Installing variable speed drives: Energy efficiency profits versus power quality losses

Replacing conventional motors by Variable Speed Drives (VSD´s) can yield considerable energy savings at some industrial applications (such as pumps or compressors). However, in some cases, these savings are decreased or even entirely eliminated by process outages due to VSD-trippings on voltage dips due to short circuits in the grid. Many industrial companies and even energy efficiency consultants do not know the exact impact of voltage dips when installing a VSD in an industrial process. This paper gives a methodology to integrate poor Power Quality when considering to buy a VSD and provides guidelines on when voltage dips can have a significant impact on the energy efficiency profits. To derive such guidelines, it is taken into account that the shut down of a VSD due to a dip mainly occurs by the tripping of the undervoltage protection on its DC-bus. Next to this, the derived guidelines are validated in a practical case study.