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cost shows that a very little improvement would render them valuable even in very large stations for the mere purpose of diminishing the machinery required, by storing the energy developed at slack times to be used in busy times The certainty of improvements in accumulators, and the possibility that the improvement may be considerable, is a strong argument for the use of the direct current wherever it is not precluded by the distance of transmission being too great.
It will be noted that I have assumed a very large station. Accumulators have another use which greatly increases their advantage in smaller stations. There are many hours in the twenty-four when it is absolutely certain that the demand will be small. If accumulators are used, the attendance of the staff may be dispensed with during those hours, and a considerable sum in wages will be saved. The proportion of wages to the whole of the charges is much greater in small stations than in large. In most small stations giving continuous supply, accumulators ought to be used notwithstanding their expenses and defects, and I believe the day is not far distant when they ought to be used in connection with most large stations also.
Effect of Use of Alternating Current
If instead of a continuous current, an alternating current with transformers is used, the modification in the account will be that the cost of conductors will be diminished, but the cost of transformers will have to be added. If the distances are small, the increased cost of transformers will exceed the saving in the conductors; if the distances are considerable, the cost of transformers will be less than the saving of conductors. In both cases the general character of the result will be the same as before, the cost of being prepared to give a supply will be considerable, and the cost of actually giving the supply will be much smaller than is generally supposed. Indeed with the alternating current this peculiarity will be even more marked, for the machinery has not only to be kept in motion however small the consumption may be, but a certain current must be maintained in every transformer. With the best transformers, this current may only have an energy 1% per cent. of the energy of the current when the transformer is fully loaded. This would increase the coal bill in the case considered by about £500 per year whether the supply was used or not.
It is possible, indeed probable, that some of my assumed figures may be shown to be too high or too low for the generality of cases. It is of no moment; let each one take any figures he pleases within reason; let him assume that the supply of electricity is made by any system he pleases; he will arrive at a result broadly similar to mine. To be ready to supply a customer with electricity at any moment he wants it will cost those giving the supply not much less than £11 per annum for every kilowatt, that is for every unit per hour, which the customer can take, if he wishes, and afterwards to actually give the supply, will not cost very much more than 13d. per unit. This is the point I have been labouring to impress, for I take it, it is essential to the commercial success of Electric Supply. It is hopeless for electricity to compete with gas in this country all along the line, if price is the only consideration. But with selected customers, electricity is cheaper than gas. Surely it is the interest of those who supply electricity to secure such customers by charging them a rate having some sort of relation to the cost of supplying them.
A Method of Calculating the Cost of Furnishing Electric Current
and a Way of Selling It
W. J. GREENE
(Reprinted from The Electrical World, Volume XXVII,
Feb. 29, 1896, pp. 222, 223)
A Method of Calculating the Cost
and a Way of Selling It
By W. J. GREENE
A manager of a central station has, directly or indirectly, two objects in view—the increasing of the revenue, and the decreasing of the expenses. A thorough knowledge of the cost of supplying current, and of the rates at which it should be sold, would naturally come under the first head, and is of great importance in insuring the permanent success of a lighting plant. The experience of the writer's own company on these features, and data formulated therefrom, may prove of some interest.
In January, 1888, the company commenced the supply of current for light, using the alternating-current system. In the Fall of 1888 a few meters were installed, and in the Spring of 1889 the use of meters was adopted exclusively, except for one or two lamps. The rate charged was one cent per ampere-hour on 50-volt current, regardless of the amount consumed. Lights were added very rapidly. The stockholders were continually called upon to provide means for enlargements to the station equipment, extensions to the circuits and purchases of converters and meters. The net earnings for a time increased in proportion to the increase in investments. In 1892, however, a very apparent falling off in the net earnings in proportion to the new capital invested was noticed. It became evident that something was wrong. Tables were therefore prepared, showing the expense of maintaining an equipment necessary to supply current for consumers having from one light and upward. In comparing these results with the actual receipts from the various consumers, it was found that only 25 per cent of residence consumers and 55 per cent of other classes used sufficient current to furnish a paying investment. A few years prior thereto fully 85 per cent of residence consumers and 95 per cent of other classes were considered profitable.