available to the operator, specifically adjustments
to the voltage or frequency adjust devices. On gen-
erator sets utilizing a droop-type speed control
system as the prime speed control, the speed and
droop portions of the control may be adjusted. No
other adjustments to the voltage and frequency con-
trol systems shall be made.
Adjustments to the
load, voltage or frequency controls shall be re-
corded on both the data sheet and recording chart(s).
Stabilization will be considered to have occurred when
four consecutive voltage and current recordings of
the exciter field either remain unchanged or have only
minor variations about an equilibrium condition with
no evident continued increase or decrease in value
after the last adjustment to the load, voltage or fre-
quency has been made.
(b) Perform this test using resistive load
Remove reactive load after stabilization.
(c) For sets with droop-type governors:
1. Load the set to 125% of rated load.
Adjust the frequency to the rated value and maintain
the load for 5 minutes.
(d) For generator sets with isochronous-
type governors, repeat step (c) above but do not ad-
just the frequency.
(e) Results. Compare these results with
the requirement of Table 16-1.
16-25. Under Frequency Protective Device Test.
a. General. For generators that power certain
types of equipment, it is extremely important that
the circuit interrupter open when the frequency fails
appreciably below rated value. Severe damage may
otherwise result to the powered equipment. To insure
that the circuit interrupter will open at or before the
critical frequency value, the generators are equip-
ped with an underfrequency protective device. The
device on this generator operates electrically. Al-
though the under frequency protective device must be
capable of functioning at any voltage throughout the
specified voltage operating range, it is necessary
only to perform the test at the specified maximum, at
rated, and at minimum voltage limits.
Instrumentation for measuring load
conditions shall be as described and illustrated in
method 205.1, paragraph 205.1.10 of MIL-HDBK-705.
(1) Preparation For Test. Connect a voltmeter
and frequency meter to the generator set terminals,
ahead of the circuit interrupter, and the remainder of
the apparatus as shown in the applicable figure of
paragraph 205.1.10 of MIL-HDBK-705.
(a) Operate the generator at rated speed and
voltage, and at no load since the generator is equipped
with an electrical-type underfrequency protective de-
vice, this test shall be repeated with the voltage ad-
justed to maximum and minimum voltage for the speci-
fied voltage operating range.
(b) With the circuit interrupter closed, slowly
decrease the operating speed until the protective de-
vice causes the circuit interrupter to open. The elec-
tric governor must be deactivated to sufficiently de-
crease the speed on Class 1, precise sets.
(c) Record the speed.
(d) Repeat the test while rapidly decreasing
the operating speed. Again record the speed.
(e) Operate the generator at rated speed and
voltage, and at rated load.
(f) Repeat steps (b), (c) and (d).
d. Results. Compare the test value of frequency
with that given Table 16-1.