Guarding Against Electrolysis at Providence.
Electrolysis in the water mains and service pipes at Providence, R. I., is being carefully guarded against by the engineering department, so far as may be, and a careful study of all stray electric currents made to the end of getting a comprehensive and intelligent statement of the problem.
An extended series of voltmeter readings have just been taken supplementary to similar tests made in July. These voltmeter readings were very painstakingly made, the indicator being watched for live minute periods at a time, and then the observer relieved. All fluctuations of currents through these short periods were noted and the high and low potential recorded. Twice a year these readings are made, but this recent one was undertaken following the mid-year observations made in July, because unusual conditions suddenly “became manifest.
It is the object of these tests to keep a close watch upon the difference of the pressure of the electric current in the rails in the streets and the water mains and service pipes in the same vicinity, this difference when plotted upon a chart showing whether there is any undue “leakage” from the regular established path for the current back to the power house or any increase in the “pressure” of the electric current upon the nearby water mains. In the event of the latter being found, it is the signal for an immediate remedying of the condition.
The test on July 14 and 15 showed that there was a marked increase in the positive readings, the positive being the highest point touched by the voltmeter needle during the five-minute established reading interval, and it was decided by the engineering department to conduct an auxiliary test under somewhat different conditions to establish the cause.
The voltmeter upon which the readings were taken Friday was connected with a service water pipe in the basement of the City Hall.
Last December a report in relation to electrolysis was made by A. A. Knudson, electrical expert. who died not iong ago. He conducted a series of tests m this city. These tests were caused by the failure of five pipes, three in Weybosset and two in Richmond street, from electrolysis. At the corner of Richmond and Weybosset streets the telephone conduit, the cables in which were connected with the return wire of the railroad company, rested directly upon the 24-in. water pipe and was also within 2 ft. or less of the 16-in. high-pressure, fire service main, and about 1 ft. from a 6-in. water main.
The conditions under which the current worked its wav back to the power station at this point and the conditions causing electrolysis were defined in the report of the electrical expert as follows:
“Two railway copper conductors called ‘negatives’ of 500,000 C. M. capacity connected the lead covering of the cables with the P. H., one at Richmond street and one opposite Union street. These were about 500 feet apart. These two heavy conductors so near together created a path of very low electrical resistance to the P. H. at this point, so that currents upon all the pipes in this locality were attracted towards the telephone conduit and the branch conduits in other streets. It was believed that the two connections were unnecessary for the purpose of protecting the telephone cables, and that one, possibly both, could be dispensed with, the point being that so long as the cables were kept ‘negative’ to rails and to earth, they were in no danger from electrolysis. Through the courtesy of the railroad company, the conductor at Richmond street was cut and a switch placed in the circuit so that tests could be made with the switch (conductor) open and closed voltmeter readings were taken in presence of the telephone company’s engineers and the railroad company’s engineers on the morning of November 19, and again at the evening ‘peak load,’ between 6 :00 and 6:30 p. m. of the same day. It was proven to the satisfaction of all concerned that this connection was not necessary as a protection to the telephone cables, and by consent of the telephone company it has been permanently abandoned and the railway company so notified by the writer. Further tests were made at the Union street connection. At this point the conductor was conveniently opened and closed by means of a clamp previously placed in it, where it was secured to a trolley pole as it came from the telephone vault, and no switch was needed. Practically the same results were found at this point, as the cables remained negative to rails and earth when the conductor was opened. Further time, however, was given the telephone engineers to make tests in other parts of the city, so that they might be sure that their cables were protected before this connection was permanently abandoned. These tests have been made.
“Had these electrical conditions described been allowed to continue, the failure of the 24-inch main under this conduit would have been only a question of time. The resulting damage, while being great, would not only have been confined to the water main, but also to the conduit and cables directly over it, and in all probability to the electric light conduit as well, which is located close to both the water main and telephone conduit.”
TEST WITH FEEDERS CLOSED.
The test in July was with the negative feeders open, as they have been since the report of the expert. The test which has just been made was with the feeders thrown into connection. In the July test the readings showed a highly positive condition, a strong difference of potential between the water pipe and the rails. Testing with the negative feeders gives a test under the conditions of a broad, wide, clear road for the electric current, to make its way hack to the power house. This should, under conditions of 110 danger, give lower readings in the station at the City Hall or a difference of potential much feeder, or the The readings just made, when compiled on the chart and compared with those of July, will show the difference that exists between the conditions existing with the feeders in and the feeders off.
While the tabulation of these readings has not been completed, enough has been disclosed to show that the readings are lower. “Those negative feeders,” says Engineer McKenna, were thrown out of use on the strength of Mr. Kuudson’s report, because we bad had so much damage to the water pipes in the immediate vicinity. The lead service pipes going into the building thereabouts pass directly underneath the telephone conduit, and the latter, being connected direct with the feeders, any curient on the water mains in that immediate neighborhood would leave the pipe and take to the conduit and the feeder and go back to the power house.
“Where the current leaves the pipe there the damage is done electrolysis setting in, and from that fact a number of the service pipes thereabouts gave out. These two feeders being so near together, acted as a kind of a siphon for the current, seeking escape back to the power house. Electricity, you know, always seeks the line of least resistance; consequently the current was pouring from the water pipes in the Weybosset street district in a manner that was threatening the life of the piping.
“The difference in potential was great and came on so suddenly last month that we had to sit up and think. It was up to us to ascertain the why and the wherefore. That is the cause of this test. The railroad people are always willing to meet us more than half way in a matter like this, and will do anything within reason to effect a remedy. It is our place to point out the condition. If the condition was permitted to continue and become greater on the positive side of the chart, there would be grave danger to the water service system in the centre of the city. By testing here in this station, we can get an idea of what is transpiring underground for a radius of half a mile. We may have to install negative feeders in other places to afford the outlet that the current is evidently seeking and preserve our pipes.”