Operating Principle of DC Generator

Basic operating principle and components of DC Generator.

1. Operating Principle of DC Generator Asst. Prof. Biswas Babu Pokharel Mid-Western University Birendranagar , Surkhet LECT-1 27 th Jan, 2020

2. Basic Principle Electrical generator is a machine which converts mechanical energy into electrical energy. In DC Generator, energy conversion is based on the principle of the production of dynamically induced emf.   e=   Water IN Water OUT Hydraulic Turbine DC Generator Slides developed by: B. B. Pokharel 2 Mechanical Coupler

3. Schematic of DC Machine Slides developed by: B. B. Pokharel 3 DC Machine Shaft (Mechanical) Output Terminal (Electrical)

4. Basic Components of DC Generator Yoke Outer Frame or yoke provides mechanical support for the poles, also acts as protecting cover. It carries the magnetic flux produced by the poles. Generally made with Cast iron. Slides developed by: B. B. Pokharel 4

5. Basic Components of DC Generator Pole Coils or Field Coils Made up from a copper wire. Initially wound for the correct dimension. Wounded coil is put into place over the core. Slides developed by: B. B. Pokharel 5

6. Armature Core & Armature Winding Armature core is a house for armature conductor or coils causes them to rotate. It is the component cut the magnetic flux of the field magnets through armature coil (winding). Important: major function of armature core is to provide the low reluctance path to the flux from N-S pole. Slides developed by: B. B. Pokharel 6 Armature Core Commutator

7. Slides developed by: B. B. Pokharel 7

8. Commutator Function of commutator is to facilitate collection of current from the armature conductors. (Known as rectifier of DC machine) It converts the ac current induced in the armature to unidirectional current. Slides developed by: B. B. Pokharel 8

9. Brushes and Bearings Function of brushes is to collect current from commutator, usually made up of carbon or graphite (called carbon brush). Carbon brushes are rectangular in shape. Slides developed by: B. B. Pokharel 9

10. Basic Operation of DC Generator Slides developed by: B. B. Pokharel 10

11. Fleming’s Right Hand Rule Thumb – Force Applied (F) Forefinger – Magnetic field Direction (B) Middle Finger – Direction of Current flow (I) Slides developed by: B. B. Pokharel 11

12. Slides developed by: B. B. Pokharel 12

13. How to connect Externally? Slides developed by: B. B. Pokharel 13 What are the issues associated with DC generator?

14. Basic Construction of DC generator Armature Coil Stator Slip Ring Carbon Brushes Slides developed by: B. B. Pokharel 14

15. How Does Slip Ring and Carbon Brush Work? Slip ring and carbon brushes simply makes an electrical contact between armature coil and outer load without disturbing the arrangement. Slides developed by: B. B. Pokharel 15

16. Functions of Commutator Slides developed by: B. B. Pokharel 16

17. Types of DC Generator Slides developed by: B.B. Pokharel 17 Characterized by how the field winding is getting supply with reference to armature winding

18. Separately Excited DC Generator Slides developed by: B.B. Pokharel 18 Motor Generator

19. Series Wound DC Generator Slides developed by: B.B. Pokharel 19 V

20. Shunt Wound DC Generator Slides developed by: B.B. Pokharel 20

21. Compound Wound DC Generator Slides developed by: B.B. Pokharel 21

22. Types of Armature Winding of DC Generator Lap Winding Wave winding Slides developed by: B.B. Pokharel 22 In this type of winding, the conductors are joined in such a way that their parallel paths and poles are equal in number. The end of each armature coil is connected to the adjacent segment on the commutator. In this type of winding, only two parallel paths are provided between the positive and negative brushes. The finishing end of one armature coil is connected to the starting end of other armature coil commutator segment at some distance apart.

23. In Summary: Slides developed by: B.B. Pokharel 23 Wave Wound Generator No. of Parallel paths = 2 Lap- Wound Generator No. of parallel path = No. of Pole

24. Voltage Generation of DC Machine Slides developed by: B.B. Pokharel 24 DC Machine Shaft (Mechanical) Output Terminal (Electrical) E g =   Where, N= Rotation of Shaft (RPM) = Flux per pole (Wb) Z = Total number of conductor in the armature P = No. of pole pairs. A = No. of Parallel Paths   e=  

25. Numerical-1 An 8-pole DC generator has 500 armature conductors, and a useful flux of 0.05 Wb per pole. What will be the emf generated if it lap-connected and runs at 1200 rpm ? What must be the speed at which it is to be driven produce the same emf if it is wave- wound? A 4-pole, lap- wound, dc shunt generator has a useful flux per pole of 0.07 Wb. The armature winding consists of 220 turns each of 0.004 Ω resistance. Calculate the terminal voltage when running at 900 rpm if the armature current is 50A. A short-shunt DC compound generator supplies 200 A at 100V. The resistance of armature, series field and shunt field windings are 0.04, 0.03 and 60 Ω respectively. Find the emf generated. Also find the emf generated if same machine is connected as a long-shunt machine. Slides developed by: B.B. Pokharel 25

26. Hopefully, you have got the idea about how DC generator actually works!! Any Queries? Slides developed by: B. B. Pokharel 26