TROUBLE SHOOTING
34
November 2010 / M-SQ20 / 25 / EN
5.3.5 Meggering
One can try to measure resistance between the housing
and the windings with a multimeter which should read
infinity. When readings are infinity but a fault is suspected
one can do a high voltage resistance test (MEGGERING)
This procedure should be carried out by an expert. The
AVR should be disconnected during this test. A 500V
‘Megger’ or similar instrument should be used. The
insulation resistance to earth of all windings should be in
excess of 2 MOhm. Should the insulation resistance be
less than this value, drying out the generator windings is
essential. Drying out can be carried out by direct warm air
(60-80ºC) from a fan heater or similar apparatus into the
generator air inlets or outlets.
5.4
Special procedures engine
5.4.1
Setting the RPM
RPM is set by the manufacturer and should not need
readjustment! However a very slight offset after running in
could occur. RPM can be measured by a frequency meter.
Before readjustment check any other explanation for the
wrong speed. Engine speed is set at the factory at nominal
1500 (50 Hz) RPM. A RPM drop of 5% at full load is
acceptable. Therefore a no load setting should be at ±
1575 RPM = 52.5 Hz. Under no circumstances should the
RPM be under full load below 1470 RPM = 49 Hz. When
no cause can be found for a wrong speed, the setting can
be adjusted:
01
01
Engine speed adjusting screw
Fig. 27 Location engine speed adjustment screw.
It is very important to identify the correct setting assembly
(see fig. 27). The screw is to be locked in position with the
lock-nut.
