MECHANICAL & ELECTRICAL CHALLENGES OF LARGE INDUCTION MOTORS DRIVING RECIPROCATING COMPRESSORS WITH THREE YEARS SERVICE
This paper presents the failure analysis and field measurements of five 7500 HP induction motors driving reciprocating compressors for a natural gas compression station. The motors were in service for less than three years when two of them suffered cooling fan failures. Four of the five motors were sent to a motor repair shop to be fitted with a modified cooling fan per the manufacturers recommendation. It was during one of the fan replacement processes that the repair shop accidentally discovered that many of the magnetic wedges were missing. The end user is not always aware if a motor is provided with magnetic or non-magnetic wedges unless identified in the motor engineering specification. This paper presents the findings from the failure analysis of the cooling fans and magnetic wedges for these motors. This failure analysis examined fan design, vibration, motor operating temperature, compressor loading profile, number of motor starts and ambient temperature. The paper also presents a comparison between direct on line motor starting and soft starting using an adjustable speed drive and the impact on motor performance. The settings and historical data gathered from the microprocessor protection relay for the motors will also be covered and discussed.