PPT - DC Generators | Electrical Machines - Electrical Engineering (EE) PDF Download

 Page 1


DC GENERATORS
There are four major types of DC generators,
namely
? Separately excited generator .
? Shunt generator .
? Series generator
? Compounded generator
? Cumulative
? Differential
Page 2


DC GENERATORS
There are four major types of DC generators,
namely
? Separately excited generator .
? Shunt generator .
? Series generator
? Compounded generator
? Cumulative
? Differential
The Equivalent Circuit of a DC Generator
Two circuits are involved in DC generators
Armature Circuit
Field circuit
? Armature circuit represents Thevenin equivalent of the entire
rotor.
? It cantain an ideal voltage source EA and a resistor RA. .
? Brush voltage drop is represented by a small battery
? The field coils, which produce the magnetic flux
? inductor LF and resistor RF
? Radj for field current control
Page 3


DC GENERATORS
There are four major types of DC generators,
namely
? Separately excited generator .
? Shunt generator .
? Series generator
? Compounded generator
? Cumulative
? Differential
The Equivalent Circuit of a DC Generator
Two circuits are involved in DC generators
Armature Circuit
Field circuit
? Armature circuit represents Thevenin equivalent of the entire
rotor.
? It cantain an ideal voltage source EA and a resistor RA. .
? Brush voltage drop is represented by a small battery
? The field coils, which produce the magnetic flux
? inductor LF and resistor RF
? Radj for field current control
Magnetizing curve of a DC Generator &
performance
? The internal generated voltage EA of a dc generator is
given by
? EA is directly proportional to the flux
? The field current is directly proportional to the
magnetomotive force and hence EA
? Brush voltage drop is represented by a small battery
? Performance of the DC generators are determined by
terminal output parameter IL and VT
? V oltage regulation also determines its performance
Page 4


DC GENERATORS
There are four major types of DC generators,
namely
? Separately excited generator .
? Shunt generator .
? Series generator
? Compounded generator
? Cumulative
? Differential
The Equivalent Circuit of a DC Generator
Two circuits are involved in DC generators
Armature Circuit
Field circuit
? Armature circuit represents Thevenin equivalent of the entire
rotor.
? It cantain an ideal voltage source EA and a resistor RA. .
? Brush voltage drop is represented by a small battery
? The field coils, which produce the magnetic flux
? inductor LF and resistor RF
? Radj for field current control
Magnetizing curve of a DC Generator &
performance
? The internal generated voltage EA of a dc generator is
given by
? EA is directly proportional to the flux
? The field current is directly proportional to the
magnetomotive force and hence EA
? Brush voltage drop is represented by a small battery
? Performance of the DC generators are determined by
terminal output parameter IL and VT
? V oltage regulation also determines its performance
The Separately Excited Generator
? A separately excited dc generator is a
generator whose field current is supplied by
a separate external dc voltage source.
? By Kirchhoff's voltage law , the terminal
voltage is
? Since the internal generated voltage is
independent of lA the terminal
characteristic of the separately excited
generator is a straight line
A separately excited dc generator
The terminal characteristic (a) with and (b) without compensating windings
Page 5


DC GENERATORS
There are four major types of DC generators,
namely
? Separately excited generator .
? Shunt generator .
? Series generator
? Compounded generator
? Cumulative
? Differential
The Equivalent Circuit of a DC Generator
Two circuits are involved in DC generators
Armature Circuit
Field circuit
? Armature circuit represents Thevenin equivalent of the entire
rotor.
? It cantain an ideal voltage source EA and a resistor RA. .
? Brush voltage drop is represented by a small battery
? The field coils, which produce the magnetic flux
? inductor LF and resistor RF
? Radj for field current control
Magnetizing curve of a DC Generator &
performance
? The internal generated voltage EA of a dc generator is
given by
? EA is directly proportional to the flux
? The field current is directly proportional to the
magnetomotive force and hence EA
? Brush voltage drop is represented by a small battery
? Performance of the DC generators are determined by
terminal output parameter IL and VT
? V oltage regulation also determines its performance
The Separately Excited Generator
? A separately excited dc generator is a
generator whose field current is supplied by
a separate external dc voltage source.
? By Kirchhoff's voltage law , the terminal
voltage is
? Since the internal generated voltage is
independent of lA the terminal
characteristic of the separately excited
generator is a straight line
A separately excited dc generator
The terminal characteristic (a) with and (b) without compensating windings
The Separately Excited Generator
Control of T erminal V oltage > two methods
? Change the speed of rotation
? E
A
= K ??? >VT = EA ?-l
A
R
A
> VT ?
? Change the field current.
? I
F
= VF/R
F
? > I
F
? > ??> E
A
= K ??? >
? V
T
= E
A
?-l
A
R
A
>VT ?
The terminal characteristic (a) with and (b) without compensating windings