THE DYNAMO AND ITS APPLICATIONS.
OBSERVATIONS OF FARADAY AND HENRY--MAGNETO-ELECTRIC MACHINES OF
PIXII AND OF SAXTON--HJORTH’S DYNAMO OF 1855--WILDE’S MACHINE OF
1866--SIEMENS’ OF 1867--GRAMME’S OF 1870--TESLA’S POLYPHASE
CURRENTS.
In the last thirty-five years of the Nineteenth Century there has grown
up into the full stature of mechanical majority this stalwart son of
electrical lineage. As the means for furnishing electrical power it
stands to-day the great fountain head of electrical generation, and in
its peculiar field ranks as of equal importance with the steam engine.
Until about 1865 the voltaic battery, which generated electricity by
chemical decomposition, was practically the only means for producing
electricity for industrial and commercial purposes. It was through its
agency that the telegraph, the electric light, and many other
discoveries in electricity were made and rendered possible. Its cost and
limited amount of current, however, restricted the limits of its
practical application, and although its current could furnish beautiful
laboratory experiments, its mechanical work was more in the nature of
illustration than utilization. But with the advent of the dynamo
electricity has taken a new and very much larger place in the commercial
activities of the world. It runs and warms our cars, it furnishes our
light, it plates our metals, it runs our elevators, it electrocutes our
criminals; and a thousand other things it performs for us with secrecy
and dispatch in its silent and forceful way. But what is a dynamo? To
the average mind the most satisfactory answer would be--that it is
simply a machine which converts mechanical power into electricity.
Attach a dynamo to a steam engine, and the power of the steam engine
will, through the dynamo, become transformed or converted into a
powerful electric current. Any other source of mechanical power, such as
a water wheel, gas engine, wind wheel, or even a horse or man, will
serve to operate the dynamo; its primary and sole function being to take
power and convert it into electricity.
The stepping stone to the dynamo in its development was the
_magneto-electrical machine_. This is a machine founded upon the general
principle observed by Faraday in 1831 and 1832, and also by Prof. Henry
about the same time, that when a magnet is made to approach a helix of
insulated wire it causes a current of electricity to flow in the helix
as long as the magnet advances. If the magnet is passed through the
helix, the current is reversed as soon as the magnet passes the middle
point. The principle is the same if the magnet be made to approach and
recede from the poles of an electro-magnet having a helix wound around a
soft iron core. Likewise the same result occurs if the electro-magnet
with its helix is made to approach and recede from a permanent magnet,
the current in the helix flowing in one direction when it approaches the
permanent magnet, and in the opposite direction when leaving the said
magnet. The movement of the two elements in relation to each other
requires some force to overcome the repellent and attractive actions,
and this force is converted into electrical energy. This is the
principle of the magneto-electric machine.
[Illustration: FIG. 17.--PIXII MAGNETO-ELECTRIC MACHINE, 1832.]
Saxton in the United States and Pixii in France were the first to
produce organized devices of this class for generating electricity from
magnetism. Pixii’s machine (1832) consisted of a permanent horse-shoe
magnet which was caused to revolve in proximity to an armature upon
which was wound a coil of insulated wire. On March 30, 1852, Sonnenberg
and Rechten obtained a United States patent, No. 8,843, for an
electrical machine for killing whales, and on August 19, 1856, Shepard
obtained U. S. Pat. No. 15,596 for the machine which came to be known as
the “Alliance” machine. Both of these machines had permanent field
magnets, and were early types of magneto-electric machines. The
efficiency of these magneto-electric machines was necessarily limited to
the strength of the inducing field magnets, which, being permanent
magnets, were a positive and fixed factor. It was an easy step to
substitute electro-magnets for permanent magnets, as the field or
inducing magnets, and also to excite the (electro) field magnet by
voltaic batteries, but the important step which resulted in the machine
which is called the “dynamo” (from the Greek “Δυναμις”--power) was yet
to come.
[Illustration: FIG. 18.--HJORTH’S DYNAMO ELECTRIC MACHINE.]
[Illustration: FIG. 19.--HJORTH’S DYNAMO ELECTRIC MACHINE, PLAN VIEW.]
