L-36(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 36 Principle of Operation of D.C Machines Version 2 EE IIT, Kharagpur
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Contents 36 Principle of operation of D.C machines (Lesson-36) 4 36.1 Introduction …………………………………………………………. ................ 4 36.2 Example of Single conductor Generator & Motor ……………………………. . 4 36.3 Rotating Machines ……………………………………………………………. .. 9 36.3.1 Driving & Opposing torques ………………………………………… 10 36.3.2 Generator mode ……………………………………………………… 10 36.3.3 Motor mode …………………………………………………………. . 11 36.4 Condition for steady production of torque ……………………………………. . 11 36.5 D.C generator: Basic principle of operation …………………………………… 13 36.6 D.C motor: Basic principle of operation ………………………………………. 13 36.7 Answer the following …………………………………………………………. . 14 Version 2 EE IIT, Kharagpur
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36.1 Introduction In the first section of the lesson we consider an example using a single conductor to behave as a generator or as a motor. Although the motion of the conductor is rectilinear, the example brings out several useful facts which are true for rotating machines as well. The following sections begin by giving some important information which are true for all most all kinds of rotating electrical machines. It is first explained that two torques namely the driving torque and the load torque will exist during the operation of the machine both as generator and motor. After going through the lesson one will understand: 1. the meaning of loading of generator and motor. 2. that motoring & generating actions go side by side. 3. the dynamics involved while the operating point moves from one steady state condition to another. 36.2 Example of Single conductor Generator & Motor 1. Generator Mode: Consider a straight conductor of active length (the length which is under the influence of the magnetic field) l meter is placed over two friction less parallel rails as shown in the figure 36.1. The conductor is moving with a constant velocity v meter/second from left to right in the horizontal plane. In the presence of a vertical magnetic field directed from top to bottom of strength B Wb / m 2 , a voltage e = Blv will be induced across the ends of the moving conductor. The magnitude of the voltage will be constant and the polarity will be as shown in the figure 36.2. In other words the moving conductor has become a seat of emf and one can replace it by battery symbol with an emf value equal to Blv Volts. At no load i.e., (resistance in this case) is connected across the moving conductor, output current hence output power is zero. Input power to the generator should also be zero which can also be substantiated by the fact that no external force is necessary to move a mass with constant velocity over a frictionless surface. The generator is said to be under no load
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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-36(TB)(ET) ((EE)NPTEL) - Module 9 DC Machines Version 2...

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