Failure Analysis of Three Slow-Speed Induction Motors for Reciprocating Load Application

The North Atlantic Refinery has three 5400-hp slow-speed induction motors driving reciprocating compressors for a Hydrogen plant. All motors were rewound on-site over the period of 1998-2002, using magnetic wedges as per the original design, and the motor protection was upgraded to microprocessor-type relays. In summer 2003, during routine maintenance, it was noted that these motors suffered substantial loss of slot magnetic wedges and had to be scheduled for rewedging over 2004-2006. This paper presents failure analysis, field measurements covering heat-run test results, and motor-performance and vibration analysis before and after motor rewedging work. This paper reviews the key factors for using magnetic versus nonmagnetic wedges in these applications and techniques available to predict loss of wedges. The use of a microprocessor relay for slow-speed induction motor protection is discussed, particularly, the thermal protection feature to address the cyclic-load pattern caused by the reciprocating compressor