Testing Insulators

Testing Insulators. — In the article on the Butte, Mont., electric power transmission plant in the February issue, an error — not due to the writer of the article — occurred in the description of the method of high voltage insulators. The arcs are established, not between projecting pins and the surface of the water in the insulators, as stated, but between quarter-inch gaps in series in the testing circuit and between the insulators. Twenty pins are mounted in a frame, the lower ends dripping into water contained within the same number of inverted insulators. When the testing circuit is closed; sparks jump across the gaps in series, and the character of the spark determines the condition of the corresponding insulator. As twenty insulators are tested at a time, this corresponds to a total spark-length of 5 inches. The transformer employed will support a spark 6 1/2 inches long.