ACTIVE MAGNETIC BEARING

ACTIVE MAGNETIC BEARING

INTRODUCTION

A bearing is a machine element, which supports another moving machine element. It permits relative motion between the contact surfaces of the members, while carrying load. Due to relative motion, friction occurs and rubbing surface wears rapidly. To  prevent this a lubricant may be used.
A question comes in mind whether it is possible to support a journal without any physical contact so that there is no wear. Is there a force, which can exerted even if there is no contact between two-surfaces. Magnetic force allows such property and thus the idea of magnetic bearing was visualized.
Already in 1842 Earnshaw had demonstrated that passive (permanent) could made but it cannot stable in all spatial direction. For successful operation the unstable direction have to be electrically served. Hence the name ACTIVE MAGNETIC BEARING.


The active magnetic bearing comprises two parts – the mechanical and electronic. The mechanical parts are similar to electrical motor with a rotor and stator. A core on the stator is wound with the coil through which the electric current that induces the magnetic field. This generates the force that supports the shaft. The electronic part of the active magnetic bearing is the control system. It includes sensors that measure the exact position of the rotor. Even slightest deviation from the desire position will trigger in electronic system to adjust the current flowing through the electromagnets that determines the strength of the magnetic field. The current are adjust so that desired rotor position is maintained even under varying load conditions. The magnetic field is dependant on the current flowing through the coils. The larger the current, the stronger the magnetic field and the load it is able to support. The load an active magnetic bearing is able to support is very high.