Southern Power Co, Rock Hill, SC (100 kv)

THE WORK OF THE SOUTHERN POWER COMPANY.

In view of the coining Southern meeting of the American Institute of Electrical Engineers at Charlotte, N. C., Mr. Fraser’s summary of the great distribution work of the Southern Power Company is most opportune. As the most important network on the Atlantic slope, and the only one in which extremely high voltage, from the present standpoint, is employed, the system is notable and its industrial importance is exceptionally great. It is, we believe, the third 100,000-volt transmission to go into operation, so that in the matter of voltage it is with the vanguard. The contrast between the earlier and later development of this great Southern plant is remarkable. The author does not state when the original Catawba plant, erected in 1904, was designed, but if 13,000 volts was considered the limit at the period when it was planned, it was certainly a limit set by the timidity of some Eastern engineer rather than by then established practice. There were quite a few plants in regular and highly successful operation at from 20,000 volts to 33,000 volts prior to 1900, and by 1904 there were hundreds of miles of transmission at 30,000 volts and above in everyday commercial service, including some lines at and above 50,000. But the system before us has made good at the present, even if it started with a handicap of ultra-conservatism. The system as it now stands includes four hydroelectric stations aggregating 98,000 hp and distributing energy to nearly 150 mills over nearly 900 miles of circuit. There are 63 substations and eight tie-in stations aggregating very nearly 150,000 kw in high-voltage transformers. To the cotton mills of the region this power is indispensable, and the cotton industry has grown under the stimulus. The nature of the load is such that low rates can be made, and the advantage of the electrical drive is now so well understood that the system grows by leaps and bounds.

The latest development is the 100,000-volt portion of the transmitting system. Nearly all of this is on steel towers with standard suspension insulators, although there is a single section of 100,000-volt line on wooden poles. It is not too much to say that the suspension insulator has made possible a new range of working voltages. No pin insulator yet designed gives, wet, anything like a similar factor of safety for 100,000 volts, and the suspension insulator is so much better as a mechanical element of line design that it will often be used for voltages well within the efficient scope of the pin insulator. As Mr. Fraser points out, the flexibility of the line support renders it necessary to lay out the pole or tower system so as to equalize the static loads. But if this be done, the suspension gives great security against extraordinary stresses. If a wire breaks, instead of throwing the whole unbalanced stress of the adjacent spans on the cross-arm to which the line insulator is secured, the suspension sways out, drops the adjacent catenaries, even if the line is tied to the suspension, and reduces the strain on the line structure to an unimportant quantity. Scientific line design is so new an art that this advantage is not yet fully grasped, important as it is; but it is in fact so great that it ought to revolutionize the construction of transmission lines. In the type of tower line described, still further advantage may be taken of the good points of suspended lines with the wrench on the pin eliminated, and the strains in case of breakage of a wire thereby greatly reduced.

It is most interesting to note that, as in other cases of going to extreme voltages, less trouble seems to be found than was expected, and in fact less than at the previous lower pressures. Much of this gain must be charged to the suspension insulators, and some also to the generally much higher insulation of the line, which renders harmless rises in potential that would break down a smaller margin over the normal strains. The Southern Power Company certainly deserves congratulation for the admirable network it has built up, for its success in going to the highest working voltage now available and, above all, for the work it has done in stimulating industry and strengthening the material resources of the South. This progressive organization has already placed the district over which its operations extend in the front rank of textile manufacturing centers of the United States, and there is no indication that its activities have reached their climax. In addition to being a great commercial enterprise of which any section of the United States might well be proud, its operations are bringing prosperity to a district having almost the bounds of a State, and stimulating a whole population from a condition of former commercial and industrial apathy to an activity comparable, in the towns at least, to that which characterizes a new Western State. A meed of praise should not be withheld from Chief Engineer Lee and his able associates for the skillful manner in which they have met the many engineering problems presented in the course of the development of the system, and whose work has resulted in advancing in many important respects the branch of electric^ power transmission engineering.

COST OF STARTING A FUBUC UTILITY BUSINESS A CAPITAL CHARGE.

