电气工程方面的英汉论文.docx

Electric Devices and SystemsAlthough transformers have no moving parts , they are essential to electromechanical energy conversion . They make it possible to increase or decrease the voltage lever that results in low costs ,and can be distributed and used safely . In addition , they can provide matching of impedances , and regulate the flow of power in a network.When we see a transformer on a utility pole all we is a cylinder with a few wires sticking out. These wires enter the transformer through bushings that provide isolation between the wires and the tank. Inside the tank these is an iron core linking coils, most probably made with copper, and insulated. The system of insulation is also associated with that of cooling the core/coil assembly. Often the insulation is paper, and the whole assembly may be immersed in insulating oil, used to both increase the dielectric strength of the paper and to transfer beat from the core-coil assembly to the outer walls of the tank to air. Figure shows the cutout of a typical distribution transformer. Few ideal versions of human constructions exist, and the transformer offers no exception. An ideal transformer is based on very simple concepts, and a large number of assumptions. This is the transformer one learns about in high school.Let us take an iron core with infinite permeability and two coils wound around it, one with N1 and the other with N2 turns, as shown in figure. All the magnetic flux is to remain in the iron. We assign sots at one terminal of each coil in the following fashion: if the flux in the core changes, inducing a voltage in the coils, and the dotted terminal of one coil is positive with respect its other terminal, so is the dotted terminal of the other coil. Or, the corollary to this, current into dotted terminals produces flux in the same direction,Assume that somehow a time varying flux is established in the iron. Then the flux linkages in each coil will be. Voltages will be induced in these two coil.On the