L-35(TB)(ET) ((EE)NPTEL) - Module 9 DC Machines Version 2...

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Module 9 DC Machines Version 2 EE IIT, Kharagpur
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Lesson 35 Constructional Features of D.C Machines Version 2 EE IIT, Kharagpur
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Contents 35 D.C Machines (Lesson-35) 4 35.1 Goals of the lesson ………………………………………………………………. 4 35.2 Introduction ……………………………………………………………………… 4 35.3 Constructional Features …………………………………………………………. 4 35.4 D.C machine Armature Winding ………………………………………………. 11 35.4.1 Armature winding: General procedure ………………………………. 12 35.4.2 Developed diagram ……………………………………………………. . 13 35.5 Lap winding ……………………………………………………………………… 13 35.5.1 Another example of Lap winding ……………………………………. . 17 35.6 Wave winding …………………………………………………………………… 18 35.6.1 An example ……………………………………………………………. 20 35.7 Answer the following ……………………………………………………………. 23 Version 2 EE IIT, Kharagpur
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35.1 Goals of the lesson In this lesson, important constructional features of a D.C machine are presented along with a discussion on D.C armature winding. Key Words : Field winding, armature winding, commutator segments & brush arrangement. After going through this section students will have clear ideas about the followings: The function of commutator & brush in a D.C Machine. Double layer winding. Coil span & commutator pitch. Lap & wave winding and number of armature parallel paths. 35.2 Introduction As pointed out earlier, D.C machines were first developed and used extensively in spite of its complexities in the construction. The generated voltage in a coil when rotated relative to a magnetic field, is inherently alternating in nature. To convert this A.C voltage into a D.C voltage we therefore need a unit after the coil terminals. This unit comprises of a number commutator segments attached to the shaft of the rotor and a pair of suitably placed stationary carbon brushes touching the commutator segments. Commutator segments together with the fixed brushes do the necessary rectification from A.C to D.C and hence sometimes called mechanical rectifier. 35.3 Constructional Features Figure 35.1 shows a sectional view of a 4-pole D.C machine. The length of the machine is perpendicular to the paper. Stator has got 4 numbers of projected poles with coils wound over it. These coils may be connected in series in order that consecutive poles produce opposite polarities (i.e., N-S-N-S) when excited from a source. Double layer lap or wave windings are generally used for armature. Essentially all the armature coils are connected in series forming a closed armature circuit. However as the coils are distributed, the resultant voltage acting in the closed path is zero thereby ensuring no circulating current in the armature.
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L-35(TB)(ET) ((EE)NPTEL) - Module 9 DC Machines Version 2...

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