Showing papers in "Transactions of The American Institute of Electrical Engineers in 1950"

Control System Synthesis by Root Locus Method

Abstract: The root locus method determines all of the roots of the differential equation of a control system by a graphical plot which readily permits synthesis for desired transient response or frequency response. The base points for this plot On the complex plane are the zeros and poles of the open loop transfer function, which are readily available. The locus of roots is a plot of the values of s which make this transfer function equal to - 1 as loop gain is increased from zero to infinity. The plot can be established in approximate form by inspection and the significant parts of the locus calculated accurately and quickly by use of a simple device. For multiple loop systems, one solves the innermost loop first, which then permits the next loop to be solved by another root locus plot. The resultant plot gives a complete picture of the system, which is particularly valuable for unusual systems or those which have wide variations in parameters.

Effect of Frequency on Perception Currents

Abstract: The predominating sensation produced by gradually increasing direct current is warmth in the palm of the hand or wrist. Sensations caused by alternating currents below 10,000 cycles are characterized by a tingling or pricking sensation which is localized in the area adjacent to the point of contact, and at very low frequencies the muscles tend to follow the alternations of the current waveform. For frequencies between 10,000 and 100,000 cycles, the sensations are similar to those at the power frequencies, but they are less intense, and perception occurs over larger areas around the point of contact. An abrupt change in the response occurs between 100,000 and 200,000 cycles when the sensation becomes one of internal heating, and heating is believed to be the only sensation produced by currents in excess of 200,000 cycles. The current required for perception increases with increasing frequency, and between about 1,000 and 100,000 cycles the current is nearly proportional to frequency. Approximately 150 men were used in these investigations and it is believed that a sufficent number were used to permit valid statistical predictions to be made, not only for the particular group tested, but also for a normal cross section of the adult male population of the country.

Transformer oil

Abstract: THE HIGHLY COMPLEX NATURE of the material, the resulting difficulty in establishing significant tests for evaluation in a reasonable time, and the varying conditions of use have combined to make the study of oils used for the insulation and cooling of transformers a painfully slow process. It is the purpose of this article to review some of the very extensive efforts made in this study and to draw at least tentative conclusions as to the present status and future possibilities of one of the most important materials in the design, manufacture, and operation of transformers.

The goerges phenomenon-induction motors with unbalanced rotor impedances

Abstract: The Goerges phenomenon is the operation of a 3-phase wound-rotor induction motor at half of synchronous speed, and it is obtained by unbalancing the rotor circuit. If the motor is started with one rotor phase opened or with rotor impedances greatly unbalanced, it will accelerate to half speed and operate stably as a motor or generator. Several investigators have made tests and analyses to find the characteristics of a motor operated in this way. In the present work a physical explanation and an equivalent circuit are given. Results of tests and calculations for a 5-horsepower motor are compared and found to be in good agreement. The unbalanced rotor impedances cause unbalanced rotor currents of slip frequency, and balanced stator currents of two frequencies, the fundamental and a subharmonic, the frequency of which depends on the speed. The motor may be operated stably at half or full speed. The torque at half speed is greater than at full speed, and may be almost as great as the rated torque for a balanced rotor. It may be desirable to operate an induction motor at half speed intermittently or as a temporary measure. Disadvantages of half speed operation are the low power factor, low pull-out torque, the subfrequency line currents, and motor vibrations.

Interrupting ability of horn-gap switches

Abstract: A HORN-GAP switch has limitations in its ability to successfully open a circuit because of the restricted space available for expansion of the arc. It is not the length of the arc but its spread, and where it goes, that is important in switch operation. The clearance available for the spread of the arc must be such that the arc cannot form a short circuit between phases or to ground.

Proposed Basic Impulse Insulation Levels for High-Voltage Systems

Abstract: Basic impulse insulation levels were established in 1941, and although many improvements have been added to systems since then, no changes have been made in the levels. This article summarizes the present knowledge of the factors on which these levels are based and recommends a new series of such levels.

Progress Report on Tidd 500-Kv Test Project of the American Gas and Electric Company---Corona, Radio Influence, and Other Factors

Abstract: The field test project for studying corona, radio influence, and other technical features of electric power transmission in the extra-high-voltage range now has been in progress on The Ohio Power Company system of the American Gas and Electric Company at Brilliant, Ohio, for over two years. This paper is a progress report of this activity. It presents problems that are unique in the study of corona, particularly the effects of the conductor surface and weather upon the corona loss. It emphasizes the importance of foul weather in determining the average loss for use in evaluating the economic aspects of corona loss. Extensive tests also have been made of the effects of corona upon radio communication services. Radio influence is probably the factor litmiting the choice of a satisfactory conductor for extra-high voltages.

