Variable Speed DC Drives

From Imrtwiki

Richard the Rio Tinto attendee indicated that they have a number of problems with there variable speed DC motors used on Drag Lines. They have a concern that the digital field control tuning is putting unnecessary load on the motors and causing winding failure.

Richard also mentioned a problem they have with wear on Double Flex couplings on dragline motors that operate in both rotational directions. This problem seems unusual and difficult to solve.

Another serious problem with these drag line DC motors is the breakdown in winding insulation values due to brush carbon dust becoming impregnated into the windings. Rio has tried a range of cleaning methods for the windings during overhaul but in some situations is not able to regain an adequate level of insulation. The only potentially useful suggestion made by the group was the possibility of using Dry Ice Blasting, which has been used successfully on other similar arduous cleaning application. Dry Ice Blasting uses thermal shock to remove surface contaminants and is useful in a number of electrical applications as it does not have the risk of effecting electrical insulation as does water and a number of other cleaning solvent.