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

In 1984, during commissioning of a two-pole 13.2 kV motor driving a compressor in a chemical plant, arcing and sparking were observed at the joints of the enclosure. Later two motor explosions, which occurred on offshore platforms, were presumably ignited by arcing and sparking at the joints of the enclosures. This information instigated further investigations. The research work and measurements, which basically apply to all 1000 r/min 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 r/min and above) motors are described