COST OF COPPER REQUIRED TO DELIVER ONE MECHANICAL HORSE-POWER at MOTOR-SHAFT WITH VARYING PERCENTAGES OF LOSS IN CONDUCTORS, UPON THE ASSUMPTION THAT THE POTENTIAL AT MOTOR TERMINALS IS IN EACH CASE 3000 VOLTS. (Westinghouse El. & Mfg. Co.)

Distances, one to twenty miles. Motor efficiency, 90%.

Length of conductor per mile of single distance, 11,000 ft., to allow for sag. Cost of copper equals 16 cents per pound.

A Graphical Method of calculating leads for wiring for electric lighting is described by Carl Hering in Trans. A. I. E. E., 1891. He furnishes a chart containing three sets of diagonal straight-line diagrams so connected that the examples under the general formula for wiring may be solved without calculation by simply locating three points in succession on the chart.

Efficiency of Long-distance Transmission. (F. R. Hart, Power, Feb. 1892.)-The mechanical efficiency of a system is the ratio of the power delivered to the dynamo-electric machines at one end of the line to the power delivered by the electric motors at the distant end. The commercial efficiency of a dynamo or motor varies with its load. Under the most favorable conditions we must expect a loss of say 9% in the dynamo and 9% in the motor. The loss in transmission, due to fall in electrical pressure or "drop" in the line, is governed by the size of the wires, the other conditions remaining the same. For a long-distance transmission plant this will vary from 5% upwards. With a loss of 5% in the line the total efficiency of transmission will be slightly under 79%. With a loss of 10% ir the line it will be slightly under 75%. We may call 80% the practical limit of the efficiency with the apparatus of to-day. The methods for long-distance transmission may be divided into three general classes: (1) continuous current; (2) alternating current; and (3) regenerating or "motor-dynamo" systerns.

There are many factors which govern the selection of a system. For each problem considered there will be found certain fixed and certain unfixed conditions. In general the fixed factors are: (1) capacity of source of power; (2) cost of power at source; (3) cost of power by other means at point of delivery; (4) danger considerations at motors; (5) operation conditions; (6) construction conditions (length of line, character of country, etc.). The partly fixed conditions are: (7) power which must be delivered, i.e., the efficiency of the system; (8) size and number of delivery units. The variable conditions are: (9) initial voltage; (10) pounds of copper on line; (11) original cost of all apparatus and construction; (12) expenses, operating (fixed charges, interest, depreciation, taxes, insurance, etc.); (13) liability of trouble and stoppages; (14) danger at station and on line; (15) convenience in operating, making changes, extensions, etc. Assuming that the cost of dynamos, motors, etc., will be approximately the same whatever the initial pressure, the great variation in the cost of wire at different pressures is shown by Mr. Hart in the following figures, giving the weights of copper required for transmitting 100 horse-power 5 miles:

The relative advantages of these systems vary with each particular transmission problem, but in a general way may be tabulated as on p. 1043.

Systems of Electrical Distribution in Common Use. (Chas. T. Scott, Proc. Engrs. Soc'y of Western Penna., 1895.)

I. CONTINUOUS OR DIRECT CURRENT.

A. Constant Potential.

110 Volts.-Distances less than, say, 1500 feet.

For incandescent lamps.

For arc-lamps, usually 2 in series.

For motors.

220 Volts, 3-wire.-Distances less than, say, 3000 feet.
For incandescent lamps.

For arc-lamps, usually 2 in series on each branch.
For motors 110 or 220 volts, usually 220 volts.

500 Volts.-Distances less than, say, 8000 feet.
For incandescent lamps, usually 5 in series.
For arc-lamps, usually 10 in series.

For motors, stationary and street-car.

B. Constant Current.

Usually about 10 amperes, the volts increasing to several thou sand, as demanded.

For arc-lamps.

For motors.

II. ALTERNATING CURRENT.

A. Constant Potential.

For incandescent lamps.

For arc-lamps.

For small motors.

Multiphase Systems.

For lighting.

For motors.

For rotary transformers for giving direct current.

B. Constant Current.

Usually 10 amperes.

For arc-lamps.

References on Power Distribution.-Kapp, Electric Transmission of Energy; Badt, Incandescent Wiring Handbook; Abbott, Electric Transmission of Energy; Bell, Electric Power Transmission; Noll, How to Wire Buildings; Cushing, Standard Wiring for Incandescent Light and Power; Crocker, Electric Lighting, 2 vols.

ELECTRIC RAILWAYS.

Space will not admit of a proper treatment of this subject in this work. Consult Crosby and Bell, The Electric Railway in Theory and Practice; Fairchild, Street Railways; Merrill, Reference Book of Tables and Formulæ for Street Railway Engineers; Bell, Electric Transmission of Power; Dawson, Engineering and Electric Traction Pocket-book.

ELECTRIC LIGHTING.

Arc Lights.-Direct-current open arcs usually require about 10 amperes at 45 volts, or 450 watts. The range of voltage is from 42 to 52 for ordinary arcs. The most satisfactory light is given by 45 to 47 volts. Search light projectors use from 50 to 100 amperes at 48 to 53 volts.

