High Clearance Between Motor Bearing and its Cover

The Importance of Identifying Ambiguous Diagnosis in Practical Case Study !!

We still present case studies focused on the ambiguous diagnosis which has a different definition for fault patterns mentioned in references.

Question: What is the fault pattern of broken rotor bars in AC motor?
Answer: From approved references, one of these patterns is looks like 1X and its harmonics in the spectrum side banded by pole pass frequency (PPF).

Unfortunately, this case study mentioned that there is another fault produces the same pattern. Now, we have a cement mill in a cement factory and the measurement was performed on motor bearing (DE). The same pattern of broken rotor bars was observed, but the root cause of this pattern is due to high clearance between motor bearing and its cover. The spectra shown below display the improvement before and after correction.

The outcome from this one is to delay your decision to take action regarding electrical fault correction and you have to revise in the first instant the internal looseness between rotor and stator as an overview.