PI Manufacturing AC generators - Manual (Page 15)

4.7 LOAD TESTING
During testing it may be necessary to
remove covers to adjust controls
exposing 'live' terminals or components.
Only personnel qualified to perform
electrical service should carry out testing
and/or adjustments. Refit all access
covers after adjustments are completed.
4.7.1 AVR CONTROLLED GENERATORS – AVR
ADJUSTMENTS
Refer to Fig. 6a, 6b, 6c, 6d or 6e for control potentiometer
locations.
Having adjusted VOLTS and STABILITY during the initial
startup procedure, other AVR control functions should not
normally need adjustment.
If however, poor voltage regulation on-load or voltage
collapse is experienced, refer to the following paragraphs on
each function to a) check that the symptoms observed do
indicate adjustment is necessary, and b) to make the
adjustment correctly.
4.7.1.1 UFRO (Under Frequency Roll Off) (AVR
Types SX460, SX440, SX421, MX341 and MX321)
The AVR incorporates an underspeed protection circuit which
gives a voltage/speed (Hz) characteristic as shown :
Fig. 7
The UFRO control potentiometer sets the "knee point".
Symptoms of incorrect setting are a) the light emitting diode
(LED) indicator, just above the UFRO Control potentiometer,
being permanently lit when the generator is on load, and b)
poor voltage regulation on load, i.e. operation on the sloping
part of the characteristic.
Clockwise adjustment lowers the frequency (speed) setting of
the "knee point" and extinguishes the LED. For Optimum
setting the LED should illuminate as the frequency falls just
below nominal frequency, i.e. 47Hz on a 50Hz generator or
57Hz on a 60Hz generator.
Important ! With AVR Types MX341 and MX321. If the
LED is illuminated and no output voltage is
present, refer to EXC TRIP and/or OVER/V
sections below.
Warning !