1. 1 Teaching Innovation - Entrepreneurial - Global The Centre for Technology enabled Teaching & Learning, N Y S S, India DTEL DTEL (Department for Technology Enhanced Learning)

2. DEPARTMENT OF ELECTRICAL ENGINEERING IV-SEMESTER POWER DEVICES AND MACHINES 2 CHAPTER NO. - 6 DC MOTOR

3. CHAPTER 5:-SYLLABUS FOR DC MOTORDTEL. Principle of operation 1 Types of Motor 2 Speed control of shunt Motor (flux,armature & voltage control method) 3 Speed control of series (flux,Rheostatic control method) 4 3

4. CHAPTER 5:-SYLLABUS FOR UNIVERSAL MOTORDTEL. Construction 1 Working 2 Characteristics and Application 3 4

5. CHAPTER-5 SPECIFIC OBJECTIVE / COURSE OUTCOMEDTEL To understand the basic concepts of DC motor, its construction, types, & methods of speed control 1 To understand the construction, working, characteristics & applications of a universal motor. 2 5 The student will be able to:

6. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLEDTEL 6 6  The direct current (dc) machine can be used as a motor or as a generator.  DC Machine is most often used for a motor.  The major advantages of dc machines are the easy speed and torque regulation.  However, their application is limited to mills, mines and trains. As examples, trolleys and underground subway cars may use dc motors.  In the past, automobiles were equipped with dc dynamos to charge their batteries.

7. DTEL 7 7  Even today the starter is a series dc motor.  However, the recent development of power electronics has reduced the use of dc motors and generators.  The electronically controlled ac drives are gradually replacing the dc motor drives in factories.  Nevertheless, a large number of dc motors are still used by industry and several thousand are sold annually. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

8. DTEL 8 8 General arrangement of a dc machine LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

9. DTEL 9 9  The stator of the dc motor has poles, which are excited by dc current to produce magnetic fields.  In the neutral zone, in the middle between the poles, commutating poles are placed to reduce sparking of the commutator. The commutating poles are supplied by dc current.  Compensating windings are mounted on the main poles. These short- circuited windings damp rotor oscillations.. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

10. DTEL 10  The poles are mounted on an iron core that provides a closed magnetic circuit.  The motor housing supports the iron core, the brushes and the bearings.  The rotor has a ring-shaped laminated iron core with slots.  Coils with several turns are placed in the slots. The distance between the two legs of the coil is about 180 electric degrees. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

11. DTEL 11 DC MACHINE CONSTRUCTION Details of the commutator of a dc motor Rotor of a dc motor LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

12. DTEL 12 Cutaway View Of A DC Motor. DC Motor Stator With Poles Visible. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

13. DTEL 13 Working Principle of a Motor When current carrying armature conductors are placed in a magnetic field produced by the current in stator field winding, the armature conductors experience a mechanical force. LECTURE 1:- CONSTRUCTION & WORKING PRINCIPLE

14. DTEL 14 LECTURE 1 THANK YOU

15. DTEL 15 LECTURE 2:- TYPES OF DC MOTORS Direct current motors are named according to the connection of the field winding with the armature. There are three types of DC Motors. 1. Series motor. 2. Shunt motor. 3. Compound motor.

16. DTEL 16 DC Series Motor  In the series motor the field winding is connected in series with the armature  Equations for a series motor :  Current equation: I = Ia = Ise  Voltage equation: V = Eb + I(Ra +Rse) + Vb LECTURE 2:- TYPES OF DC MOTORS

17. DTEL 17 DC Shunt Motor  In the DC shunt motor the field winding is connected in shunt with the armature  Equations for a series motor : The current equations are Ish = V/Rsh I = Ia + Ish The voltage equation is V = Eb + IaRa +Voltage drop at brushes LECTURE 2:- TYPES OF DC MOTORS

18. DTEL 18 DC compound Motor D.C. motor having both shunt and series fields is called a compound motor. Equations for a Differential Compound motor : The current equation is I = Ise = Ish + Ia The voltage equation is V = Eb + IaRa + Vb + I Rse LECTURE 2:- TYPES OF DC MOTORS

19. DTEL 19 Cumulative Compound motor  If the shunt field is in parallel with both armature and series field the machine is called Cumulative compound motor. Equations for a Cumulative Compound motor : The current equation is I = I sh + I a Ia = Ise The voltage equation is V = E b + I a R a + V bd + I a R se LECTURE 2:- TYPES OF DC MOTORS

20. DTEL 20 LECTURE 2 THANK YOU

21. DTEL 21 LECTURE 3:- SPEED CONTROL Speed Control Of DC Shunt Motor Armature control or Rheostatic control method V = Eb + Ia (Ra + Rext) Eb = V - Ia (Ra + Rext) As the controller resistance Rext is increased the value of voltage drop Ia(Ra + Rext) also increases and Eb decreases. N α Eb α V - Ia (Ra + Rext) Ф The speed will also decrease.

