Installation and Working Cost of Central-Stations.

Until the balance-sheet of some large central-station has been published, it is impossible to do more than surmise what relation the earning power of the generating plant bears to the initial cost. Those central-stations which are working successfully in this country at the present time are either too small for a reliable estimate to be formed, or, as in the case of the Grosvenor Gallery, the space is too cramped for the large amount of machinery which it has been found necessary to add in order to meet the increasing demands for light. In order to obtain an approximate idea of the cost of installing a station capable of maintaining 10,000 lights, the following data ([Table III].) given in Mr. Crompton’s paper before the Society of Telegraph Engineers are extremely valuable and will be examined with interest.

Although the figures given are necessarily empirical and open to criticism, the cost with both systems of distribution is approximately the same, and may be taken roughly at £5,860 per 1,000 lights, which amount, according to Professor Forbes, would be reduced to £3,914 per 1,000 lights if the installation was put down according to American practice, and at the initial cost of the Westinghouse alternating current system.

Mr. Crompton also compares the working cost of the two systems ([Table IV].).

Table III.

Cost of 10,000-Light, or 600-Kilowatt,[6] Plant.

 A.T.—ALTERNATING TRANSFORMER DISTRIBUTION.
Generating station, buildings, chimney shaft, £
 water tanks, and general fittings11,000
Dynamos and exciters—865 kilowatts, including
 spare sets, divided as convenient5,540
Motive power, i.e., engines, boilers, steam and
 feed connections, belts, &c., at £8 12 s. per I.H.P.12,470
500 transformers, i.e., one to every pair of houses, at £15 each 7,500
2,000 yards primary or charging main, exterior
 to area of supply, at £308 per 100 yards6,160
20,000 yards distributing main, 50 mm. sectional
 area, at £91 7 s. (see [Table I].)14,270
Regulating gear 500
£ 57,440
 B.T.—ACCUMULATOR TRANSFORMER DISTRIBUTION.
Generating station, buildings, chimney stack, £
 water tanks, and general fittings8,000
Dynamos—600 kilowatts, in six sets of 100 kilowatts each4,800
Motive power, i.e., engines, boilers, steam and
 feed connections, &c., at £8 12 s. per I.H.P.8,600
4 groups of accumulators, in all 240 cells, in
 series, at £40 per cell, including stands9,600
2,000 yards charging main, at £306 17 s. 6 d.
 per 100 yards ([see Table II].)6,137
20,000 yards distributing main, 161·25 mm. sectional
 area, at £100 12 s. 6 d. ([see Table II].)20,125
Regulating gear 2,500
£ 59,762

Table IV.

Working Expenses and Maintenance of 10,000-Light, or 600-Kilowatt, Plant.

Direct Alternating
Transformer System.
Materials—£ s.d. £s. d.
 Coals: 4,380 tons at 17s.3,723 00
”  2,550 ”17s. · ·
 Oil, water, and petty stores:
1,500 hours at 7 s. 6 d.
7,250 hours at 1 s.925 00
1,400 hours at 5 s. · ·
Total cost of material 4,6480 0
Labour—
 2 foreman drivers at 45 s.; 6 drivers at 30 s.;
 9 firemen at 24 s.; sundry labour
 1 foreman driver at 45 s.; 2 drivers at 30 s.;
 3 firemen at 24 s.; sundry labour1,388 80
Salaries—
 1 chief at £500; 2 assistants at £200 each; 4 clerks at £80 each 1,220 00
 1 chief at £500; 1 assistant at £200; 4 clerks at £80 each · ·
2,6088 0
Maintenance of Plant—
 Motive power and dynamos: 10 per cent. on £18,0101,801 00
””10 per cent. on £13,400 · ·
 Buildings and fittings: 5 per cent. on £11,000550 00
”” 5 per cent. on £8,000 · ·
 Transformers: 10 per cent. on £7,500750 00
 Accumulators: 15 per cent. on £9,600 · ·
 Mains: 7½ per cent. on £20,4301,532 50
”2½ per cent. on £26,262 · ·
 Regulating gear: 10 per cent. on £50050 00
”” 10 per cent. on £2,500 · ·
4,6835 0
11,93913 0
 2,100 units × 365 days = 766,500 units. Cost per unit · · 3·75 d.
Continuous Battery
Transformer System.
Materials—£ s.d. £s. d.
 Coals: 4,380 tons at 17s. · ·
”  2,550 ”17s.2,167 00
 Oil, water, and petty stores:
1,500 hours at 7 s. 6 d.
7,250 hours at 1 s. · ·
1,400 hours at 5 s.350 00
Total cost of material 2,5170 0
Labour—
 2 foreman drivers at 45 s.; 6 drivers at 30 s.;
 9 firemen at 24 s.; sundry labour
 1 foreman driver at 45 s.; 2 drivers at 30 s.;
 3 firemen at 24 s.; sundry labour975 00
Salaries—
 1 chief at £500; 2 assistants at £200 each; 4 clerks at £80 each · ·
 1 chief at £500; 1 assistant at £200; 4 clerks at £80 each1,020 00
1,9950 0
Maintenance of Plant—
 Motive power and dynamos: 10 per cent. on £18,010 · ·
””10 per cent. on £13,4001,340 00
 Buildings and fittings: 5 per cent. on £11,000 · ·
”” 5 per cent. on £8,000400 00
 Transformers: 10 per cent. on £7,500 · ·
 Accumulators: 15 per cent. on £9,6001,440 00
 Mains: 7½ per cent. on £20,430 · ·
”2½ per cent. on £26,262656 100
 Regulating gear: 10 per cent. on £500 · ·
”” 10 per cent. on £2,500250 00
4,08610 0
8,59810 0
 2,100 units × 365 days = 766,500 units. Cost per unit · · 2·7 d.

