自动化专业英语2.pptVIP

第4段 The conductors placed in the slots of the stator or rotor are interconnected to form windings. The winding in which voltage is induced is called the armature winding. The winding through which a current is passed to produce the primary source of flux in the machine is called the field winding. Permanent magnets are used in some machines to provide the major source of flux in the machine. 第5段 The voltage induced in the terms of the armature winding is alternating. A commutator-brush combination is used as a mechanical rectifier to make the armature terminal voltage unidirectional and also to make the m.m.f. wave due to the armature current fixed in space. The brushed are so placed that when the sides of an armature turn(or coil) pass through the middle of the region between field poles, the current though it changes direction. This makes all the conductors under one pole carry current in one direction. As a consequence, the m.m.f. due to the armature current is along the axis midway between the two adjacent poles, called the quadrature axis. 第6段 The field circuit and the armature circuit can be interconnected in various ways to provide a wide variety of performance characteristics – an outstanding advantage of DC machines. In addition, the field poles can be excited by two field windings, a shunt field winding and a series field winding. The shunt winding has a large number of turns and takes only s small current (less than 5% of the rated armature current). This winding can be connected across the armature (i.e., parallel with it), hence the name shunt winding. The series winding has fewer turns but carries a large current. It is connected in series with the armature, hence the name series winding. If both shunt and series winding are present, the series winding is wound on top of the shunt winding. 第7段 The varies connections of the field circuit and armature circuit are shown in Fig. 2. In the separately excited dc machine (Fig.2a), the field winding is