电气毕业设计用外文翻译(中英文对照)--负载运行的变压器及直流电机导论(编辑修改稿)

电气毕业设计用外文翻译(中英文对照)--负载运行的变压器及直流电机导论(编辑修改稿)内容摘要：

wn.. (The geometrical position of the brushes in an actual machine is approximately 90 electrical degrees from their position in the schematic diagram because of the shape of the end connections to the mutator.) The magic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distribution。 for convenience we shall continue to assume a sinusoidal fluxdensity wave in the air gap. The torque can then be found from the magic field viewpoint. The torque can be expressed in terms of the interaction of the directaxis airgap flux per pole d and the spacefundamental ponent 1aF of the armature . wave . With the brushes in the quadrature axis, the angle between these fields is 90 electrical degrees, and its sine equals unity. For a P pole machine 12)2(2 ad FPT  In which the minus sign has been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental 1aF of the sawtooth armature . wave is 8/ 2 times its peak. Substitution in above equation then gives adaada iKimPCT   2 Where ai =current in external armature circuit。 aC =total number of conductors in armature winding。 m =number of parallel paths through winding。 And mPCK aa 2 Is a constant fixed by the design of the winding. The rectified voltage generated in the armature has already been discussed before for an elementary singlecoil armature. The effect of distributing the winding in several slots is shown in figure ,in which each of the rectified sine waves is the voltage generated in one of the coils, mutation taking place at the moment when the coil sides are in the neutral zone. The generated voltage as observed from the brushes is the sum of the rectified voltages of all the coils in series between brushes and is shown by the rippling line labeled ae in figure. With a dozen or so mutator segments per pole, the ripple bees very small and the average generated voltage observed from the brushes equals the sum of the average values of the rectified coil voltages. The rectified voltage ae between brushes, known also as the speed voltage, is mdamdaa WKWmPCe   2 Where aK is the design constant. The rectified voltage of a distributed winding has the same average value as that of a concentrated coil. The difference is that the ripple is greatly reduced. From the above equations, with all variable expressed in SI units: maa Twie  This equation simply says that the instantaneous electric power associated with the speed voltage equals the instantaneous mechanical power associated with the magic torque , the direction of power flow being determined by whether the machine is acting as a motor or generator. The directaxis airgap flux is produced by the bined . ffiN of the field windings, the . characteristic being the magization curve for the particular iron geometry of the machine. In the magization curve, it is assumed that the armature . wave is perpendicular to the field axis. It will be necessary to reexamine this assumption later in this chapter, where the effects of saturation are investigated more thoroughly. Because the armature . is proportional to flux times speed, it is usually more convenient to express the magization curve in terms of the armature . 0ae at a constant speed 0mw . The voltage ae for a given flux at any other speed mw is proportional to the speed,. 00 amma ewwe  Figure shows the magization curve with only one field winding excited. This curve can easily be obtained by test methods, no knowledge of any design details being required. Over a fairly wide range of excitation the reluctance of the iron is negligible pared with that of the air gap. In this region the flux is linearly proportional to the total . of the field windings, the constant of proportionality being the directaxis airgap permeance. The outstanding advantages of DC machines arise from the wide variety of operating characteristics which can be obtained by selection of the method of excitation of the field windings. The field windings may be separately excited from an external DC source, or they may be selfexcited。 ., the machine may supply its own excitation. The method of excitation profoundly influences not only the steadystate characteristics, but also the dynamic behavior of the machine in control systems. The connection diagram of a separately excited generator is given. The required field current is a very small fraction of the rated armature current. A small amount of power in the field circuit may control a relatively large amount of power in the armature circuit。 ., the generator is a power amplifier. Separately excited generators are often used in feedback control systems when control of the armature voltage over a wide range is required. The field windings of selfexcited generators may be supplied in three different ways. The field may be connected in series with the armature, resulting in a shunt generator, or the field may be in two sections, one of which is connected in series and the other in shunt with the armature, resulting in a pound generator. With selfexcited generators residual magism must be present in the machine iron to get the selfexcitation process started. In the typical steadystate voltampere characteristics, constantspeed prime movers being assumed. The relation between the steadystate generated . aE and the terminal voltage tV is aaat RIEV  Where aI is the armature current output and aR is the armature circuit resistance. In a generator, aE is large than tV。 and the electromagic torque T is a countertorque opposing rotation. The terminal voltage of a separatel。