NIAGARA FALLS POWER APPLIANCES.
In the last chapter I described some
of the appliances used in connection with the power-house.
There are many things that are commonplace as electrical
appliances when used with currents of low voltage
and small quantity, that become extremely interesting
when constructed for the purpose of handling such
currents as are developed by the dynamos used at Niagara.
For instance, it is a very commonplace and simple
thing to break and close a circuit carrying such a
current as is used for ordinary telegraphic purposes,
but it requires quite a complicated and scientifically
constructed device to handle currents of large volume
and great pressure. If such a current as is generated
by a dynamo giving out 5000 horse-power under a pressure
of 2200 volts should be broken at a single point in
a conductor, there would be a flash and a report,
attended with such a degree of heat and such power
for disintegration that it would destroy the instrument.
The circuit-breakers used at Niagara
are constructed with a very large number of contacts
made of metal sleeves, or tubes, say one inch in diameter,
so constructed that one will slide within the other;
the sleeves being slotted so as to give them a little
spring that secures a firm contact. These are
all connected together electrically, on each half
of the switch, as one conductor, so that when the switch
is closed the current is divided into as many parts
as there are points of contact in the switch.
Suppose there are 100 of these contact-points, a one-hundredth
part of the current would be flowing through each one
of them. If, now, these points are so arranged
that they can be all simultaneously separated, the
spark that will occur at each break will be very small
as compared with what it would be if the whole current
were flowing through a single point, and it would be
so small that there would be no danger attending the
opening of the switch. These switches are carefully
guarded, being boxed in and under the control of a
single individual.
There is another apparatus that is
a necessary part of every manufacturing or other kind
of plant that uses electricity from this power-house,
and this is called the transformer. Many of you
are familiar with the box-shaped apparatus that is
used in connection with electric lighting when the
alternating current is used. Where simply heating
effects are required, such as in electric lighting,
for instance, the alternating current can be used
to greater advantage than the direct current when
it has to be carried to some distance, owing to the
fact that it may be a current of high voltage.
A greater amount can be carried through a small conductor;
thus greatly reducing the cost of an electrical plant
that distributes power to a distance. A transformer
is an apparatus that changes the current from one voltage
to another.
In the ordinary electric-light plant,
such as is used in a small town or village, the current
that is sent out from the power-station has a pressure
of from 1000 to 1500 volts, according to the distance
to which it is sent. It would not do, however,
for the current to enter a dwelling at this high pressure,
because it is dangerous to handle, and the liability
to fires originating from the current would be greatly
increased. At some point, therefore, outside of
the building, and not a great distance from it, a
transformer is inserted which changes the voltage,
say, from 1000 down to 50 or 100, according to the
kind of lamps used. Some lamps are constructed
to be used with a current of fifty volts and others
for 100 or more. The lamp must always be adapted
to the current or the current to the lamp, as you choose.
The human body may be placed in a circuit where such
low voltage is used without danger, but it would be
exceedingly dangerous to be put in contact with a
pressure of 1000 or more volts, such as is used for
lighting purposes.
In principle the transformer is nothing
more or less than an induction-coil on a very large
scale. The ordinary induction-coil, such as is
used for medical purposes, is ordinarily constructed
by winding a coarse wire around an iron core.
This core is usually made of a bundle of soft iron
wires, because the wires more readily magnetize and
demagnetize than a solid iron core would. Around
this coil of coarse wire, which we call the primary
coil, is wound a secondary coil of finer wire.
If now a battery is connected with the primary coil,
which is made of the coarse wire, and the circuit
is interrupted by some sort of mechanical circuit-breaker,
each time the primary or battery circuit is opened
there will be a momentary impulse in the secondary
circuit of a much higher voltage; and at the moment
the primary circuit is closed there will be another
impulse in this secondary circuit in the opposite
direction. The latter impulse is called the initial
and the former the terminal impulse. A current
created in this manner is called an induced
current. The initial current is not so strong
as the terminal in this particular arrangement.
If we should take hold of the two
wires connected with the two poles of the battery
and bring them together so as to close the circuit,
and then separate them so as to break it we should
scarcely feel any sensation if there were
only one or two cells, such as are ordinarily used
with such coils. But if we connect these wires
to the coils of the induction apparatus and then take
hold of the two ends of the secondary coil and break
and close the primary circuit we should feel a painful
shock at each break and close, although the actual
amount of current flowing through the secondary wire
is not as great as that which flows through the primary;
but the voltage (or electromotive force) is higher,
and thus is able to drive what current there is through
a conductor of higher resistance, such as the human
body. For this reason there is more current forced
through the body, which is a poor conductor, than can
be by a direct battery current which has a lower voltage.
