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“In its power to assume always that form of energy which happens to be
the most useful lies the great importance of electricity.” This
importance has been brought to the notice of the public by means of the
many recent exhibitions. Public interest has been roused and there is
everywhere a desire for information and a guide through this far
reaching field for discovery and invention. And, although there are many
works treating on electricity and electric light, people specially want
a short and concise though thorough description of the various schemes
by which electric light is produced. In this thesis the object is to
give a brief treatise on one of the many schemes of producing light by
electric currents viz—The Thomson-Houston System.
In pursuing the subject of electricity, the first thing noticed is the
analogy and difference between the dynamo and its older and more
powerful rival the steam engine. The resemblances are, First as in the
development of the steam engine, but few of the improvements and
inventions in electrical machines were made by mathematical leaders.
Watt ran across the idea of the seperate condenser while repairing the
Newcomen model and applied the expansion of steam to the steam engine by
a mechanical accident rather than by his own ingenuity, and so we find
the first designers of the dynamo were mechanics rather than
philosophers. Secondly the tendency to disregard old methods and
instruments because of new discoveries and inventions has, as in the
steam engine, hindered the advancement in electrical science. As an
example it has become customary to regard frictional and statical
electric machines, for practical purposes, as obsolete, but recent
discoveries seem to hint that they may yet be utilized. Lately Prof.
Dodge has shown that dust and vapor whirling in the air may be settled
by a discharge of electricity consisting of a continuous series of
electric sparks. This has been utilized to clear the atmosphere in lead
smelting works from the fumes of volatized lead and with its application
comes the invention of Wimhurst which produces with a minimum of
mechanical labor a continuous series of electric sparks and works
admirably.
The differences between the engine’s and dynamo’s developement are:
_First_ the marvelously rapid developement of the dynamo as compared
with that of the steam engine. Since 1867 when the term “dynamo electric
machinery” even to scientific men had but little signification, the
dynamo has been brought to a very high degree of perfection. _Secondly_,
the development of the dynamo has reached a much higher degree of
perfection than that of the steam engine. Among the best steam engines
twenty per cent effeciency is considered as very good while a good
dynamo gives out in the form of electricity, ninety per cent of the
mechanical energy put in it. But the class of people who improved and
made the steam engine what it is were as well educated in one sense as
were the men who brought out the dynamo. While it is true that in Watt’s
time the knowledge concerning steam was very meagre, yet the practical
men who _made_ the dynamo, did it by themselves as nearly all the
teachers of electricity knew nothing except what may be called
electrical tricks. As has been said[1] “The teachers and writers of
textbooks, practically did not know that there was anything in common
between the electricity from a rubbed glass machine and voltaic
electricity, or to be brief, that there was a science of electricity as
distinguished from mere natural history.” In fact as late as 1870 there
were really no textbooks on electricity. Even now electrical knowledge
is so meagre as to warrant the same writer’s expression, “We can not
imagine a mechanical engineer mistaking a few inches for a few miles or
a grocer compounding an ounce of sugar with a carload, but this gives
too truthful an idea of the vagueness that still exists.”
In the distant future, electricity will be used for electric lighting
only as subordinate to other uses to which it may be applied such as
heating houses, taking place of stoves for cooking, being used as a
substitute for the steam engine. In fact the motor is rapidly becoming
of as much practical use as the electric light. The principle of the
motor is just this; a certain amount of mechanical energy say thirty
four horsepower per minute into the form of electric currents, which by
the way gives enough current to run 45, 2000 candle power lamps, send
the current and distance through suitable conductors and attach them to
similar dynamo or dynamos but in such a manner that the current in the
second set of dynamos flows in the reverse direction to that of the
first; when, the armature of the second dynamo or dynamos will revolve
and at the pulley or pulleys of the dynamos, aside from friction, will
be given out 95% of the thirty-four horsepower, the loss being due to
the resistance of the conductors. Now in practice a motor is placed on
the arc light circuit the same as a lamp, for energy less than twelve
horsepower. It does not affect the lights and is a clean, neat way of
obtaining energy.
