Nidec 22765-01, Manual

Page: 196 / 227

Page 25
Restoring Residual Magnetism/Field Flashing
The direct current necessary to magnetize the revolving field is
obtained from the exciter. Upon starting the generator, current and
voltage is induced into the exciter by the magnetic lines of force set up
by residual magnetism of the exciter field poles. Residual magnetism
of the exciter field poles may be lost or weakened by a momentary
reversal of the field connection, a strong neutralizing magnetic field
from any source, or non-operation for a long time. If the generator
fails to generate voltage after it has come up to rated speed, it may be
necessary to restore residual magnetism.
To restore the small amount of residual magnetism necessary to begin
the voltage build up, connect a 12 or 24-volt battery to the exciter field
coil circuit and flash as follows:
1. Open the output circuit breaker, and stop the engine.
2. Disconnect the exciter field coil wires EF1 at the terminal EF1
and EF2 at the terminal EF2, and connect the battery positive
lead to the field coil lead EF1.
3. Flash the field by touching the battery lead to the field coil circuit
terminal EF2.
4. Disconnect the battery leads.
5. Reconnect the field coil lead EF1 to terminal EF1, and reconnect
the field coil lead EF2 to terminal EF2.
6. Start the generator, and check for voltage build up. Reflash if
the generator output voltage does not build up, or flash with the
generator running, the field coil wires connected to the regulator,
and a 3-amp or larger diode off the positive terminal of the
battery per Figure 17.
Figure 17 Field Flashing Setup with Field Wires Connected to Regulator
12 or 24 V
battery
+
-
3 amp or
larger diode
Voltage
regulator
F-
F+
EF1 EF2