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36
Islington would be a fair estimate of the extra cost of electricity
if charged at 6d. per Board of Trade unit. If, however, the damage
and injury caused by gas to ceilings, pictures, and goods of every
description is taken into account, electricity would, on the above
figures, doubtless prove much more economical as an illuminant
than gas.
PRINCIPAL SYSTEMS OF ELECTRIC LIGHTING.
There are three principal systems of electrical distribution in
working at the present time. These are:—
1. The Low Tension Continuous Current System.
2. The High Tension Alternating Current Transformer
System.
3. The High Tension Direct Current System, with Motor
Transformers.
The first mentioned System, the Continuous Current at low tension.
is sometimes used with what is called the two wire distribution and
in other instances with three wire distribution. By the two wire
system the area in which the current can be distributed efficiently and
economically appears to be limited to a radius of say half-a-mile from
the supply station, while by the three wire system, this radius is
extended to about three-quarters of a mile or a mile from the central
station. The Corporation of Bradford and Brighton are working on the
two wire system, while St. Pancras is on the three wire system. The
mode of distribution of the low tension system is that currents varying
from 100 to 200 volts are distributed from a centrally situated station
or stations, either running direct or using accumulators.
The main advantages claimed for this system are:—
(a.) Use of accumulators for supplying light load, thereby
enabling the engines to be stopped and the station
closed during the night.
(b.) Utilization for motor power.
(c.) Safety in working.
(d.) Adaptability to small and concentrated areas.