(a) Calculate the short-circuit current using
consecutive voltage and current readings of the ex-
the peak-to-peek amplitudes of the current trace and
alter field either remain unchanged or have only
the steady state ammeter reading prior to application
of the short circuit. See figure 512. l-II
no evident continued increase or decrease in value
after the last load, voltage or frequency adjustment
(3) Tabulate the above results and the mal-
has been made.
function idicator indication for each line connection
at each voltage connection and compare the results
(c) In one step, increase the load current
to the overload current value specified in table 7-1
(the increase in current may be accomplished by any
7-19. CIRCUIT INTERRUPTER TEST (OVERLOAD
practical means, e.g. reactively or using reduced
a. General. A circuit interrupter is connected
between the generator voltage reconnection system
and the generator output terminals to disconnect the
The frequency shall be maintained at rated
conditions, the load current shall be kept
generator output from the load and to protect the
constant and the load current shall be bal-
generator from a sustained overload current. The
anced equally among the phases. Simul-
circuit interrupter is operated from a current sensor
taneously with the load current increase,
external to the interrupter.
start the stop watch.
b. Apparatus. Instrumentation for measuring
load conditions and field voltage and current shall be
time, in seconds, required for the circuit interrupter
as described and illustrated in MIL-HDBK-705. In
addition, a stopwatch or an oscillograph with galvan-
ometers matching network and a non-inductive shunt
(e) The generator set contains an overload
as described and illustrated in MIL-HDBK-705,
malfunction indicator. Check and record its indication.
Method 106.1, paragraph 106.1.3 and galvanometers
having a flat frequency respond (within plus or minus
5%) from dc to 3000 Hz.
(f) Allow the generator set to cool at rated
load for a minimum of 15 minutes.
c . Procedure.
(g) Repeat steps (c) thru (f) except that the
(1) Preparation for test. Connect the load and
load current is increased to the overload current value
field instrumentation in accordance with the applicable
in Phase A only. Phases B and C remain at the rated
figure of MIL-HDBK-705, Method 205.1, paragraph
load current value.
205.1.10 for one voltage and frequency.
(b) Repeat step (g) except that the load is
increased to the overload current value in phase B
only. Phases A and C remain at the rated load value
If the circuit interrupter fails to operate
(i) Repeat step (g) except that the load is
any time during the performance of this
increased to the overload current value in phase C
method, manually open the circuit inter-
only. Phases A and B remain at the rated load value
rated value before reclosing the circuit
d. Results. The data sheets shall show, as a
interrupter. Record on the data sheet the
minimum, whether or not the circuit interrupter oper-
failure of the interrupter to operate and
ated, the time(s) required for the interrupter to oper-
the total elapsed time the overload was
ate, the indication of the malfunction indicator, the
on the set.
overload conditions ) and the stabilization data. Com-
(a) Start and operate the generator set at
rated voltage, rated frequency and rated load.
7-20. CIRCUIT INTERRUPTER TEST (OVER
VOLTAGE AND UNDER VOLTAGE).
(b) Allow the generator set to stabilize at
rated load, voltage and frequency. During this period,
a. General. To protect the load from generator
malfunction (e. g., overvoltage or undervoltage) a
recorded at minimum intervals of 10 minutes. If
necessary, adjustments to the load, voltage and fre-
circuit interrupter is connected between the generator
voltage reconnection system and the generator output
quency may be made to maintain rated load at rated
voltage and frequency. Adjustment to the load, voltage
terminals. A voltage sensing circuit operates the
or frequency shall be noted on the data sheet. Stabili-
circuit interrupter if an overvoltage or undervoltage
zation will be considered to have occurred when four
condition occurs and thus protects the load from a