HIGH POTENTIAL CIRCUITS.
NEW light on the subject of high potential circuits has been thrown by Captain William Brophy, of the wire department of Boston, in a lecture recently delivered by him before the Electric Potential Club of that city, of which we give an abstract, the title being “The Insulation of Overhead and Underground Circuits Having a Difference of Potential of 2,000 volts and over.”
In his paper Capt. Brophy referred to the legislative enactment compelling the owners of all electric wires within a certain prescribed district to place them underground prior to the first day of January, 1890, and which includes electric wires cf every name and nature, with the single exception of the overhead trolley of the West End Street Railway Company. “The reason for this exception (he said) seems inexplicable. It is somethingthat I have been unable to fathom.’’ He then went on to say. “It is plain that if the electric light, power, telegraph, telephone, fire and police wires are dangerous enough to be removed from poles and other structures and placed under the surface of the street, the bare trolley should find a similar resting place.”
After explaining the manner in which the law had been enforced by the commissioner of wires, Hon. John R. Murphy, Chief Electrician Brophy spoke of the method of lighting the streets with electricity, and of the great increase in voltage, dealing in his address, with constant current dynamos and circuits wherein the difference of potential varies with the number of lamps in the circuit. “ Quite recently (he stated). 125-light dynamos have been constructed and putin operation, which means a difference of potential of 6,250 volts, independent of the resistance of the rest of the circuit. The voltage in the primary circuits from alternating dynamos, in which is maintained a difference of potential throughout their entire length of from 1,000 to 2.000 volts, does not, he said,increase with the increase of the capacity of the dynamos from 650 to 8,000 and 10,000 lights, yet this increased energy is sufficient to afford ample food for thought to those on whom devolves the duty of so insulating such circuits as to reduce the loss of energy to a minimum and prevent accidents topersons and loss bv fire.”
Speaking of insulation, Capt. Brophy stated that the same supports and practically the very same insulating covering of the wires that were used for overhead circuits of five arc lights are used as circuits of 125 lights at the present day, and the same style of glass insulator used for telegraphic circuits is used to-day for arc light circuits with a difference of potential at the dynamo of between 6,000 and 7,000 volts, and for constant potential circuits with a difference of potential of 2,000 volts through their entire length. “It cannot be denied (lie continued) that the insulation of high potential circuits has not kept pace with the increased amount of electrical energy maintained therein. The almost perfect insulation of underground wires and cables has already been accomplished, and the question now to be met and answered is, Can the same grade of insulation be secured for overhead circuits? My answer is, Yes, if the same grade of insulation is used, and, No, if the present grade of insulation and construction is continued. If the same grade of wires used in the underground circuits is used, however, I would not advise any one to adopt this plan, as the proper place for such conductors is under ground; and, while the cost, compared with that of overhead construction, is very great, the amount of energy saved that is now lost would, I believe, pay a handsome dividend on the money invested, to say nothing of the immunity from loss and injury to the community and the absence of vexatious damage suits. All high potential circuits should be placed under ground, and I believe it can be done with ultimate profit to their owners. But we have, and I fear will continue to have for some years to come overhead circuits. High potential circuits should be supported on wooden poles and crossarms, and the wires of all low potential circuits should be excluded from such poles. It is not well to place such wires on fixtures placed on roofs or other portions of buildings, but, if they are so placed, they should be beyond the reach of persons standing or working on the roofs.”
In Captain Brophy’s opinion, the so-called insulating covering in use at the present time for high potential overhead circuit, is a delusion and a snare. ” It would be better (said he) to hang out the danger signal at once by using bare copper wire than to continue the use of this flimsy fraud that affords no protection to human life or property, but lures innocent people on to injury and death. Such circuits should not be run between the branches or through the foliage of trees. When it cannot be avoided, the highest class of insulated wire should be used, and this incased in lead or iron. I believe the time is coming when all circuits will be placed underground, and the transformers also. Instead of placing the latter on the outer walls and roofs of buildings and in some portions of their interior, they will be placed in suitable vaults beneath the streets and sidewalks, and each one will be of sufficient size to supply a large number of lamps or motors.
“The danger to life from high potential circuits, comes from two causes—establishing a derived circuit from any one point thereof through the person to the ground, and from the ground to some other point of the circuit, or by closing the circuit through the hotly. The danger from fire is mainly due to imperfect insulation. While the placing of alternating circuits under ground removes one source of danger, another is added. On such circuits a second ground is not necessary to injure or kill a person who accidentally connects any portion of one of these circuits to the ground through himself. A person standing on, or touching with one hand an iron pole, and with the other a bare or poorly insulated wire, or the iron case of a transformer that is in contact with the primary coil contained therein, will,owing to the failure of the insulation, surely receive a severe or fatal shock, although the circuit be perfectly free from grounds.”
Having told of the loss of one life, even though the circuit of which the accident occurred was clear of grounds, Captain Brophy urged the necessity of the possible insulation of the wires of these circuits and the greatest care in placing transformers, in order to prevent a recurrence of similar fatalities. In closing, he expressed tin* hope and wish that the Electric Potential Club, as a semi scientific organization, would never hesitate to warn the public of any real dangers that, might exist in connection with the transmission of electrical energy. “I consider (said he} that it would be a crime to lull the public into a sense of false security. It would equally be one to alarm it needlessly.”
Quite an interesting discussion followed the reading of the paper,in which General Manager Sergeans of the West End railroad said that he could not remember any accident happening by reason of the failure of the trolley itself. With all the other wire removed, he felt that the trolley was as safe as the insulated light wires. He expressed the hope that the time would come when the trolley wires would disappear, and that means would he devised whereby every trolley company could draw its current for the motors in some better way.
Electrician J. H. Farnham of the N. E. Telephone Company spokeof the difficulty of running wires without coming in contact with trees, and said that the loss of insulation to overhead wires was very great.
Mr. W. J. Denver of the New England Telephone Company was of the opinion that it behooved any electric company running high currents to insulate their circuits just as well as they know how, and that then there would not be the slightest danger of their doing it too well. He thought it. would be better to let the electric wires stand naked, as then the chances would be that the people would know that they were dangerous things to handle.
Electrician Blodgett, of the Boston and Albany Railroad Company, stated that it could never be known when the high-tension currents would give trouble. He cited an instance where the crossing of a high-tension wire with a telegraph wire made trouble in an office seventy miles distant.
Mr. Barker, chairman of the gas and electric light commission, like all the speakers, congratulated Capt. Brophy on his able address, and said in conclusion : “ There is no such branch of any government with which 1 i.m familiar that has vested in it such extraordinary powers in respect to individual property nnd the management of corporate affairs as the gas and electric light commission of this commonwealth. If the problems which that jurisdiction bring are a complex puzzle to you, and call for serious differences of opinion, you must not be surprised, if, occa sionally, the jurisdiction of the board seems to be an affliction and an infliction upon you. As more eases an’ passed upon by the board and its work and policy are more clearly defined and better understood, it will be found laboring for the best interest both for the public and the corporation.”