L-38(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 38 D.C Generators Version 2 EE IIT, Kharagpur
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Contents 38 D.C Generators (Lesson-38) 4 38.1 Goals of the lesson ………………………………………………………………. . 4 38.2 Generator types & characteristics. ………………………………………………. .. 4 38.2.1 Characteristics of a separately excited generator. ……………………… 5 38.2.2 Characteristics of a shunt generator. …………………………………… 7 38.2.3 Load characteristic of shunt generator. ………………………………… 10 38.2.4 Prediction of approximate load characteristic from OCC & R f line. …… 10 38.3 Compound generator ……………………………………………………………. .. 12 38.4 Tick the correct answer …………………………………………………………… 14 38.5 Solve the following ……………………………………………………………… 15 Version 2 EE IIT, Kharagpur
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38.1 Goals of the lesson Students are expected to learn about the classification of d.c generators and their characteristics in this lesson. After going through this lesson they will be able to: 1. differentiate different types of d.c generators along with their schematic representations. 2. identify, looking at the circuit diagram of a given generator, the types of the generator i.e., whether the generator is shunt, separately excited or compound generator. 3. sketch the important characteristics (no load and load characteristics) of different types of generators. 4. identify various factors responsible for internal voltage drop. 5. understand the conditions to be fulfilled so as to build up voltage in a shunt generator. 6. predict the load characteristic of a shunt generator from its open circuit characteristic. 7. locate the shunt and series field coils in the machine and comment on their relative number of turns and cross sectional areas. 38.2 Generator types & Characteristics D.C generators may be classified as (i) separately excited generator, (ii) shunt generator, and (iii) series generator and (iv) compound generator. In a separately excited generator field winding is energised from a separate voltage source in order to produce flux in the machine. So long the machine operates in unsaturated condition the flux produced will be proportional to the field current. In order to implement shunt connection, the field winding is connected in parallel with the armature. It will be shown that subject to fulfillment of certain conditions, the machine may have sufficient field current developed on its own by virtue of its shunt connection. In series d.c machine, there is one field winding wound over the main poles with fewer turns and large cross sectional area. Series winding is meant to be connected in series with the armature and naturally to be designed for rated armature current. Obviously there will be practically no voltage or very small voltage due to residual field under no load condition ( I a = 0).
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This note was uploaded on 08/03/2010 for the course ELECTRICAL EE212 taught by Professor Shetty during the Spring '10 term at International Institute of Information Technology.

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L-38(TB)(ET) ((EE)NPTEL) - Module 9 DC Machines Version 2...

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