Spring and Damping Coefficients of Synchronous Machines and Their Application

Abstract: This paper develops simple formulas for spring and damping constants of synchronous machines. These formulas include the effects of induced currents in the damper winding and field. An approximation to the effect of primary resistance in producing a negative damping torque is given. An equivalent circuit is given which can represent accurately the mechanical system of several engine-driven generators or compressors operating in parallel. It is concluded that the conventional representation of synchronizing power as full-load power over full-load angle is sufficiently accurate for most cases, but that it is well to have a more accurate method for special cases.

Transverse Flux Induction Heating

Abstract: FOR SEVERAL years following 1941, the author was engaged in the development of radio-frequency induction heating for the flow-brightening of electrolytic tin plate. Lines are in operation today melting the electrolytically deposited tin coating on 30-inch-wide steel strip at speeds of 1,300 feet per minute with a power input of 1,200 kw to the strip. The radio-frequency currents flow in rectangular helical coils around the strip and induce currents in the strip and heat it without contact. The magnetic field and the flux through the coils are directed along the length of the strip and the author chooses to call this method “longitudinal flux induction heating.”

Loading of Hydrogen-Cooled Generators at Elevated Gas Pressures

Abstract: This paper presents a study, based on calculations and tests, of the heating characteristics of hydrogen-cooled generators at elevated gas pressures, and discusses various criteria for determining the capability of generators at elevated pressures. It is shown that the assumption of constant temperature rise of the windings above cold gas temperature, as a basis for limiting the output at elevated hydrogen pressures (particularly the rise of the armature winding by embedded detector) is misleading, and that a more realistic basis of rating is the assumption of constant total temperature of the winding copper, for constant temperature of ingoing cooling water at different loads and hydrogen pressures.

Audible Noise of Power Transformers

Abstract: TRENDS in power-system design require installations of large power transformers in thickly populated areas These trends have been brought about by increasing capacities of existing stations and by transforming power closer to the ultimate customer than has been done in the past1 As a result, power-transformer manufacturers have been asked to build low-noise-level designs for these installations Simultaneous with these new requirements being placed on them, manufacturers have been developing new materials, processes, and material applications; and to advance the art, certain of these improvements are being incorporated in designs Themanufacturer then finds himself faced with the problem of designing for low noise levels and, at the same time, improving his product in quality, cost, and dependability The way in whichthese two parts of the problem are related will be shown in this article

Series-Connected Saturable Reactor with Control Source of Comparatively High Impedance

Abstract: The object of this analysis is to form a clear picture of the function of the saturable reactor with resistive load, and to derive simple, and yet reasonably accurate equations. Four modes of operation are analyzed for normal and underexcitation and one mode of operation for overexcitation. The results of the mathematical derivations are condensed into graphs in normalized form. With the aid of these graphs the effect of any circuit parameter can be readily understood. A numerical example is included to demonstrate the usefulness of the normalized graphs for the quick calculation of the saturable reactor.

Resistance Commutation

Abstract: Thorburn Reid considered the commutation problem in rotating machines as arising from reactance in the coils being commutated by the varying brush contact resistance. This paper extends Reid's treatment to include the effects of reactance in the coils which are not being commutated, and shows that these noncommutating coils are an important factor in commutation performance. An equivalent circuit for a simplified commutator machine is developed and used as the basis for the analysis given in Appendixes I through VI. By means of this equivalent circuit, the average brush terminal voltage is seen to approach the value of the commutating reactance voltage under severe commutating conditions. Voltage pulses near the end of the commutation period are shown to be produced by a parallel influence of the noncommutating and the commutating coils. A testing device based on the equivalent circuit is described in Appendix VI, and consists of a mechanical inverter connected so as to separate the functions of the brushes in reversing current through the commutating coils, and in passing current through the noncommutating coils. When connected to the armature of a particular machine, the testing device is used to measure the commutating reactance and the brush contact resistance under simulated operating conditions. By means of this device, a correlation between brush electrical wear and severity of commutating conditions is established, which helps to confirm the basic theory.