API 541 Variable Speed Medium Voltage Motors Applied in a Class I, Division 1 Hazardous Location—A Case Study

When a petrochemical installation requires the use of Class I, Division 1 electric motors for hazardous areas, end users in North America must find motors certified to the applicable national standards for such equipment. In North America, National Fire Protection Association 70 (NFPA 70 or National Electrical Code or NEC) and Canadian electrical code electric motors with explosion-proof certification are not unusual for low voltage installations, but are uncommon when larger power medium voltage applications are required. Medium voltage motors with Class I, Division 2 suitability are common, but are hard to find with an explosion-proof certification. Petrochemical applications for medium voltage motors also commonly require use of the American Petrochemical Institute Standard 541 (API 541). Further, some applications additionally require use of an adjustable speed drive to vary the speed of the driven equipment to fit operational considerations. In one recent instance, when an end user attempted to specify a 1500-kW motor with the combination of explosion-proof certification, adjustable speed suitability, and API 541 features/testing, no manufacturer in the world had such a motor available. While other solutions were considered, the end user preferred the straightforward approach that a Class I, Division 1 motor offered and decided to work with a manufacturer of motors meeting International Electrotechnical Commission (IEC) flameproof standards to satisfy the combination of all application requirements for this installation. There are many differences between the NEC and IEC systems governing hazardous areas and motor certifications are not interchangeable. The end user's engineers had to learn and understand the differences between these systems and this case study addresses many of the technical requirements, issues, and effort required to successfully deliver this motor to the project.