, 1890-07-24

IOsS Nm ics ulfttlly WIFI lne
load, that IL, that the max
imum drop IL only reached
when the system is carrying
Its maximum load, which Is never
more than an hour or two In tile
evening. As the load decreases the
efficiency goes up till at very light
load 1t IL practically 100 per cent. of
the energy Mt the terminals of the
dynamo; whereas In AN alternating
system with no lamps In circuit, but
with the primaries of the convert
ers on, there will he from onc-tenth
to one-siXth OF the maximum cir
cult flowing through the primary
circuit without doing any useful
work whatever, except to raise the
temperature of the surrounding at
mosphcrc by heating the converters.
With regard to the practical con-
struction of the two systems we
have several considerations to bear
In mind. Suppose we have to
choose which system to adopt for
any given location and are not pref
udiced In favor of either system. If
we have not very far to- go to reach
the bulk of our customers, say with
In one mile, then unqucstionably
the direct system IL the cheapest
and most efficient, and should he
used where reliability, economy and
safety are considerations. In one
case you need n big coalpile and IN
the other a good-sized bank account.
To make u few figures on con-
struction let us suppose we have to
take n number of lights, say 100, n
distance of IA mile. To do this we
will require for the alternating sys-
tenn two miles of No. Y B and :
okonite or other tirst-class insulated
wire, which will weigh somewhere
about $50 pounds, this Mt loss In
the line of q per cent, whvh IL
about the average allowed. Eor the
direct system we will need two miles
OF No. . naked wire and one mile
| (for the neutraD of No. : Il and 5,
which will weigh In an aggregate
about 1870 pounds. This Is IA ratio
of about 81 to in favor Of the al
ternating system; but when we
take into consideration the higher
price per pound paid for insulated
wire and the cost of converters, the
advantage i'm point of cost over the
direct system will be very little, If
any; of course those figures hold ap-
proximnbly good for any num-
ber of lights A few re-
marks here may not be out
of place on the relative dimensions
of the "outsde' and neutral wires
of the three-wire system. There
seems to be very little uniformity in
the proportions used In different
places. Some makers use of very
small wire i'm proportion, while 9TH
ers use wire of the same carrying
capacity as the positive and mega
tive wires.
This latter plan Ia certainly the
safest, but 1t Is not at all necessary.
1t seems to me to be great waste of
copper. In the first place, the neu-
trail is not supposed to carry any
larger amount of current. In u
well-constructed installation there
should be no current whatever on
the neutral wire mt any time. IL Is
only In case of an accident, such as
IL short circuit on one side of the
System. that its carrying capacity is
taxed to any extent, and then u
smallineutralis is II positive advantage,
for the resistance it offers to the.pas-
sage of large current will be de-
cided help to save the machine from
damage, as | have seen proved more
than once. "A good practical propo-
sition for feeders, and which believe
Is used by the Edison co. in their
underground system, is II neutral of
! the diameter of the outside wires.
In overhead work the mains may
have the same proportion, but house
! wiring should have u neutral of the
same cross section as the positive
and negative wires OH account of its
liability to get heated ifa fuse should
blow on one side.
Looking at the relative amount of
live wire required for the two sys-
TENS 1t will be seen that the alter
mating has n very marked advan-
tage indeed, but these relative pro-
portions don't hold good when we
consider house wiring. The Quanti-
| ty of current In this case will be ap-
proximately for the alternating
system, b amperes at 1000 volts on
the line and 100 amperes at so volts
on the secondary or house circuit;
while for the direct system the
quantity throughout will be 25 am
peres ut 200 volts, allowing umpere
and ! ampere per lamp respectively.
Let us suppose the distance from
1.-THE line ut the outside of the build
ng to the lamps is 100 feet and that
the converter is placed on TIE pole.
To carry this secondary current
100 feet mt n loss of = per cent. will
require POO feet of No. 0OOO B. IL y,
weighing about 100 pounds without
insulation, or at n loss OF per cent,
about double this amount. While
for the direct system at n loss of .
per cent. 800 feet of No. o will be
needed weighing about twelve
pounds, or at loss of per cent, q
No. weighing about twenty-four
pounds. These weights are without
Insulation, the weight of which va
ries with the quality used. 1t will
be noticed that the ratio of the
weight of copper is about fifteen to
one in favor of the direct system.
Regarding insulation, the low ten
sion system has II great advantage
over the high tension alternating
system, for In almost all cases naked
line-wire Is perfectly safe, or at most
IA very cheap grade of insulation
may be used to prevent trouble from
falling telephone and telegraph
wires. Whatever damage that can
be done will be at the dynamo, as
there is no danger to life from acci-
dental contact with the wires, while
with the alternating current 1t IL alb.
solutely necessary to use the
best obtainable insulated wire 80 rs
to guard against danger to life and
also injury to the dynamo for a
short circuit on an alternator is al
most sure to destroy the arma-