Curious electrical problem at Apple River, WI

A CURIOUS difficulty with the electric transmission system which supplies power from Apple River Falls for lighting the town of St. Paul, Minn., U.S.A., was recently recorded in the Electrical World and Engineer. The electric line is operated at 25,000 volts, and, on its way, crosses the St. Croix River on the Wisconsin Central Railroad bridge. The six wires are supplied on 8-inch x 9-inch oak beams, extending out 16 feet from the south side of the structure, at the level of the track, each wire being 18 inches from its neighbor, and over 12 inches above the supporting arm below. In June and July of each year that section is visited by large numbers of a pale-green diptherous insect familiarly known as the “shad-fly.” A large portion of the power transmitted is utilized as direct-current, through the medium of six-phase rotary converters, and when one evening about eight o’clock the converters when “out of step,” thereby paralyzing the whole system, the attention of the operators at the generating station was at once directed to the St. Croix bridge, about five miles away, by a series of brilliant electric discharges. The line was cut out, and an emergency crew despatched to repair the supposed breakdown. They were much puzzled upon their arrival to find everything in perfect order, no evidence of any short circuit being visible on either wires, insulators or cross-arms. After some delay the current was again turned on, and the cause of the trouble then became apparent, for the flies soon gathered in such numbers on some of the arms that they formed a solid bridge from wire to wire, and the flash of each discharge, while it destroyed thousands, only added fuel to the flames by attracting additional thousands to the spot. The shutdown lasted about an hour, and it was found necessary to station an attendant upon the bridge, who was provided with a wooden hoe attached to a long pole, with which, from time to time, he dislodged the insects from the cross-arms, as soon as they collected in dangerous numbers.