MI L-DTL-53133/ 6B
below the new steady-state frequency shall be not more than 1.5 percent of rated
frequency.
3.12 Frequency adjustment. By means of the frequency adjust device, it shall be
possible to adjust the frequency, (when the set is operating at any constant load)
between 390 and 420 Hz but not below 370 Hz nor above 430 Hz. I t shall not be
possible to adjust frequency to a value which will actuate the overspeed protective
device.
3.13 Voltage waveform. The deviation factor for the line-to-line and line-to-neutral
voltage waveform for each voltage connection shall be not more than 5 percent, nor
shall any single voltage harmonic be more than 2 percent. 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.
3.14 Voltage unbalance. Maximum difference between line-to-line voltages shall be
not more than 5 percent of rated voltage for the 240/ 416-volt connection under the
conditions of a single phase, line-to-line unity pf-load of 25 percent of rated current and
no other load on the generator.
3.15 Phase balance voltage. With the set operating at rated voltage and frequency
and no load, maximum difference in the three line-to-neutral voltages shall be not more
than 1 percent of the rated line-to-neutral voltage. The maximum difference between
the voltage of the 120-volt windings of any phase shall not exceed 3 volts.
3.16 Voltage modulation. The voltage modulation of the output voltage for any
load, up to and including rated load, shall not exceed 1 percent. This requirement shall
apply to all line-to-line and line-to-neutral voltages.
3.17 Voltage regulation. The voltage regulation from no load to rated load and from
rated load to no load shall be not more than 1 percent of the rated voltage for all
voltage connections throughout the voltage ranges specified in 3.22.
3.18 Voltage short-term stability (30 seconds). At every constant load from no load
to rated load, the voltage at the set terminals shall remain within a bandwidth equal to
1 percent of rated voltage.
3.19 Voltage long-term stability (4 hours). At constant ambient temperature,
constant barometric pressure, constant frequency and any constant load from no load
to rated load, the voltage shall remain within a bandwidth of 2 percent of rated voltage
in a 4-hour operating period.
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