MCSA Case Histories—Diagnosis of Cage Winding Defects in SCIM s Fitted with End Ring Retaining Rings

This chapter presents two case histories to illustrate the difficulty of detecting broken rotor bars in cage rotors with end ring retaining rings (ERRs), which were used in large, HV, 2‐ and 4‐pole, 60 Hz, squirrel cage induction motors (SCIMs). In first case history, ten broken rotor bars in a copper fabricated cage winding (ERRs fitted) of a 6800 kW/9115 HP, 2‐pole SCIM driving a seawater injection pump. A root cause failure analysis (RCFA) is also presented in this case history. In second case history, one broken rotor bar and 46% faulty bar to end ring joints in a copper fabricated cage winding in a 4270 kW/5724 HP, 2‐pole SCIM driving a seawater injection pump. Broken rotor bars may well still be making partial face‐to‐face contact with the end rings, producing an motor current signature analysis (MCSA) result which would imply that there were less broken bars than, in fact, is the case.