| |
 Summary.-A
newly developed gas-electric generator, recently made available to the
industry, is described. There are two types, the small units having a
capacity of 40 kw. and the larger ones a capacity up to 160 kw. The gas-electric
generators described have unique features of voltage control, which is
an essential requirement when generators are used in the field with incandescent
lamps as a load. They have been designed to have minimum weights for their
capacities and are more silent in operation than any units heretofore
built.
It is
the purpose of this paper to describe some developments that have been
made in the past year toward producing suitable gas-electric generators
for supplying current used in motion picture production on location. During
the earlier years of sound motion pictures, the limitations imposed by
the recording operations restricted the taking of pictures almost exclusively
to sound-proofed stages. In the past two years technologic advance in
recording equipment and operation has made it entirely practicable to
carry on location work.
In order
that the shots taken of scenes away from the studios may attain to the
same high quality as those taken in the studios, it is necessary for both
day and night work on location to utilize the advantages of lighting by
artificial means. The supplementing of daylight with artificial illumination
is designated in studio vernacular as "booster" lighting.
In most
cases the current for booster lights may be supplied by generators having
capacities up to 60 kw. The lighting of night scenes to a large extent
parallels that of lighting stages, large values of current in this case
being required. Current for location lighting may be obtained from either
of two sources. Where power companies have transmission lines reasonably
close to the location, those lines may be tapped and portable motor-generator
sets connected to them to produce the 115-volt direct current, which is
standard in the industry. Many desirable locations isolated from a commercial
supply require the use of electric generators driven by prime movers.
Gas engine
driven generators are not new to the industry. In the days of silent pictures
many satisfactory plants were built, using aeronautical engines connected
to direct-current generators and mounted on trucks.
Fig. 1 40-kw, gas-electric generator set.
The
advent of sound pictures made obsolete most of the gas-electric generators
of the old type. The engines heretofore used were principally war-time
Liberty, Curtis, OX 5, and Hispano, engines. The valve actions were always
noisy, and the engines themselves in most cases had fallen into disrepair
and were unreliable.
As location
work was revived, the small booster lighting plants were developed, and
the better types of automobile motors were found suitable. Very satisfactory
plants have been built utilizing Chevrolet, Cadillac, Lincoln, and other
engines that could develop sufficient power to suit the various requirements.
The plant illustrated in Fig. 1 is capable of delivering 350 amperes at
125 volts as operated under motion picture conditions, and under continuous
operation will deliver 250 amperes at that voltage. The essential characteristics
of the booster plant are light weight, minimum size, reliability, and
quietness of operation. The plant, the interior of which is shown in Fig.
2, is equipped with a Ford V-8 engine, capable of producing 70 hp. at
3250 rpm. This motor was selected because of
Fig. 2 Interior view, 40-kw, gas-electric generator set.
its compactness and the reliability that it has demonstrated for motor
car use. It is connected to an electric generator which is specially designed
to match the power output of the motor. This generator attains its rated
voltage at 1200 rpm. Its armature shaft is flexibly connected to the engine
crank-shaft. The frame of the generator is rigidly attached to the end
bell of the generator so that the engine-generator assembly may be mounted
on a three-point support. The supporting points rest on suitable rubber
pads to reduce the transmission of sound. The radiator and fan are mounted
on the generator end of the frame to avoid having to conduct the heat
radiated by the engine and its exhaust pipes over the generator. The generator
is self-ventilated, and in many hours of service has proved well adapted
for the purposes for which it had been designed. This little power plant
is six feet long, two feet wide, and three feet, ten inches high, weighing
only 2100 pounds, so that it may be readily transported from place to
place on a truck carrying additional equipment. It is covered completely
by a sheet metal housing insulated with sound-proofing material; the housing
is made in sections to facilitate repairing.
The unique
feature of the plant is the system of voltage control and engine governing.
The use of filament lamps has made close
Fig. 3 160-kw, gas-electric generator set.
control of the voltage very necessary, since a sudden rise of voltage,
due to a reduction of the load, tends to burn out the lamps. During the
nominal shooting period it is essential that the voltage be maintained
constant, in order that the illumination of the units be uniformly maintained.
Hand control is inadequate, because the least inattention on the part
of the operator might allow wide voltage fluctuations and consequent detrimental
effects.
In taking
sound pictures it is essential that the generating equipment operate as
silently as possible, as often the locations are in canyons and valleys,
the reverberation characteristics of which make noisy equipment impracticable.
