ELECTROLYSIS IN BRITISH MAINS
Legislation to Prevent Its Spread.
At the annual convention of the British association of Waterworks Engineers, held last year at Leicester, W. H. Humphreys, waterworks engineer of York, read a paper on “Electrolysis in water pipes,’” as the result of the single-wire electric trolley roads which were built in England in the ’Eighties.
In England it was not till 1893 that the Board of Trade called on Parliament to lay down as to the protection of telephone and telegraph companies that were using the earth return, and were being interfered with by electric trolley roads and electric light companies, which were using electricity for traction purposes and electric circuits and high-tension current on their circuits. Parliament being desirous of uniformity in practice, appointed a committee of both houses, presided over by Lord Cross, and the subject was objectively brought before the committee, which, on the authority of Lord Kelvin, W. H. (afterwards) Sir W. H. Preese, appreciated the fact (although some still doubted) that the question of voltage must be considered. That question was raised that it was not one of specific electrolytic action in the pipe itself, but of much graver import, as to how far the additional cause of corrosion, added to natural causes of corrosion, would accelerate the destruction of the pipe, the whole danger being preventable.
The committee, however, was not of opinion that, in the then state of electrical science, it should insist upon electrical trolley cars using insulated return conductors, as it would retard the development of electric traction. At the same time, however, it “regarded with apprehension a large extension of the system of overhead wires in crowded centres.” In the eyes of the committee the danger from fusion or electrolytic action appeared to have risen from a faulty system of constructing electric tramways, and its opinion was that it could be so reduced by improved methods of construction as to become a practically negligible quantity. The committee also recommended that all regulations on the subject of construction should rest with the Board of Trade; one being that a return conductor, if in contact with the ground, should be of such section and resistance as to have no difference of potential sufficient to set up injurious leakage currents in the earth. It was also added that after the use of electric power had been sanctioned, no alterations should be of obligation, except such as made for the public safety, or under it were proved to the satisfaction of the Board of Trade that pipes were being substantially injured by stray currents of electricity escaping from the conductors; and this had to be done only providing that it did not cause substantial additional expenditure. The regulations issued by the Board of Trade provide, among other things, for “regulating the employment of uninsulated metallic returns of low resistance; for preventing fusion or injurious electrolytic action of, or in gas or water pipes, etc.” It also requires the conductors for transmitting energy from the generator to the motor to be insulated and known as “the line.” The return may be uninsulated; but, if so, it must be connected with the negative terminal of the generator, which must also be directly connected through a current indicator to two separate earth connections not less than twenty yards apart. Instead of these connections, one may be made to a water main of not less than three-inch internal diameter. with the consent of the owner and the supplier of the water, and provided that it can be satisfactorily shown to the Board of Trade that such earth connections cannot be made and maintained without undue expense. These earth connections must be sunk that electric contact may be secured with the general mass of earth, and so that an electro-motive force not exceeding four volts shall suffice to produce a current of at least two amperes from one earth connection to the other through the earth—a test being made at least once a month to see if this requirement is complied with. No portion of either earth connection shall be placed within six feet of any pipe of less than three-inch internal diameter, which is mechanically connected to the earth connections already mentioned. When the return is partly or entirely insulated, the uninsulated return shall be separated from the general mass of earth and from any pipe near it. the several lengths of rails shall be connected, and means shall be adopted to reduce the difference produced by the current between the potential of the uninsulated return at any one point and that at any other point; and the efficiency of the earth connections already mentioned maintained.
As to the remedy for electrolysis: Many are suggested: but electrical experts are so much at variance. One thing, however, is clear—namely, that only by the double-wire or the conduit system can electrolytic action be entirely prevented. The fact is. however, that daily the single wire system is being extended through the British Isles, and it is under these circumstances that a remedy must be found.” The negative terminal of the dynamo may be connected to the underground pipes, thereby raising the whole of the electrical circuit in potential positive with the pipes and the general earth, so that, when there is any leakage current passing between the electric system (including the uninsulated rails) and the pipes, it will tend to corrode the rails and preserve the pipes— an arrangement “all right for the pipes.” The Wordingham method—a very costly one—is to feed the tramway system from stations to sub-stations, spaced at such short intervals along the lines as will keep down the loss of pressure in the rails to a very low amount. The Ganz system of electric traction, the Schuckerc system of surface-contact tramway traction with alternating current; the Westinghouse alternating-conduit system—all much used outside of Great Britain—are reported as free from the faults of the single wire system. The double wire system, which is used with great success on the continent of Europe, runs the cars without any rails, and should, therefore, be welcomed by waterworks engineers.