5-3 DESCRIPTION of GENERATOR OPERATION
INITIAL EXCITATION INITIAL EXCITATION
STATOR STATOR
PERMANENT MAGNETO PERMANENT MAGNETO
FIELD COIL
ROTOR ROTOR
7 ----_---It
RESISTOR or RESISTOR or
/
---
r-
DIODE DIODE
MAIN COIL
CONDENSER COIL
Fig. 5-7
5-3-l GENERATION of NO-LOAD VOLTAGE
(1) When the generator starts running, the permanent magnet built-in to the rotor generates 3 to 6V of
AC voltage in the main coil and condenser coil wound on the stator.
(2) As one or two condensers are connected to the condenser coil, the small voltage at the condenser
coil generates a minute current @ which flows through the condenser coil. At this time, a small flux
is produced with which the magnetic force at the rotor’s magnetic pole is intensified. When this
magnetic force is intensified, the respective voltages in the main coil and condenser coil rise up.
As the current @ increases, the magnetic flux at the rotor’s magnetic pole increases further. Thus the
voltages at the main coil and condenser coil keep rising by repeating this process.
(3) As AC current flows through the condenser coil, the density of magnetic flux in the rotor changes.
This change of magnetic flux induces AC voltage in the field coil, and the diode rectifier in the field
coil circuit rectifies this AC voltage into DC. Thus a DC current %$ flows through the field coil and
magnetizes the rotor core to generate an output voltage in the main coil.
(4) When generator speed reaches 2700 to 2800 rpm (50Hz type) or 3000 to 3300 rpm (60Hz type), the
current in the condenser coil and field coil increases rapidly.
This acts to stabilize the output voltage of each coils. If generator speed further increases to the rated
value, the generator output voltage will reach to the rated value.
5-3-2 VOLTAGE FLUCTUATIONS UNDER LOAD
When the output current g flows through the main coil to the appliance, a magnetic flus is produced and
serves to increase current 3 in the condenser coil. When current @ increases, the density of magnetic
flux across the rotor core rises. As a result, the current flowing in the field coil increases and the
generator output voltage is prevented from decreasing.
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