air chamber through the at least one second outlet and into the high-velocity outlet stream to be ejected from the open-ventilation system through the outlet; and wherein the open-ventilation system further comprises a filter enclosure formed on the upper side of the electrical machine that contains a large filter adapted to remove from the air any particles not collected by the air cleaner, the inlet of the filter enclosure being connected with the at least one first outlet of the air cleaner by ducting, the outlet of the filter enclosure being connected with the inlet of the electrical machine by ducting, and the outlet of the electrical machine being connected with the fan by ducting. an air chamber having at least one conical inlet through which air is drawn in from the surroundings by the fan of the open-ventilation system; at least one first outlet through which air that is substantially particle free is drawn out of the air chamber by the fan of the open-ventilation system; at least one second outlet through which air is drawn out of the air chamber by the high-velocity outlet stream of the open-ventilation system; and rotating means contained within the air chamber and drivable to rotate about an axis to subject the air within the air chamber to a centrifugal force such that any particles within the air chamber and air are thrown radially outwardly towards the at least one second outlet;