Risk of ignition due to transition currents in medium voltage motors for classified locations

Research work and measurements which basically apply to all 1000 RPM and above machines of multisection enclosure design are discussed. In the presence of a flammable vapor, the current transfers at enclosure joints are a potential ignition source. These eddy currents in the enclosure are created by stray fields emerging from the active part of the motor consisting of stator and rotor. On the basis of the investigations, necessary remedial measures for large high-speed (1000 RPM and above) motors are described. It is concluded in order to prevent the potential danger of explosion. Large high-speed motors with multisection enclosure should be equipped with adequately sized equipotential bonding across the enclosure joints in order to discharge the circulating eddy currents.<>