As noted in our news columns last week, the Railroad Commission of Wisconsin, has in a case affecting the Madison Gas & Electric Company, re-affirmed its opinion that the cost of up-building a public utility business until it shows earning power is a proper capital charge. This is one of the most important principles to which this commission adheres in its valuations of public utility plants as a basis for rate-making. In the brief abstract of the decision which is available, the commission appears to have taken substantially the same position in this matter which it has held in other similar cases. The decision, however, states that it is not meant that costs arising from “had management, extravagance, unduly high capital charges, etc.” can equitably be taken into account. It is evident that it is proposed to differentiate carefully between proper charges for development and those, which, in the judgment of the commission, it is improper to continue in the capital account. As every charge of this nature is, therefore, subject to inquiry to determine, whether or not it is to be allowed, the managements of companies under the jurisdiction of the commission will hope that analysis of their financial history will not reveal causes of excessive capital cost that will not be approved by the commission. The fact that exhaustive inquiries of this character will be made will deter companies which may be subject to such investigation from charges to capital account that are not in conformity with the studied opinions of the commission on this subject, which check is no less valuable to the stockholders than to the public. Thus the present policy of the State may so guide all corporate affairs that no serious discrepancies between capital cost and capital value will arise in the future, except as they relate to affairs antedating the present law. Capital charges that arise from the fair development expenses of public utilities should be allowed in valuations for rate-making purposes, and it is gratifying that this principle is becoming firmly established.

ELECTRIC CONDUCTIVITY OF DIELECTRICS.

It is a remarkable fact that although the conducting properties of commercially pure metals is known and predictable to within about i per cent, after taking the effects of temperature into account, the conducting properties of insulating materials vary between very wide limits. Different competent observers have even proposed different types of formulas for representing the law of disruptive distance as a function of voltage, some having apparently found a nearly simple proportionality, others a straight line relation not in simple proportion, and again others a parabolic relation, or equation of the second degree. Not only is the conductivity of an insulator dependent upon the impressed electric intensity, but it is also affected in a marked degree by the duration of application, by moisture, by temperature, and by more obscure causes. Sometimes these influences are interdependent, as when an increased duration of an impressed intensity increases the temperature in the dielectric, and so brings about superposed secondary effects. Everything goes to show that electric conductivity in the substance of a conductor is a much simpler and more definite property than electric conductivity in a dielectric. In fact, it is questionable whether conductivity, beyond a certain limited amount, can exist in a dielectric without causing the substance to be decomposed locally, and so to cease to exist in its original form. Be that as it may, the properties of insulators are of greater importance to, and call for greater research from, electrical engineers today than the properties of conductors. As referred to in the Digest this week, the Physikalische Zeitschrift has recently published an article on this subject by Herr Walter Dietrich. The experimental results indicate that the conductivity of insulating substances at temperatures up to 200 deg. C. varies according to an exponential law.

ORGANIZING TRANSMISSION WORK.

The “forward” policy that is now so marked in the work of the National Electric Light Association finds a further exemplification in the proposal to organize in that body an energy transmission committee and section, with the object of studying the many practical questions and problems that have arisen of late in connection with the generation of electrical energy in bulk for delivery and distribution at a distance. The adoption of this program coincides happily with the celebration this year of the twenty-fifth anniversary of the association, and thus marks significantly the new point of departure in the art and in the society itself. There is, moreover, some fitness in the development of such a plan under the administration of a Western president, to whose personal initiative it must be attributed. Foresight and wisdom are shown in the determination to make this new departure a feature of the St. Louis meeting next May. The energy transmission companies are increasing so rapidly they might soon “swarm off” into an association of their own; but on the other hand, a general and very sensible opinion prevails against the creation of any more sectional engineering bodies, while as a matter of fact nearly all the large energy transmission companies are already within the National Electric Light membership. If it should seem desirable, the new transmission section under the flexible constitution of the parent body can make itself autonomous, able to meet independently at any time and place it chooses, still keeping in close touch with the main organization with which it is identified and has so many interests in common.

