AC Variable Speed Drives (VVVF)

From Imrtwiki

Initially there was a question related to variable speed AC drives fitted to old motors. Chris from Hunter Water had some experience and indicated that common problems were insulation breakdown can occur, there can be problems with earthing/grounding issues and current circulating through bearings. The standard solution of electrical damage to bearings was to use an insulated bearing on the non-drive end bearing and to use an earthing brush on the output shaft. Hunter water specifies insulated bearing on VVVF drives of > 75kW. Also they have shaft earthing brushes as standard on all large motors.

Hunter water stated they used VVVF drives as soft starters in situations where Direct On Line (DOL) starts might cause damaging water hammer.