DCMOTORSintr.doc

DCMOTORSintr.doc - 1 INTRODUCTION TO DC MOTORS 1....

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1 INTRODUCTION TO DC MOTORS 1. Generation of electromotive force and mechanical force Fig.1 illustrates the generation of electromotive force (EMF), i.e. voltage e , and mechanical force F . Symbols: B – magnetic flux density, Φ – magnetic flux, i – current, v - speed (a) (b) N S N Φ l v e (Β) + N S N Φ l F i (Β) Fig.1 Generation of: (a) EMF e ( right hand rule), (b) force F ( left hand rule) Fig.2 shows linear machines where in Fig.2.a is illustrated the generation of EMF e , in Fig. 2.b – generation of mechanical force F , in Fig.2.c – linear generator where the both e and F are produced if the winding circuit consisting of N turns is closed through the load impedance Z l , and in Fig.2.d – linear motor supplied from the battery of voltage V. In case of linear generator the induced voltage E > V, and for linear motor E < V, and the current i is reversed to that in generator. e N l + v Φ - N F Bil =⋅ eB v l E BvlN eN ⋅ =⋅ (a) i N l - + F Φ N (b) FB i lN
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2 (c) - e N + v Φ Z L i F l V EeN EV =⋅ > generator (d) - e N + v Φ i F l V < motor Fig.2 Linear electric machines: (a) generation of voltage e , (b) generation of force F , (c) linear generator, (d) linear motor 2. Linear DC motor with permanent magnets (a) N S F i (b) N S F i commutator brushes Fig.3.(a) Brushes placed directly on the wire, (b) Brushes placed on the commutator
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3 3. Rotating motor Motor with rotating moving part (rotor) (see Fig.4) can be regarded as a transformation of the linear motor. (a) armature winding (rotor) field winding (stator) Φ magnetic flux + Direction of current Direction of torque and speed (b) armature winding (rotor) field winding (stator)
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4 (c) armature winding (rotor) field winding (stator) commutator Fig.4 Rotating DC motor with toroidal rotor: (a) 2-pole motor, (b) 4-pole motor, (c) 4- pole motor with a commutator ( a ) ( b ) + - E E V R a I a L a Fig.5.(a) Armature winding after removing of toroidal core, (b) diagram of the armature circuit
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5 DIRECT CURRENT MACHINES 1. Construction and principle of operation A scheme of a primitive, single coil winding dc machine with two magnetic poles is shown in Fig.1. The stator has salient poles that are excited by field winding supplied by the dc source. The field current I f produces the flux Φ f . The rotor consists of single-turn coil, which is connected to two semicircle copper segments (moveable with the coil), which together with two (stationary) “brushes” constitute the commutator . If the coil rotates the emf is induced in both sides of the coil with the direction that can be determined by the right-hand rule. After one half of turn the direction of the induced voltage in the coil sides changes, but due to the commutator the polarity of the voltage across the brushes remains unchanged. V Φ commutator armature winding field winding + - ω e,i e,i R L + - V f I f I a d q Fig.1 A scheme of the single-turn dc generator The flux distribution in the air gap is symmetrical about the pole axis called direct axis or d-axis (Fig.2). The brushes are placed along quadrature (or q ) axis , perpendicular to the d-axis . The voltage induced in the coil changes with respect to
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This note was uploaded on 02/06/2012 for the course EE 4002 taught by Professor Scalzo during the Fall '06 term at LSU.

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DCMOTORSintr.doc - 1 INTRODUCTION TO DC MOTORS 1....

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