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DRYING ELECTRICAL INSULATION
Electrical components must be dried before
placing in operation if tests indicate that the
insulation resistance is below a safe value.
(See Generator testing for test procedure.)
Machines that have been idle for sometime
in unheated and damp locations, may have
absorbed moisture. Sudden changes in
temperature can cause condensation or the
generator may have become wet by
accident. Windings should be dried out
thoroughly before being put into service.
The following are recommended drying
methods.
Space Heaters
Electric space heaters can be installed inside
of the generator. When energized (from a
power source other than the generator) they
will heat and dry the inside of the generator.
If an alternate source of electricity is not
available, enclose the generator with a
covering and insert heating units to raise the
temperature 15-18 degrees F (8-10 degrees
C) above the temperature outside of the
enclosure. Leave a hole at the top of the
enclosure to permit the escape of moisture.
Oven
Place the machine in an oven and bake it at a
temperature not to exceed 194 F (90°C). The
voltage regulator and any electronic
component accessories must be removed
from the generator when using this method.
Forced Air
A portable forced air heater can be used by
directing heat into the air intake (conduit
box) and running the generator with no load
and without excitation (this can be
accomplished by removing the regulator
fuse). Heat at point of entry should not
exceed 150° F (66° C).
"Short Circuit" Method
Using this method can dry out the generator
quickly and thoroughly.
WARNING:
BE SURE THAT ALL OF THE
FOLLOWING STEPS ARE
PERFORMED AND ALL PRECAU-
TIONS TAKEN AS PERSONAL
INJURY OR SERIOUS DAMAGE TO
THE GENERATOR COULD RESULT.
1. Disconnect exciter leads Fl and F2 from
the regulator.
2. Connect a battery or other dc power source
approximately 20-35 volts to the exciter lead
Fl and F2. An adjustable voltage source
desirable, however, a rheostat (rated
approximately 2 amps) in series with the dc
power source will work.
3. Short circuit the generator output lead
wires to each other (L1 to L2 to L3). If using
jumpers, be sure they are large enough to
carry full load amps.
4. Start the generator and measure the
current through the output leads with a clip-
on ammeter.
5. Adjust the voltage source to produce
approximately 80% of the rated ac
nameplate current but in no case exceed
nameplate amps. If a adjustable source is not
available and current is excessive, use a
lower dc source voltage or larger resistor in
series with the source.
Running time will be determined by the
amount of moisture present in the machine.
Insulation resistance checks should be taken
every one to four hours until a fairly
constant value obtained. (See section -
Generator testing for instructions on
measuring insulation resistance.)
26
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