Montpelier examiner. [volume] (Montpelier, Idaho) 1895-1937, 1912-03-01
THE GENERATION AND APPL!-
CATION OF ELECTRIC POWER
BY ARTHUR JoBsoN

In the last article the writer dis
cussed the fundamental principle in
volved in the operation of trans
former; a device for raising or lower
ing the voltage of an alternating
electric current. The reader may ask
why 1t is ever desired to raise or
lower the voltage in the transmission
and distribution of electric current.
The reader will remember that the
power in watts delivered to an cleo
trical circuit is equal to the voltage
impressed upon the circuit multiplied
by the current in amperes. Let us
suppose that at an electric power
generating station we are required to
furnish a two-wire, long distance
transmission line with 100000 watts
200 K. w. Within reasonable limits
we have the choice of selecting any
current and voltage we wish in de-
livering the 100000 watts to the line,
the only condition being that the
voltage multiplied by the current
must always be equal to the power in
watts above specified. Suppose we
decide to deliver power to the line at
a pressure of 2,200 volts. Then cur
rent flowing through the wires would
be about 45.5 amperes. This is OBJ
tanned by dividing 100, 900 by 2,2OO.)
If we selected 5000 VOLTS as the trans
mission line voltage the current
would then be 90 amperes 100000
divided by 5000. If we selected
10000 volts the current would then
be 5amperes QO0, 900 divided by 10000
or If we selected $4,000 volts the cur
rent would be tive amperes, and SO
on. When a wire is carrying an elec
tric current there is always some loss
of energy or power in the wire due to
its electrical resistance. This loss of
power is proportional to the quantity
of current flowing and the resistance
of the wire. The loss Is not affected
by the voltage impressed upon the
circuit. For instance the electrical
resistance of 20 miles of No. 10 copper
wire tabout one-eighth in diameter)
is approximately 100 ohms. This
may be found In wiring stables, and
has been determined by experiment
If this wire were carrying two
: amperes of current the loss of power
. in the 20 miles of wire would be 480
watts. This Is determined by squar-
ing the current and multiplying the
result by 100, the resistance in ohms.
II the wire were carrying 90 amperef
e the loss of power would be 48,O0(
D watts, or 100 times the amount Of
: power lost when the wire was carry
ing only two amperes. We could re,
duce the loss of $4,000 watts very
!, much by selecting wire larger thar
z No. 10, and still maintain the current
of 90 amperes. For current of q
amperes suppose we did not wish Il
have the loss greater than 1900 watts
J In this case the 20 miles of coppe
;. wire would have to be No. 90, o
: about three-eights of an inch II
|. diameter. and would weigh abou
- Hlu6 bAulSS hb iluCh dS 1uO ~ Ililtb "
No. 10 copper wire.
The above examples will show th
- reason for reducing the current q
much as possible, in transmitting
y definite quantity of power, and cor
a respondingly raising the voltage. T
II do this results In great saving c
connar yvira in casa the distanea owe
which the power Is to be transmitte
a, is quite appreciable. AS concret
st example to illustrate the saving |
ID copper In transmission line fo
m comparatively high and low voltage
Of let us assume the following cond
ir tiOns;
Suppose q certain town require