This step consisted in taking the current induced in the revolving helix
or armature (by the field magnets) and sending it back through the coils
of the field magnets which produced it, thereby increasing the energy of
the field magnet coils, and they in turn with an increased efficiency
and reciprocal action induce still stronger currents in the armature
coils, and so a building up process, or principle of mutual and
reciprocal excitation, is carried on until the maximum efficiency is
reached. This principle was the discovery of Soren Hjorth, of
Copenhagen, and is fully described in his British patent, No. 806 of
1855, for “An Improved Magneto-Electric Battery.” As the prototype of
the dynamo, it is worthy of illustration. In the illustration, Figs. 18
and 19, _a_ is a revolving wheel bearing the armature coils, _C_
permanent magnets, _d_ electro-magnets (field magnets), and _g_ the
commutator. Quoting from his specifications, he says: “The permanent
magnets acting on the armatures brought in succession between their
poles, induce a current in the coils of the armatures, which current,
after having been caused by the commutator to flow in one direction,
passes round the electro-magnets (field magnets), charging the same and
acting on the armatures. By the mutual action between the
electro-magnets and the armatures an accelerating force is obtained,
which in result produces electricity greater in quantity and intensity
than has heretofore been obtained by similar means.”
Although the principle of the dynamo was clearly embodied in the Hjorth
patent, its value was not appreciated until some time later. Eleven
years later Wilde (U. S. Pat. No. 59,738, Nov. 13, 1866), employed a
small machine with permanent magnets to excite the coil-wound field
magnets of a larger machine. But Siemens (British Pat. No. 261 of 1867),
taking up the principle employed by Hjorth, dispensed with his
superfluous permanent magnets, having found that the residual magnetism,
which always remained in iron which has once been magnetized, was
sufficient as a basis to start the building up process. Farmer,
Wheatstone and Varley also recognized this fact about the same time.
Siemens’ patent also was the first embodiment of what is known as the
bobbin armature. Gramme and D’Ivernois (British Pat. 1,668 of 1870, and
U. S. Pat. No. 120,057, of Oct. 17, 1871), were the first to bring out
the continuously wound ring armature.
Active development now began in various types and by various inventors,
including Weston, Brush, Edison, Thomson and Houston, Westinghouse, and
others, who have brought the dynamo to its present high efficiency.
The revolving coils of the dynamo are called the armature, and the fixed
electro-magnets are called the field magnets, and these latter may be
two or more in number. When two are used they are arranged on opposite
sides of the armature, and form what is known as the bipolar machine. A
larger number constitutes the multipolar machine. The field magnets in
the multipolar machine usually are arranged in radial position around
the entire circumference of the revolving armature, and are held in a
fixed circular frame. To give a clear idea of the principles of the
dynamo, the bipolar machine is best suited for illustration, and is here
given in Figs. 20 and 21, in which Fig. 20 represents the dynamo
complete, and Fig. 21 a detail of the end of the armature and
commutator. This armature consists of coils or bobbins of insulated
wire, each section having its terminals connected with separate
insulated plates on the hub, which plates are known as the commutator.
When any section of the armature approaches the pole of a field magnet,
the current induced in that section of the armature coils by the field
magnet, is taken off from a corresponding plate of the commutator by
flat springs, seen in Fig. 20, and known as brushes. The field magnets A
and B, Fig. 20, are shown with only a few turns of wire about them for
clearer illustrations of the connections, which are made as follows: The
wire _a_ is extended in coils around the field magnet B, and thence
around field magnet A, and thence to the upper brush on the commutator,
thence through the wire coils or bobbins of the rotary armature C, and
thence by the lower brush to the wire _b_. The terminals of the wires
_a_ and _b_ extend to the point of utilization of the current, whether
this be electric lights, motors, or other applications. In this
illustration, the circuit, it will be seen, passes through both the
coils of the field magnets and the coils of the armature, involving the
principle of mutual excitation.
[Illustration: FIG. 20.--BIPOLAR DYNAMO.]
There are two principal kinds of dynamos--those producing the
alternating currents, and those producing the continuous current. In the
first the current alternates in direction, or is composed of an infinite
number of impulses of opposite polarity: one polarity when a section of
the armature coil is approaching a north field magnet pole or receding
from a south pole, and the other polarity when receding from a north
field magnet pole and approaching a south pole. In the continuous
current machine, the commutator and brushes are so arranged as to take
up all the impulses of the same polarity and conduct them away by one
brush, and gathering all the impulses of the opposite polarity and
conducting them away by another brush. Thus the current of each brush,
in the continuous current machine, is always of the same polarity, and
the polarity of one being always positive, and that of the other
negative, the current flows continuously in the same direction. A third
species of dynamo is the pulsatory, in which the current flow is
invariable in direction, but proceeds in waves.
[Illustration: FIG. 21.--ARMATURE OF BIPOLAR DYNAMO.]
A change in the character of the current generated by the dynamo is made
by what is known as the “transformer,” in which the principle of the
induction coil is made available. In this way, for instance, the high
potential currents generated by the powerful water wheels at Niagara
Falls are taken twenty miles to Buffalo, and are there transformed into
other currents of lower potential, suited to incandescent lighting and
other various uses. A similar scheme is in process of fulfillment in the
establishment of a water power electric plant near Conowingo, Maryland,
on the Susquehanna River, to furnish electrical power to Baltimore,
Wilmington and Philadelphia.
