5.13 DRYING THE WINDING
5.13.0 General points
All electric machines must be stored under dry conditions.
If a machine is placed in damp surroundings, it must be
dried before it is put into service. Units operating
intermittently or placed in areas with high temperature
variations, are exposed to dampness and must be dried
very thoroughly if necessary.
5.13.1 Drying method
5.13.1.1 General points
During the drying operation measure the winding insulation
and the polarization index each 12 hours.
To survey the insulation progress, record the measured
values and plot the obtained progress function of the time.
When the insulation value becomes constant, the machine
can be considered as dry.
When the resistance is constant, it may be assumed that
the machine is dry. This operation may take up to 72 hours,
depending on the size of the machine and on the degree of
dampness.
CAUTION:
TAKE FIRE-PREVENTION MEASURES DURING THE
DRYING OF THE MACHINE.
ALL THE CONNECTIONS MUST BE TIGHTENED.
5.13.1.2 Drying generator in a stopped position
The procedure " Drying generator in rotation" should be
preferred to the following one if it is possible to run the
generator at its nominal speed
Several thermometers must be positioned onto the winding
and the temperature must not exceed 75°C (167°F). If one
of the thermometers exceeds this value, immediately
reduce the heating effect.
Dry by using an external source of heat, for example,
heaters; lamps; or hot air blowers.
Leave openings to exhaust the damp air.
5.13.1.3 Drying generator in rotation
CAUTION
THIS OPERATION MUST BE DONE BY A QUALIFIED
OPERATOR
Disconnect the machine from the mains
Short circuit the machine stator at the machine terminals
Disconnect the Voltage regulator. If booster current
transformer used, short-circuit the booster.
Run the machine at its nominal speed (to air cool the
machine) with cooling system in operation.
Energized the machine (exciter field) using an separate ex
citation source. Use a DC source (batteries ...).
Install an amp meter on excitation supply line.
Adjust the excitation current to get 2/3 of the nominal
excitation current (refer to name plate data or alternator
test report)
Warm up during 4 hours, stop and leave it to cool down
(winding temperature < 50°C)
Check the winding insulation and the polarization index
If necessary conduce other drying period...
V1
U2
V2
W2
W1
U1
DC
S
R
E
+ -
A
S - Stator
R - Rotor
E - Exciter
Electric Power Generation
Installation and maintenance
5654
en - 2017.
10
/
a
LSA 5
2
.2
MHV
Industrial Range Alternators
- 4 pole
32
