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FRIDAY, June 7, 1907


Paper-Methods of Charging for Electric Motive Power. By G. SEMENZA

2 Report-Committee on Standard Rules for Electrical Construction and Operation. ERNEST H. DAVIS, Chairman

3 Commercial Programme


I Commercial Programme (continued)


Executive Session


The meeting was called to order at ten o'clock on Friday morning by President Williams, who announced the first order of business to be the paper contributed by Signor Guido Semenza, of Milan, Italy, on Methods of Charging for Electric Motive Power. The paper was read by Mr. Ferguson.



When I received from your president the kind invitation to present at the convention a paper on the systems of charging for electric service in Italy, my first impression was that I had only a few things of a slight interest to bring before an American convention. But, considering that foreign practice is always interesting when different from one's own, a brief narration of what has been done and what is going to be done in our country with reference to the above subject may meet with your appreciation.

The abundance of water-power easily available at short distances from manufacturing cities and districts and the complete absence of coal mines in Italy have largely contributed to the diffusion of electric power, and to such an extent as to make the country unique from this point of view.

All the waterfalls, large and small, are at present utilized or are in course of utilization. In northern Italy visits can be made to a group of hydraulic plants of from 20,000-hp down to 50-hp capacity and from 2000 feet down to 30 feet fall and transmissions varying from a few hundred metres to 140 kilo


As the water supply of rivers is not constant and during some of the seasons is very scarce, the central stations find it necessary to run steam engines to supply the deficiency, and as it has been to some extent demonstrated, there is a convenience in cutting off the peaks of the load with steam; hence nearly all the largest water-power plants are supplemented with auxiliary steam plants.

These particular conditions of the development have of course given a special character to the methods of charging, particularly for motive power. In this paper I shall deal with this aspect of the case only, as methods of charging for illumination do not in Italy offer any new or interesting points.

At first, electric energy for motive power had to fight against the competition of steam and gas engines and the schedules of rates were devised to overcome that severe rivalry. The sale

of very large amounts of energy for motive power was started in Italy by two companies-the Società Generale Italiana Edison. di Elettricità, which had to supply electricity to a large town. with large and small factories of all kinds and for home industries; the Società Lombarda per Distribuzione di Energia Elettrica, which had to supply electricity over a large district covered with small towns in which factories were established.

There were thus two different cases to consider, representing two extremes with reference to the question of rates. In the first case the distribution had to be fractional and each small customer had to be specially taken care of in order to meet his particular requirements. In the second case the company had to deal with a few large customers who, in general, would require a regular and constant supply of energy.

The Società Lombarda per Distribuzione di Energia Elettrica solved the problem in the most simple way by the adoption of a flat rate. We all know the drawbacks of a flat rate. In the present instance the choice was justified by the fact that at the time when the business was started there was no clear idea as to what the load diagram was going to be. Water-power cost the same, whether used for 6, 12 or 24 hours per day; thus each kilowatt could be sold for 24 hours' use per day at a fixed rate. This is very simple and clear. But when the load diagram shows a steep Alpine peak and the water diagram a low point, and one wished to sell all the power at disposal for 9 or 10 months in the year it is necessary to install a steam-plant. In this event a flat rate is not the most convenient for the business Flat rates induce customers to be wasteful, and this is of no advantage to any one.

Many other companies have followed the Società Lombarda in the method of charging for service, thus the flat rate is the one mostly used in Italy, and to give you an idea of what is done I here report a few schedules of some of the companies.

The Società Lombarda per Distribuzione di Energia Elettrica sells power at 3600 volts at the following annual rate per kilowatt and 12 hours' use per day:

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The Società per Lo Sviluppo delle Imprese Elettriche in Italia has a sliding scale of rates varying, per kilowatt-annum and 24 hours' use per day, from $58 per 10 kilowatts to $50 per 50 kilowatts.

The Acquedotto De-Ferrari Galliera has a sliding scale of charges for 24 hours' use per day varying from $108 per kilowatt-annum for powers of 5 kilowatts to $50 for powers up to 100 kilowatts.

At Rome the kilowatt-annum for 24 hours' use per day is charged $40 for powers above 10 kilowatts.

The Milan Edison Company followed quite a different plan. As I have said, it had to deal with all kinds of customers. A flat rate was out of the question, as one could not charge the same rate to a customer taking 0.5 horse-power as to a customer taking 500 horse-power. Moreover, even supposing it possible to charge a scale of rates for different powers, there was always the difficulty of some customers using motors one hour per day and other customers using them all the 24 hours.

It was therefore necessary to adopt the meter system, and after a careful study of the matter, the principle of the maximum demand was also introduced. Thus the schedule of rates had to embody a variable scale according to the maximum power demanded, and consequently a Wright system was involved.

The object of this method of charging for energy being to compete with gas and steam motors, a preliminary inquiry was instituted to establish the law of variation of the cost of the motive power to customers using heat motors of different sizes and for different numbers of hours per day. The result was plotted in a curve and served as a basis for the schedule.

The necessity for keeping as close as possible to the curve prevented the schedule from being worked out on simple principles, and the result was rather complicated.

To each value of the maximum demand a special Wright system was applied; the first rate on the Wright system varying with a curve similar to the one above mentioned; the second rate, with variations to keep the result in accordance with the rest.

But these Wright scales do not apply to the whole use.

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