MI L-DTL-53133/ 10C
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.
3.20 Voltage drift. With the set operating at constant load and frequency, a change in
ambient temperature up to 33 C° (60 F° ) in an 8-hour period shall not cause the voltage to
change by more than 1 percent, set temperature stabilization being accomplished at both
the initial and final ambient temperature conditions.
3.21 Voltage transient performance. Performance of the set under transient conditions
(as measured by an oscillograph) shall be as follows (reactive droop compensation of the
voltage regulator being inoperative):
a. With the set initially operating at no load, rated voltage, and rated frequency, the
terminal voltage of the set shall not drop to less than 75 percent of no load voltage
when a balanced 3-phase, 0.4 pf (or less) lagging, static load having an impedance
of 0.5 per unit is suddenly applied to the output terminals of the set. When
connected to the specified load, the output voltage shall recover to a minimum of
95 percent of rated voltage within 0.7 seconds and shall stabilize at or above this
voltage. The above specified voltage dip shall not be exceeded when a fully-loaded
induction motor of the above specified impedance is used in place of a static load,
and no reactions shall be set up to prevent full acceleration of the motor with rated
torque applied to its shaft.
b. When the set is initially operating at rated frequency, rated voltage, and following
any sudden change in load from no load to rated load, the instantaneous voltage
shall not drop to less than 88 percent of rated voltage and shall reach stable
conditions within 0.5 seconds; no overshoot or undershoot of the final voltage shall
not exceed the initial voltage transient in amplitude. The above requirements shall
also apply when the load is suddenly changed from rated load to no load, except
that the initial voltage transient shall not exceed 112 percent of rated voltage.
c. The generator set shall be capable of across-the-line starting a motor rated at 1
horsepower per kW of set kW rating. The starting current rating of the motor shall
be NEMA Code F and the motor shall be loaded with a flywheel having an inertia
equal to that of the motor rotor.
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