December 31, 1915.

THE COLLIERY GUARDIAN.

1337

and headings, is for undercutting only, and requires an
air pressure varying from 50 to 80 lb. per sq. in. (3)
Type “ Z ” is a heavier and more powerful machine,
specially designed for working with low air pressures,
30 to 401b. per sq. in., and for cutting extremely hard
coal with a higher pressure.

The “ X,” or light type cf machine, ought to find a
ready market in India and other colonies, where the
miners are not a particularly robust class; whilst the
“ Y ” type will probably be found more suitable for the
collieries in our own country; and “ Z ” will be useful
where abnormal conditions prevail.

The standards are supplied in any length, and when it
is desired to “ shear ” as well, a special hinged quadrant
or sector is supplied, which permits the machine to be
set at any angle on the upright column. For shearing,
the machine is set to the middle of the column, and
then, by slackening one nut only, the whole quadrant
and machine are swung into position for vertical cutting,
as is shown in fig. 5. Where the machine is used for
longwall work, a sole plate or sledge can be fitted for a
small extra charge.

The machine is supplied complete with column and
gear, 50 ft. of protected rubber hose, with couplings and

, \......-A'

1 AM <AVZy-Vi A, '

Fig. 5.—“Hardiax” Coal-cutter arranged
for Shearing.





cock, cutter rods up to 7 ft. 6 in., and five cutter picks,
etc.; and we have no hesitation in recommending the
machine to the consideration of owners and managers
who are on the look out for a really good coal cutter of
this type.

Experiments with Coal Savers. — The Chancellor of the
Exchequer, in reply to Sir J. Rees, in the House of Commons
last week, said he understood that for several months experi-
ments with seldonite and other preparations of rock salt, etc.,
had been conducted by the fuel experts of the staff of his
Majesty’s Office of Works. Experience had shown that the
most effective method of reducing the consumption of coal in
Government offices was to reduce the area of the fire grate,
or, in the case of central heating, to lower the usual temper-
ature. These measures were being taken generally through-
out the Civil Service, and already considerable economy had
been effected by their adoption.

United States Imports and Exports of Coal.—The following
is a comparative statement of coal imports and exports of the
United States for September 1914-15, and the nine months
ending September 1914-15, in long tons :—

September.	Nine months.

<

Imports:	1914.

Anthracite, total ...	2,355...

Bituminous, total... 128,771 ..

United Kingdom. 102 ..

Canada .......... 101,646...

Japan ................ 90...

Australia......... 26,933...

Other countries... ' — ...

Coke ............... 16,977...

Exports:

Anthracite, total ... 395,088...

Canada .......... 389,213...

Other countries... 5,875...

1915.	1914.	1915.
134...	18,257..	2,524
126,282...	990,284..	. 1,077,799
500...	8,410..	16,110
111,000...	771,158..	. 869,634
5,200...	44,539 .	62,119
9,578...	164,124..	. 127,356
4...	2,053..	2,580
2,982 ..	■83,980..	36,602
289,790 3,062,057..		. 2,594,754
276,583...3,017,158..		. 2,538,305
13,207...	41,899..	56,449

Bituminous, total... 1,857,520..	1,832,977..	10,902,780..	.12,421,500
Italy 	 —	.  Canada	1,202,930.  Panama 	 23,166..  Mexico 	 42,312..  Cuba 	 97,787..  West Indies	 64,099  Argentina 	 55,567..  Brazil 	  45,846..  Uruguay 	 4,929..  O ther countries... 320,884..	.. 324,925.  .. 944,800.  .. 59.969.  21,787..  . 109,269.  44,835.  . 56,305..  . 61,223..  4,275..  . 205,589.	/. 7,241,856"  .. 214,131..  .. 257,380..  .. 793,898..  .. 479,923..  .. 193,786..  . 201,071..  61,443..  1,459,292..	. 2,348,870  . 5,682,455  . 389,419  . 238,033  . 843,805  . 353,440  .	719,019  . 544 194  . 135,065  . 1,167,260
Total coal	2,252,608..  Coke 	 673,372..  Bunker coal 	 28,510..	.2,122,767.13,964,837..  . 651,788...5,711,948..  . 59,395... 485,171..		.15,016,314 .5,678,815  . 573,084

The Design of High Pressure Distribution Systems.*

By J. R. BEARD, M.Sc., A.M.I.C.E.

