Transcript Chapter 7
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint Slides to accompany Electric Machinery Sixth Edition A.E. Fitzgerald Charles Kingsley, Jr. Stephen D. Umans Chapter 7 DC Machines 7-0 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION 7-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION 7-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION 7-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Tmech Ka d ia Constant determined by the design of windings 7-4 Current in external armature circuit Direct axis air-gap flux per pole Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Rectified coil voltages and resultant voltage between brushes in a dc machine. ea Ka d m Speed voltage 7-5 Angular speed ea ia Tmech m Power Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Typical form of magnetization curves of a dc machine. ea m 7-6 Kad ea 0 m 0 m ea 0 ea m 0 n ea ea 0 n0 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Equivalent Circuit (Not in the textbook): ia Lf if Rf Ra La ea For steady-state, current is dc, therefore Lf and La can be neglected. 7-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Field-circuit connections of dc machines: (a) separate excitation, (b) series, (c) shunt, (d) compound. 7-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Volt-ampere characteristics of dc generators. 7-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7.1 INTRODUCTION Speed-torque characteristics of dc motors. 7-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. EXAMPLE (Final Exam 2006) : Assume that a 240 V self-excited shunt motor is supplied by a line current of 102.4 A when it is loaded with a full load at a speed of 1000 rpm. The armature-circuit resistance and the shunt-field circuit resistance of the motor are 0.1 ohm and 100 ohm, respectively. Assume that a breaking resistor of 1.05 ohm is used for dynamic braking (breaking means that voltage source is removed and immediately a resistor is connected to the terminals of the DC machine) and determine the following. a)The value of counter emf Ea. b)The full-load torque of the motor c)The value of the armature winding current at the time of initial breaking. d)The value of initial dynamic breaking (initial torque during breaking) 7-11 Ra Rf Ea Vt Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The End of This Chapter 7-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dc machine armature winding with commutator and brushes. (a), (b) Current directions for two positions of the armature. Figure 7.7 7-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Waveform of current in an armature coil with linear commutation. Figure 7.8 7-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Armature-mmf and flux-density distribution with brushes on neutral and only the armature excited. Figure 7.9 7-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Flux with only the armature excited and brushes on neutral. Figure 7.10 7-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Armature, main-field, and resultant flux-density distributions with brushes on neutral. Figure 7.11 7-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Motor or generator connection diagram with current directions. Figure 7.12 7-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Short-shunt compound-generator connections. Figure 7.13 7-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Magnetization curves for a 250-V 1200-r/min dc machine. Also shown are fieldresistance lines for the discussion of self-excitation in Section 7.6.1. Figure 7.14 7-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Equivalent circuit for analysis of voltage buildup in a self-excited dc generator. Figure 7.15 7-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cross section of a typical permanent-magnet motor. Arrows indicate the direction of magnetization in the permanent magnets. Figure 7.17 7-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (a) Dimension definitions for the motor of Fig. 7.17. (b) approximate magnetic equivalent circuit. Figure 7.18 7-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Equivalent circuit of a permanent-magnet dc motor. Figure 7.20 7-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Section of dc machine showing compensating winding. Figure 7.22 7-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Schematic connection diagram of a dc machine. Figure 7.24 7-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Series-connected universal machine. Figure 7.25 7-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Typical torque-speed characteristics of a series universal motor. Figure 7.26 7-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1200 r/min magnetization curve for the dc generator of Problem 7.4. Figure 7.27 7-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Series crane motor (Problem 7.22): (a) hoisting connection and (b) lowering connection. Figure 7.28 7-30