Chapter1-DC machine 《Electric Machinery 电机学（英汉双语）》课件.ppt

Chapter 1 DC Machines Brief Content 1.1 Introduction to dc machines 1.2 Armature windings 1.3 Magnetic fields of dc machines 1.4 Induced voltage and electromagnetic torque 1.5 Equivalent circuit of a dc machine 1.6 Power flow and losses in dc machine 1.7 Operation characteristics of dc generator 1.8 Operation characteristics of dc motors 1.9 Speed control of shunt dc motor 1.10 Starting of dc motor 1.11 Braking of dc motor 1.12 Commutation 1.1.1 The Construction of DC Machines Stator and Rotor Air gapwhich is separating stator and rotor Stationary part: Frame, Field Pole and Brushes Rotating part: Armature core，Winding Shaft and Commutator DC Machines The armature winding is placed in the rotor slot and connected to rotating commutator which rectifies the induced voltage The brushes which are connected to the armature winding, ride on commutator 1.1.3 Excitation types of DC Machines Separately excited DC machine Shunt (excited) DC machine Series (excited) DC machine Compounded (excited) DC machine Example 1-1 A dc generator, its rated power PN=10kW, rated voltage UN=230V, rated speed nN=2850r/min, rated efficiency ?N=0.85. Calculate its rated current and its rated input power? Solution: the rated current of the dc generator is IN=PN/UN=10*1000/230=43.48 (A); The rated input power is P1=PN/?N =10*1000/0.85 = 11 765 (W). Example 1-2 A dc motor, its rated power PN=17kW, rated voltage UN=220V, rated speed nN=1500r/min, rated efficiency ?N=0.83. Calculate its rated current and its rated input power? Solution: the rated input power of the dc motor is P1=PN/?N =17*1000/0.83 = 20 482 (W); Its rated current is IN=P1/UN=20 482/220=93.1 (A). 1.2 Armature winding of DC Machines Different connection ways of loops to commutator segments(换向片) affect the number of parallel current paths（并联支路数）, the output voltage（输出电压），the number and position of the brushes（电刷的数目和位置） r