Читать книгу Central-Station Electric Lighting - Killingworth Hedges - Страница 6

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An American electrical engineer graphically sums up this question in the following manner:—“There are two ways of starting a central-station for electric lighting—the investment or the speculative plan, or the fair means or the foul. The first has its legitimate end, but the latter is the border ruffian or money-or-your-life policy, which enters a territory already sufficiently covered, not for fair competition, but to make money by being bought out.” Happily, here, we have at present only to deal with the first plan, and the question naturally arises, “Is electric lighting a paying investment?” It certainly will not be if the object in view is only to compete with gas in a limited district where perhaps it is being sold at 2s. 6d. per 1000 feet, for, as long as there is a ready market for the coke and other by-products, gas will remain in possession of the field. The heat from gas, which is found so undesirable by the wealthier classes, is advantageous to those who perhaps cannot afford a fire; in fact, gas has been truly called the “poor man’s friend,” and, until electricity can be supplied at a nominal price, it will be useless to expect any revenue from the poorer districts of large cities. Quite an opposite result may be looked for when the electric mains are laid at the doors of the wealthy householder, or through the business neighbourhoods. Shop-owners especially are found to immediately take up electric light, from the fact that no fumes are given off to destroy goods or tarnish silver or gilding, and because it can be so easily applied in a shop window so as to efficiently light the contents without producing shadows. The great object to be aimed at in selecting a district to be served from a central-station is a “constant demand,” and for this reason it is advantageous to include a business neighbourhood with shops, public-houses, and restaurants, which require the light for a definite period every day, and probably will each take more than double the amount of an ordinary dwelling-house; in fashionable neighbourhoods especially, it is not unusual to find a large number of houses vacated at the close of the season, the interest on that portion of the electric system which is unemployed will have to be set against the profits of other periods of the year.

The number of gas lights which are actually used at one time in a house is found to average only two-thirds of the total number fixed, and with electric light this number is reduced to one-half; economy is at once the rule with electric light, partly because of the novelty of the illuminant, and also on account of the facility of lighting and extinguishing by simply turning a tap or switch. The number of hours artificial light is wanted in a residential district may be taken at about 1000 hours per annum, that is to say, the light is required for about four hours a day in winter and two hours in summer; this amount is very much exceeded in clubs, shops, and even in large houses, but 1000 hours is a safe figure, and, if the supply is taken by meter, an annual payment equivalent to 1000 hours’ supply should be a fixed amount to be paid for, whether used or not. Mr. Crompton estimates that a Londoner, who is a tenant or owner of a house having three reception rooms, ten bedrooms, and usual offices, spends about £25 a year for his lighting, which is made up as follows:—gas bill, £15; lamp, oil, candles, matches, about £10. There would be about fifty burners fixed; and, supposing fifty electric lights to be substituted, he could be supplied with electricity for £25 a year, at a fair profit to the supply company if they charged 8d. per Board of Trade Unit, as practice has shown that the total number of lamp-hours with fifty electric lamps is not more than sixty-two, so that two Units,[1] or 1s. 4d. per day, would be sufficient for the lights he would require.

The diagram, Fig. 1, taken from a London residential district, shows how the number of lamps on at one time vary; the district is supposed to be wired for 10,000 lamps, and the plant as equal to the supply of 600 kilowatts, or 600,000 watts; the number of lamps is small until about 3 o’clock, when it gets dusk on a winter afternoon; it then increases steadily until about 6.30 o’clock, when the curve goes up with a rush; about this time a great number of people are preparing for dinner, and probably the lights are on both in the dining-room and bedrooms. The curve falls, and at about 8 it begins to sink gradually until 10 o’clock; a great many people appear to go to bed about this time, but a few sit up to 1 o’clock; until 6 the next morning hardly any supply is taken, when the servants get up and prepare the rooms for the day. The diagram, Fig. 2, is taken from the Edison Company’s central-station at Cincinnati, and agrees fairly with the London demand for light. Another interesting fact has been ascertained from the observations taken at the Mauer Strasse station in Berlin, namely, that the output varies with the temperature, it goes up or down with the thermometer. The reason is easily explained; gas is laid on side by side with the incandescent lamps, and the burners are first lighted when it is cold to warm the apartments; in warm weather the electric light alone is used. From these and other diagrams the very important fact has been obtained, that the average daily output of a station throughout the year is less than one-third of the total capacity of the generating machinery, so that, although the station from which the diagram in Fig. 1 was taken could maintain 10,000 16 candle-power lamps simultaneously alight, the average daily output of electricity would only equal 3500 constantly lighted; and, as the first cost of the station is dependent on the size of the plant, the saleable output is the important factor which governs the profits.

Fig. 1.

Fig. 2.