An important development in electrical generation and transmission is to
be found in what is known as the _polyphase_, _multiphase_, or
_rotating_ current, pioneer patents for which were granted to Tesla May
1, 1888, Nos. 381,968, 381,969, 382,279, 382,280, 382,281 and 382,282.
Realizing the possibilities of the dynamo, the Legislature of New York
in 1888 passed a law, which went into effect in 1889, in that State,
substituting death by electricity for the hangman’s noose. The criminal
is strapped in the chair, seen in Fig. 22, one terminal of the wire from
the dynamo is strapped upon his forehead, and the other to anklets on
his legs, and like a flash of lightning the deadly energy of the dynamo
performs its work.
Not the least of the applications of the dynamo is its use in
electro-metallurgy for plating metals, and also for promoting chemical
reactions. The electric furnace, stimulated into higher heat by the
dynamo than can be otherwise obtained, has brought about many valuable
discoveries, and made great advances in various arts. The metal
aluminum, and the hard abrasive or polishing and grinding material known
as “carborundum” are the products of the electric furnace, and so is the
product known as “calcium carbide,” which, when immersed in water, gives
off acetylene gas and is a product now universally used for that
purpose, and rapidly increasing in commercial importance.
[Illustration: FIG. 22.--ELECTROCUTION CHAIR.]
In Fig. 23 is seen the Acheson electric furnace for producing
carborundum. The electric current traverses the furnace through a series
of horizontal electrodes at each end, and highly heats a central core of
carbon, which is disposed in a mass of silicious and carbonaceous
material, and which latter is converted by the heat into silicide of
carbon, or carborundum. In Fig. 24 is shown a continuous electric
furnace constructed as a revolving wheel, under the Bradley patents. Rim
sections 5 are placed on the wheel on one side and filled with a mixture
of carbon and lime, through which the electric current is passed from
the dynamo _g_. The heat of the current fuses the mass and converts it
into calcium carbide, and as the wheel slowly revolves the rim sections
5 are removed from the opposite side, and the mass of calcium carbide,
seen at _x_, is broken off. The electrolytic production of copper
through the agency of the dynamo amounts to 150,000 tons annually, and
the commercial reduction of aluminum by the electric furnace has grown
from eighty-three pounds in 1883 to 5,200,000 pounds in 1898, and its
cost has been reduced to about 33 cents per pound.
[Illustration: FIG. 23.--PART SECTIONAL VIEW OF CARBORUNDUM FURNACE.]
The storage battery, holding in reserve its stored up electric energy,
also owes its practical value entirely to the dynamo which charges it,
and thus makes available a portable source of supply.
[Illustration: FIG. 24.--BRADLEY ELECTRIC FURNACE FOR PRODUCING CALCIUM
CARBIDE.]
To contemplate the dynamo with its clumsy, enormous spools, it suggests
to the imagination of the average observer the gigantic toy of some
Brobdingnagian boy--but the dynamo is no toy. It is the most compact,
business-like, and dangerous of all utilitarian devices. To touch its
brushes may be instant death, for the dynamo is the prison house of the
lightning, and resents intrusion. Hidden away from public gaze in some
sequestered power house, and working night and day like some tireless,
dumb, and mighty genii, it sends its magnetic thrills of force silently
through the many miles of wire extending like radii from some great
nerve center through the conduits in our streets, and stretching from
pole to pole like giant cobwebs through the air. Responding to its
force, thousands of little incandescent threads leap into radiant
brightness and shed their mellow and genial light in our offices, our
stores, hotels, and homes. Brilliant arc lamps, rivaling the sun in
power, make night into day, and produce along our streets coruscations,
silhouettes, and dancing shadows in spectacular and unceasing pageants.
From the towering lighthouses of our coasts its beams are thrown
seaward, and a beacon for the mariner shines beyond all other lights.
The great search light of our ships is in itself but a hollow mockery
until the dynamo whispers in its ear the word “light!” and then its
beam, reaching for miles along the horizon, discovers a stealthy enemy,
or signals the safe return to port. The mighty force of the dynamo
entering the electric motors on the street cars turns the wheels and
transports its load with scarcely a passenger inside realizing how it is
all done. The same energy turns the electric fan, and with kindly
service soothes the weary sufferer, and at another place remorselessly
takes the life of the condemned criminal. The dynamo is one of the great
factors of modern civilization, and its potential name, like that of
“dynamite,” rightly defines its character.
[Illustration: FIG. 25.--MODERN MULTIPOLAR DYNAMO.]