Cross-Compound Turbine-Generator Turning-Gear Synchronization Study II-Field Test Investigation

1. The internal phase angle between rotors at the instant of initial field excitation was found equally as important as the magnitude and rate of application of excitation voltage in affecting the turning-gear synchronization process for this particular machine. As both elements have identical generators and turning speeds, and nearly equal inertias, the optimum initial phase angle was found near 0 degrees. For cross-compound machines having widely dissimilar elements and different nominal turning speeds, however, the same conclusions may not apply. The worst initial phase angle for synchronizing this machine was found to be near 180 degrees. Although initial phase angle is normally a purely random variable, monitoring devices such as those used in these tests may be warranted in some cases for remotely indicating phase difference angle for use during either manual or automatic start-up operation. 2. The optimum excitation voltage level for smoothest synchronization was found to be near 60-65 volts for each machine, or about 60% of rated opencircuit excitation. With excitation reduced to 38 volts (37% open-circuit) or increased to 80 volts (75% open-circuit) synchronization failure resulted. Best results were obtained by presetting the exciter voltage to the desired level followed by simultaneous closure of both field breakers. Sequential operation of field breakers gave less satisfactory results, and, in some cases, resulted in synchronization failure. 3. Data from the tests illustrated in Figs.