When vibration problems occur, the magnitude and direction of the vibration can give a good indication of where to look for the cause. When vibration is higher in the vertical plane, one of the first things we should examine is the base/foundation of the motor. If the high vertical readings are compounded by indications of an eccentric airgap, such as high axial vibration and a predominant twice-line-frequency vibration, a "soft foot" or twisted frame is often to blame.

Mechanical resonance can be defined as the amplification of the vibration level of a mass or structure at its natural frequency, caused by excitation from an external source. For a rotating mass, this amplification occurs at the critical speed(s). Electrical resonance causes an amplification of the magnitude of voltage or current, or both. The increase in amplitude, whether mechanical or electrical, increases the stress on motor components and negatively affects operation, e.g., increased vibration, instability, increased energy consumption, and premature failure. By receiving energy from an external source, the resonant condition can cause the magnitude of the disturbance to continue to increase until a fault occurs. Mechanical resonance can lead to breakage of motor and drive components, and electrical resonance can result in winding failure. In this article we will discuss mechanical and electrical resonance associated with motors and drives, and provide some solutions to address them.

We'll begin by clarifying what is meant by a "soleplate." In this article, the soleplate is the steel plate or baseplate on which an electric motor or similar rotating machine is mounted. In addition to issues related to soleplate condition assessment and restoration, the article will also cover other areas related to the concrete foundation upon which the machine and soleplate are mounted.

While the majority of EASAns don't get involved with field construction of motor bases, most do have an important motor base in the service center. The baseplate used in conjunction with the test panel is important, especially when measuring vibration levels of a running motor. This article reviews a few basic steps to make sure that the baseplate functions correctly.