| |
Since the earliest use of artificial light on motion-picture
locations, portable engine-driven lighting-power sources have been needed.
This paper describes the design features and performance characteristics
of a new 650-amp 120-v, d-c, engine generator set which is much smaller
and lighter in proportion to its power output than any of the previous
equipments.
IN THE DESIGN of engine-generator
equipment for supplying power on locations many factors must be judiciously
considered in order to provide adequate "efficiency of utilization." Of
prime importance is the balance of maximum power vs. flexibility and portability.
 As an
example, a single 150-kw plant.1 now widely
used in the industry, will satisfy the overall power requirements for
most locations. The Mole-14002 is such a
plant but, although it is more portable than any other of equal capacity,
it is 118 in. long X 54 in. wide X 73 in. high and weighs 11,660 lb. The
trend toward an increase in the amount of work at remote locations has
resulted in the need for more portable and flexible units to supplement
the comparatively larger types.
A considerable
handling and transportation advantage would result if power capacity equivalent
to the single 150-kw plant could be produced by two smaller packages with
a combined weight appreciably below that of the larger single unit. The
smaller plants could be loaded on or trailed behind the equipment trucks,
or even be carried by the same truck upon which lighting equipment is
mounted during operation. In emergencies a plant of sufficiently small
dimensions and weight may be transported to location by air.
By utilizing
two smaller units electrically connected for 3-wire distribution, a saving
of 30% in cable is effected over the 2-wire system of the larger plant.
The
larger plant is at times operated at no more than half capacity on locations
where full capacity is required only for peak demand. If two smaller plants
were employed only one need be operated during the slack periods.
A shut-down
of the larger plant, when it is the sole source of power, may bring production
to a standstill, whereas, if two smaller units are operating and one of
them requires attention it may be possible to rearrange production so
work can be continued with one machine.
After
lengthy discussions with those in the industry who use the equipment,
the Mole-Richardson Co. proceeded with the development of a compact, extremely
portable power plant having about half the capacity of the Mole-1400 unit.
Since
the prime objective was the reduction of size and weight as compared to
previous designs, a survey was conducted to determine the maximum, practical
operating speed for both engine and generator. This is doubly important
because the weight per kilowatt of delivered power may be reduced as the
rotating speed is increased. It was learned that the General Electric
Co. could produce a special d-c generator of the desired capacity with
an operating speed as high as 3,600 rpm which is higher than normally
encountered in d-c generator equipment of this capacity.
After
a thorough study of the various types of available engines, the Cadillac
automotive engine appeared to be the most promising. This choice was made
after discussion of the engine's performance characteristics and the proposed
application with Cadillac engineers in Detroit.
To verify
the conclusions which had been reached, one engine was purchased and installed
in an existing power plant in the Mole-Richardson Co.'s rental department.
Its performance under actual operating conditions was carefully studied
for a period of eight months before deciding to proceed with the development.
Fig. 2. Top of engine.
The
generator (Fig. 1) with performance matching the speed-horsepower characteristics
of the Cadillac engine was developed through the combined efforts of General
Electric and Mole-Richardson engineers. In the design, precautions were
taken to provide more generator capacity than the Cadillac engine could
mechanically deliver in order to prevent possible damage to the generator
from overload.
It is
a 2-wire generator rated at 650 amp, 125 v, d-c, for duty cycles normally
encountered in location service. Its rated speed ranges from 2,800 to
3,200 rpm, which corresponds to a good operating region on the Cadillac
speed-power curve. It is a single-bearing machine with class B insulation
throughout. It is approximately flat compounded with the shunt field suitable
for automatic voltage regulation. The weight of the generator is only
1,050 lb as compared to approximately 2,000 lb for commercially rated,
lower-speed machines of equivalent capacity. The ripple voltage is less
than 1/2 of 1% of rated voltage, a feature which limits the emission of
objectionable hum of arc lamps on the set.
The
8-cylinder, 90°, V-Type Cadillac engine is rated at 160 hp at 3,800 rpm
and weighs 785 lb. For the first time this development permitted the use
of an engine which is smaller and of less weight than the generator which
it drives.
