November 3, 2016 – For a major inspection process, a Senegalese cement manufacturer had to replace their old coal mill and install a technically and mechanically compatible replacement motor in 2015. Tasked with this assignment, Menzel Elektromotoren from Berlin was faced with a particularly dusty challenge. The motor, which provides the plant with finely ground coal dust to meet the plant's primary energy needs, is operated in a hazardous area classified as zone 22. While ground coal offers better caloric properties than briquets, particles of conductive dust left on slip rings and brushes may cause sparks and lead to an explosion. The motor therefore required a design that would reliably prevent dust ingress during all operating stages.
To meet these challenging requirements, the German manufacturer of custom motors engineered a rugged unit with IP65 ingress protection. Because a squirrel-cage motor requires a high starting current and has a lower starting torque, a slip ring motor was chosen. A special motor construction was then devised for the application: the system features special terminal boxes for the stator and rotor, a non-magnetic cable entry plate, and hazardous area terminal clamps for the auxiliary terminal boxes. In addition, the motor housing is slightly larger to ensure the operating temperature does not exceed +125 °C. Additional fixing points between the radiator and housing facilitate tightening of the sealing in-between.
The engineers also reinforced Menzel's standard viewing windows for the slip ring chamber with bolted covers and plexiglass to ensure proper tightness. Thanks to these measures, the replacement motor has received a Ex II 3D Ex tc IIIB T125°C Dc explosion protection marking and reliable delivers top performance in zone 22.