William R. Finley

An induction motor — Keep it running

This paper discusses factors that affect the life and durability of an induction motor. Various topics include overall construction of an induction machine and its components, field and operating conditions, motor vibration, operating temperatures, installation practice and proper motor selection for special environment and application conditions. Sound motor design, proper selection of the motor to suit the application, proper field installation, and good maintenance are key factors essential for long term motor reliability.

Motor vibration problems — Understanding and identifying

Vibration problems in large induction motors can be extremely frustrating and may lead to greatly reduced motor reliability. It is imperative, in all production operations that downtime be avoided or minimized. If a motor problem does occur, the source of the problem needs to be promptly identified and corrected. With proper knowledge of the sources of motor vibration, proper vibration measurement and diagnostic procedures, it is possible to more quickly identify the root cause of motor vibration. This paper intends to assist the operators of cement plants in avoiding erroneous conclusions that may be reached as a consequence of not understanding the root cause of the vibration; conclusions that may result in trying to fix an incorrectly diagnosed problem, wasting time and money in the process. By utilizing the proper data collection and analysis techniques, the true source of the vibration can be more accurately determined: This analysis includes, but is not limited to vibration related to: · Electrical imbalance - stator, rotor bar · Mechanical unbalance - rotor, coupling, driven equipment · Resonance and critical speeds · Mechanical effects - looseness, rubbing, bearings · External effects - base, driven equipment, misalignment. This paper includes a diagnostic guide (Table I) listing of the causes of electrically and mechanically induced vibrations in large motors, along with the characteristics of these vibrations. In addition, a field example is provided from a cement plant facility wherein a vibration problem was discovered, the root cause was determined and the vibration issue was solved.

Motor Vibration Problems: How to Diagnose and Correct Vibration Errors

Vibration problems in large induction motors can be extremely frustrating and may lead to reduced motor reliability. It is imperative that downtime is avoided or minimized in all production operations. If a motor problem does occur, the source of the problem needs to be promptly identified and corrected. With proper knowledge of the vibration sources, appropriate vibration measurement, and diagnostic procedures, it is possible to quickly identify the root cause of motor vibration. This article, based in part on [1], aids cement plant operators in avoiding erroneous conclusions that may be reached as a consequence of not understanding the root cause of the vibration and problems that may result in trying to fix an incorrectly diagnosed problem, wasting time and money in the process. By utilizing the proper data collection and analysis techniques, it is possible to accurately determine the true source of the vibration.

Vibration diagnostic challenges in electric motor applications

Electric motors have unique vibration characteristics mainly due to the coupling between electric and mechanical forces and the construction of their rotors. Rotors are made up of stacked parts and a copper or aluminum cage material that is casted, welded or brazed and shrunk fit on a shaft which may also have welded arms. This built-up construction of different materials with different thermal reactions affects rotor motion in a complicated manner at different speeds and thermal loading conditions. Since motors are the primary source of rotational motion in a typical drive train, high vibration will usually be evaluated on the motor first before moving onto the rest of the drive train components. Unfortunately other components cannot be tested alone to identify if they are the source of the problem. This often results in losing valuable commissioning or operating time. Vibration identifications can be started by using readily available diagnostic tables. Problems can occur when the process of identification goes beyond the capability of the tables to provide a clear answer. This paper discusses case studies on vibration diagnostics of electric motors, where a wider scope of the drive train and its support must be considered in order to arrive at the correct diagnosis. Particular emphasis is given to the identification of the original problem and cause of the vibration issue.

Vibration Diagnostic Challenges: Case Studies in Electric Motor Applications

Electric motors have unique vibration characteristics mainly due to the coupling between electric and mechanical forces and the construction of their rotors. Rotors are made up of stacked parts and a copper or aluminum cage material that is casted, welded, or brazed and shrunk to fit on a shaft, which may also have welded arms. This built-up construction of different materials with different thermal reactions affects the rotor motion in a complicated manner at different speeds and thermal-loading conditions. Since motors are the primary source of rotational motion in a typical drivetrain, one will usually evaluate high vibration on the motor first before moving on to the rest of the drivetrain components. Unfortunately, other components cannot be tested alone to identify if they are the source of the problem. This often results in a loss of valuable commissioning or operating time. Vibration identification can be started by using readily available diagnostic tables, but problems can occur when the process of identification goes beyond the capability of the tables to provide a clear answer. This article discusses case studies on vibration diagnostics of electric motors where a wider scope of the drivetrain and its support must be considered to arrive at the correct diagnosis. Particular emphasis is given to the identification of the original problem and the cause of the vibration issue.

Rotating machines — Pros and cons of monitoring devices

Rotating machines such as motors, generators, turbines, and compressors utilize many different types of monitoring devices. These devices are critical for the long term reliable operation of rotating machines. Some measuring devices will add significant knowledge of the performance and therefore add value and reliability, while others add little to no value but will add substantial cost. The pros and cons of using each of the many different types of devices and what can be determined from the measurement need to be evaluated before installation. Simply installing the device may not add the expected reliability. This paper will discuss parameters of monitoring, setting of control limits, and the application of various monitoring devices.

Longevity of an induction motor

This paper discusses factors that affect the longevity and durability of an induction motor. Various topics include overall construction of an induction machine and its major components, field and operating conditions, motor vibration, operating temperatures, installation practice and proper motor selection for special environment and application conditions. Sound machine design, proper selection of the motor to suit the application, proper field installation, and good maintenance are key factors essential for long term motor reliability and its performance.