The Whirling Speed of the Induction Motors and Unbalanced Magnetic Pull (Ump)-A Review

The evaluation of whirling speed and related whirling motion of the rotating elements (such as shafts) is one of the crucial problems to be addressed by design as well as maintenance engineers. This paper reviews on whirling speed of electrical machines, precisely, an induction motor and an introduction to phenomenon called unbalanced magnetic pull (UMP). In an induction motor, the shaft- rotor assembly is the actual physical rotating element. For this rotating element, at a particular speed, the the natural frequency of transverse vibration is equal to the frequency due to operating speed, then that speed is called as ‘critical speed' or ‘whirling speed' of that particular rotating element. The UMP incorporates the facts as; the electromagnetic forces existing between stator and rotor are produced due to electromagnetic fields in the electric machines' air gap. This total force exerted on the rotor by virtue of its (i.e. rotor's) eccentric position is termed as ‘unbalanced magnetic pull (UMP)'.