Generators are generally classified according to their methods of field excitation. Armature Windings In the design of d. In this chapter, we shall discuss the various aspects of armature reaction and commutation in a d. As we shall see, the weakening of flux due to armature reaction depends upon the position of brushes. Therefore, there are two parallel paths for the current as long as the short circuit exists. The result is that armature m.
The action of armature flux on the main flux is known as armature reaction. It is clear that armature flux is directed downward parallel to the brush axis. It may be noted here that in the conventional way of representing a developed armature winding, full lines represent top coil sides i. Along with hard work include smart work for your goal. A simplex wave-wound armature has two parallel paths irrespective of the number of poles. Electronics differs vastly from electrical and electro-mechanical science, and it is one of the fasted growing technological fields. Thus if the coil span is 9 slots, it means one side of the coil is in slot 1 and the other side in slot 10.
With no current in the armature conductors, the M. K Mehta, Rohit Mehta Book Principle of Electrical Machines By V. The reader may see the action of the commutator in reversing the current in a coil as the coil passes the brush axis. Thus laminating a core increases the core resistance which decreases the eddy current and hence the eddy current loss. E generated under load conditions will be less than the e. The equivalent electric circuit is shown in Fig. The compound generator can be cumulatively compounded or differentially compounded generator.
If an armature is changed from simplex lap to duplex lap without making any other change, the number of parallel paths is doubled and each path has half as many coils. The air gap reluctance is constant and hence linear relationship. If you have any other trouble downloading electrical machines by vk mehta rohit mehta post it in comments and our support team or a community member will help you! The coil sides at the top of slots are given odd numbers and those at the bottom are given even numbers. This is an easiest way to send files to someone who cannot accept them live. Here we are given O.
The sparks may bum the brushes and overheat and carbonise the commutator. Mechanical losses These losses are due to friction and windage. He was a merit scholar all through his academic and engineering career. On the other hand, the distorting component of armature reaction distorts the main flux. In next page click regular or free download and wait certain amount of time usually around 30 seconds until download button will appead. Note that current in coil A is 10 A but in the reverse direction to that before the start of commutation. As we go round the commutator, the successive brushes have positive and negative polarities.
The coil side 12 at the bottom of a slot is joined to coil side 3 at the top of another slot. This is what a commutator does. When one tour of armature has been completed, the winding should connect to the next top conductor progressive or to the preceding top conductor retrogressive. It may be noted that with the increase of armature current, both demagnetizing and distorting effects will increase. This loss is generally included in armature copper loss. The chapters in the book are designed as in-depth studies of the core concepts, and clearly elucidate the fundamental principles, methods, and circuits involved in electronics.
When the current in the coil undergoing commutation changes, self-induced e. Generator Characteristics Introduction The speed of a d. The interpoles perform the following two functions: i As their polarity is the same as the main pole ahead for a generator , they induce an e. This distortion and field weakening takes place in both generators and motors. Consequently, the external characteristic turns back dotted curve as shown in Fig. The insulating coating has a high resistance, so very little current flows from one lamination to the other. When a conductor passes a pair of poles, one cycle of voltage is generated.
It distorts the main field. Electrical technology, as a subject, covers various divisions of electrical engineering like basic electrical engineering, electronics, control systems, instrumentation and communication systems. The voltage build up graph will be similar to that of shunt generator except that now load current instead of field current for shunt generator will be taken along x-axis. If a continuous solid iron core is used, the resistance to eddy current path will be small due to large cross-sectional area of the core. It is because the voltage appearing across the brushes varies from zero to maximum value and back to zero twice for each revolution of the loop. It may be noted that the main cause of sparking during commutation is the production of reactance voltage and carbon brushes cannot prevent it.
It consists of slotted soft-iron laminations about 0. The winding goes from commutator segment 1 by conductor 1 across the back to conductor 12 and at the front to commutator segment 2, thus forming a coil. These changes occur in every coil in turn. Iron or Core losses These losses occur in the armature of a d. Therefore, the resultant pitch is the algebraic sum of the back and front pitches. A compensating winding is an auxiliary winding embedded in slots in the pole faces as shown in Fig.