Underfrequency Limiter

The output from one winding of the generator sensing transformer is applied to the underfrequency limiter

circuit. It is the function of this circuit to reduce the generator output voltage when the generator is operated

at less than rated speed. The percentage of generator output voltage that will be obtained for a specific

reduction in frequency is illustrated in Figures 1-1 and 1-2. The horizontal axis of the graph represents

generator frequency and the vertical axis represents the percent of nominal generated output voltage. Volts

per-hertz operation is obtained by jumping the terminals located on TS3. Limiting for 50 or 60 Hz is obtained

by proper positioning of the jumper on TS4. (Refer to Section 3. Jumper Connections)

Parallel Compensation

When two generators are operating in parallel, if the field excitation on one generator becomes excessive

and causes a circulating current flow between generators, this current will appear as a lagging power factor

(inductive) load to the generator with excessive field current and as a leading power factor (capacitive) load

to the other. The parallel compensation circuit causes the exciter-regulator to decrease the field excitation

on the generator with the lagging power factor load and increases the excitation on the other generator to

minimize the circulating currents.