Nidec LSA 52.3 - Winding Drying; General Information; Drying Method; Drying Generator in a Stopped Position

Electric Power Generation
Installation and maintenance
5382 en - 2022.11 / h
LSA 52.3 / LSA 53.2 / LSA 54.2
Industrial Range Alternators
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5.11 WINDING DRYING
5.11.0 General information
All electrical machines must be stored dry. If a machine is
placed in a damp environment, it should be dried prior to
start-up. Units operating intermittently or placed in areas
with high temperature variations, are exposed to dampness
and must be dried very thoroughly if necessary.
5.11.1 Drying Method
5.11.1.1 General information
During the drying operation, measure the coil insulation
and polarisation index every 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.
5.11.1.2 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 on the winding
and the temperature must not exceed 75°C (167°F). If one
of the thermometers exceeds this value, immediately
reduce the heating.
Dry by using an external source of heat, for example,
heaters, lamps, or hot air blowers.
Leave openings to exhaust the damp air.
5.11.1.3 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 a booster current
transformer used, short-circuit the booster.
Run the machine at its nominal speed (to air cool the
machine) with the cooling system in operation.
Energise the machine (exciter field) using an separate
excitation source. Use a DC source (batteries, etc.).
Install an ammeter 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 polarisation index.
If necessary, repeat the drying.
V1
U2
V2
W2
W1
U1
DC
S
R
E
+
-
A
S - Stator
R - Rotor
E - Exciter