A Study On Electric Machines Engineering Essay

A Study On Electric Machines engineering EssayThe classical set of machines represents the a concurrent induction, simultaneous, DC machines, and variable reluctance machines. Among these classical machines, the asynchronous machine is most widely used in a large range of applications and is able to operate as a motor (converting galvanizing power into mechanical power) or as a generator (converting mechanical power into galvanizing power). The machine can be fed via a power electronic converter or committed directly to an AC or DC supply. Electric machines are majorly base on 4 principles. The first principle is that an galvanizing current cook a magnetized field around it that can be reinforced by more than a thousand times when go across by dint of iron out.The second principle is called motor action and is defined by a force perpendicular to both the direction of the electrical current and the charismatic field. This induced force is given byF= i (L)B charismatic flu x densityL= length of cablei= order of current in the wireThe third principle is that an electrical conductor moving in a charismatic field has an electrical current induced in it creating an electromotive force. The induced electromotive force is expressed by the meeting formula?ind= (v) Lv velocity of the wireL length of conductor in the magnetic fieldB magnetic flux densityThe fourth principle is that a change in the magnetic field in a tour can designer an induced potentiality to this circuit. This effect is based on the Faradays law that states that when a flux passes through a turn of coil, a voltage proportionate to the rate of change of the flux will be induced.?ind = N mo of turns of wire in coils?ind voltage inducedF flux passing in the coil(http//mysite.du.edu/jcalvert/tech/elmotors.htm)An electric machine has two intrinsic electrical voices The stator and the rotor coil coil. The stator (derived from the word stationary) is the stationary part of the machine f orming a hollow cylinder consisting of individual electro-magnets shaped towards the middle. The rotor (derived from the word rotating) is located inside the stator and consists of a group of electro-magnet staged around a cylinder, mounted on the motors shaft with its poles facing toward the stator poles. The rotor is the rotating component of the machine.(http//www.reliance.com/mtr/mtrthrmn.htm)(http//www.reliance.com/mtr/mtrthrmn.htm)In general, when the change of flux is associated with mechanical motion, it is the plate of electromagnetic energy conversion. Regarding the revolution machines, the voltage is generated in groups of coils, often called pulls, by three different ways. The first technique is by mechanical rotation of the windings through a magnetic field, the second is mechanical rotation of the magnetic field past the winding, and third by the design of the magnetic circuit so that the reluctance varies with the rotation of the rotor. So these methods generate a time-varying voltage caused by the cyclic charge of the flux linking a specific coil. The armature winding of a machine is a combination of such coils interconnected so that their generated voltage is close to the desired. In a DC machine, the armature is the rotating member or rotor. As for the AC machine, the armature is the stationary member or stator.The coils pointed out antecedently are wound on iron cores in order to maximise the coupling between the coils, to increase the magnetic energy density associated with electromechanical interaction, and to shape and distribute the magnetic fields according to the requirements of each incident machine design. Eddy currents will be induced in the armature iron since it is subjected to a time varying magnetic flux. To minimize this eddy-current loss, thin laminations for the armature of AC machines construct the armature iron. The magnetic circuit is completed through the iron of the former(a) machine member, and excitation coils, or field windings, may be set(p) on that member to act as the primary source of flux. perm magnets may be used in small machines, and developments in permanent magnet technology are resulting in their use in bigger machines. In variable reluctance machines, there are no windings on the rotor, and the operation depends on the non uniformity of air-gap reluctance associated with variations in rotor position.(electric machinery fifth part edition (LIBRARY))AC electric machinesAC machines are motors converting AC electrical energy to mechanical energy and generators that convert mechanical to AC electrical energy. AC electric machines are divided into two types Asynchronous (induction) and synchronous machines. The difference between these two types is that induction machines pretend their field currents supplied by magnetic induction while the field current in synchronous ones are supplied by a separate DC source.(Electric machinery fundamentals).The principle of rotating magnetic fie lds is the main rule of the operation to most ac motors. The magnetic field created by the poles will make the rotor rotate reservation the stator poles progressively change. This change will make the rotor follow and rotate with the magnetic field of the stator. As each change is made, the poles of the rotor are attracted by the opposite poles on the stator, forcing the rotor to rotate with the stator field.(http//www.reliance.com/mtr/mtrthrmn.htm)The rotor is rotating within the stator at angular velocity ?n, the magnitude of the flux density vector B at any weight down a around the stator is given by B= BM cos(?t-a). Then the voltage induced in the stator that has N turns of wire is expressed by eind= NF?cos(?t).The voltage induced is sinusoidal with amplitude depending on the flux, angular velocity and a constant depending on the construction of the machine.In a three phase set of coils, the voltages induced will have same magnitude but they are shifted by 120 degrees.eaa(t)= NF? sin(?t)ebb(t)= NF? sin(?t-120)ecc(t)= NF? sin(?t-240)The rms voltage of each phase is EA= pNFf