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9. Braking of dc Motors

9. Braking of dc Motors. Regenerative. F. m. F. m. Speed. w. w. 3. F. 2. 1. F. l. F. F. l. mg. mg. T(. T(downhill). Torque. Speed. 1. T(uphill). Torque. Review of Basic Equations. Example.

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9. Braking of dc Motors

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  1. 9. Braking of dc Motors

  2. Regenerative

  3. F m F m Speed w w 3 F 2 1 F l F F l mg mg T( T(downhill) Torque Speed 1 T(uphill) Torque

  4. Review of Basic Equations

  5. Example • A 440 V dc motor has a rated armature current of 76 A at a speed of 1000 rev/min. The armature resistance of the motor is 0.377 W, and the rotational losses is 1 kW. The load of the motor is bi-directional.

  6. a. Calculate the no load speed of the motor. b. If the armature current is 60 A during a regenerative braking, calculate the motor speed c. Calculate the load torque during regenerative braking d. Calculate the speed during regenerative braking e. Calculate the power delivered by the source under normal motor operation. f. Calculate the generated power during regenerative braking.

  7. Solution

  8. Speed V 1 w 2 o1 3 1 V 2 w o3 4 Torque T 1 Regenerative Braking during Speed Reduction

  9. Dynamic Braking

  10. Ra Ib Rb Vf If Ea w

  11. R b2 R R b3 b1 B I I I b1 b2 b3 Speed A I a Current

  12. Dynamic Braking of Unidirectional Load

  13. Constant Torque

  14. Example • A 440 V dc Separately Excited motor has a rated armature current of 76 A at a speed of 1000 rev/min. The armature resistance of the motor is 0.377. Assume that the load torque is gravitational. A dynamic braking technique employing a braking resistance of 2  is used. Calculate the new steady state speed.

  15. Solution Compute

  16. Solution

  17. Counter Current Braking

  18. Counter Current Braking • Plugging • Terminal voltage reversl

  19. Counter Current Braking: Plugging

  20. Speed V 1 w 2 o1 3 1 V 4 2 Torque w T o3 sc 5 T 1

  21. Speed V 1 w 2 o1 3 1 V 4 2 Torque w T o3 sc 5 T 1

  22. Counter Current Braking: Terminal Voltage Reversal (TVR)

  23. Speed 2 1 Torque 3 Current (I) 4 T l T l

  24. Speed 2 1 Torque 3 Current (I) 4 T l T l

  25. Reduction of Braking Current by Adding Resistance

  26. Example 9.5 • A dc motor has an armature resistance of 1 , and K = 3 Vsec. When the motor’s terminal voltage is adjusted to 320 V, the motor speed is 1000 r/min. A TVR braking is applied, calculate the value of the braking resistance that would reduce the maximum braking current to twice the rated current.

  27. Solution

  28. Reduction of Braking Current by Reducing Armature Voltage

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