Showing papers in "Transactions of The American Institute of Electrical Engineers in 1945"

The Frequency of Occurrence and the Distribution of Lightning Flashes to Transmission Lines

Abstract: A STUDY of Franklin's correspondence on the subject of electricity shows his clear perception of the proper function of a lightning conductor; he also discusses such still controversial problems as bonding and the relative advantages of vertical rods and horizontal wire systems. On the other hand, no direct reference∗ as to the protective ratio of a vertical conductor could be found in his papers. Although this question was raised shortly after the introduction of the lightning conductor and has been discussed ever since, no general agreement so far has been reached. In what follows, this problem will be investigated from a new angle, and it will be shown to be even more involved than has been recognized hitherto.

Per-Unit Impedances of Synchronous Machines - II

Abstract: THE preceding part1 of this paper derived the generalized per-unit equations of the synchronous machine. The machine impedances were divided into two groups: those measurable from the stator terminals (x d , x d ′, r, and so forth) called the definitive impedances, and those internal impedances which cannot be measured from the stator terminals (X afd , X ffd , R ffd , and so forth), called the nondefinitive impedances. The per-unit values of the definitive impedances are independent of the base rotor currents, but part I showed that the per-unit values of the nondefinitive impedances are functions of the base rotor currents, and accordingly are subject to misuse and misinterpretation unless the rotor-current bases are explicitly defined. These rotor-current bases and their corresponding base-current ratios are the fundamental quantities in any per-unit system, and this concluding part II is devoted to a fuller exposition of the base-current ratios of the more important per-unit systems.

The Direct-and Quadrature-Axis Equivalent Circuits of the Synchronous Machine

Abstract: THE EQUIVALENT-CIRCUIT method of analysis is a tool of unquestioned competence in the solution of machine and system problems involving a number of simultaneous equations. Its efficacy in obtaining practical results has been demonstrated in many diverse applications. In particular, the complete equivalent circuit of the synchronous machine — complete in the sense that the field-winding circuit and the multiple damper-winding circuits are individually included — is used whenever a detailed knowledge is needed of the operation of all the rotor circuits. Specific examples of its use are in the design of the damper-winding circuits, in problems involving single-phase and asynchronous operation, in the determination of damping and synchronizing torque, and in the determination of the transient and subtransient impedances; these few by no means exhaust the list.

Impedances Seen by Relays During Power Swings With and Without Faults

Abstract: WE are at present in a period of power-system development during which it is essential that the best use be made of manpower and materials. To meet this requirement, equipment must be re-evaluated and refinements made in the design of apparatus and methods of system control. Loads on existing lines must be increased with continuity of service maintained. Of vital importance at this time is a thorough understanding of the operation of distance relays. The characteristics of the relays, and the system impedances “seen” by them, determine their performance. If it is known exactly what impedances are seen by a system of relays, their performance during power swings, with or without a fault on the system, can be predicted; and more important, relays having characteristics best suited for specific applications can be selected.

Transient Electrical Torques of Turbine Generators During Short Circuits and Synchronizing

Abstract: THE calculation of shaft and frame stresses in turbine generators during short circuits or synchronizing is dependent upon a knowledge of the electrical torque developed at the rotor air gap. This torque generally contains unidirectional, fundamental-frequency, and second-harmonic components, all of which are damped. It is the steady components of torque which are of interest in the calculation of system stability, while all the components are of interest to the turbine generator designer.

Symmetrical Components as Appkied to the Single-Phase Induction Motor

Abstract: THIS PAPER is intended to show in detail the application of the method of symmetrical components to the solution of single-phase-induction-motor performance characteristics. By the use of this method single-phase-motor theory follows very closely the simpler case of the balanced polyphase-motor theory. The author of this paper is of the opinion that a clearer concept of the physical theory can be obtained as contrasted to other methods — either from the revolving-field or the cross-field concepts.

Design of Induction-Heating Coils for Cylindrical Nonmagnetic Loads

Abstract: Equations are presented whereby the authors' previous paper1 is extended to the design of coils for heating magnetic loads, where the load remains in a fixed position relative to the coil during the heat. In heating magnetic materials, there is considerable variation in impedance of the coil circuit as the load temperature changes. The present paper first develops certain general principles by which a variable impedance circuit may be designed to absorb a predetermined maximum power, on the basis of constants determining the maximum and minimum impedance. Methods then are given by which these constants may be calculated for carbon steel loads of types SAE 1015 to SAE 1045, or their equivalent. In practice, these methods apply to most through heating and some surface heating applications. The accuracy of calculations is substantiated experimentally.

