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Chapter: Electrical machines - Electromechanical Energy Conversion and Concepts in Rotating Machines

Energy In Magnetic Systems

1. Electromechanical-Energy-Conversion Principles 2. Forces and Torques in Magnetic Field Systems

Energy In Magnetic Systems


It is often necessary in today's computer controlled industrial setting to convert an electrical signal into a mechanical action. To accomplish this, the energy in the electrical signal must be converted to mechanical energy. A variety of devices exist that can convert electrical energy into mechanical energy using a magnetic field. One such device, often referred to as a reluctance machine, produces a translational force whenever the electrical signal is applied. There are several variations of the reluctance machine but all operate on the same basic electromechanical principles.


The principles of electromechanical energy conversion are investigated. The motivation for this investigation is to show how the governing equations of an electromechanical device can be derived from a magnetic circuit analysis. An expression for the mechanical force will be derived in terms of the magnetic system parameters.


1. Electromechanical-Energy-Conversion Principles


The electromechanical-energy-conversion process takes place through the medium of the electric or magnetic field of the conversion device of which the structures depend on their respective functions.


Transducers: microphone, pickup, sensor, loudspeaker

Force producing devices: solenoid, relay, electromagnet

Continuous energy conversion equipment: motor, generator


This chapter is devoted to the principles of electromechanical energy conversion and the analysis of the devices accomplishing this function. Emphasis is placed on the analysis of systems that use magnetic fields as the conversion medium.The concepts and techniques can be applied to a wide range of engineering situations involving electromechanical energy conversion.Based on the energy method, we are to develop expressions for forces and torques in magnetic-field-based electromechanical systems.


2. Forces and Torques in Magnetic Field Systems


The Lorentz Force Law gives the force on a particle of charge in the presence of electric and magnetic fields.


F: newtons, : coulombs, : volts/meter, qEB: telsas, : meters/second

In a pure electric-field system, F=qE


In pure magnetic-field systems, F=q*(v*B)

For situations where large numbers of charged particles are in motion F=J*V most electromechanical-energy-conversion devices contain magnetic material.


Forces act directly on the magnetic material of these devices which are constructed of rigid, nondeforming structures. The performance of these devices is typically determined by the net force, or torque, acting on the moving component. It is rarely necessary to calculate the details of the internal force distribution. Just as a compass needle tries to align with the earth’s magnetic field, the two sets of fields associated with the rotor and the stator of rotating machinery attempt to align, and torque is associated with their displacement from alignment. In a motor, the stator magnetic field rotates ahead of that of the rotor, pulling on it and performing work.For a generator, the rotor does the work on the stator.

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