The sensing voltage is the three-phase AC voltage at terminals 20, 22 and 24. The ratio of the sensing voltage to the generator voltage depends on the following conditions:
- The connection point of the sensing leads to the generator leads
- The use of power transformers (PT)
The reference voltage is set by the voltage adjust potentiometer or by an external voltage adjust potentiometer. The reference voltage is the desired voltage on the output of the generator at rated frequency.
The knee frequency is adjusted by turning the knee frequency adjustment. Without setting the knee frequency, generator voltage would follow generator frequency proportionally. If the generator frequency is above the adjusted knee frequency, the regulator maintains the generator voltage at the reference voltage.
If the generator frequency drops below rated frequency, the regulator will regulate the voltage to a lower reference voltage. This helps the engine to recover quickly during block loading. The reference voltage is proportional to the generator frequency. There are two slopes that can be selected: 1 V/Hz and 2 V/Hz. The jumper between terminals 6A and 8 creates a 1 V/Hz slope. In this case, a 1 percent change in frequency below the knee frequency adjustment will produce a 1 percent lower reference voltage. In order to select a 2 V/Hz slope, remove the jumper between terminals 6A and 8. In this case, a 1 percent change in frequency below the knee frequency adjustment will produce a 2 percent lower reference voltage.
When a generator set operates in parallel with another generator set, it is necessary for the output voltages to match in order to prevent circulating currents. Depending on the power factor, the droop raises the reference voltage or the droop lowers the reference voltage. This slight raising of the output voltage or lowering of the output voltage results in the reactive load sharing between gensets that are operating in parallel.
Because of a time delay from the moment when the regulator senses a change in voltage to the moment when the generator voltage is increased or decreased, the generator voltage can become unstable (or hunt). The time delay varies. This delay depends on time constants for the exciter and the generator. The stability circuit slows the response of the regulator in order to stabilize the voltage. The stability adjustment is used in order to ensure that the regulator responds as quickly as possible, while still keeping the voltage stable.
The over excitation protection will shut the regulator off at 90 VDC ± 5%. The over excitation protection takes the output to zero in greater than 30 seconds. The output can be 125 VDC for greater than 10 seconds.
The generator set must be shut down or the input voltage to the regulator must be held below 6 VAC for a minimum of 2 seconds in order to reset the regulator.