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.
