Search

The purpose of the paper is to describe a method of analysis for taking into account the effect of insulation variability in the determination of breakdown voltages and allowable operating stresses. The method is applicable to systems containing large areas of insulation, or large numbers of units of insulation in parallel. General equations are derived, giving the breakdown voltage and number of failures to be expected, in terms of two parameters; the mean breakdown voltage and the variability of the insulation, both of which are determined from tests made on samples. It is shown how the results may be applied to the special case of electric power cables, for comparing the relative merits of different cables, and for determining the safety factor required to take account of the inherent variability and consequent unreliability of the insulation. The necessity of considering the variability as well as the so-called strength of insulation is emphasized, and its importance brought out in terms of allowable operating stresses and failures. A graphical method of analysis is described, which makes use of probability paper, changing the probability scale from ``per cent'' to ``failures per hundred miles per year'' in the case of cables. Predictions of theory are compared with the results of practise, using results from experiments made to determine the effect of electrode area on breakdown voltage. Good agreement is shown between the two.

In the application of various types of locomotives to switching service, it is at times quite desirable to have data concerning the energy requirements involved. A convenient figure for expressing such requirements in relation to work done is watt hours per ton-mile. The determination of such a figure involves certain difficulties peculiar to switching service, in that trailing loads and distances moved are continually varying. The electrified Oak Point Yard of the New York, New Haven & Hartford Railroad in New York City offered an excellent opportunity for determining figures of watt hours per ton-mile for different kinds of switching. Accordingly two electric locomotives were equipped with the necessary instruments, and a total of 391/6 hr. of operation was observed and recorded. The paper describes in some detail the entire procedure of the tests and lists in tabulated form the data obtained. Basic figures necessary for calculating watt hours per ton-mile, it was found, could be expanded to give a much broader scope to the results, so that many interesting data became available. Incidentally, the data will permit of even further expansion where certain special figures or factors are desired. Although electric locomotives of different types were used, the results set forth in the paper should be considered without regard to either type. It is hoped that data concerning switching operations on other railroads may become available.

This paper covers an electric ice removal system as applied to a recent experimental airplane. The system is described in detail from the power generators to the ice removal blankets and includes such items as extent of ice protection coverage, construction and installation of ice removal blankets, system electric power requirements, and system control. The paper does not treat the subject of ice protection in any of its theoretical aspects. The complete ice protection system installation is believed to be the first of its kind in this country.

Marking a new milestone in the history of the transmission of electric power, the 275 kv system that will transmit power from Boulder Dam to Los Angeles, Calif., embodies many novel engineering features. These features are discussed in this paper. The paper includes not only a description of the line and the terminal equipment and facilities, but also a discussion of the effects of the characteristics of each portion of the system on the performance of the system as a whole. The engineering studies and laboratory research on system stability, corona, high voltage impulses, lightning, conductor vibration, tower stresses, footing uplifts, and other factors are described, and the use of such data in the selection of line voltage conductors, insulation, clamps, lightning protection, towers, and appropriate generating, transforming, and receiving end equipment is shown.

The steel mill power systems to be discussed in this paper may be as small as about 15,000 kw installed capacity and may approach or even exceed a capacity of 200,000 kw. If the steel mill has blast furnaces and coke ovens with waste fuel available, part of this capacity will be from turbine generators. Where possible there will be a tie to the electrical utility; and in many mills all of the electric power is provided by the electrical utility. The utilization voltages for the steel mill usually will include 440 volts, 2,300 volts, and 6,600 or 13,200 volts for the large motors or furnaces. Generation will usually be at 6,900 or 13,800 volts, although some older 2,300-volt machines are still in service. Formerly there was only limited use of voltages above 6,900 but there is an increasing need for higher transmission voltages. These include 22, 33, and 69 kv.

The trend in recent years toward large concentrations of electric power at important centers and the necessity for stable transmission over ever-increasing distances have resulted in a demand for high voltage switching equipment with unusually short operating time. This paper describes the development along conventional lines of a circuit breaker of the deionizing grid type capable of interrupting within 3 cycles a short circuit on a 287.5-kv 60-cycle line.

The purpose of the paper is to present for consideration a new method of interconnecting sources of power and load centers in a large district with a well developed and well distributed load. The central idea is the superposition of a high tension network of single-circuit lines over the whole district for the purpose of supplying a medium in which current may flow in any general direction as changing conditions may dictate. This is similar to the underground network of the Edison Companies in the large cities. With such a layout available, power any where in the district may be fed into the network and it may be taken out at any other point without serious loss of energy. The network is connected directly to load centers as well as to existing generating centers and thus greatly assists the present distribution lines distributing power and also stabilizes the potential at each load center reached. The charging current of the network may largely neutralize the lagging component of the load with favorable design. A concrete illustrative network is worked out in considerable detail, covering the present load with an equal amount of new future load in the interconnected systems of Alabama, the Carolinas, Georgia and Tennessee, with a branch to the Appalachian Power Company in Virginia. The result shows a very effective, efficient and low cost system for this territory. The plan is applicable to other districts as well.

