This means in practice the battery will not be discharged fully at any time, except in emergencies, for which it has a reserve sufficient to carry a load of 500 horse power for over an hour. A capacity of 2,000 horse power hours is theoretically equivalent to 1,492 kilowatt hours, but as a horse power hour, at the engine, would represent not over 0.85 electrical horse power hours, it follows that the practical equivalent capacity of battery is 1,275 kilowatt hours. Taking the cost purposely at the highest figure, 65 cents per kilowatt hours, the initial cost of battery of 1,300 kilowatt hours erected, will be $84.500. The depreciation at 15 per cent. and interest at 6 per cent., or in all 21 per cent., will make the annual cost $1,775, or $4.86 per day for a year of 365 days. The estimated savings of this case, in consequence of making the load steady, was equivalent to 5 3 tons of coal. The battery, however, will add to the total energy produced, enough to cover the energy less which it introduces. The battery supplies 6 per cent. of the energy at a loss of 75 per cent., which means 4.5 per cent. of the whole energy produced. The plant will therefore have to generate some 24.380 horse power hours instead of 23,260, representing 18.315 pounds more steam and 1,869 pounds more coal. The net saving would therefore be about 4.47 tons. In a station already built, such as this one, the only saving is that in coal. If coal cost less than $1.10 per ton, the project would not pay; at $2 a ton it would effect a saving of $2.08 per day, and a corresponding amount at other prices. In the case of a new station, however, the saving would be materially greater, for it would include the interest on a certain capital that it economized in the equipment. Instead of a maximum capacity of 2,200 horse power assumed here, the plant need not be built for more than 1,500 horse power capacity to do the same work. We have a saving in the cost of 700 horse power, amounting to probably at least $7,700, the interest and depreciation on which taken at a low figure, 12% per cent. for the two, amount to $960 per year, or $2.64 per day.

In many cases the problem is slightly different. The road has developed and extended until the power station capacity is overtaxed. In many such instances calculation based on a full study of the conditions involved would probably show that the increased capacity could be obtained more cheaply by simply adding a storage battery to the station, the fact being that the station capacity is really large enough already when once the fluctuations are disposed of. In many such cases it will doubtless be found that, owing to the gain in efficiency, the cost of power would not be much increased, if at all; and in a few cases where the efficiency is now desperately low, it might even cost less for more cars.

Your committee has selected the example given for a detailed case, first because the data obtainable regarding it are more complete than for any other case; second, because it has been always considered that a road of 150 to 200 cars was a "limiting" case, where the storage battery was likely to be of little, if any, utility.

The smaller the station the more perceptible the effect on the efficiency will of necessity be. The quantity factor becomes smaller, but the rate factor is usually larger, until on small roads of 10 cars and less may amount to 60 per cent.; the load itself sometimes running up to 2 or 3 times average value.

In the case shown in Figure 3, of which the data are unfortunately incomplete, the battery rate factor would be about 55 per cent. of the maximum

(400 horse power), representing a delivery rate of 220 horse power, and the capacity would be 880 horse power hours, or about 558 kilowatt hours. It would probably be better in this case, as there are only a few extreme jumps in the curve, to reduce the rate factor and depend on the engine to rise in capacity 10 to 15 per cent. when such extreme loads occur. By doing this, the rate factor could be reduced to 25 per cent. and the battery capacity to about 260 kilowatt hours. It may be, in fact, that experience will show that the rate factor should be constant, or nearly so for all cases, to obtain best economy (least annual cost). Under these conditions the battery would involve an expense of only 78 cents per day for interest and depreciation. The engine capacity need not exceed 180 horse power; the load would be about 180 to 185 horse power, except for the early and late hours of the run, when part of the plant would be shut down as in the first case considered. The daily output is about 4,000 horse power hours, to which may be added about 5 per cent. for loss due to the battery, making 4,020 horse power hours. The saving effected by reason of steadier load would be in the neighborhood of a ton, according to the engine used. The hours of running could also be shortened to 20, as in the previous case.

WATER POWER.

The use of storage batteries is destined to important applications where water power is used for railway power generation. In such cases, since the power costs relatively little, the gain in efficiency is not of so much moment as are the regulating quality and the ability to store energy. Where the supply of power is constant, but limited, the rate of consumption can never exceed the rate of production. The consequence is that in railway waterpower stations, either the potential fluctuates seriously or else a sufficient margin of available power must be allowed, which means that the power cannot be worked to the limit. With the storage battery, not only the turbine can be loaded to the full limit, but the load may even be greater, if there is sufficient time in the intervals between heavy loads to accumulate a reserve power in the batteries.

REGULATION.

