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
27th 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.
 𝑊ℎ𝑒𝑟𝑒 𝐵 𝑎𝑛𝑑 𝑉 𝑎𝑟𝑒 𝑣𝑒𝑐𝑡𝑜𝑟 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑖𝑒𝑠.
e=𝐵 𝑙 𝑉
Water IN
Water OUT
Hydraulic
Turbine
DC
Generator
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Mechanical
Coupler

3. Schematic of DC Machine
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DC
Machine
Shaft
(Mechanical)
Output
Terminal
(Electrical)

4. Basic Components of DC Generator
 Yoke
1. Outer Frame or yoke provides mechanical support for the poles, also acts as protecting
cover.
2. It carries the magnetic flux produced by the poles.
3. Generally made with Cast iron.
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5. Basic Components of DC Generator
 Pole Coils or Field Coils
1. Made up from a copper wire.
2. Initially wound for the correct dimension.
3. Wounded coil is put into place over the core.
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6.  Armature Core & Armature Winding
1. Armature core is a house for armature conductor or coils causes
them to rotate.
2. 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.
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Armature
Core
Commutator

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8.  Commutator
1. Function of commutator is to facilitate collection of current from the armature
conductors. (Known as rectifier of DC machine)
2. It converts the ac current induced in the armature to unidirectional current.
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9.  Brushes and Bearings
1. Function of brushes is to collect current from commutator, usually made up of
carbon or graphite (called carbon brush).
2. Carbon brushes are rectangular in shape.
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10. Basic Operation of DC Generator
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11. Fleming’s Right Hand Rule
Thumb – Force Applied (F)
Forefinger – Magnetic field Direction (B)
Middle Finger – Direction of Current flow
(I)
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12. Slides developed by: B. B. Pokharel 12

13. How to connect Externally?
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What are the issues associated
with DC generator?

14. Basic Construction of DC generator
Armature
Coil
Stator
Slip
Ring
Carbon
Brushes
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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.
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15

16. Functions of Commutator
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17. Types of DC Generator
DC
Generator
Self
Excited
Shunt
Wound
Series
Wound
Compound
Wound
Separately
Excited
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Characterized by how the
field winding is getting
supply with reference to
armature winding

18. Separately Excited DC Generator
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MotorGenerator

19. Series Wound DC Generator
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V

20. Shunt Wound DC Generator
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21. Compound Wound DC Generator
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22. Types of Armature Winding of DC Generator
 Lap Winding
 Wave winding
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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:
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Wave Wound Generator
No. of Parallel paths = 2
Lap- Wound Generator
No. of parallel path = No. of Pole

24. Voltage Generation of DC Machine
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DC
Machine
Shaft
(Mechanical)
Output
Terminal
(Electrical)
Eg =
𝑁 ∅ 𝑍
60
(
𝑃
𝐴
) 𝑉𝑜𝑙𝑡𝑠
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=𝐵 𝑙 𝑉

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.
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26.  Hopefully, you have got the idea about how DC generator actually
works!!
Any Queries?
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