MI L-DTL-53133/ 7C
3.11 Frequency transient performance. Following a sudden increase or decrease in load
up to and including rated load, the governing system shall re-establish stable engine
operating conditions within 2 seconds. The maximum transient frequency change above or
below the new steady-state frequency shall be not more than 4 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) as follows:
- Between 58 and 62 but not below 65 Hz for the 60 Hz operating condition.
- Between 48 and 52 but not below 45 Hz for the 50 Hz operating condition.
I t shall not be possible to adjust the frequency for operation within the 48 to 52 Hz range
when the frequency selector switch is in the 60 Hz position; and it shall not be possible to
adjust for operation in the 58 to 62 Hz range when the frequency selector switch is in the
50 Hz position. Further, it 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. With the set operating at rated voltage and frequency and no
load, maximum difference between line-to-line voltage 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. 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 one phase shall
be not more than 1 volt.
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.
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