The process of making storage batteries absorb from or give back to a circuit, any desired rate of current, consists merely in varying the working potential of the battery in relation to that of the dynamo or circuit to which it is coupled, same as load can be divided up in any desired proportion between two dynamos in multiple by simply varying their E. M. F. relatively to each other. In the case of storage batteries, unfortunately, the working E. M. F. is not the same when charging as discharging, nor is it the same for different rates of current, or even for the same rate at various periods of the charge or discharge. Hence constant adjustment is necessary. In lighting stations, the desired relation of working potential to control the charge or discharge is effected usually by putting more or less cells in circuit. This method* would be inadequate for the fluctuations met with on railway power circuits, by reason of its lack of quick*For further details regarding this method, see the Street Railway Journal, November, 1890, and June, 1893; the Electric Engineer, December 3, 1895, August 30, 1892.

ness and of flexibility. The means provided must be such as to make the change of relation adapt itself to every change of load automatically, instantly, and to any desired degree. This can be accomplished by introducing in the battery circuit B B (Fig. 11), a variable source of potential, such as produced by a small dynamo A to which the name "booster" has been given. In the figure, the working current sent over the line L passes through the field magnet coil M, being suitably proportioned by a shunt T, and thus enables the fluctuations of load themselves to control the working potential of the batteries so as to produce any desired relation.

The figure is intended merely to show the principle, the details admit of great modifications and improvements over those shown.

SUB-STATIONS.

It makes little or no difference in the compensating action of the batteries whether they could be coupled to the circuit at the station or at sub-stations located at various points at a distance from the station. There would result from the use of sub-stations a greater uniformity of potential over the whole system and a saving in copper, but one must offset against this the extra cost of the space, the extra attendance and expense of such sub-stations. They may be warranted, for this reason, only in very large systems covering large and relatively distant territory, also in inter-urban lines.

CONCLUSIONS.

The investigation and study by your committee of the facts and data bearing on this subject as outlined herein above, would seem to your committee to warrant the following conclusions:

1. Great progress has been made in Europe during the last two or three years in the manufacture and perfection of storage batteries suited for central station purposes.

2. Storage batteries have been introduced in a large number of electric lighting central stations on a large commercial working scale, as factors of reserve and regulation, with a view of securing economy of initial cost and cost of operation, with satisfactory financial results, as a general rule which has few, if any, exceptions so far as your committee could ascertain.

3. The benefits derived in lighting central stations from the judicious use of storage batteries are so valuable in individual cases, that the possibility of attaining like benefits, even in lower degree, in railway power stations, would justify the investigation of their use by actual experiment, where this can be done under favorable conditions.

4. While the conditions differ and are essentially more severe in railway power stations, there is no reason apparent why storage batteries may not be used successfully and advantageously for the purpose of securing greater uniformity of potential at the station or on the line, or of promoting and improving the efficiency of the plant.

5. Even assuming the highest values for initial cost and depreciation of the storage batteries, the indications point to the possibility of realizing a gain in economy in all stations operating 200 cars and less, when coal is worth $2.00 per ton and over, while the economy will be much greater should the initial cost and depreciation prove actually lower in practice. Advantages are also secured which, though not affecting the economy directly, do so indirectly by affording additional convenience in operation.

6. The indications are that in some cases a power plant could be built and operated at less cost by using storage batteries, than without.

7. The capacity of an existing plant can probably, in most cases, be increased more cheaply by adding storage batteries than by adding more generating machinery, while at the same time the cost of operation will be reduced.

8. The question whether storage batteries are expedient and practicable, and to what extent for any particular case, should be, and can only be, in the present state of our knowledge, determined for each case individually, by a careful analysis of the facts and conditions involved, by a competent engineer. 9. Practical experience in a certain number of stations alone can lead to definite rules or indications in regard to the best size of battery, the best methods of regulation, the most favorable conditions of use, and like questions. 10. Perfection in the details of the use of storage batteries in railway plants will be the result of a certain evolution or series of improvements, the same as in other details of the equipment of a plant.

Respectfully submitted,

C. O. MAILLOUX,

Committee.

DISCUSSION ENSUING.

The President: Is there any discussion of the paper desired?

REMARKS OF MR. C. O. MAILLOUX.

Mr. Mailloux: Mr. Chairman and gentlemen, I earnestly hope that the members of the Association will take full opportunity to discuss this paper. What we want is to get at the truth and at the facts. They are using storage batteries in Europe very successfully in central stations, and it seems as though we might be able to use them here; yet we do not. As a step in the direction of advancing our knowledge of this matter, it seems to me that we ought to go into a careful analysis of this paper and consider it from every point of view.

As street-railway men you are all interested in getting the full percentage of your earnings; and you should be just as much interested in getting the full percentage of your production of power. It is not enough to get ninety-nine per cent. of the nickels received on the road; you want the full hundred. It is quite as necessary and desirable to get the full hundred per cent. of the coal consumed; and it is there especially that the storage battery in central stations has a field of possible use. I say possible, because I do not want to be understood as saying that it is practicable or feasible, although the indications all point very strongly that way.

Our experience with the storage battery in this country has been negative, passive and generally unsatisfactory. The experience abroad has been quite the reverse. It is, in my opinion, due to the fact that there they have not attempted to accomplish so much. They have more solid and substantial batteries, and they have taken advantage of the fact that in central stations, where portability is of no importance whatever, there is no objection to putting a large amount of material in the battery and making the batteries sufficiently robust and large, even though they may have a much lower capacity for the same weight and

cost.

Hence, it does seem as though it would be possible to accomplish results in this country by using storage batteries such as are now made in Europe. I do not believe that storage batteries hitherto made in this country would have any hope of being at all successful for such purposes as are considered in the present