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Equation involved

Learn about the equations involved in DC motors and how speed control is manipulated. Explore factors influencing EA and τind, terminal characteristics, speed regulations, and applications of DC motors.

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Equation involved

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  1. Equation involved Manipulated (explained in pg 446-447)

  2. EA depends on 3 factors: • Flux in the machine, ϕ • Speed of the machine’s rotor, ωm • Constant depending on the construction of the machine

  3. τind depends on 3 factors: • Flux in the machine, ϕ • The armature current, IA in the machine • Constant depending on the construction of the machine

  4. DC Motor • Will be given in class

  5. AND SHUNT MOTOR SEPARATELY EXCITED Note: When the V = constant, there is no practical difference in behavior between separately excited and shunt motor.

  6. Terminal Characteristics

  7. T– IA Characteristics

  8. ωm- τind Characteristics

  9. Speed control of Shunt Motor • Adjusting the field resistance ,Rf (to control ϕ) • Adjusting the terminal voltage, VT applied to the armature • Inserting a resistor in series with the armature circuit

  10. SERIES MOTOR

  11. Terminal characteristics

  12. τ–I characteristics

  13. τ- ω characteristics

  14. Speed control of Series Motor • . • . • .

  15. COMPOUNDED MOTOR

  16. Terminal characteristics

  17. τ– I characteristics

  18. Speed control of compound motor • Change the field resistance, Rf • Change the armature resistance, Ra • Change the armature voltage, VA

  19. DC MOTOR STARTER • When motor is at rest, there is not yet a back e.m.f. • When the full supply voltage is applied, then the starting current is very high because the armature resistance, RA is very small. • This excessive starting current will blow out fuses and may damage the brushes too. • To avoid this starting current, a resistance is inserted in series with the armature and is gradually cut out as the motor gains speed and develops the back e.m.f which then regulates in speed.

  20. Speed Regulations • DC motors are often compared by their speed regulations. • Speed Regulations (SR) of the a motor is defined by or

  21. Efficiency of motor To calculate the efficiency of a dc motor, the following losses must be determined: • Copper losses • Brush drop losses • Mechanical losses • Core losses • Stray losses

  22. Application of DC motors

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