MI L-DTL-53133/ 8C
operating conditions within 1 second. The maximum transient frequency change 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 condition of
a single phase, line-to-line, unity pf-load of 25 percent 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, the 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 be not more than 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 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.
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