by the rated voltage of the generator and multiply by
100 to convert to percentage.
(4) To determine the maximum overshoot and
undershoot at each load step, and express this as a
percentage of its rated voltage, proceed as follows:
(a) From the meter recording charts, deter-
mine the maximum amount that the voltage trace goes
beyond the line (3) of the observed voltage band follow-
ing the load change.
See figure 16-1 for illustration
of overshoot and undershoot.
(b) Divide the result obtained in (a) by
rated voltage (as given on the generator nameplate),
then multiply by 100 to convert to percentage.
Do not use the constant operating voltage
at each load as the divisor in the compu-
tation. Use only the rated voltage of the
(5) To determine the time required to restore
stable voltage conditions after each load change
(a) The prescribed steady state voltage
bandwidth, extended to the point at which the voltage
trace leaves the prescribed steady state band, shall
be considered as the time at which the transient con-
The point at which the voltage trace
enters and remains within the prescribed band after
a load change shall be considered as the point at which
(b) Measure the distance (in inches) on the
chart from the point where the voltage trace leaves
the prescribed steady state band to the point where
it re-enters and remains within the prescribed voltage
band for the next load condition.
(c) Divide this distance by the chart speed
(in inches-per second).
This will give the voltage
recovery time, in seconds.
(6) Determine the voltage regulation for all
load changes (e. g. rated load to no load, 1/2 rated
load to no load to 1/4 load, etc. ) as follows:
(a) Using the indicating voltmeter readings
subtract the load value of voltage from the no load
value for each load change (e. g. step (a) to step (b)).
(For voltage regulators utilizing single-phase voltage
sensing, the value of voltage in the sensed phase only
shall be used in the above calculations.
regulators utilizing multi-phase voltage sensing the
average value of the sensed voltage shall be used. )
(b) Convert each of the values obtained in (a)
above to a percentage of rated voltage by dividing by
the rated voltage and multiplying by 100. This is the
voltage regulation expressed in percent.
(c) Repeat paragraph 16-15d. (1) above sub-
stituting frequency for voltage.
(d) Compare the results tabulated in para-
graphs 16-15d. (1) and 16-15d. (6)(c) with the require-
ments of Table 16-1.
16-16. Frequency Adjustment Range Test.
a. General. It is necessary that the frequency of
a generator set be adjustable to provide rated fre-
quency at various load conditions as required in
certain applications and to synchronize two or more
generator sets for parallel operation.
b. Apparatus. Instrumental ion for measuring
load conditions, field voltage and current, and
ambient temperature shall be as described and
illustrated in MIL-HDBK-705.
(1) Preparation for test. Connect the load and
field instrumentation in accordance with the applicable
figure of MIL-HDBK-705, Method 205.1, paragraph
(a) Start and operate the generator set
and allow it to stabilize at rated load, rated
voltage and rated frequency.
During this period, readings of the load and field
instrumentation shall be recorded at minimum in-
tervals of 10 minutes. If necessary, adjustments to
the load, voltage and frequency may be made to
maintain rated load at rated voltage and rated fre-
quency. However, adjustments available to the
operator, specifically adjustments to voltage and
frequency adjust devices. Adjustments to the load,
voltage or frequency shall be noted on the stabiliza-
tion data sheet. Stabilization will be considered to
have occurred when four consecutive voltage and
current readings of the exciter field either remain
unchanged or have only minor variations about an
equilibrium condition with no evident continued in-
crease or decrease in value 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 the control panel frequency adjust device.
(c) For each of the conditions in the follow-
ing steps allow approximately 2 minutes between each
adjustment and the subsequent instrument readings.
(d) Adjust the generator set frequency for
the specified maximum frequency at rated load.
Read and record all instrument readings.
(e) Adjust the generator set frequency for
the specified minimum frequency at rated load.
Read and record all instrument readings.
(f) Reduce the load to zero.
(g) Adjust the generator set frequency for
the maximum attainable frequency. Read and record
all instrument readings. If the overfrequency or