Introduction.

The general distribution of electrical energy to
individual consumers, at high pressures, is of compara-
tively recent development, one of the first schemes in
this country being that which was inaugurated in the
year 1901 for the purpose of supplying power to ship-
yards on the Tyne, and which has since grown into the
extensive system that now covers the principal industrial
districts of Northumberland, Durham, and North
Yorkshire. High pressures had previously been used,
but only for transmission purposes to enable the power
stations to be situated outside the areas of supply in
order to utilise special advantages, such as waterfalls,
cheap sites, plentiful condensing water, or easy delivery
and storage of coal. In such cases the high-pressure
energy was transmitted to a point near the centre of the
area of supply where the whole of it was transformed to
low pressure for distribution to the consumers. Such
schemes, for example, were Dr. Ferranti’s pioneer high-
pressure transmission from Deptford to London, and
various water power schemes in America and on the
Continent.

The advantages of supplying concentrated power leads,
of, say, 100 kw. and over, direct from the power station
at high pressure, and transforming to the working
voltage at individual sub-stations adjacent to the load
centres, have since been generally realised, and the
last decade has seen an enormous development, both in
the number and in the size of such high-pressure distri-
bution-systems. Side by side with the development of
high-pressure distribution for power purposes, similar
methods were found essential for the various railway
electrification schemes, and also for the supply of power
to the larger tramway systems which were spreading out
over an area that it was impossible to supply at low
pressure from a single power station. Up to the present
the method of distribution for lighting has not been
radically altered, although occasionally the existence of
a high-pressure distribution system, primarily installed
for other purposes, has resulted in bulk supplies being
given to outlying districts. It is, however, being more
generally realised that only under exceptional circum-
stances is it possible to find near the centre of a large
lighting load conditions which permit of economical
generation, and consequently the original Deptford
example is being more widely followed. In many such
cases, owing to the ease with which a sub-station—unlike
a power station—can be installed in almost -any position,
there is a growing tendency to split up the more exten-
sive and cumbersome low-pressure networks into several
sections, each fed by a separate sub-station. As the use
of electricity for lighting and other domestic purposes
■increases, there is little doubt that these sections will
gradually decrease in area, with a consequent increase
in the number of high-pressure feeding points, so that
in this, as in other branches of electricity supply, the
distribution will eventually be at high pressure practi-
cally to the consumers’ terminals.

Not only is the cost of distribution at high pressures
considerably less than at low pressures, but also it is
thus possible for a single power station to supply
economically over an enormously greater area than that
which was previously practicable, and in consequence,
by better diversity factor and larger and more efficient
generating plant, great reductions have been effected in
the cost of electricity. The maximum economy from
these advantages is still for from being obtained, and
there is therefore every prospect that in the future the
growth of high-pressure distribution systems will be
equally as rapid as it has been in the past. The growth
should, however, be in size and not in number, since,
in order to reap the full benefit of improved diversity
factors and increased efficiency of generation, it is
essential that each system should supply the whole of
the demands of the area which it serves, and also that
the area served should be as large as possible.

In the present instance, the term “ distribution
system ” is restricted to mean the mains which convey
the electrical energy from the power stations where it
is generated to the sub-stations where it is transformed
to a form suitable for the consumers’ use, together with
the switchgear controlling them; and only three-phase
alternating-current systems are dealt with, as it is
generally recognised that these are most suitable for
high.-pressure distribution.

General Principles.