22. DTEL 22 Flux control (Field Control Method) In this method a variable controller resistance is connected in series with the shunt winding. If Rext is increased the field current and hence flux Ф will decrease. Since N α Eb Ф. LECTURE 3:- SPEED CONTROL

23. DTEL 23 Voltage Control Method In this method, the shunt field of the motor is connected permanently to a fixed exciting voltage, but the armature is supplied with different voltages by connecting it across one of the several different voltages by means of suitable switchgear. The armature speed will be approximately proportional to these different voltages. The intermediate speeds can be obtained by adjusting the shunt field regulator. LECTURE 3:- SPEED CONTROL

24. DTEL 24 Voltage Control Method Ward Leonard System This system is used where an unusually wide and very sensitive speed control is required as for colliery winders, electric excavators, elevators and the main drives in steel mills and blooming and paper mills. M1 is the main motor whose speed control is required. The field of this motor is permanently connected across the dc supply lines. By applying a variable voltage across its armature, any desired speed can be obtained. This variable voltage is supplied by a motor-generator set which consists of either a dc or an ac motor M2 directly coupled to generator G. The motor M2 runs at an approximately constant speed. The output voltage of G is directly fed to the main motor M1. The voltage of the generator can be varied from zero up to its maximum value by means of its field regulator. By reversing the direction of the field current of G by means of the reversing switch RS, generated voltage can be reversed and hence the direction of rotation of M1. It should be remembered that motor generator set always runs in the same direction. LECTURE 3:- SPEED CONTROL

25. DTEL 25 Voltage Control Method LECTURE 3:- SPEED CONTROL

26. DTEL 26 Speed Control Of Dc Series Motor Armature control or Rheostatic control method V = Eb + I(Ra + Rext + Rse) Eb = V - Ia (Ra + Rext + Rse) As the controller resistance Rext is increased the value of voltage drop Ia(Ra + Rext + Rse) also increases and Eb decreases. N α Eb α V - Ia (Ra + Rext) Ф The speed will also decrease. LECTURE 3:- SPEED CONTROL

27. DTEL 27 Flux control (Field Control Method) In this method a variable resistor Rd (diverter resistance) is connected in parallel with the series field winding. By changing the diverter resistance,current Id can be changed, thereby current Ise can be changed. As the speed N α 1 α 1 Ф Ise Therefore speeds above normal value can be obtained. LECTURE 3:- SPEED CONTROL

28. DTEL 28 LECTURE 3 THANK YOU

29. DTEL 29 LECTURE 4:- UNIVERSAL MOTOR  Universal motor A series motor built to operate on either alternating current (ac) or direct current (dc). It is normally designed for capacities less than 1 hp (0.75 kW).  It is usually operated at high speed, 3500 revolutions per minutes (rpm) loaded and 8000 to 10,000 revolutions per minute unloaded. For lower speeds, reduction gears are often employed, as in the case of electric hand drills or food mixers. As in all series motors, the rotor speed increases as the load decreases and the no-load speed is limited only by friction and windage. UNIVERSAL MOTOR

30. DTEL 30 Construction of Universal motor Construction of a universal motor is similar to the construction of a DC series motor. However, the whole magnetic path (armature, stator field circuit etc) is laminated. Lamination is necessary to minimize the eddy currents which induce while operating on AC. The armature is of wound type having straight or skewed slots and commutator with brushes resting on it. The commutation on AC is poorer than that for DC, because of the current induced in the armature coils. For that reason brushes used are having high resistance.DC series motor LECTURE 4:- UNIVERSAL MOTOR

31. DTEL 31 Working of universal motor A universal motor works on either DC or single phase AC supply. When the universal motor is fed with a DC supply, it works as an DC series motor. That is, when flux due to field winding and flux due to armature winding interact each other, a torque is produced which causes rotor to rotate. When fed with AC supply, it still produces unidirectional torque. Because, as armature winding and field winding is connected in series, in same phase, direction of the current in armature as well as field winding reverses at the same time. And hence, regardless of AC or DC supply, universal motor works on the same principle that DC series motor works. LECTURE 4:- UNIVERSAL MOTOR

32. DTEL 32 LECTURE 4 THANK YOU

33. DTEL 33 LECTURE 5:- Characteristics Speed/load characteristics Speed/load characteristics of a universal motor is similar to that of DC series motor. The speed of a universal motor is low at full load and very high at no load. Usually, gears trains are used to get the required speed on required load. The speed/load characteristics are (for both AC as well as DC supply) are shown in the figure. LECTURE 5:- UNIVERSAL MOTOR (CONTINUED)

34. DTEL 34 Applications of universal motor  Universal motors find their use in various home appliances like vacuum cleaners, drink and food mixers, domestic sewing machine etc.  The higher rating universal motors are used in portable drills, blenders etc. LECTURE 5:- UNIVERSAL MOTOR (CONTINUED)

35. DTEL 35 THANK YOU LECTURE 5