When More Voltage Means More Distance
Charles P. Steinmetz
W HEN about 40 years ago, Edison first transmitted electricity at constant pressure, that is, constant voltage, he used 110 volts and soon afterward 220 volts. At this electrical pressure or voltage, electricity can be sent economically for about half a mile to a mile, and when it becomes desired to send electric power over longer distances, higher voltages, that is, higher elec trical pTessures, become necessary, just as a higher water pressure or higher air pressure is necessary to send water
... or air over a greater distance. Thus steadily in these 40 years, transmission voltages have been increased, until now we are beginning to use 220,000 volts, a pressure just 1000 times as high as that considered the highest safe pressure only 40 years ago. The question, which the layman always asks, is, "How far can electricity be transmitted economically?" Suppose we want to double the distl ance to which to send the electric power. This means twice as long a transmission line, and twice the cost. Therefore, to have the same economy, that is, the same transmission line cost per horsepower of electric energy sent over it, we have to send twice as much power over the line of twiee the length. Suppose then we use the same elec tric current but twice the voltage to get twice the power. With the same cur rent, the loss of power per mile of line would be the same, and as the line is now twice as long, the total loss 'of power would be douhled, and as twice as much power is sent over the line. the loss per horsepower of energy sent over the line is the same, that is, the efficiency of transmission is the same as before. We see thus, that by in creasing the voltage or elec tric pressure, and the power sent over an electric trans mission line, in proportion to the distance of tran�mission, that is, to the length of the line, we get the same effi ciency and the same econ omy, that is, the same per centage loss of the trans mitted power, and the same (approximate) cost per horsepower transmitted. Chief Consulting Engineer, General Electric Company other of these cities, for the simple reason that in the industrial East all the millions of horsepower of electric energy which Niagara could deliver, even if completely developed, would find a market and would be consumed within a few hundred miles of Niagara, long before the present day electrical limits of trans mission are reached, and obviously nobody would build transmission lines to send the power over thousands of miles, when he could find a market for his power within a few hundred miles. The question of the maximum distance over which electric power can be transmitted, therefore, has al most entirely "eliminated itself as a serious engineering problem, and while electricity could be transmitted eco nomically in large bulk, if so desired, for over a thou sand miles, even with the largest water powers, with rare exception, all the available water power will be taken up, and find a market, long before the electrical limits of transmission are reached. days and as the layman looks at it still today, that is, a transmission from a water power over a long line to a consumer, such as a city, etc. But our present day transmission lines are almost always distribution circuits and interconnecting cir cuits, that is to say they form a part of a network of electric lines, which link together various sources of electric power, water powers and steam powers, and the various places of consumption, cities, mines, factories and mills, and so forth. That is, a network of electric lines begins to cover the country similar to the net work of railway tracks, and while the network of railway tracks, built three-quarters of a century ago, takes care of the transportation, distribution and sup ply of all the materials, so now a network of electric lines is being developed and is spreading all over the country of so adequate a volume as to take care of the transmission, the distribution and the supply as the second essential necessity of our civilization.