April 20, 1917.

THE COLLIERY GUARDIAN.

775

MANCHESTER GEOLOGICAL AND
MINING SOCIETY.

A meeting of the Manchester Geological and
Mining Society was held on Tuesday, 17th inst.,
Mr. William Pickup presiding.

The following new members were elected:—Member
(federated): D. E. Thomas, Denton’s Green-lane, St.
Helens. Associate member (federated), F. J. Aspinall,
Alderlea, Broadgate, Preston. The following firms
have become subscribing members of the society: —
The Park Collieries, Garswood, Wigan; the St.
Helens Colliery Company Limited, St. Helens; and
Messrs. Ackers, Whitley and Company, Leigh.

ELECTRIC SUPPLY TO COLLIERIES.

A paper on “ Electric Supply to Collieries” was
read by Mr. G. S. Corlett, M.I.M.E. He said that
he did not propose to discuss all, or even a large
number, of the problems which might fairly be
covered by the title of the paper. He would, how-
ever, endeavour to examine the conditions under
which the supply of electric energy to collieries was
usually furnished, and sundry considerations affect-
ing the cost thereof. It should be noted that nothing
referred to the small amounts of energy required for
such purposes as bells, telephones, and the like.

Most of the data referred to were taken from the
contracts for supply still in force, and being dealt with
by him in the course of his professional duty. Such
information was obviously confidential, and therefore
it had been thought undesirable to indicate localities,
or to state the terms of contract in precise figures,'
but every care had been taken to ensure the accuracy
of such figures as were quoted. Broadly speaking, all
colliery supply might be classified as either generated
—produced on the colliery premises for the purpose
of the colliery or group of collieries—or purchased—
i.e., furnished by an outside source of supply.

The objects of such supply were:.—(1) To perform
one or more of the operations incidental to coal
getting; (2) to be available continuously or for such
shorter periods as might be required; (3) to be reli-
able, so that there might be no interruption to the
continuity of any desired operation, this to be pos-
sible without undue attention on the part of the
management; (4) to be flexible, i.e., that permanent
or temporary increased loads or reduced loads for
periods could be economically dealt with; and (5) to
be cheap, viz., that the total annual cost, including
capital charges, should be the lowest possible figure.

Generated versus Purchased Supply.

It was, in his opinion, quite impossible to make any
broad statement as to the general desirability or
otherwise of providing the supply by purchase or
generation. The conditions differed to such a wide
extent that any attempt to dogmatise wTould be futile.
In order to arrive at a sound conclusion, it would be
necessary to review various considerations, the more
important of which were : —

(1)	Choice.— Although there was a supply of elec-
tricity in most coal fields, distributed in many direc-
tions, and to an. extent that was rapidly increasing,
yet there were still many collieries outside the prac-
tical range of such supply. Should a supply be avail-
able, it was further necessary to see: (a) That it fur-
nished the kind of current required. Frequently,
additional supply had to be considered when an exist-
ing generating plant was either too small, or of
unsatisfactory type. In such cases, the new supply
should be suitable for the motors already installed.
Though the conversions from alternating current to
direct current and from one periodicity to another
were simple engineering problems, they involved con-
siderable capital outlay, and increased running costs
owing to the losses incidental to the conversion, (b)
That it should be continuously available, reliable, and
flexible. Should there be no such supply, a local
generating plant must be provided, and the further
points mentioned might he ignored except so far as
they affected the design of the plant.

(2)	Finance.—(a) The cost of a suitable generating
station with sufficient stand-by plant should be ascer-
tained. (b) The cost of generated and purchased cur-
rent should be compared, not only in the earlier stages
of the installation, but over a period of at least five
years. To make that comparison in a manner likely
to be of real value, a considerable amount of trouble
was necessary, (c) In those cases, by no means infre-
quent, where the amount of available capital was
strictly limited, it was worth while considering whether
the money could be more profitably used for other
improvements than in the purchase of a generating
plant.

(3)	Engineering.—(a) Load: It was relatively easy
to design a suitable generating station when the final
requirements were definitely known, but the greater
the doubt as to future needs, the greater the difficulty
of design. While it was impossible to forecast colliery
requirements accurately, it was always desirable to
consider the question of load, to estimate carefully the
rate of increase, aiid how the load would be distri-
buted over the 24 hours. Further, the probabilities
of major extensions should be considered, such as the
opening out of additional seams, whether water now
standing in disused workings, or otherwise being dealt
with, might not later be pumped at the particular
pit. All those points had a very distinct bearing on
the design of the power station, and consequently on
the cost.

