Diesel Gen-set Operation Instructions
68
If the Gen-set does not operate immediately, make sure that condensation removing
heater installed on alternator is energized and operates normally. Measuring of
insulation resistance is still necessary before starting of operation next time.
Warning: never carry out short connection of three-phase winding when AVR
and alternator is connected to a loop as winding will be damaged when current
exceeds rated current of the alternator.
6.4 Typical drying curve
No matter the alternator is dried by what way, record insulation resistance value once
every half hour and tabulate these records into a graph as shown in Figure 9-4.
Figure 9-4 Typical drying curve
Figure 9-4 shows typical drying curve of a very humid alternator. This curve shows
that insulation resistance reduces and then rises to a stable value gradually after rising
for a short period of time. Insulation resistance under stable state at point A must be
higher than 1 MΩ. (If winding is only lightly affected with damp, it may not be
observed at dotted line part in the figure).
The drying process will at least last 1 hour when “A” point is reached.
Note: insulation resistance will reduce significantly when temperature of winding
rises. References of above insulation resistances are values measured when
Min. insulation resistance
Insulation resistance
Time
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