If now we should take a battery of a number of cells,
so as to get a voltage equal to that given off by
the secondary coil, and connect it with the fine-wire
coil instead of the coarse-wire coil thus
making what was before the secondary coil the primary by
breaking and closing the battery circuit as before
we shall get a secondary or induced current in the
coarse-wire coil, but it will be a current of low
voltage, and will not produce the painful sensation
that the secondary coil did.
We have now described the principle
of a transformer as it is worked out in an ordinary
induction-coil. As has been stated, at Niagara
Falls the current comes from the dynamos with an electromotive
force or pressure of 2200 volts. For some purposes
this voltage is not high enough, and for other purposes
it is too high; therefore it has to be transformed
before it is used! For some purposes this transformation
takes place in the power-house, and for others it
takes place at the establishment where it is used.
For instance, take the current that is sent to Buffalo,
a distance of from twenty to thirty miles. The
current first runs to a transformer connected with
the power-house, where it is “stepped-up”
(to use the parlance of the craft) from a voltage of
2200 to 10,000. It is carried to Buffalo through
wire conductors that are strung on poles, and is there
“stepped-down” again through another transformer
to the voltage required for use at that place.
The object of raising the voltage from 2200 to 10,000
in this case is to save money in the construction
of the line of conductors between the two points.
If the voltage were left at 2200 the conductors
remaining the same as they are now the
loss in transmission would be very great, owing to
the resistance which these wires would offer to a
current of such comparatively low voltage as 2200.
To overcome this difficulty if the voltage
is not increased it would be necessary to
use conductors that are very much larger in cross-section
(thicker) than the present ones are. And as these
conductors are made of copper the expense would be
too great to admit of any profit to the company.
If we go back to an illustration we
used in one of the early chapters on electricity we
can better explain what takes place by increasing the
voltage. If we have a column of water kept at
a level say of ten feet above a hole where it discharges,
that is one inch in diameter, a certain definite amount
of water will discharge there each minute. If
now we substitute for the hole that is one inch in
diameter one that is only one-half inch in diameter
a very much smaller amount of water will discharge
each minute, if the head is kept at the same point namely,
ten feet. But if now we raise the column of water
we shall in time reach a height which will produce
a pressure that will cause as much water to discharge
per minute through the one-half-inch hole as before
discharged through the one-inch hole with only the
pressure of a ten-foot column. This is exactly
what takes place when the voltage is “stepped-up,”
which is equivalent to an increase of pressure.
It will be seen from the foregoing
that these transformers have to be made with reference
to the use the current is to be put to. In general
shape they are alike in appearance, the difference
being chiefly in the relation the primary sustains
to the secondary coils. There is another kind
of transformer that is used when it is necessary to
have the current always running in the same direction.
This transformer, as heretofore explained, does not
change the voltage of the current, but simply transforms
what was an alternating into a direct current.
By alternating current we mean one that is made up
of impulses of alternating polarity first
a positive and then a negative. The direct current
is one whose impulses are all of one polarity.
The direct current is required for all purposes where
electrolysis (chemical decomposition by electricity,
as of silver for silver-plating, etc.) is a part
of the process. The alternating current may be
used without transformation in all processes where
heat is the chief factor. For motive power either
current may be used, only the electromotors have to
be constructed with reference to the kind of current
that is used.
The rotary transformer, which may
be driven by any power, consists of a wheel carrying
a rotating commutator so arranged with reference to
brushes that deliver the current to the commutator
and carry it away from the same, that the brushes
leading out from the transformer will always have
impulses of the same polarity delivered to them.
In the parlance of the craft, the transformers that
are used to change the voltage from high to low, or
vice versa, are called “static transformers,”
simply because they are stationary, we suppose.
The others are called rotary, or moving transformers,
to distinguish them from the other forms. The
operation of the latter is purely mechanical, while
the former is electrical. In some instances where
the static transformers are very large they develop
a great amount of heat, so much that it is necessary
to devise means for dissipating it as fast as created.
In some instances this is done by air-currents forced
through them, but in others, where they are very large,
oil is kept circulating through the transformer from
a tank that is elevated above it, the oil being pumped
back by a rotary pump into the tank where it is cooled
by a coil of pipe located in the oil, through which
cold water is continually circulating. By this
means cold oil is constantly flowing down through
the transformer, where it absorbs the heat, which in
turn is pumped back into the tank, where it is cooled.
Having now traced the energy from
the water-wheel through the various transformations
and having described in a very general way the apparatus
both for generating electricity and for transforming
it to the right voltage necessary for the various
uses to which it is put, we will proceed in our next
chapter to follow it out to the points where it is
delivered, and trace it through its processes, and
the part it plays in creating the products of these
various commercial establishments.