In 2015, a Senegalese cement manufacturer had to replace their old coal mill for a major inspection process, and install a technically and mechanically compatible replacement motor.
Menzel Elektromotoren was tasked with this assignment.
The motor provides the plant with finely ground coal dust to meet its energy needs and is operated in a hazardous area classified as zone 22. Particles of conductive dust left on slip rings and brushes could cause sparks that lead to an explosion, so the motor required a design that would prevent dust ingress during all operating stages.
Menzel 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.
hese measures meant that the replacement motor received a Ex II 3D Ex tc IIIB T125°C Dc explosion protection marking and performs reliably in zone 22.