(b) Fuel; Under this head might be grouped such
questions as: the nature of the fuel available, its cash
and calorific value, whether it could readily be sold in
normal times or not. Was . the existing boiler plant
of sufficient capacity, and at a high enough pressure to

furnish the required load economically, or did the con-
ditions justify new high-pressure boilers? Was there
a supply of heat energy, such as exhaust steam, or
waste heat from coke ovens or elsewhere, which could
be used at times when the load was required ?

(c) Life of Collieries: It was usually desirable to
estimate the probable life of the colliery, and so ascer-
tain whether capital outlay on a generating station
was economically sound; the shorter the estimated
life, the more closely should that point be scrutinised.
Doubtful conditions affecting or likely to affect the
working period should be weighed up, such as possible
water troubles, faults, or variation in the quality or
demand for the coal.

General.—In addition to the points he had already
enumerated, and to which it was suggested a cash
value could be allocated or approximated, there was
another consideration, which he was unable to express
in £ s. d. For want of a better term, that might be
called the convenience factor, and it applied only to
supply from an outside source. At week-ends, holi-
day periods, stoppage of work from accident or labour
troubles, there were undoubted advantages in being
able to run any individual motor when necessary with-
out running a generating station. That advantage
was more marked in the smaller single pit installations
than in those of larger capacity dealing with a group
of pits. It might be argued that the investigation
suggested was much more elaborate than was really
necessary. He readily agreed that it was frequently
dispensed with wholly or in part, but that it would pay
to carry out fully he was firmly convinced.

Purchased Current.

Apart from special arrangements to meet abnormal
conditions, current was usually charged on one of the
following methods : —

(1)	Flat rate : that was a uniform rate for all cur-
rents consumed.

(2)	Differential rate : that was two distinct flat rates
in force, one applying to certain hours only, the other
to the remaining hours. In practice, the proposal
usually worked was for a certain rate for day shift,
and one appreciably lower for night work and week-
ends.

(3)	Maximum demand: that also consisted of two
separate items, namely—(a) a fixed charge per kilo-
watt demanded per month or per year; (b) a further
rate per unit for all current consumed.

To each of these three methods of charges a coal
variation clause was generally added, whereby the
rate per unit varied according to the market price of
coal.

It was a fact that the cost to the supply company of
furnishing the same amount of current to two different
consumers might differ to a very wide extent. For
example, consumer A used 10 kw. 10 hours per day,
and consumer B used 100 kw. one hour per day. Each
would use the same number of units, but to supply B’s
needs the station must have available 10 times the
power required for A, and therefore the total charge
to B ought to be greater than to A.

Stating the proposition in more general terms,
equitable tariffs should: (u) ensure the supply com-
pany a reasonable return on the capital expended to
meet the demand and on the cost of production; (b)
enable each consumer to obtain his supply on the most
favourable terms, and should only pay his own pro-
portion of the cost.

Turning again to the three methods of charge, it
might therefore be said that the flat rate had the
merit of simplicity, but no other that he had been able
to discover, and that the differential rate was seldom
available; but when a supply company desired an
increased night load, and the consumer’s demand was
appreciably greater by night than by day, then a tariff
on those lines was mutually beneficial. The night
rate was frequently about 70 per cent, of the day rate.
With regard to maximum demand, for general supply
this system was undoubtedly the most satisfactory,
equitable to the supplier and the consumer, and had
been largely adopted. By many, however, it was con-
sidered difficult to follow, and more or less wrapped
in mystery. In principle it was extremely simple.
The maximum demand rate was designed to cover the
supply company’s fixed charges for furnishing, not the
possible, but the actual demand made. Similarly, the
rate per unit covered, or was intended to cover,
running costs, the main item being fuel. In practice,
the period for which the maximum demand was
measured was generally 15, 20, or 30 minutes, and was
always, assuming accuracy of the control clock, the
same period. That was to say, on 15 minutes lag from
9 to 9.15, 9.15 to 9.30, and so on, and never 9.5 to 9.20,
9.20 to 9.35. This instrument really measured the
actual number of units passing in the period of lag,
and further multiplied the total by the correct factor
(4, 3, or 2 for 15, 20, or 30 minutes) to bring the result
to an hourly basis. It carried a dial with a needle,
which showed the highest maximum demand previ-
ously registered, and such indication remained until
a higher maximum demand occurred, the needle being-
moved forward accordingly, or until the instrument
was re-set to zero.

Contracts for Supply.

Supply for collieries was usually furnished under
special contracts for a term of years, and the follow-
ing were the more important points to consider in
connection therewith: —

Guaranteed Revenue.— The broad principle of a
minimum payment was' generally adopted without
question, but the details frequently prolonged negoti-
ations. The amount should bear some relation to the
cost incurred by the supply company in delivering to
the consumer’s premises. Whether the payment
should be cumulative or non-cumulative was open to

argument. In a recent case, a mile away from the
nearest mains, the calculated annual value of the
current at the rates offered was £1,800 per annum, and
the supply company proposed, on a seven years’ con-
tract, that the following payments should be guaran-
teed : Not less than £1,000 at the end of the first year,
not less than £2,000 at the end of the second year,
not less than £3,000 at the end of the third year, and
so on. Hence, as soon as a total sum of £7,000 had
been paid, the consumer’s liability for any further
dead rent ceased. In view of the uncertainty of
mining operations, a cumulative arrangement was best
for the consumer, and not unfair to the supply com-
pany, provided the amount was not too low.

