Failure analysis of three slow speed induction motors for reciprocating load application

This refinery has three 5400 HP slow speed induction motors driving reciprocating compressors for a hydrogen plant. All motors were rewound on site over a period 1998-2002 using magnetic wedges as per the original design and the motor protection was upgraded to microprocessor type relays. In summer 2003 it was noted that the motors suffered substantial loss of slot magnetic wedges and had to be scheduled for re-wedging over 2004-2005. The paper presents failure analysis, field measurements covering heat run test results, motor performance and vibration analysis before and after motor re-wedging work. The paper reviews the key factors for using magnetic versus non-magnetic wedges in these applications and techniques available to predict loss of wedges. The use of a microprocessor relay for slow speed induction motors protection is discussed particularly the thermal protection feature to address the cyclic load pattern caused by the reciprocating compressor.