Generators

DC Generators
Principle of Generator Action
Types of DC Generators
Separately Excited
Self Excited
Voltage Regulation
Power and Efficiency
Power Stages
Losses in DC Generators
Efficiency

Principle of Generator Action
Requirements for Generator Action or Generating Voltage
Presence of magnetic lines of force
Motion of conductors cutting the flux
When a conductor moves at constant speed across a uniformly dense
magnetic field, voltage is generated in the conductor.
1 volt is generated for every 100,000,000 lines cut per second

Principle of Generator Action
Commutation

Principle of Generator Action
Average Voltage of a Generator
If the magnetic field is not uniform, the generated voltage can be defined by
its average value as defined by
𝐸
???
=
Ø
?
× 10
−8
?????
Where
𝐸
???
Average generated voltage per conductor
Volts
Ø
Total flux cut by the conductor
Maxwells
?
Time during cutting took place
Seconds

Principle of Generator Action
General Voltage Equation
𝐸
?
=
𝑃 × 𝑧 × ??? × Ø × 10
−8
60 × 𝜕
Where
𝐸
?
Generated voltage
Volts
𝑃
Number of poles
Unitless
𝑧
Number of armature conductors
Unitless
???
Speed of the armature
Rev per min
Ø
Flux per pole
Maxwells
𝜕
Number of parallel paths
Unitless

Principle of Generator Action
General Voltage Equation
For Lap Winding
𝜕 = ?𝑃
Where
? = 1
for simplex winding
? = 2
for duplex winding
𝜕
Number of armature paths
Unitless
?
Multiplicity factor
Unitless
𝑃
Number of poles
Unitless

Principle of Generator Action
General Voltage Equation
For Wave Winding
𝜕 = 2?
Where
? = 1
for simplex winding
? = 2
for duplex winding
𝜕
Number of armature paths
Unitless
?
Multiplicity factor
Unitless

Types of DC Generators

Types of DC Generators
Separately Excited
Field
windings
are
energized
by
an
external DC source.
The generated voltage
is purely dependent on
the amount of current
passing
through
the
field windings.

Types of DC Generators
Equivalent
Circuit
of
a
Separately
Excited
Generator
𝑉
𝐿
= 𝐸
?
− 𝐼
?
?
?
+ ?
?
− 𝑉
?
𝐼
?
=
𝐸
?
?
Where
𝑉
𝐿
Voltage across the load
Volts
𝐸
?
Generated voltage
Volts
𝐼
?
Exciting current
Amperes
?
?
Field winding resistance
Ohms

Types of DC Generators
Equivalent
Circuit
of
a
Separately
Excited
Generator
𝐼
?
∝ Ø
?
Where
𝐼
?
Exciting current
Amperes
Ø
?
Field flux
Maxwells

Types of DC Generators
Self Excited
Field
windings
are
energized
by
the
output of the generator
itself.

Types of DC Generators
Shunt Generator
A
generator
whose
field
windings
(shunt
winding) are connected across or in parallel
with
the
armature
conductors
and
the
brushes.

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- Fall '19
- Magnetic Field, DC GENERATORS