10
In addition remove the AVR housing cover and turn "VOLTS"
control fully anti-clockwise.
Start the generating set and run on no-load at nominal
frequency. Slowly turn "VOLTS" control potentiometer
clockwise until rated voltage is reached. Refer to Fig. 1 for
potentiometer location.
Important!
Do not increase the voltage above the
rated generator voltage shown on the
generator nameplate.
The "STABILITY" control potentiometer will have been pre-
set and should normally not require adjustment, but should
this be required, usually identified by oscillation of the
voltmeter, refer to Fig. 1 for potentiometer location and
proceed as follows:-
1.
Run the generating set on no-load and check that
speed is
correct and stable.
2.
Turn the "STABILITY" control potentiometer
clockwise,
then turn slowly anti-clockwise until the generator
voltage starts to become unstable.
The correct setting is slightly clockwise from this position (i.e.
where the machine volts are stable but close to the unstable
region).
4.7 LOAD TESTING
Warning!
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 ADJUSTMENTS
Refer to Fig. 1 for control potentiometer locations.
Having adjusted "VOLTS" and "STABILITY" during the initial
start-up procedure, the AVR control functions "UFRO", "OVER/V" and
"EXC. TRIP" 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.
4.7.2 UFRO (Under Frequency Roll Off)
The AVR incorporates an underspeed protection circuit
which gives a voltage/speed (Hz) characteristic as shown in
Fig. 2.
Fig. 2
The UFRO control potentiometer sets the "knee point".
Symptoms of incorrect setting are a) the light emitting diode
(LED) indicator, adjacent to 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.
Important!
If the LED is illuminated and no output
voltage is present, refer to EXC TRIP
and/or OVER/V sections below.
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.
4.7.3 OVER/V (Over Voltage)
Over voltage protection circuitry is included in the AVR to
remove generator excitation in the event of loss of AVR
sensing input or a short circuit of AVR power device. AVR
terminals E1, E0 are connected to the generator windings
independently of the AVR serving terminals.
A shunt trip circuit breaker is connected across AVR
terminals K1, K2 these connections under normal operation
being connected together.
If an over voltage condition is detected the AVR generates
an output pulse via terminals B0, B1 which activates the
shunt trip mechanism within the shunt trip circuit breaker.
This in turn opens circuits AVR terminals K1., K2., and de-
excites the generator.
The generator must be stopped to reset an overvoltage trip.
Incorrect setting would cause the generator output voltage to
collapse at no-load or on removal of load, and the LED to be
illuminated,
The correct setting is 300V +/-5% across terminals E1, E0.
Clockwise adjustment of the “OVER/V” control potentiometer
will increase the voltage at which the circuit operates.
