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Introduction to DC Machines

Introduction to DC Machines. Advantages Adjustable speed Develop rated torque at all speeds Higher torque than an equivalent AC machine Uses Robots Automotive Railroads. Elementary 2-pole DC motor. Poles created by DC current in the field winding or by a permanent magnet.

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Introduction to DC Machines

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  1. Introduction to DC Machines • Advantages • Adjustable speed • Develop rated torque at all speeds • Higher torque than an equivalent AC machine • Uses • Robots • Automotive • Railroads ECE 441

  2. Elementary 2-pole DC motor Poles created by DC current in the field winding or by a permanent magnet ECE 441

  3. Flux through the “window” of a 1-turn armature coil as a function of position ECE 441

  4. Voltage induced in the armature coil ECE 441

  5. Flux Distribution and Induced Voltage The induced voltage is AC ECE 441

  6. ECE 441

  7. Average Value of one-half cycle ECE 441

  8. Rectify the other half-cycle Ea ECE 441

  9. Express in r/min ECE 441

  10. ECE 441

  11. Commutation / Mechanical Rectification • “Neutral” position • Coil shorted by the brushes • No armature voltage generated – coil sides not cutting any flux • No current ECE 441

  12. Commutation (continued) • Brushes contact the armature conductor • CCW rotation • Coils sides cut flux • Current in A as shown • Current in B as shown ECE 441

  13. Commutation (continued) • “Neutral” position • As before, coil shorted by the brushes • No armature voltage generated – coil sides not cutting any flux • No current ECE 441

  14. Commutation (continued) • Brushes contact the armature conductor • CCW rotation • Coils sides cut flux • Current in B as shown • Current in A as shown • Currents are in the same direction as before! ECE 441

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