Sometimes overlooked safety concerns with large engineered ASD systems

Large Engineered Adjustable Speed Drive Systems are typically rated above 7kV, 5,000 or 10,000hp and are considered “engineered products and systems” (i.e. “one-of-a-kind” or “one-off” designs) as opposed to “off the shelf” equipment. As such, they require more attention to application, design, system validation and commissioning than typical “off-the-shelf” equipment and systems. Hazards associated with different drive topographies are often overlooked during the design stage. In many cases the design engineer considers the drive as a “Black Box” without sufficient understanding of the internal drive design as required to identify and mitigate concerns. In some cases, manufacturer's claims may help reinforce this attitude. However, a basic understanding of drive topography can not only help identify concerns but also provide mitigation opportunities. In many cases hazard concerns could easily be mitigated during design if identified in a timely manner but may become significantly more difficult and expensive once the equipment is in service. This paper reviews some of the more common drive topologies and associated issues that can create significant safety hazards if unrecognized and mitigated. Safety by design techniques are discussed to help mitigate the unique hazards identified.