The increasing use of electric apparatus on aircraft has brought about the need for rather large sources of electric power for these planes while they are on the ground without engines running. The development of these ground power units from the original storage batteries through the makeshift postwar era to the present highly specialized units is traced in this paper. Units from 5 to 60 kw now are used for this purpose. These units consist of portable engine driven sets as well as induction motor driven units for use in the hangars. These units must all be equipped with special voltage controls and with complete radio interference suppression. The larger units are furnished with a great variety of portability, some being self-propelled. These units must be built in 12, 28, and 120 volt direct current as well as 120-volt 400-cycle alternating current.

The modern fighting airplane requires a large amount of electric power for its successful operation. The aircraft generator provides a reliable source of power at the lowest possible weight. The development of these generators has required close co ordination of design, testing, and interpretation of test results. The tests include raw material, parts, laboratory, life, mechanical, and flight tests. This paper describes tests which have been made and the interpretations which have led to improvements in d-c aircraft generators.

In the field of transportation of petroleum and its products by pipe line, the 24-inch and 20-inch lines, built by War Emergency Pipelines, Inc., from Texas to the Middle Atlantic Coast as emergency war projects, rank as world record breakers. The 24-inch line for crude oil is the largest ever built, and pipe-liners have picturesquely named it the Big Inch. The 20-inch products line is the largest for refined products and the longest line in existence, and is called the Little Big Inch. All pumping stations on both of these lines are operated by electric power, and in its application a number of interesting engineering problems developed. Results of the consideration given to these problems to meet successfully the anticipated operating conditions are given in this paper, and may be grouped as covering 1. Adequate protection of main pump motors and their circuits when supplied with power through transformers having various connections. 2. Use of capacitors for maintaining voltage on ``soft'' power systems, and their proper switching for optimum effect. 3. Power-utilization-equipment performance obtained as the result of emergency engineering under war conditions.

This paper is intended to describe the electrification of the world's largest open cut copper mine, and also covers briefly main line transportation and miscellaneous uses of electrical energy at the concentrating plants, that are located approximately 18 miles from the mine. This electrification project was an economical and progressive step in copper mining and developed some very interesting engineering problems. Electric shovels, both alternating and direct current, together with the special type of electrical locomotive required for this particular service, are discussed. The rather elaborate trolley and feeder system required to transmit power to a fleet of 23 electric shovels and 39 electric locomotives, scattered over a 725-acre area, is described. The main power system, together with mill, railway and shovel substations, is briefly described. Some operating statistics are given, to assist in visualizing the magnitude of the operations.

Considerable need has been felt for accurate methods of soluttion of the problem of temperature rise under variable loading in order that the maximum use may be made of the large investment in power cables. In this paper a rigorous solution of the problem of temperature rise from sheath surface to conductor is attempted, making use of Bessel functions. The heat flow cycle is resolved into harmonics, and each harmonic solved separately for temperature at the conductor. The various harmonics of temperature are then combined in their proper phase relation to obtain the temperature cycle. For purposes of assigning emergency ratings a solution is arrived at for suddenly applied steady loads, making use of the Fourier integral. The problem is solved rigorously for single-conductor cables and three-conductor cables of shielded (type ``H'') construction. Modifications of the constants of the cables are described which will allow the theory to be applied to cables of standard belted construction with reasonable accuracy. The probable errors involved in the assumptions necessary in the solution are discussed. It is believed that knowing the temperature of the air at the sheath surface, the temperature of the conductor can be calculated within 4 or 5 per cent of the correct value if the constants of the cable are known within this accuracy. The method can also be applied to solution of the temperature rise of the sheath surface provided the constants of the duct bank are known with sufficient accuracy.

THE rapid growth of a-c arc welding in the last ten years has resulted in a-c welding becoming a large fraction of all arc welding rather than a negligible proportion. As power loads due to a-c arc welding become larger, questions arise in the minds of users and power-supply authorities about power requirements of a-c welders and the effect of a-c welders on power circuits. In some instances arc welding has been confused with resistance welding, although the two are entirely different from the standpoint of power supply. This paper presents data useful for determining the effects of a-c arc-welding loads on electric power circuits.

