MI L-DTL-53133/ 1B
system shall maintain frequency within a bandwidth equal to 3 percent of rated frequency in
a 4-hour operation period.
3.9 Frequency drift. With the regulation set at not more than 3 percent and with the set
operating at constant load and voltage, a change in ambient temperature of up to 33 C°
(60 F° ) in an 8-hour period shall not cause the frequency to change by more than 2 percent,
set temperature stabilization being accomplished at both the initial and final ambient
temperature conditions.
3.10 Frequency transient performance. Following any sudden increase in load, including
from no load to rated load, the governing system shall re-establish stable engine operating
conditions within 3 seconds, and the maximum transient frequency change below the new
steady-state frequency (undershoot) shall be not more than 3 percent of rated frequency.
Following any sudden decrease in load, including from rated load to no load, the governing
system shall re-establish stable engine operating condition within 3 seconds, and the
maximum transient frequency change above the new steady-state frequency (overshoot)
shall be not more than 4 percent of rated frequency.
3.11 Frequency adjustment. By means of the frequency adjust device, it shall be
possible to adjust the frequency, when operating at any constant load, between 58 and 62
Hz. I t shall not be possible to adjust the frequency to a value which activates the overspeed
protective device.
3.12 Voltage waveform. The deviation factor and any single voltage harmonic for the
line-to-line and line-to-neutral voltage for each voltage connection and load connection shall
be not more than the following:
a. The deviation factor shall not exceed 6 percent in the single phase connections or 5
percent in the 3-phase, 120/ 208 volt connection.
b. Single frequency harmonics shall not exceed 3 percent in the single phase
connections or 2 percent in the 3-phase, 120/ 208 volt connection.
I n addition, there shall be no evident discontinuities, spikes, or notches in the waveform
when viewed on an oscilloscope having a bandwidth of DC to 1.5 MHz and usable viewing
screen of 8 x 10 cm. The oscilloscope gain shall be adjusted such that one cycle of voltage
wave covers approximately the entire viewing screen.
3.13 Voltage unbalance. Maximum difference between line-to-line voltages shall be not
more than 5 percent of rated voltage for the 120/ 208-volt connection under the conditions
of a single phase, line-to-line unity pf-load of 25 percent rated current and no other load on
the generator.
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