Fig. 3. Right side of engine.
Because there is no commercially available engine which can be applied
to a motion-picture power plant without modification it was necessary
to make the following revisions on the Cadillac motor:
1. Carburetor
replaced by dual downdraft industrial type (Fig. 2).
2. Governor
added to adjust and maintain speed.
3. Mechanical
take-off device assembled beneath distributor for governor drive.
4. Oil
filter added.
5. Exhaust
manifold castings replaced by water-jacketed exhaust manifolds of Mole-Richardson
design (Fig. 3).
6. Water-pump
casting modified to divert cooling water through waterjacketed exhaust
manifolds.
7. Battery
generator relocated.
8. Oil
drain line with shut-off valve installed.
9. Crankcase
ventilating tube added for stationary application.
10.
Electric fuel pump installed to assist mechanical fuel pump in maintaining
adequate pressure at carburetor (Fig. 4).
11.
Overspeed governor of Mole-Richardson design assembled on crankshaft to
interrupt ignition circuit in the event of excess speed.
12.
Fuel filter added.
13.
Carburetor air cleaner relocated for access to cool air (Fig. 1).
14.
Water temperature safety switch installed in engine block to warn operator
in the event of overheating.
15.
Oil pressure safety switch added to interrupt ignition circuit should
loss of oil pressure occur.
16.
Hydra-matic flywheel replaced with standard type machined to accommodate
generator coupling.
17.
Engine fan removed.
Fig. 4. Lower right front of engine.
One end of the armature of the single bearing generator is coupled to
and supported by the engine flywheel. The coupling is of a flexible laminated
steeldisk type with no deteriorating parts and has proven itself by application
in other fields. A welded steel adapter housing (Fig. 1) was designed
to mount the generator frame to the engine bell housing with rabbet fits
to assure alignment of the axes of rotation of engine crankshaft and generator
armature.
The
engine and generator coupled together as an integral mechanical unit is
supported on a welded steel box section main base frame by four rubber
mountings to minimize transmission of vibrations to the base and enclosing
structure.
The
housing (Fig. 5) is made of fireproof materials throughout and designed
for convenient operation and maintenance. It is constructed in sections:
one end, two sides and one top for disassembly convenience at times of
major overhaul. Five access doors are provided for routine inspection
and maintenance. The operator's control panel, electrical outlet bus-bar
compartment, and external fuel line entrance is located on one end-section
of the enclosure. The opposite end of the enclosure is formed by the radiator.
With the top and sides removed (Fig. 6) the working parts are exposed,
yet the plant may be operated for test.
Fig. 5. Mole-700 Power Plant, closed for transport.
The heat is removed from the engine cooling water by the combination of
a large tube and fin radiator and fan (Fig. 7) at the generator end of
the plant. The 30-in. diameter fan is belt driven from a sheave on the
generator armature shaft and has six variable-pitch blades which are thermostatically
controlled to automatically maintain approximately 180 F cooling water
temperature. Hence, no more air is drawn through the radiator than is
required for adequate engine cooling, and noise which would result from
an excess air speed is prevented. A maximum air flow rate of approximately
7000 cu ft/min is sufficient for full load operation in an ambient temperature
of 115 F such as might be encountered on a desert location. After the
air is drawn through the radiator it is deflected by a sloping partition
through adjustable door openings at the top of the enclosure (Fig. 8).
A fan
on the coupling end of the generator armature draws outside air from a
screened opening below the radiator through air ducts (Fig. 9) into the
commutator end of the generator and exhausts it into the engine compartment.
after which it passes out of the enclosure through one of the top ventilating
doors.
The
control panel (Fig. 10) has all of the necessary instruments, switches,
etc. for control of both the engine and electrical power circuits. The
engine controls are located on the left side of the panel and those applicable
to the generator are on the right. Engine governed speed may be adjusted
by setting the governor control knob. The generator voltage may be controlled
either manually with a rheostat, or automatically by a voltage regulator,
and the selection between the two is accomplished by positioning the field
control selector switch. OFF and ON pushbuttons operate the main line
contactor which controls the power-supply voltage at the bus-bar compartment.