The trends and amount of electric power use and cost at bituminous coal mines are of interest to the executive, the operating man, and the engineer alike. A study of the data based on a single year, or even a few years, could result in misleading conclusions; but the data from over 400 representative mines for the past 26 years make it possible to determine the trends quite accurately. These trends, illustrated by graphs and tables, are discussed in this paper.

A general survey and description of the various types of supervisory systems for control and indication of remotely located electrical apparatus is given in the paper, the author first of all comparino the better known remote-control system with the supervisory system in general practise today. Description is given of the selector, distributor, audible, code-visual, synchronous-relay-visual and the carrier-current systems, the principles and features of each being discussed. The subject of telemetering is also included, together with an expression of the author's ideas of future possibilities for each of the systems above enumerated.

Increased cost involved in serving electric power to customers, and the aim to lower rates, have accelerated the need for most efficient utilization of existing generating and distribution equipment. The paper describes a method for loading power circuit breakers on a temperature basis for the purpose of taking advantage of their inherent current carrying ability. Several years of practical application of the basic theory has proved entirely satisfactory on various types of electric equipment and has, in many cases, established considerable savings on new investments. While these savings apply to a lesser degree to circuit breakers than to other major power equipment, their application in accordance with temperature, rather than name plate rating, has put the use of new and existing facilities on an equally sound engineering basis.

This paper discusses briefly the philosophy underlying power transformer practices on the American Gas and Electric Company system. It includes power transformers used in generating, transmission, and distribution stations. It does not include transformers generally used on distribution lines to serve residential customers, or special purpose transformers not directly associated with the transmission and distribution of power. The size and extent of the interconnected electric system on which the transformers are used are described, and the requirements of such a system discussed. Considerations entering into the selection of transformers, their general design requirements, operation, and maintenance, including principles of loading, flexibility of use, and spare transformer practices, are amplified in considerable detail. Over-all economics are emphasized. The power transformer is a most important piece of apparatus in modern electric power systems, being second only to the generator. It makes possible the widespread use of power. In larger sizes it is the largest, heaviest, and most costly piece of electric equipment, except for the generator. In total rated capacity it far outranks all other elements; hence it is worthy of the utmost attention in our search for construction and operating economies. Fortunately, the present-day power transformer is a most dependable piece of electric equipment. It has become so reliable that interruptions to service because of transformer failure are rare. Notwithstanding, however, there is great need for less costly transformers that are still more reliable and require less maintenance. These are the goals we seek.

The intensive manufacturing activity accompanying the present defense program has stimulated interest in industrial electric power distribution. The ultimate objective is one of effectively satisfying electric power requirements with reasonable first cost consistent with a fair standard of safety and service reliability. This paper presents the fundamental aspects of industrial power distribution, with particular reference to low-voltage power supply to distributed electrical machinery, and compares various basic system designs, including large concentrated substations and distributed load-center substations with radial and secondary network modifications, as to safety, service reliability, simplicity, and so on, relative to estimated installed cost. The comparative analysis comprehends the complete electrical system between high-voltage supply bus and utilization terminal of low-voltage feeders. The ideal size of unit substation as influenced by operating voltage and load density is covered. Principles of system design here disclosed are applicable not only to new plant construction but to expansion or modernization of existing plants as well.

In electric power stations, it is often necessary to make accurate measurements of current or power when the instruments are located near to the cables carrying large alternating currents. The magnetic field produced by these currents may constitute a serious source of error in the measurements unless careful precautions are taken to guard against such disturbing effects. This paper summarizes the various principles and methods for detecting and minimizing the errors which may arise from this source. The principal methods are; (1) to so arrange the cables carrying the large currents that they produce as little stray magnetic effect as possible; (2) to use instruments of the shielded or of the astatic type; (3) to repeat readings with the instrument connections reversed; and (4) to avoid all loops in the connecting leads.

In the operation of an electric power distributing system involving various kinds of networks, a fundamental necessity is that each transforming and transmitting unit carry a reasonable share of the total load. In the case of a single system that has been developed in a coordinated manner the problem of load division has not in general been troublesome and has been solved by judicious selection of parallel circuits, use of reactors, proper system set-up, etc. The advent of inter-company connections has brought together systems of varying characteristics, changed the relation between the basic elements involved, and in some cases has made difficult the control of power flow over tie lines small in comparison to the systems which they unite. It is the purpose of this paper to discuss the case of load control where closed rings or parallel path circuits are involved. After briefly reviewing the principles of voltage phase angle and power flow, a description is given of some actual tests performed on a very large interconnected system with a 250-mi. transmission loop, involving five power companies and a total generator capacity well over 1,000,000 kw. The results of these measurements are analyzed for the purpose of checking theoretical against actual values and forming a basis for the solution of problems of a similar nature.