The practical problems awaiting discussion in the energy transmission art are bewildering in range and variety, and the new section will suffer no lack of elements of debate, though it will soon uncover a deplorable variety of methods and practice. It is an extraordinary condition, to say the least, that the corporations that stand more than any others in America for the sound principles of conservation of natural resources, should have been peculiarly those upon whom it is sought to center public discontent. No energy transmission company can long exist or discharge its function which does not execute every item of the conservation creed; and we know of no company aiming otherwise than to protect its watershed, cherish the forests, accumulate water in freshets against the days of drought—and lessen coal consumption. But the public has it all the other way around, and little realizes how capital has thus far been lavished to promote conservation of pretty well everything save dividends. The new section has a rare chance to do some educational work, quite aside from, and in addition to, its consideration of turbines and flumes, pole lines and insulators. The central-station industry as a whole has a vital interest in this matter. In all our great cities the distribution depends essentially on energy transmission methods. But when one goes into the open country he encounters in thousands of instances the old methods of production of “current” on so small a scale that it is literally simple and barbaric. The modern energy transmission methods dictate that most of these plants—even when they remain independent as to ownership— shall be fed from central sources of supply. The answer how this may be done should lie with the new transmission section of the National Electric Light Association.

DURABILITY OF STEEL CONSTRUCTION

The very large use of steel towers for supporting electrical circuits brings to the fore the problem of the probable life of such structures, a problem which has already come to be a matter for serious consideration in the case of bridges and other engineering structures. Steel such, as is used in these works is peculiarly susceptible to corrosion from chemical and electrolytic causes. There have been numerous cases of bridges and such like structures requiring practical rebuilding or replacement in less than a score of years, and it is a familiar fact that the ordinary types of iron poles for electrical purposes have in very many instances shown weakening from corrosion at the ground line, at the end of a term of years scarcely, if at all, longer than the life of a well-cared-for wooden pole. In some of these bridge cases there have been special causes of deterioration, like locomotive smoke in extreme amounts, but broadly, experience seems to indicate that the life of structural steel exposed to the weather is popularly very much over-estimated. This fact ought to be borne in mind in figuring and designing steel pole lines for transmission purposes. The design of the supporting structures for such work has been in the past extremely crude, which increases the danger of shortened life from corrosion. Steel towers are at tacked at the base, at every exposed joint, and probably also are exposed to the same sort of danger that results in the digestion of wooden insulator pins on high-tension lines.

No piece of steel can be so thoroughly galvanized by the ordinary process as to resist corrosion for any considerable time. At one place or another trouble begins under the coating unless the structure is persistently protected by thoroughly applied paint. The joints and rivets are peculiarly susceptible to corrosion, and unless the utmost care can be taken in keeping structures inspected and painted, to protect as far as possible from active corrosion, there is every reason to expect a good deal of trouble within 15 or 20 years. Most steel towers are made of too light material and of too intricate design for satisfactory life. American engineers have been in the habit of making extreme and needless requirements of stiffness in the towers, some going even so far as to assume the simultaneous breaking of all the wires supported when under the heaviest possible load (an accident which has been practically unheard of in the history of pole lines), as the criterion of suitable strength. On top of such absurd requirements for load they have demanded stiffness instead of encouraging the flexibility which relieves the strains due to the line by flexure within the elastic limit, and have still further insisted on cheapness as a final virtue. Now, a structure at once needlessly stiff, needlessly strong and very cheap is not easy to design, and in attempting economy of material to meet the last requirement the tendency has been toward somewhat intricate tower structures made of material altogether too thin for sound construction. It is this light construction, with innumerable joints and rivets, that is likely to lead to trouble from corrosion.

A line that is to be a permanent investment is worth putting up well and should be designed as an engineering structure with permanence in view; otherwise, the economy of steel tower construction is likely to be forfeited through unexpected brevity of life. A steel tower line designed to stand any practical strain, to yield and relieve abnormal strains, as in the Semenza type used in Italy and now being introduced here, and to last for a long term of years, can easily be secured by intelligent engineering. The next thing is so to care for it that it will not go out of service from local corrosion, which is likely to be the fate of a very large proportion of the steel towers now in use. It is not only necessary that the steel be well galvanized, but that it should be well protected by paint, especially for the purpose of keeping the weather out of riveted joints, and should be inspected and repainted as conscientiously as if the line were a wooden line to be watched for incipient rotting. With such precautions carried out there is every reason to believe that a steel pole line will give a useful life of half a century or more. If, on the other hand, a line is built of extremely light towers designed to meet fanciful requirements of stiffness while economizing material to the last possible degree, they are likely to be of material far too light to permit even moderate corrosion without disastrous results; and such a line, put up with implicit trust, with indifferent galvanizing, and seldom painted and inspected, is more than likely suddenly to fail before it has been in service for many years and to become a continual source of anxiety and annoyance, particularly since thin sections of steel may be dangerously corroded without showing the injury except on pretty careful inspection.