Description of power development at Telluride & Provo, mentions Provo Insulators

PIONEER WORK OF THE

TELLURIDE POWER COMPANY

A Historical Record of Its Origin and Development That

As Interesting as the Traditional Romance, of

Much Historical Value and of High

Technical Worth."

A paper read before the International Electrical Congress, at St. Louis, by Mr. P. N. Nunn,

chief engineer of the Telluride Power Company.

Concluded from yesterday.

Much of the data obtained from these experiments was incomplete, requiring caution in its use, due largely to the time and study required in solving, step by step, the problems and difficulties met at every stage of the work. However, that much of value was obtained is shown by the subsequent successes at Provo. Sufficient had been learned to warrant the commercial adoption for the first time of 40,000 volts, nearly thrice the voltage of any previous plant; to lead to the manufacture of transformers which after seven years continuous operation are still in daily service; to determine the design of the Provo-type insulator; the method of line construction, distance between wires, and the importance of wave form, and to make possible this great advance in long-distance, high-voltage transmission.

This experimental work was begun; carried on and finally utilized by the Telluride company in the regular and necessary course of its growing business; yet it must be added that important services were rendered by Mr. V. C. Converse; under whose direction the transformers had been designed and constructed, and who participated throughout the greater part of the work during all experiments with actual high pressure transmission, and subsequently by Mr. Ralph B. Mershon, in the elaborate instrumentation and laboratory practice, including a notably ingenious method of reading high-tension losses upon lower tension circuits, devised by him and used in substantiating the accuracy of the earlier measurements; also that different types of insulators were contributed by the General Electric and Westinghouse companies and by Mr. Fred D. Locke, on account of their friendly interest in the work

The original plant at Provo contained two 750-kilowatt, 60-cycle, 800 volt, three-phase, General Electric generators, direct connected at 300 revolutions per minute to twin horizontal turbines and under 125 feet head, a six paned Wagner switchboard, two banks of oil transformers, and two outgoing circuits. All contents thus in duplicate were assembled in two complete, independent units, designed for operation independently, or paralleled at both high or low pressure. Prior to the power-factor indicator, a devise which answered a somewhat similar purpose was installed, consisting of a wattmeter on the low pressure paralleling bus, with current coil in one bus and shunt across the other two. This indicated cross current and was used in adjustment of field charges. Transformers were each 250 kilowatts, 800 to 40,000 volts, star-connected at both high and low pressure, with neutrals grounded.

Triple-pole air switches and four foot fuses formerly connected each bank of transformers with its transmission line. One form of air switch opening six feet, contained no metal except conductors, and was composed entirely of paraffined wood and rawhide, without porcelain, glass, or other insulator.

During the first year of operation the transmission comprised a single 22-mile line to one receiving point at Mercer, where the arrangement was similar to that at the power house, save that two reducing transformers were connected two-phase, three-phase, grounded neutral, for 350-volt two-phase induction motors. The Provo-Eureka line, forty-three miles long carries seven-strand aluminum cable equivalent to No. 5 copper was added to complete the triangle thus formed and permit cutting out either of the three sides without interrupting service.

The Logan plant was completed in 1901, containing two 1,000 kilowatt, revolving field alternators, direct connected at 400 revolutions to double-discharge twin turbines under 212 feet head. This plant is connected with the Provo system by duplicate lines over 100 miles long passing the cities of Ogden and Salt Lake. The Provo and Logan plants are thus operated in unison through nearly 200 miles of transmission. Distributing plants at Mercer, Eureka, Bingham, Salt Lake, and Provo are also junction points of the duplicate lines, equipped with switches in each incoming line, as well as in circuit with the transformers, so that in case of threatened trouble the patrolman can without delay have his section cut off for immediate repair without interrupting service.

The three conductors of each transmission form an equilateral triangle twenty-six inches between wires, carried by a seven foot cross arm and the top of the pole. Extra long pins raise the insulators from six to twelve inches above the cross arms, are of selected locust, kiln dried, and soaked in boiling bitumen. Those upon the first line were attached in the usual manner with metal braces. The burning of cross arms and poles on account of broken insulators during prolonged wet weather, occurred most frequently at these braces. When the next lines were built in 1899 treated wooden braces were substituted with results so favorable that all metal braces were soon replaced.. It was still observed, however, that even light leakage seemed to concentrate around the lag bolts, carbonizing the wood and finally loosening the bolts.

