Power Tech Generators PTS-30 Operator's Manual page 154

After adjusting the voltage and stability, the AVR will not typically require further adjustment.
However, if voltage collapse or poor voltage regulation result when a load is applied, additional
adjustments may need to be made. Please see the subsections below on the other possible adjustments
to determine if one or more of these will fix the problem being experienced. Be sure to read through each
carefully to be sure the correct adjustment is being made and to be sure it is done correctly.
The UFRO is an under speed protection circuit that produces a volts/frequency (speed) characteristic
whenever the speed of the generator shaft goes below a set threshold called the knee point. The UFRO
needs adjustment if the generator is under load and a) the LED remains constantly lit or b) if voltage
regulation is poor.
The knee point can be adjusted by using a small flathead screwdriver to turn the UFRO potentiometer.
Please refer to the proper AVR diagram in section 2.4.4 to locate the UFRO potentiometer. Turning the
UFRO potentiometer clockwise will lower the knee point frequency (speed) setting and turn off the LED.
Ideally, the knee point should be set so that the LED lights whenever the frequency becomes less than
the nominal frequency. For a 50 Hz generator, this would be about 47 Hz, while for a 60 Hz generator; it
would be about 57 Hz.
The figure below shows the relationship between voltage and frequency within the UFRO. Note when the
UFRO potentiometer is turned counterclockwise (CCW) the knee point is shifted to the right. If it is turned
clockwise (CW) the knee point is shifted to the left.
CW
Knee Point
100%
95%
90%
85%
80%
75% 80% 85%
Frequency (Speed) Percentage
(Typical Setting Shown)
Only for AGR341 & AGR321 AVRs
In the event of a short circuit from line-to-line or line-to-neutral or a large overload, PMG-excited AVRs
such as the AGR341 and AGR321 provide maximum excitation power. Therefore, these AVRs utilize an
over excitation circuit to protect the generator windings. This circuit detects high excitation and after a set
amount of time, typically 8-10 seconds, it removes the excitation. If the excitation trip is not set properly,
the output of the generator will fail when loaded or slightly overloaded and the LED will stay lit. The
CCW
90% 95% 100%
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