But however true the foregoing may be, the greatest present use of
electricity is to start and maintain light. There are several so-called
systems, embracing dynamos, lamps, regulators, etc, from which I select
the Thomson-Houston as the one for the purpose of describing for several
reasons, _first_, it is at least as good as the average system of which
there is a mushroom growth; _second_, valuble information was kindly
offered by the parent Company; _third_, a good plant is near to which
free acess was given, and _fourth_, we have at the Mechanical Hall of
this University, a dynamo, loaned by the parent Company, which affords
information without any inconvenience. As each part of the system comes
up to be described a little of its history will be given. As the first
part of a system necessary to be produced is the current generator we
will first describe
_The Thomson-Houston Dynamo._
In considering the current generator the first thing to be decided upon
is the definition of the term dynamo. The following is thought to be a
correct definition,—A dynamo or dynamo electric machine is a machine
which is used to convert energy in the form of mechanical motion into
energy of electric currents, or _vica-versa_. Those used to generate
currents of electricity are called dynamos, those used to generate
mechanical motion are known as motors.
In attempting to make clear the theory of the dynamo, we will recall
some simple experiments. In Fig. 1, send a current around B from right
to left. Now A being free to move vertically either up or down, connect
its binding posts to a _galvanometer_ (that is, an instrument used to
tell the direction of a current and also used to test the _relative_
strength of two or more currents) and move A up suddenly when a current
will be generated in A whose direction will be the same as that of the
current in B. Now this current is not created energy, because in
lifting[2] the coil A, work is expending against the attraction between
the coils, as between two currents flowing in the same direction there
is an attraction. If we pursue this experiment in its various forms we
will find the following statement known as Lentz law is true, viz: “If
the relative positions of two conductors A and B be changed of which B
is traversed by a current, a current is induced in A in such a direction
that by its electro dynamic action on the current in B it would have
imparted to the conductor a motion of the contrary kind to that by which
the inducing action was produced.”
The theory of this law is that around every wire carrying a current
there is a magnetic whirl (Fig. 3). Now if the conducting wire be passed
through a hole in a horizontal plate of glass and iron filings be sifted
upon the latter they will arrange themselves, as shown in Fig. 2., along
lines, radial in this case, known as lines of force, which arranging is
due to the magnetic attraction of the current in the wire upon the iron
filings. Now in B. Fig. 1, every portion of the wire has just such a
whirl and just such lines of force, or magnetic field, and when A is
moved each part of the wire of A cuts one or more lines of force of the
many magnetic fields making up the magnetic field of the entire coil B.
Now when the wire of coil A cuts magnetic field of B a current is
generated in A acording to the following statement known as Faraday’s
Law; “When a conductor in a field of force moves in any way so as to cut
the lines of force there is an electromotive force produced in the
conductor in such a direction that supposing a figure swimming in the
conductor to turn to look along the positive direction of the lines of
force (in Fig. 1, toward axis of B), and the conductor be moved to his
right, he will be swimming with the current so induced.” Hence in Fig.
1, the current generated in it will be from left to right.
Practically Faraday’s principle means just this: by moving a wire across
a space where there are magnetic lines, the motion of the wire as it
cuts the magnetic lines sets up around the cutting wire a magnetic whirl
or in other words sets up a current in that wire.
The foregoing laws are the “principles of the dynamo,” yet after their
deduction, the progress of the evolution of the dynamo was slow and
attended by many dificulties. Between 1860 and 1870 however, a working
knowledge of these laws became the property of thousands of mechanics,
and by comparing the number of inventions before and after that date
(1860) the present generous growth of systems, dynamos and lamps, prove
that inventions were almost in proportion to the number of people who
had any electrical knowledge. In 1866 Wilde produced a toy
magneto-electric machine for giving shocks, in which he used excited
electromagnets. In the same years Varley and others produced a machine
which excited its own field magnets the type of all machines used in
practice. With this principle of Varley’s and Pacinnotti’s ring, Gramme
produced in 1871 his since famous continuous current generator, one of
which the second dynamo electric machine ever brought to this country
can now be seen at the engine house at Purdue University. In 1877 Silas
Brush brought out his famous dynamo and it may be interesting to know
that he designed and had one made without experimenting in the least. In
the following year a patent was issued to Messrs. Elihu Thomson and
Edwin J. Houston, Professors of electricity in Philadelphia on the
present though much improved _Thomson Houston Dynamo._
[Illustration:
_Fig. 1._
_Fig. 2._
_Fig. 3._
_Fig. 4._
_Fig. 5._
_Fig. 6._
_Fig. 7._]
To go back to Lentz and Faraday’s laws and carefully consider them we
can but assent to S. P. Thompson’s “fifteen propositions on the dynamo”
which are:—1. A part of the energy of an electric current exists in the
form of a magnetic whirl surrounding the wire.