Oil whirl rotordynamic instability phenomenon-diagnosis and cure in large induction motor

Abstract

Reliable design and operation of rotating machinery is critical to achieve bottom line production goals and financial results in petrochemical, transportation and chemical products processing industries. Of the many factors which may cause failure and or reliability issues in these industries, one of the most frustrating and involving relates to bearing failures or high vibration problems. One of the choices for rotating equipments is oil lubricated journal bearings. Oil film journal bearings are susceptible to large-amplitude, lateral vibrations due to a ldquoself-excited rotordynamic instabilityrdquo known as oil whirl. During oil whirl the rotor orbits in its bearings at a frequency approximately half the rotor speed. Oil whirl is usually caused by lightly loaded bearings, excessive bearing clearances, weak foundation and/or improper oil viscosity. At the inception of non-synchronous oil whirl the amplitude of rotor motion progressively builds at a frequency of approximately less than half of that of the rotor speed and does not damped out. If left uncontrolled oil whirl may lead to catastrophic bearing failures and equipment damage due to high vibration values. This paper will discuss the cause of oil whirl, its effect, how to detect it and its solution.