Adequate muffling of the exhaust and the use of suitable sound-insulated
housing in these modern plants have made it possible to operate the sets
reasonably close to the sound recording equipment.
The development
of high-power equipment for use on large night locations presented a more
difficult problem than the designing of suitable booster equipment, because
the greater power involved necessitated heavy equipment and engines of
large displacement; yet, for convenience in such operations, portability
must be maintained.
Fig.
3 illustrates the latest development in the larger portable gasoline generators.
The plant is capable of delivering a current of
Fig. 4 Interior view, 160-kw, gas-electric generator set.
1400 amperes at 125 volts intermittently, and is capable of delivering
1000 amperes continuously. To deliver this power a gasoline motor of 270
hp. is used.
The
unit shown is equipped with a Hall-Scott model 168 Invader Engine having
six cylinders of 5 1/2-inch bore by 7-inch stroke, operating with a compression
of 100 pounds. Operating on standard gasoline it delivers 270 hp. at 2100
rpm., and 248 hp. at 1800 rpm. Although probably other motors might have
been used, this one was selected because a good opportunity had been afforded
to observe its operation for over a year, a large number of motors of
this type being used in water-taxis in Los Angeles harbor. It was also
of advantage that the manufacturer's plant was located at Oakland, California,
which made close contact possible when making certain changes required
for the service. The engine was primarily designed for marine use, but
the Hall-Scott engineers re-designed the crank case and removed the reverse
gear that had been a part of the standard unit, making the engine adaptable
to our requirements.
The generator
in this plant was especially designed by the General Electric Company
to match the power curve of the gas engine. It is very compact, weighing
only 2100 pounds. The generator attains its rated voltage at 1200 rpm.,
and delivers 1000 amperes continuously at 1600 rpm. No difficulty has
been encountered in generating 1450 amperes under the usually intermittent
demands of picture production. The generator is practically flat-compounded
at 1800 rpm., and performs well within the speed range noted above. The
large commutator provides ample surface for brush contact. The generator
is self-forced-ventilated.
The motor
is mounted on a sub-frame supported on 3 points, and is connected by a
flexible coupling to the generators. The job has been carefully engineered
to provide accurate alignment under all operating conditions. The radiator
is of the sectional type, and consists of two separate cores of six sections
each, connected to headers at the top and bottom, the cores being separated
by a two-inch air space; the air is circulated through the radiator by
a fan of the aeronautical type, driven by a variable-speed motor supplied
with current by the main generator. By varying the speed of the cooling
fan, the temperature of the water may be maintained at 180¡F. at the water-jacket
outlet, this temperature being correct for most efficient operation.
Since
the motor was designed for marine use, it was necessary to add a centrifugal
pump, so as to provide the volume of water required for radiator cooling.
The engine is supplied with full-force feed lubrication with oil that
is filtered and cooled to 150 degrees by a water-cooled heat interchanger.
The speed
of the engine is controlled by a centrifugal governor adjustable to various
speeds at the controlling panel. In addition to providing normal regulation
of voltage by compounding the generator, a voltage regulator has been
installed. All controls are concentrated in a panel on which are mounted
the ignition and auxiliary switches, a tachometer, water and oil temperature
indicators, charging ammeter, hand throttle, oil-pressure gauge, generator
ammeter and voltmeter, shunt field rheostat control, voltage-regulator
relay, and circuit breaker operating lever.
The engine
is mounted in a closed compartment, which is ventilated through louvers
by the carburetor intake air. The walls of the compartment are sound-proofed
with suitable insulating material; and since the engine has been carefully
designed to operate quietly, sounds that would be detrimental have been
reduced to a minimum, permitting operation under heavy load within 200
feet of the microphone on open locations.
Mufflers
are mounted in a compartment above the engine, the exhaust manifold connecting
to three mufflers of large capacity. Exhaust noises have been reduced
to a point where they are not objectionable. The generator has been placed
between the engine and the radiator in order that the temperature of the
generator may not rise above the optimum value.
This
175-kw. set is mounted on a tandem wheel truck, which carries ample gasoline
in its tanks for ten hours of operation under maximum load. With the exception
of the gasoline tank the entire plant is self-contained, and may be lifted
from the truck. This is an essential feature because these plants are
often used on ships, in baggage cars, in scenes taken from trains, and
other unusual places.
|
|
