Electric Motors Diagnostics

introduction

Condition monitoring is growing coincident with growing industries. Electrical motors are the most common machines which are used in different industries. So monitoring of these machines can be effective enough in decreasing maintenance expenditures. The most common electromotors used in different industries are squirrel cage induction electromotors. In the last two decades, different diagnostics methods such as vibration analysis, motor current signature analysis, thermography and lubricant analysis were introduced and used for monitoring of these machines. Motor current signature analysis is one of the appropriate diagnostics techniques since many of electrical defects such as rotor bars crack or broken rotor bars, shortcut in stator windings, bearing defects and … can be distinguished using this technique. The main advantages of using induction motors instead of the other types of electromotors are easy maintenance & cost effectiveness. Vibration issues in these electromotors can be defective and result in decreasing reliability. Minimizing or eliminating of equipment down time is an essential affair in production plants. Diagnosis and analysis the vibration of such electromotors is relatively difficult due to rotating magnetic field. The main sources of vibration in electromotors are as following: – Electrical unbalance of motor – Mechanical unbalance including motor, coupling or driven equipment unbalance – The effect of mechanical defects such as looseness, rub, bearing defects and … on electromotor – The effect of external defects such as foundation, driven machine misalignment and … on motor – Windings faults, rotor and stator related faults