Dc motor

Motor detail,group presentation of sonargon university

1. Welcome to our presentation

2. Prepared by

3. TOPICS DC Motor

4. TOPIC S T O DISCUSS Introduction to DC MOTORS. Construction. Principle. Working . Types. Applications.

5. o A dc motor in single words is a device that converts direct current (electrical energy) into mechanical energy. INTRODUCTION

6. Construction of DC MOTOR Now w e will d i sc u ss about pr a ctical construction of DC motor :- A DC motor has the following parts Yoke Pole & Pole shoes Field winding Armature of DC motor Commutator Brushes of motor Bearing

7. Construction of DC MOTOR

8. Construction of DC MOTOR Yoke Yoke of dc motor serves two purposes, It holds the magnetic pole cores of the motor and acts as cover of the motor . It carries the magnetic field flux.

9. Construction of DC MOTOR Y oke

10. Construction of DC MOTOR Yoke In small motor , yoke are made of cast iron. Cast iron is cheaper in cost but heavier than steel. But for large construction of DC motor , where weight of the machine is concerned, lighter cast steel or rolled steel is preferable for constructing yoke of DC motor .

11. Construction of DC MOTOR Pole There are mainly t wo types of construction available. Solid pole care, where it made of a solid single piece of cast iron or cast steel. Laminated pole core, where it made of numbers of thin, limitations of annealed steel which are riveted together.

12. Construction of DC MOTOR Pole

13. Construction of DC MOTOR Pole The thickness of the lamination is in the range of 0.04" to 0.01". The pole core is fixed to the inner periphery of the yoke by means of bolts through the yoke and into the pole body.

14. Construction of DC MOTOR Pole & Pole shoes The pole shoes are so typically shaped, that, they spread out the magnetic flux in the air gap and reduce the reluctance of the magnetic path.

15. Construction of DC MOTOR Pole & Pole shoes

16. Construction of DC MOTOR Field winding The field coils or pole coils are wound around the pole core. These are a simple coil of insulated copper wire or strip, which placed on the pole which placed between yoke and pole shoes as shown.

17. Construction of DC MOTOR Field winding

18. Construction of DC MOTOR The purpose o f arma t ure core i s t o ho l d the ar m ature w i n d i ng reluctance p a t h f or t he and pr o vide l ow f l ux thr o ugh the armature from N pole to S pole. Cylindrical or drum shaped armature core is build up of circular laminated sheet. In every circular lamination, slots are either die - cut or punched on the outer periphery Armature:

19. Construction of DC MOTOR Armature Core of DC Motor

20. Construction of DC MOTOR Armature of Dc Air ducts are also punched of cut on each lamination for circulation of air through the core for providing better cooling. Up t o diameter o f 4 ", the circ u lar stampings are cut out in one piece of lamination sheet. But above 40", diameter, number of suitable sections of a circle is cut. A complete circle of lamination is formed by four or six or even eight such segment.

21. Construction of DC MOTOR Commutator The main function of commutator is to collects electric current from armature winding and sends it to the load as direct current. It actually takes alternating current from armature and converts it to direct current and then send it to external load.

22. Construction of DC MOTOR Commutator

23. Construction of DC MOTOR Commutator It is cylindrical structured and is build up of wedge shaped segments of high conductivity, hard drawn or drop forged copper. Each segment is insulated from the shaft by means of insulated commutator segment.

24. WORKING PRINCIPLE OF DC MOTOR Step 1: Initially considering the armature is in its starting point or reference position where the angle α = 0. ∴ τ = BIL w cos0 = BILw Since α = 0, the term cos α = 1, or the maximum value, hence torque at this position is maximum given by τ = BILw. This high starting torque helps in overcoming the initial inertia of rest of the armature and sets it into rotation.

25. Step 2: Once the armature is set in motion, the angle α between the actual position of the armature and its reference initial position goes on increasing in the path of its rotation until it becomes 90° from its initial position. Consequently the term cosα decreases and also the value of torque. The torque in this case is given by τ = BILwcosα which is less than BIL w when α is greater than 0°.

26. Step 3: In the path of the rotation of the armature a point is reached where the actual position of the rotor is exactly perpendicular to its initial position, i.e. α = 90°, and as a result the term cosα = 0. The torque acting on the conductor at this position is given by. τ = BILwcos90° =

27. BACK EMF OF DC MOTOR o When the motor Armature continue to rotate due to motor action the Armature conductor cut the magnetic flux emf is induced in them is known as back emf . o It Denot e d by E b E b ═ ΦZNP /60A

28. TYPES OF DC MOTOR SERIES WOUND DC MOTOR SHUNT WOUND DC MOTOR COMPOUND WOUND DC MOTOR

29. SERIES WOUND DC MOTOR A E R a I L + I a A A _ I SE YY + _ M V SUP P L Y

30. SERIES WOUND DC MOTOR Armature current ═series field current═line current,i═I E b ═V - I(Ra+Rse) Power drawn P ═VI The crooss sectional area of of the wire used for field coil has to be fairly large to carry the armature current but owing to the higher current the number of turn of wire in them need not be large.

31. SHUNT WOUND DC MOTOR E R a I L V SUPP L Y FF I f I a AA + _ F M A

32. SHUNT WOUND DC MOTOR In this type of e x c i t a t ion , arm at u r e an d fi e ld w i n dings a r e connected across a constant source of supply. The field current I f is drawn from the same source as that of armature current.

33. COMPOUND WOUND DC MOTOR o Compoud wound :- which has two field windings; one connected inparallel with the armature and the other in series with it. A E R a I L V I a AA I SE Y YY + _ I Sh Z ZZ R sh S UP P L Y M

34. o There are two types of compound dc motor connections :- Short shunt connection :- When the shunt field winding is directly connected across the armature terminals it is called short-shunt connection. Long shunt connectin :- When the shunt winding is connected that it shunts the series combination of armature and series field. it is called long-shunt connection.

35. CHARACTERISTICS OF SHUNT MOTOR o the connections of a d.c. shunt motor. The field current Ish is constant since the field winding is directly connected to the supply voltage V which is assumed to be constant. Hence, the flux in a shunt motor is approximately constant.

36. o The connections of a series motor. Note that current passing through the field winding is the same as that in the armature. If the mechanical load on the motor increases, the armature current also increases. Hence, the flux in a series motor increases with the increase in armature current and vice-versa. CHARACTERISTICS OF SERIES MOTOR

37. CHARACTERISTICS OF COMPOUND MOTOR o A compound motor has both series field and shunt field. The shunt field isalways stronger than the series field. Compound motors are of two types:- Cumulative-compound motors in which series field aids the shunt field. Differential-compound motors in which series field opposes the shunt field. o Differential compound motors are rarely used due to their poor torque characteristics at heavy loads.

38. o the connections of a cumulative-compound motor. Each pole carries a series as well as shunt field winding; the series field aiding the shunt field. CHARACTERISTICS OF COMULATIVE COMPOUND MOTOR

39. Use Of DC Motor Common In Cars,Trucks ,Aircraft and Many Other Vehicles Lathes Drills Boring mills Shapers Spinning and Weaving machines..

40. Use Of DC Motor Electric traction Cranes Elevators Air compressor Vacuum cleaner Hair drier Sewing machine

41. question

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