TM 9-6115-604-34NAVFAC P-8-633-34(e) Voltage stability. The voltage shall remain within a bandwidth equal to 1 percent of the ratedvoltage at every constant load.(f) Voltage transient response.1 The instantaneous ms voltage shall not drop to less than 80 percent of the rated voltage, andshall reach stable condition within 3 seconds with sudden changes from no load to half load, andhalf load to full load. Overshoot or undershoot of the final voltage shall not exceed the initialvoltage transient in amplitude.2 The instantaneous rms voltage shall not rise to more than 130 percent of the rated voltage, andshall reach stable conditions within 3 seconds with sudden changes from half load to no load.Overshoot or undershoot of the final voltage shall not exceed the initial voltage transient inamplitude.3 When a balanced three-phase 0.4 pf, or less, lagging static load with an impedance of 0.5 perunit is applied to the output terminals of the set. Operating at no load, rated voltage, and ratedfrequency, the instantaneous ms voltage shall not drop to less than 60 percent of the ratedvoltage.12-24. FREQUENCY ADJUSTMIENT RANGE AND UNDERFREQUENCY TRIP.a.General. The frequency of the generator set must be adjustable to provide rated frequency at various loadconditions, and to synchronize two or more generator sets for parallel operation.b.Apparatus. Instrumentation for measuring load conditions, field voltage and current, and ambient temperatureshall be as illustrated in Figure 12-3 and Figure 12-5.c.Procedure(1)Preparation for test. Connect the load and field instrumentation in accordance with Figure 12-3 and Figure12-5.(2)Test.(a)Start and operate the generator set and allow it to stabilize at rated load, voltage, and frequency.During this period, readings of the load and field instrumentation shall be recorded at minimumintervals of 10 minutes. If necessary, adjustments to the load, voltage, and frequency may be madeto maintain the rated load at the rated voltage and frequency. Adjustments to the voltage andfrequency, however, shall be limited to those available to the operator: specifically, adjustments tothe voltage and frequency adjust devices. Adjustments to load, voltage, or frequency shall be notedon the stabilization data sheet. Stabilization will be considered to have occurred when fourconsecutive voltage and current readings of the exciter field either remain unchanged, or have onlyminor variations about an equilibrium conditions with no evident continued increase or decrease invalue after the last load, voltage, or frequency adjustment has been made.(b)No further adjustments shall be made to any set control for the remainder of this test except for thecontrol panel frequency adjust device.(c)For each of the conditions in the following steps, allow approximately 2 minutes between eachadjustment and the subsequency instrument readings.(d)Adjust the generator set frequency for the specified minimum frequency (57.5 at 60 Hz, 47.5 at50Hz) at rated load. Read and record all instrument readings.(e)Reduce the load to zero.(f)Adjust the generator set frequency for the maximum attainable frequency. Read and record allinstrument readings. If the over-frequency or overspeed protection device acutates, read and recordall instrument readings just prior to the point of actuation, and note on the data sheet that theprotection device actuated.(g)Adjust the generator set frequency for the minimum attainable frequency. Read and record allinstrument readings, and trip point.(h)Repeat steps c(1) and (2), for each frequency.d.Results. The data sheet shall show the maximum and minimum frequencies attained at rated load, themaximum and minimum frequencies attained at no load, and actuation of the protection devices. Comparethese results with the requirements of Table 12-3.12-34
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