5-3
DESCRIPTION
Of
GENERATOR OPERATION
5-3-1 PRIMARY EXCITING ACTION
One of the differences between the old type and the new
-
type is that the new type has an exciting coil
(EC)
while
the old type does not.
The old type used a rotor of carbon steel sheets that started
the primary exciting action of the generator with its residual
r-----l
I
I
magnetism.
This
type loses its residual magnetism if the gen-
1'
I
erator is disassembled and stored and may fail to generate
I
electric power when it is started after storage. The new type
FC
I
/
I
p
,
I
EC
I
I
\
I
I
is equipped with an exciting coil on the engine magnet for
primary exciting action to eliminate such an occurance.
The primary exciting action of the new type is explained
below.
When the generator is started, the permanent magnet on the
engine rotates to generate voltage in the exciting coil.
This
voltage is regulated by a diode in the
AVR
to feed current
into the generator field coil
(FC).
(See Fig.
5-15.)
The rotor turns an electromagnet with that current and
rotates
so
that voltage is generated in the stator coils (main
coil, sub coil, and
DC
coil). The voltage generated in the sub
coil is regulated by the
AVR
to feed current in order to in-
crease the field and current. (See Fig.
5-16.)
As
a result,
the rotor magnetism increases.
Ths
operation is repeated to
generate the rated voltage at
50
Hz
or
60
Hz
in the main
coil and
DC
coil.
5-3-2 VOLTAGE REGULATING MECHANISM
Connect a load to the
AC
output terminal and increase cur-
rent. Output voltage will vary as shown in Fig.
5-17
depend-
ing on whether an automatic voltage regulator is used or not.
When
AC
output is drawn, the engine becomes loaded and
its rpm falls.
Also,
the
AC
voltage falls due to the voltage
drop caused by the internal resistances of the coil. The
AVR
caused by the internal resistances of the coils. The
AVR
detects this voltage drop and its built-in
SCR
automatically
increases the current that
floCs
to the field coil.
As
a result,
the rotor magnetism increases, the voltage decrease caused
by the load current
is
raised, and the output voltage
is
kept
constant. If the
AC
output is reduced, the
SCR
operates in
the opposite way to similarly keep the output voltage con-
stant.
I I
ENGINE MAGNETO
!"-"-J
Fig.
5-
15
MC
i
Fig.
5-
16
WITH 'AVR
-A
Fig.
5-
17
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24
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