A well-designed distribution system is that which
secures the following essential characteristics at a
minimum total annual cost :—(a) Safety in operation
both as regards the operating staff and the public
generally; (5) suitability of the supply for the purposes
for which it is required; (c) freedom from interruption
of supply.

Safety in operation is of primary importance, since
with high pressures, accidents are frequently fatal. The
other two limitations have a commercial basis. In all
its various uses, electricity is a competitor with other
forms of energy, many of them very firmly established,
and if -it is not supplied in suitable form, or if the
supply is subject to interruption, the sale will be
restricted. For example, the cost of power is such a
small proportion of the total cost of running a works
that material irregularity in the supply would quickly
involve more loss than the whole cost of the power bill.
In such circumstances a supply of electricity would not
be a paying proposition if it could be obtained for
nothing.

Failure of supply is usually caused by the breakdown
of apparatus, and the primary precaution is therefore

* From a paper read before the Institution of Electrical
Engineers.

careful attention to the design, manufacture and main-
tenance of the various parts of the system; but since
no apparatus can be made absolutely immune from
breakdown through external damage, the secondary pre-
caution is to make arrangements so that the effects of
a breakdown to any part of the system are localised as
much as possible. In some cases such precautions may
mean increased capital cost, but they undoubtedly result
in a net economy if a broad view is taken. Fortunately,
however, well-designed apparatus does not necessarily
cost more than badly designed apparatus; and it is
possible to cheapen the system by closer localisation of
breakdowns.

The chief items which make up the annual cost are
the following, and it i-s the sum total of these which
should be a minimum :—(1) Interest on capital expendi-
ture; (2) repairs and provision for depreciation; (3)
switchgear attendance; (4) energy losses in the mains.

It may be useful to consider briefly these items in
turn, and to note in what ways they are interdependent,
and how they are affected by the essential characteristics
previously detailed.

(1)	It is unnecessary to say anything as to the
desirability of keeping down capital expenditure; the
chief danger is usually lest this point should receive too
much attention at the expense of other items. There
is, however, a further way of reducing interest charges,
namely, by a low rate of interest, and this can only be
secured by a permanent and steady business. This is
a further argument for extending and consolidating the
area of supply so that the revenue of the undertaking is
less subject to trade fluctuations.

? °

Or-6r-O

6 O--O

ch- a

a

■o-----o----

Fig. 1.—North-east Coast Distribution System.
(Note.—Generating stations shown cross-hatched.)

(2)	A low cost of repairs goes hand in hand with low
depreciation charges, since both depend on the perman-
ence of apparatus and its freedom from breakdown.
Money is doubly well spent on these points, since it not
only reduces repairs and depreciation, but provides the
first precaution already postulated as necessary to ensure
security of supply.

(3)	Particularly in the case of static sub-stations,
which have not an operating staff continually on shift,
attendance is largely a matter of operating switches
should a fault occur on some part of the system. Apart
from cost, such attendance is often very difficult to
arrange for, and there is therefore a strong reason for
reducing it as much as possible. This can be done by
closer localisation of breakdowns, so that the only part
of the system which is affected is that in the immediate
neighbourhood of the fault, thus at the same time taking
the second precaution postulated as necessary to ensure
security of supply. The cost of attendance is not only
a question of amount, but also of quality, and cheaper
labour can be employed if apparatus is designed to
prevent automatically the more serious mistakes in
operation. Such design tends to increase safety in
operation, which has been previously mentioned as the
first essential characteristic of the system.

(4)	Loss of energy in the mains can be reduced by
increased capital expenditure, and it is therefore a ques-
tion of the correct balance between the two. It can also
be reduced by linking up the various parts of the system
in order to utilise the diversity of their loads, a process
only rendered possible by again using means for localis-
ing the effects of breakdowns.

The essential characteristics of the system are not
incompatible with designing it on the basis of minimum
annual cost, since though they may in a few cases