Ebook Electric machinery fundamentals (5th edition): Part 2
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Ebook Electric machinery fundamentals (5th edition): Part 2
CHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2co a constant flux, and thus more constant output voltages.•Understand and be able to use the equation for induced voltage and torque in a de machine.•Understand commutation.•Understand problems with commutation, including armature reaction and effects.•Understand the power flow diagram for de machi Ebook Electric machinery fundamentals (5th edition): Part 2nes.DC machines are generators that convert mechanical energy to de electric energy and motors that convert de electric energy to mechanical energy. MEbook Electric machinery fundamentals (5th edition): Part 2
ost de machines are like ac machines in that they have ac voltages and currents within them—de machines have a de output only because a mechanism exisCHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2s commutating machinery.The fundamental principles involved in the operation of de machines are very simple. Unfortunately, they are usually somewhat obscured by the complicated construction of real machines. This chapter will first explain the principles of de machine operation by using simple exam Ebook Electric machinery fundamentals (5th edition): Part 2ples and then consider some of the complications that occur in real de machines.7.1 A SIMPLE ROTATING LOOP BETWEENCURVED POLE FACESThe linear machineEbook Electric machinery fundamentals (5th edition): Part 2
studied in Section 1.8 served as an introduction to basic machine behavior. Its response to loading and to changing magnetic fields closely 404DC MACHCHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2n a straight line— they rotate. The next step toward understanding real de machines is to study the simplest possible example of a rotating machine.The simplest possible rotating de machine is shown in Figure 7-1. It consists of a single loop of wire rotating about a fixed axis The rotating part of Ebook Electric machinery fundamentals (5th edition): Part 2this machine is called the rotor, and the stationary part is called the stator. The magnetic field for the machine is supplied by the magnetic north aEbook Electric machinery fundamentals (5th edition): Part 2
nd south poles shown on the stator in Figure 7-1.Notice (hat the loop of rotor wire lies in a slot carved in a ferromagnetic core. The iron rotor, togCHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2ance of ail is much higher than the reluctance of the iron in the machine. To minimize the reluctance of the flux path through the machine, the magnetic flux must take the shortest possible path through the air between the pole face and the rotor surface.Since the magnetic flux must take (he shortes Ebook Electric machinery fundamentals (5th edition): Part 2t path through the air, it is perpendicular to the rotor surface everywhere under die pole faces. Also, since the ah gap is of uniform width, the reluEbook Electric machinery fundamentals (5th edition): Part 2
ctance is the same everywhere under the pole faces. The uniform reluctance means that rhe magnetic flux density is constant everywhere under the pole CHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2itude and shape of the voltage, examine Figure 7-2. The loop of wire shown is rectangular, with Sides ab and cd perpendicular to the plane of the page and with sides be and da parallel to the plane of the page. The magnetic field is constant and perpendicular to rhe surface of the rotor everywhere u Ebook Electric machinery fundamentals (5th edition): Part 2nder the pole faces and rapidly falls to zero beyond die edges of rhe poles.To determine the total voltage £l01 on the loop, examine each segment of tEbook Electric machinery fundamentals (5th edition): Part 2
he loop separately and sum all the resulting voltages. The voltage on each segment is given by Equation (1—45):^ = (VXB)H(1-45)1Segment ab. In this seCHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute c Ebook Electric machinery fundamentals (5th edition): Part 2nder the pole face and is zero beyond the edges of the pole face. Under the pole face, velocity V is perpendicular to B. and (he quantity V X B points into the page. Therefore, the induced voltage on the segment ISCb" = (V X B) • 1vBl positive into page under the pole face0beyond the pole edges (7-1 Ebook Electric machinery fundamentals (5th edition): Part 2)(đ)FIGURE 7-1A simple rotating loop between curved pole faces, (a) Perspective view; (b) view of field lines; (c) lop view; (d) front view.UL MALHINbEbook Electric machinery fundamentals (5th edition): Part 2
KY l-uFIGURE 7-2Derivation of an equation for fhe voltages induced in the loop.2Segment be. In this segment, the quantity V X B is either into or our CHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute cCHAPTERDC MACHINERYFUNDAMENTALSLEARNING OBJECTIVES•Understand how voltage is induced in a rotating loop.•Understand how curved pole faces contribute cGọi ngay
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