MI L-DTL-53133/ 3B
percent of rated frequency. The system shall not permit repetitive frequency variations,
commonly called "hunting", even though within the allowable 2 percent band.
3.8 Frequency long-term stability (4 hours). At constant ambient temperature,
constant barometric pressure, constant voltage, and any constant load from no load to
rated load, the 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.
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