powerline frequency which is proportional to the difference between the command signal and 
the generator output. The resulting error signal is rectified in a phase-sensitive demodulator 
and then passed through a d-c amplifier. Power level is increased to a maximum of 30 watts 
which is sufficient to drive the generator to full output. Transient response of the regulator 
is improved by the lead network in the feedback loop which provides a damping factor of 
about 0.6. Full-scale output voltage may be set for either 150 or 300 volts by the range switch 
which controls feedback signal and amplifier gain. Amplifier gain is sufficient to hold the 
generator output to within + 1 percent of the command setting for changes in load or battery 
voltage. 
4.5 MOTOR ALTERNATOR 
Power for the error regulator and all electronic instruments is supplied by the motor- 
alternator set. This specially-designed set consists of a 36 volt, 12,000-rpm, d-c shunt motor 
driving a 115-volt, 400-cps, 3-phase, 750-watt alternator. A governor on the motor maintains 
the speed constant within 2 percent. The duty cycle of the alternator set is continuous. The 
motor can withstand the 49 volts which is applied by the battery charger during charging 
operations between runs. 
4.6 BATTERY CHARGER 
The battery charger requires a 3-phase, 600-volt source capable of delivering 20 amperes 
of current and it can deliver up to 300 amperes at 49 volts d. c. The charger is capable of 
quick-charging the 40-ampere-hour battery at a 200-ampere rate while simultaneously supplying 
power to a motor-alternator set and two motor-generator sets. The charger is fan-cooled and 
consists of three single-phase, tapped-primary transformers feeding a 3-phase bridge selenium 
rectifier. The charger features a timing relay adjustable from zero to 8 hours which automati- 
cally turns the charger off at the end of a preset charging period. The timing cycle starts when 
the charging rate switches from the high rate to the low rate. A 10-kva, 3-phase, 480/600-volt 
autotransformer is provided to enable operation of the 600-volt charger from a 480-volt supply. 
4.7 STARTING EQUIPMENT 
Reduced-voltage starting of the motor-alternator and motor-generator sets is accom- 
plished by inserting additional resistance in the armature circuit of the motors. These re- 
sistors are automatically cut out of the circuit by time-delay relays which short them out at 
preset time intervals. The running contactor in the model is the final shorting step and when 
it pulls in and seals, the starting cable may be disconnected from the model after the STOP 
button is pushed. The START-STOP pushbutton station, the resistors, and the time-delay 
relays are mounted on the battery charger. 
II-8 