Period of Lag.—Choice of the length of lag was
seldom available, owing to the desire for standardisa-
tion on the supply company’s part. In one instance
within his experience, alternative proposals were made
for maximum demand at 15 and 30 minutes lag, and
the rates wbre in the ratio of 80 to 100 per cent. The
shorter the lag, the lower should be the ratio of maxi-
mum demand charge.

The load conditions determined, when a choice was
possible, which was the correct procedure. In cases
where the load was constant, and a maximum for long
periods, it was obvious that the demand would be
identical for any time lag, and hence the lowest rate
should be adopted. Where the running machinery
consisted of intermittent working plant, such as main
and tail haulages, it was equally evident that a longer
time lag was desirable.

Be-setting to Zero.—Every agreement should specify
clearly the times at which the maximum demand indi-
cator should be re-set to zero. Neglect of this point
might considerably affect the annual cost. The
arrangements varied to a large extent, as was shown
by the following schedule of contracts now in opera-
tion, which provided for the re-setting of the meters: '

(a)	Monthly throughout the contract; (b) monthly for
the first three years, then yearly ; (c) yearly throughout
the contract; (cZ) at the termination of the contract,
i.e., a maximum demand once established was never
reduced.

Clearly method (a) was most favourable to the con-
sumer, and (cZ) the least considerable. A simple illus-
tration would perhaps emphasise that point. Assume
a maximum demand rate of £4 per kilowatt year, and
a steady day load of 50 kw. for, say, endless haulage,
and 50 kw. for night pumping. If from any cause,
such as carelessness on an attendant’s part, the two
loads were run simultaneously, the extra costs would
be: —

(a)	For monthly re-setting —2S_JzP - £16 13s. 4d.

1 •-

(b)	For yearly re-setting 4 x 50 = £200.

(c)	For re-setting at termination, £200 per annum
for each unexpired year.

Whilst the responsibility for the correct running of
his plant properly belonged to the consumer, he should
not be unreasonably penalised for an isolated act.
Provision ought to be made to meet such contingencies,
'and also to afford relief if the load be permanently
reduced by, for example, closing a mine.

Maximum Demand Charges. — These were usually
based on one of the following methods: (a) Fixed rate
for all loads; (b) sliding scale, i.e., a steadily decreas-
ing charge for a steadily increasing load; (c) semi-
sliding scale, which really meant that the first block of
kilowatts (say, 100 or 200) were charged at one rate,
the next block at a lower rate, and all in excess at a
still lower figure.

It was not necessary to point out that methods (b)
and (c) afforded an inducement to the consumer to
increase his demand, and had doubtless been drafted
with that object in view. The actual figures attached
to the respective rates formed the only basis for deter-
mining which method to adopt in any particular case.

Coal Variation.—This applied only to the charge per
unit metered, which was, of course, sound practice.
Cost of coal of a certain calorific value generally, but
by no means universally, formed the basis. It was
essential that the basis should be clearly defined and
so stated that any competent engineer could, in the
event of dispute, decide the matter at issue.

General.—In the preceding paragraphs, he had
endeavoured .to discuss quite impartially the more
important aspects of such contracts, but he would
state emphatically that to ensure a mutually advan-
tageous arrangement, the contract as a whole should
be reviewed on broad lines. Should the consumer
insist on excessive protection on all the points raised,
it was at least probable that the supply company would
increase the rates.

Load Factor.

By this expression was meant the ratio of the actual
unit used to the possible units if the load was main-
tained uniformly. Thus one kilowatt year would equal
8,760 units—the number of hours in a year. If the
actual units metered were 4,380 on a demand of 1 kw.,

i £ 4- it i 4,380 -f- 100
then the load factor would be -———-------

8,760

= 50 per cent.

In the vast majority of colliery installations the
higher the load factor, the lower would be the running
cost, and that applied whether the supply be pur-
chased on the maximum demand basis or generated.
With purchased current, the cost came automatically
in front of the principals when the periodical account
had to be dealt with; and variations not infrequently
called for explanation. Whether that be so or not,
the cash value of any improvement in load factor could
be ascertained definitely. With generated current,
exact records were not always available, and the total
monthly cost was seldom brought out; consequently,
approximate values could only be stated for the sug-
gested alteration. He was also aware that a low load