With the exception of the amount allowed for depreciation of the accumulators, which time alone can show to be correct, the expenses may be said to be over rather than under-estimated; the 15 per cent. depreciation given in [Table IV]. is under what has hitherto been found necessary to allow for the renewal of the plates of a secondary battery.

If the mean of the two results in [Table IV]. are taken, the working cost per Board of Trade Unit will be 3·22d., which shows that with both systems, after making due allowance for interest on capital, directors’ fees, bad debts, and other sundries omitted by Mr. Crompton, there is a probability of a very fair return on the capital expenditure, and the prospect of a handsome dividend for an electric lighting company who can sell electricity at the average price of 7d. per Unit.

The cost of maintaining and working electric lighting plant at private installations is usually much in excess of a supply from a central-station; but where the installation is over 500 lights, the difference is not very great.

The working cost at the Athenæum Club of 387 lamps for the past year is given as follows:—

 £s.d.
Gas for gas-engine446710
Oil””7138
Water ””3500
Wages17521
Sundries3030
Maintenance of lamps, etc.9841
Repairs10311
£ 95919

Average cost of lighting by gas and oil for previous years, for two-thirds number of lights £840.

At the Naval and Military Club, 420 lights cost £821 18s. for the same period, a steam-engine being used instead of a gas-engine.

The annual report of the cost of the electric light at the South Kensington Museum shows that in a larger installation, consisting both of arc and incandescent lamps, the annual cost of the latter is much less than in either of the clubs mentioned. At the Museum there are 860 16 candle-power lamps, working 655½ hours per annum, or 562,387 lamp hours; the total cost for working last year was £386, which includes £66 for repairs of engines, boilers, dynamos, and maintenance of lamps; but rent, interest on capital, depreciation of plant, and management is not included. The light is used only three evenings a week, so that the wages of the attendants are proportionately in excess of what they would be in a central-station.

The cost of arc lighting for street purposes may be estimated from the following tenders. At Taunton the local electric light company offered to extend the lighting of streets from 29 to 60 arc lamps of 1,200 candle-power nominal on the Thomson-Houston system, at the following rate:—

Per annum.
£s. d.
Burning on average of 6 hoursper night each lamp17 76
7” ”18 126
8” ”19 176

The posts and supports to be provided and fixed by the company, or, if the town council found the same, the company would allow a deduction at the rate of 5 per cent. per annum upon the outlay made by the council. The lamps are usually about 400 feet apart.

The actual cost of operating arc lights on this system is given in the following detailed expenses of a six hours’ run of a 50-light plant for the street lighting of an American city:—

2,600 lb. Ind. nut and slack coal, at $1·30 per ton$1·69
Engineer, one night, at $50·00 per month1·67
Superintendent or electrician, one night, at $50·00 per month1·67
Trimmer, one day, at $40·00 per month1·33
48 pairs of carbons, at $18·50 per month89
Waste, &c., at $20·00 per year05
Water rent, at $40·00 per year11
Half-pint cylinder oil, at 60c. per gallon04
One pint engine and dynamo oil, at 50c. per gallon06
One day repairs on machine and lamps, including globes, at $120·00 per year33
One day taxes on 50-light plant, assessed at $5,000, at 2¼ per cent.31
One day interest on 50-light plant ($10,000), at 6 per cent.1·67
Making a total of$9·82
10½ d. or 20·45 cents. per lamp. £15 10 s. per annum.

If, in addition to the 50 street lights, 33 other arc lights are maintained, the total cost is reduced for a six hours’ run to $13·25, or £2 15s. 2d. for the 83 lights, 8d. or 15·96 cents per lamp, £12 3s. 4d. per annum.

[Table V]. has been calculated by M. Decker, of Nuremburg, and gives the comparative cost of working 150 lamps by electricity and by gas. The gas price (1) is that paid in Paris, namely, 6s. 9d. per 1000 cubic feet; column (2) is the price usually taken commercially, which includes the fixed charges. The price of electricity is given: 1st, when a steam-engine is available; 2nd, when it is necessary to lay down a special engine; 3rd, when a gas-engine is used the gas is charged at a trifle over the price in column (1).

Table V.

Total Cost per Hour and per Lamp.

AB CD EF GH
Pence. Pence. Pence. Pence. Pence. Pence.
500 1·38 0·485 1·055 1·2160·418 0·552
800 2·190·371 0·780 1·0070·399 0·513
1,200 3·290·314 0·608 0·8650·380 0·352
3,600 9·870·219 0·1520·352 0·4850·361 0·465
Arc Lamps.
500 1·385·235 4·24610·459 11·485
800 2·193·971 3·0897·552 9·272
1,200 3·293·087 2·4416·004 7·581
3,600 9·872·185 1·5103·591 5·586