The candle-power of an arc light varies according to the direction in which the light is measured; thus we have, 1, mean horizontal candle-power; 2, maximum candle-power, which is usually found at an angle below the horizontal; 3. mean spherical candle-power; 4, mean hemispherical candlepower, below the horizontal.

The nominal candle-power of an arc lamp is an arbitrary figure. A 450. watt arc is commonly called 2000 c.-p. and a 300-watt arc is 1200 c.-p. These figures greatly exceed the true candle-power. Carhart found with an arc of 10 amperes and 45 volts a maximum c.-p. of 450, but with the same watts 8.4 amperes, and 54 volts he obtained 900 c.-p. Blondel. however, found the c.-p. a maximum usually below 45 volts. Crocker explains the discrepancy as probably due to a difference in size and quality of the carbons.

Current for arc lighting is furnished either on the series, constant current, or on the parallel constant potential system. In the latter the voltage of the circuit is usually 110 and two lamps are connected in series. In currents with higher voltages more lamps are used in series; for instance 10 with a 500-volt circuit

Alternating current open arcs usually take about 15 amperes at 30 to 35 volts. With the same energy and carbons, the mean spherical candlepower is about one half that of the continuous-current open arc.

Enclosed Arcs -Direct current enclosed arcs consume about 5 amperes at 80 volts. or 400 watts. The chief advantages of the enclosed arcs, on constant potential circuits are the long life of the carbons, 100 to 150 hours, as compared with 8 to 10 hours for open arcs; simplicity of construction, absence of sparks, agreeable quality and better distribution of light.

Alternating-current enclosed arcs usually take a current of 6 amperes at 70 or 75 volts. With 70 volts and 6 amperes, in a 104-volt circuit, the apparent watts at the lamp terminals are 625 and at the arc 420. the actual watts being 445 and 390 respectively. The watts consumed in the inductive resistance average 35 to 45.

Incandescent Lamps.-Candle-power of nominal 16 c.p. 110-volt

0.51 ampere.

Ordinary lamps take from 3 to 4 watts per candle-power. A 16 candlepower lamp using 3.5 watts per candle-power or 56 watts at 110 volts takes a current of 56110 For a given efficiency or watts per candle-power the current and the power increase directly as the candlepower. An ordinary lamp taking 56 watts, 13 lamps take 1 H.P. of electrical energy, or 18 lamps 1.008 kilowatts.

Variation in Candle-Power, Efficiency, and Life.-The table on p. 1046 shows the variation in candle-power, etc., of the General Electric Co.'s standard 100 to 125 volts, 3.1 and 3.5 watt lamps, due to vari

ation in voltage supplied to them. It will be seen that if a 3.1 watt lamp is run at 10 per cent below its normal voltage, it may have over 9 times as long a life, but it will give only 53 per cent of its normal lighting power. and the light will cost 50 per cent more in energy per candle-power. If it is run at 6 per cent above its normal voltage, it will give 37 per cent more light, will take nearly 20 per cent less energy for equal light power, but it will have less than one third of its normal life.

The candle-power of a lamp falls off with its length of life, so that during the latter half of its life it has only 60 per cent or 70 per cent of its rated candle-power, and the watts per candle-power are increased 60 per cent or 70 per cent. After a lamp has burned for 500 or 600 hours it is more economical to break it and supply a new one if the price of electrical energy is that usually charged by central stations.

Specifications for Lamps. (Crocker.)-The initial candle-power of any lamp at the rated voltage should not be more than 9 per cent above or below the value called for. The average candle-power of a lot should be within 6 per cent of the rated value. The standard efficiencies are 3.1, 3.5, and 4 watts per candle-power. Each lamp at rated voltage should take within 6 per cent of the watts specified, and the average for the lot should be within 4 per cent. The useful life of lamp is the time it will burn before falling to a certain candle-power, say 80 per cent of its initial candle-power. For 3.1 watt lamps the useful life is about 400 to 450 hours. for 3.5 watt lamps about 800, and 4 watt lamps about 1600 hours.

Special Lamps. The ordinary 16 c.-p. 110-volt is the standard for interior lighting. Thousands of varieties of lamps for different voltages and candle-power are made for special purposes, from the primary lamp, supplied by primary batteries using three volts and about 1 ampere and giving c.-p., and the 4 c.-p. bicycle lamp, 4 volts and 0.5 ampere to lamps of 100 c.p. at 220 volts. Series lamps of 1 c.-p. are used in illuminating signs, ampere and 12.5 to 15 volts, eight lamps being used on a 110-volt circuit. Standard sizes for different voltages, 50, 110, or 220, are 8, 16, 24, 32, 50, and 100 c.-p.

ELECTRIC WELDING.

The apparatus most generally used consists of an alternating-current dynamo, feeding a comparatively high-potential current to the primary coil of an induction-coil or transformer, the secondary of which is made so large in section and so short in length as to supply to the work currents not exceeding two or three volts, and of very large volume or rate of flow. The welding clamps are attached to the secondary terminals. Other forms