Fig. 6. Left side, with top and sides removed.
Fig. 7. Radiator and fan.
Fig. 8. Left side, doors open, radiator baffle removed.
Fig 9. Air ducts to generator
Fig 10. Control panel
Several safety features are provided to prevent damage to the plant. An
oil pressure switch interrupts the ignition circuit should loss of oil
pressure occur, and a water temperature switch causes a warning light
to glow on the control panel if the engine overheats. A centrifugal overspeed
governor interrupts the ignition circuit in the event of excess speed.
An overload relay causes the main line contactor to open the electrical
power circuit in the event of a short-circuit in the external distribution
system. Also, to protect against a failure in the thermostatic control
of the pitch of the radiator fan blades, a mechanical means is provided
to lock the blades in full pitch.
Silencing
of an engine generator set for motion-picture and television location
work entails a compromise between the degree of noise reduction and portability.
Previous experience gained with the sound insulation design of similar
equipment leads to a solution which satisfies both requirements particularly
well. The wall construction consists of an outer 20-gauge sheet steel
skin with Minnesota Mining undercoating applied on its inner surface.
A fibrous asbestos material is sprayed over the undercoating to form an
additional sound absorbing layer about 3/4 in. thick, and is protected
by two coats of casein base paint and metal hardware cloth.
Fig. 11. Mole-700 Power Plant, prepared for air transport
The bottom of the plant is closed with covers consisting
of 3/4 in. thick Celotex between 18-gauge steel sheets. An acoustical
partition (Fig. 1) within the housing made of 1/2 in. thick Celotex faced
on both sides by 1/8 in. thick Transite prevents engine mechanical noise
from escaping through the radiator. All access doors are gasketed. A blanketed
baffle spaced a short distance in front of the radiator reduces the air
and fan noise and serves as a guard against radiator damage during handling
and transportation.
The
engine exhaust is muffled by a series-parallel system of silencers (Fig.
1). One 3-pass muffler is connected to the exhaust of each 4-cylinder
bank with their outputs joined at the input of a third muffler.
Provisions
are made for a variety of types of handling and transporting the equipment
(Fig. 5). Casters permit the plant to be conveniently positioned, and
steel tubes pass laterally through each end of the base frame for wheel
axles or sling bars. Tubular openings at the ends of the base are provided
for jacks. The main base frame forms a permanent skid which may be used
with rollers with casters removed, and its construction is suitable for
assembly of trailer wheels, axles, springs, etc.
The
resulting Mole-700 Power Plant 36 in. wide X 82 in. long X 62 in. high.
weighing 4,200 lb and capable of generating 650 amp at 120 v, d-c, has
a capacity heretofore unequaled with respect to size and weight. Two units
are electrically equivalent to one Mole-1400 Power Plant, yet their combined
weight is 3,260 lb, or 28%, lighter.
With
the operator's panel, bus-bar compartment, and connection point for fuel
line at one end, the radiator at the opposite end, and the ventilation
doors, engine exhaust, and carburetor aircleaner on top, both sides of
the enclosure are free of operating components. It is thereby possible
for a multiplicity of plants to be positioned side by side and conveniently
controlled by one operator.
The
dimensions and weight of the overall unit are such that it may be readily
transported by air. For example, an emergency situation was recently alleviated
by flying one of the Mole-700 Power Plants overnight from Hollywood to
Detroit (Fig. 11). The additional expense of air transportation is often
negligible as compared to the resulting savings realized by minimizing
loss of production time.
The
equipment has already demonstrated its usefulness, having satisfactorily
performed on numerous locations throughout the United States, Canada and
Hawaii over the past several months. The application of new engineering
ideas directed toward minimum size and weight has resulted in a new, useful
and dependable power package more compact and flexible than any of the
previous types of similar equipment.
References
- "Report of Studio-Lighting Committee," Jour. SMPE, 51: 431-436, Oct.
1948.
- M. A. Hankins and Peter Mole, "Designing engine-generator equipment
for motion picture locations," Jour. SMPTE 55. 197-212, Aug. 1950.
|
|
