ARMY TM 9-6115-464-34
AIR FORCE TO 35C2-445-2
NAVY NAVFAC P-8-624-34
Average the three valid power readings. This average is the observed maximum power value.
Correct the observed maximum power value to standard conditions using the procedure in
MILHDBK-705, Method 220.2, paragraph 220.2.3. This is the corrected maximum power value.
3. Compare these results with the requirements of table 4-1.
4-24. 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 equipped with an underfrequency protective device. The device on this generator
operates electrically. Although 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.
b. Apparatus Instrumentation for measuring load conditions shall be as described and illustrated in method
205.1. paragraph 205.1.10 of MILL-HDBK-7050.
(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 device, this test shall be repeated with the
voltage adjusted to maximum and minimum voltage for the specified voltage operating range.
(b) With the circuit interrupter closed, slowly decrease the operating speed until the protective device
causes the circuit interrupter to open. The electric governor must be deactivated to sufficiently
decrease 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 in table 4-1.