Note: Before adjusting the stability, ensure that the selector switch on the R250 is correctly set for the rated frequency of the generator. Use position 9 on the selector switch for 50 Hz operation, or position 6 for 60 Hz operation.
In order to obtain an optimal setting for stability, monitor the line voltage on the generator output terminals and the excitation voltage on the R250 AVR. Use terminals "E+" and "E-" on the R250 AVR in order to monitor the excitation voltage. A rapid change in the voltage (oscillation) between terminals "E+" and "E-" will indicate unstable regulation.
Rotate the potentiometer for the stability adjustment "P2" to the middle position. Start the engine. Adjust the speed of the engine in order to achieve an output frequency of 48 Hz for a generator that is rated for 50 Hz or 58 Hz for a generator that is rated for 60 Hz. Run the generator with no load.
Adjust the voltage level to the rated voltage. After the generator has reached the rated voltage, observe the regulation of the line voltage and rotate the stability adjustment "P2" in the counterclockwise direction until the voltage starts to oscillate. Rotate the stability adjustment "P1" in the clockwise direction in order to slow the response time slightly.
Note: The best response times to the load changes are obtained at the limit of instability.
Set the engine operating speed to the desired nominal frequency. Set the selector to the desired operation for the operating frequency. The selector will be set to either constant V/Hz or LAM operation. Verify that the voltage output from the generator is stable throughout the load range of the generator.