For the Logan line of 1900 and all later lines, therefore, the cross arms were mortised through the poles and wedged and pinned with hard wood — thus discarding all metal except conductors. This construction was inaugurated by Mr. A. L. Woodhouse, who, upon the close of the high pressure experimental work in Colorado, of which he was in charge, became and still is superintendent of the Utah department. It has proven amply strong, not expensive, and during the four years operation of the 400 miles thus constructed very few poles have been burned.

Provo type insulators, designed by Mr. V. G. Converse, have been used throughout. Many have broken, but these have usually shown the effect of guns or stones. In fact, there has not been a single breakage, except in one lot, improperly annealed, clearly due to either internal or dielectric stresses. It is difficult to see where any other insulators could have done better unless bullet proof.

College tests to the contrary not withstanding, leakage losses are inappreciable, except during several storms, and these not serious where insulators are unbroken. It is a mistake to suppose that Utah climate is favorable. During the rainy season it is as wet as any, and the alkali dust of the so-called salt storms is as trying as sea coast spray. At times dense volumes of this impalpable dust from the great desert are accompanied by clouds of fog. Is this damp, sticky state, the dust completely covers to a considerable depth the under as well as the upper surface of insulators, as well as poles, cross arms, and pins. Over these surfaces streamers gradually creep, until meeting at the pole, they break into an arc, like that which was ;photographed by Mr. C. E. Baker, the line patrolman at Mercer, and which has several times been published. A quick turn of the generator rheostat at the critical instant breaks the arc, without interrupting service of induction motors.

The arrangement of power houses and transmissions already described is such that the opening of paralleling switches may resolve the system into a single transmission from 100 to nearly 400 miles in length, with a generator at each end yet side by side. If one generator be removed, synchronized as a motor with the other and loaded by its water wheel, any length of transmission may by manipulation of a paralleling switch, be alternately cut in and out between them. Since switch boards and instruments are connected, measurements made are immediately comparable. In this manner, losses and power factor may be measured, and the corrective effect of charging current observed.

Solid aluminum wire, first used in 1898, was slightly alloyed to increase strength, but proved worthless, breaking frequently with square, glass-like fractures. It was at once replaced with commercially pure seven strand cable, still in use. Similar cables have generally been employed for subsequent lines, while spans have been successfully increased to 180 and 200 feet, with less deflection than with copper wire.

The experience with oil transformers for 10,000 volts at Telluride, and the refusal of manufacturers to give any guarantee whatever for other transformers for higher pressures, led the Telluride company, when undertaking this 40,000 volt transmission, to manufacturer its own. The first equipment was made at the Wagner company's works under designs and supervision of Mr. Converse. The later ones were made by the Converse Transformer Company. When erected, the oil in the tank and the transformer in an oven were slowly raised to and then maintained during 24 hours at a temperature of 125 degrees C. The transformer was then immersed in the oil, and both continued at the same temperature for a further 24 hours. As bearing upon the question of fire risk due to oil transformers, it may be of interest to note that of the large number of these high-pressure transformers used during the last seven years, chiefly in isolated sub stations containing much wood and seldom visited, all but four are still in operation; that these four were destroyed by fire of doubtful origin, and that only one transformer has required repair other than change of oil.

The plant at Norris, Montana, designed and constructed in 1901 by Mr. O. B. Subr, superintendent (now resident engineer of the Ontario Power Company) contains at present two low-speed, 1,000 kilowatt units. A duplicate transmission of 60 miles conveys power to the city of Butte. These lines as well as both raising and reducing transformers, were designed for the use of 40,000, 60,000, or 80,000 volts. Longer pins are used than in Utah, and conductors form a triangle of 108 inches. While producing the present limited amount of power, and awaiting a suitable insulator, the lower voltage has been used.

In conclusion it may be said that the Provo plant — the first transmission at more than 16,000 volts — while undertaken materially in advance of the art, and not exempt from its share of troubles, has nevertheless been fully successful as a financial venture, and not without value in the progress of science. Long periods of perfect operation, monotonous in their uneventfulness, have proved beyond question the success of high pressures for long distances. The new and larger power house at Olmsted, at the mouth of Provo Canyon, completed this season, is modern in every detail. It contains three 3,600 horsepower generators, operating under 340 feet head. Air switches and fuses are everywhere giving place to oil switches with time-limit automatics, and constant reconstruction to meet increasing demands keeps the system abreast of present practice. Thus the Telluride Power Company, while again and again a pioneer in power transmission must not be associated alone with the experimental methods of early days, but in the future be found still engaged in progressive, practical pioneer work.