3 Classification of DC Machine (1).pptx

DC Machine Classification

1. Classification Of DC Generator

2. Classification of DC Generator DC Generator Separately Excited DC Generator DC Shunt Generator Short Shunt Long Shunt Self Excited DC Generator DC Compound Generator DC Series Generator

3. Separately Excited DC Generator These are the generators whose field magnets are energized by some external dc source such as battery. A circuit diagram of separately excited dc generator is shown in figure. I a  = Armature current I L  = Load current V = Terminal voltage E g  = Generated emf

4. Separately Excited DC Generator Here armature current I a  is equal to load current I L . So, I a = I L Then, I L =I (say) Voltage across the load, V = E g  -( I a ×R a ) Power generated, P g   = E g ×I Power delivered to the load, P L   = V×I

5. Self Excited DC Generator These are the generators whose field magnets are energized by the current supplied by themselves. In these type of machines field coils are internally connected with the armature. Due to residual magnetism some flux is always present in the poles. When the armature is rotated some emf is induced. Hence some induced current is produced.

6. Self Excited DC Generator According to the position of the field coils the Self-excited DC generators may be classified as… 1. Series wound generators 2. Shunt wound generators 3. Compound wound generators

7. Self Excited DC Generator Series Wound Generator In these type of generators, the field windings are connected in series with armature conductors. So, whole electric current flows through the field coils as well as the load. As series field winding carries full load current it is designed with relatively few turns of thick wire. The electrical resistance of series field winding is therefore very low (nearly 0.5Ω ).

8. Self Excited DC Generator Let, R se  = Series winding resistance I se  = Current flowing through the series field R a  = Armature resistance I a  = Armature current I L  = Load current V = Terminal voltage E g  = Generated emf

9. Self Excited DC Generator Then, I a  = I se  = I L =I (say) Voltage across the load, V = E g  - I a ( R a +R se ) Power generated, P g   = E g ×I Power delivered to the load, P L   = V×I

10. Self Excited DC Generator Shunt Wound Generator In these type of DC generators the field windings are connected in parallel with armature conductors. In shunt wound generators the voltage in the field winding is same as the voltage across the terminal.

11. Self Excited DC Generator Shunt Wound Generator The effective power across the load will be maximum when I L  will be maximum. So, it is required to keep shunt field current as small as possible. For this purpose the resistance of the shunt field winding generally kept high (100 Ω) and large no of turns are used for the desired emf.

12. Self Excited DC Generator Shunt Wound Generator R sh  = Shunt winding  resistance I sh  = Current flowing through the shunt field R a  = Armature  resistance I a  = Armature current I L  = Load current V = Terminal voltage E g  = Generated emf

13. Self Excited DC Generator Shunt Wound Generator Here armature current I a  is dividing in two parts, one is shunt field current I sh  and another is load current I L . So, I a =I sh  + I L Then, I L =I (say) Voltage across the load, V = E g  -( I a ×R a ) Power generated, P g   = E g ×I Power delivered to the load, P L   = V×I

14. Self Excited DC Generator Compound Wound Generator Compound wound generators have both series field winding and shunt field winding. One winding is placed in series with the armature and the other is placed in parallel with the armature. This type of DC generators may be of two types- 1. Short shunt compound wound generator 2. Long shunt compound wound generator .

15. Classification of DC Motor DC Motor Separately Excited DC Motor DC Shunt Motor Short Shunt Long Shunt Self Excited DC Motor DC Compound Motor DC Series Motor

16. Separately Excited DC Motor These are the motors whose field magnets are energized by some external dc source such as battery. A circuit diagram of separately excited dc motor is shown in figure. I a  = Armature current I L  = Load current V = Terminal voltage E b  = Back emf

17. Separately Excited DC Motor Here armature current I a  is equal to load current I L . So, I a = I L Then, I L =I (say) Voltage across the load, V = E b  + ( I a ×R a ) Total i /p power, P i   = V f I f + V t I a

18. Self Excited DC Motor In these machines, instead of a separate excited DC motor, the field winding is connected across the main voltage terminals . . I n self-excited motors, the field winding can be connected either in series or in parallel with the armature winding. These different types of connections give rise to very different types of machines, as we will study in this section.

19. Self Excited DC Generator According to the position of the field coils the Self-excited DC motors may be classified as… 1. Series Wound Motor 2. Shunt Wound Motor 3. Compound Wound Motor

20. Self Excited DC Generator Shunt Wound Motor In these type of motor, The armature and field winding are connected in parallel and the armature voltage and field voltage are the same.

21. Self Excited DC Generator Let, R f  or R sh = Shunt winding resistance I f  or I sh = Current flowing through the shunt field R a  = Armature resistance I a  = Armature current I L  = Load current V = Terminal voltage E b  = Back emf

22. Self Excited DC Generator Then, in case of shunt motor I L  = I f  + I a Voltage across the load, V = E b  + (I a ×R a ) Total i /p power, P i = V t × I L

23. Self Excited DC Generator Series Wound Motor A series wound motor is also called a universal motor. In this type of motor the field winding and armature winding are connected in series. The field winding carries the same current as the armature winding.

24. Self Excited DC Generator Series Wound Generator R se  or R f = Series winding  resistance I se  = Current flowing through the series field R a  = Armature  resistance I a  = Armature current I L  = Load current V = Terminal voltage E b  = Back emf

25. Self Excited DC Generator Shunt Wound Generator Here armature current I a  is dividing in two parts, one is shunt field current I sh  and another is load current I L . So, I L = I se  = I a Then, I a  = I se  = I L =I (say) Voltage across the load, V = E g  + I a (R a + R se ) Total i /p power, P i = V t × I L

26. Self Excited DC Generator Compound Wound Motor If both series and shunt field windings are used, the motor is said to be compounded motor . This type of DC motor may be of two types- 1. C umulative compound motor 2. Differential compound. motor .