Application of Capacitors for Power-Factor Improvement of Induction Motors

Abstract: POWER-FACTOR improvement of induction-motor loads by means of shunt capacitors has been a common practice for many years. Recently, the practice of connecting the capacitors directly at the motor terminals has developed in order to permit switching of the capacitors and motor as a unit. This will not result in adverse motor operation if the number of capacitors is selected properly. There is very little written material regarding operating experience, although capacitor and motor manufacturers have accumulated some experience.1,2,3,4 This experience has shown that frequently too large a capacitor rating was used, resulting in overvoltage due to self-excitation when the motor starter was opened; in some cases the voltage rose to 200 per cent causing failure of motor insulation, indicating lamps, and other devices. In several instances, the motor coupling and shaft were damaged when too large a capacitor bank was used and the motor switched by a reduced-voltage autotransformer-type starter. In some cases, motors have been damaged from overload because allowance was not made in the overload setting for the reduction in line current due to the capacitors. In other cases, instruments and meters connected in the current-transformer secondary circuit have been damaged due to overvoltage.6

The Design of Bus-Bar Industrial Distribution Systems: an Epitomization of Available Data

Abstract: THE PURPOSE of this paper, evidenced in its title, is to acquaint the designer of bus-bar industrial distribution systems with the extent and whereabouts of the theoretical and experimental data available for design purposes. Attention is confined to those factors that essentially determine the operating characteristics of a bus-bar distribution system: voltage drop, temperature rise, and short-circuit capacity.

Coincidence-factor relationships of electric-service-load characteristics

Abstract: This paper contains a demonstration of the existence in practice of relationships between group coincidence factors and number of consumers, and between group coincidence factors and consumers' load factors. Empirical relationships developed from test observations are analyzed from theoretical considerations, formulated in a general manner, and qualified as to the significance of the quantitative values.

Treatment of High-Altitude Brushes by Application of Metallic Halides

Abstract: It has been found that the rapid wear of brushes under high-altitude conditions can be prevented by the treatment of the brushes with a suitable metallic halide. Carbon, electrographitic, and metal-graphite brush grades all respond to such treatments. A great many nondeliquescent metallic iodides, bromides, chlorides, and fluorides have been tested and found to prevent brush dusting on the heavy-duty electric units of aircraft. These treatments also have been applied with considerable success to earth-surface machines operating under severe commutating conditions. A mechanism by which this class of chemical compound may react to maintain a satisfactory low-friction film on a commutator is proposed.

Determination of Transient Shaft Torques in Turbine Generators by means of the Electrical-Mechanical Analogy

Abstract: A brief description is given of the mechanical-transients analyzer and its application to the determination of the shaft torques in turbine generators during transient disturbances, such as electric short circuits and synchronizing out of phase. This device employs the principle of the electrical-mechanical analogy with analogous electric circuits to represent a given mechanical system and special electric circuits for producing the desired transient excitation functions. With the analyzer a detailed study has been made of the shaft torques that can occur in turbogenerators with mechanical systems having both one and two modes of vibration. The relative severity of various types of faults has been determined together with the effect of external system or fault resistance and generator loading. Short circuits produce rotor air-gap torques containing damped unidirectional, fundamental electrical frequency, and second-harmonic frequency components. In the practical range of machine design, the fundamental-frequency component has the dominant effect on the resulting transient shaft torques for the more severe types of disturbances. The types of short circuits studied include three-phase, line-to-line, single-line-to-ground, and double-line-to-ground faults from no load and full load and with varying amounts, of external resistance. It was found that for short circuits at no load with no external resistance a line-to-line fault results in the most severe shaft torques. For faults with low external resistance (of the order of one per cent per phase), a double-line-to-ground fault produces the highest shaft torques which for mechanical systems of low natural frequency may exceed the torques produced by a line-to-line fault with zero resistance. However, for values of external resistance as high as the machine subtransient reactance, the shaft torques are lower than with zero resistance. The most severe fault torques are produced by line-to-line short circuits from full load with no external impedance. Synchronization at angles greater than 30 degrees can produce transient shaft torques which in some cases are more severe than those resulting from short circuits.

Winding-Fault Detection and Location by Surge-Comparison Testing

Abstract: Surge-comparison methods of testing insulation were investigated with the objective of locating as well as detecting faults. Experience of other investigators was confirmed and limitations of methods and equipment studied. Supplementary methods and equipment were devised to extend the field of usefulness of this basic type of tester, especially to the testing of very large machines with multiple-parallel windings. Apparatus studied included a-c motors from fractional-horsepower single-phase to very large three-phase types; a large variety of d-c armatures; and numerous armature, stator, and magnet coils. This surge-comparison tester has proved to be suitable for use by electrical manufacturers and by service and repair shops, as it can be used for testing most common types of electric windings.

Measurement of Stray-Load Loss in Induction Motors

Abstract: This paper is written to present test data confirming the accuracy of the reverse-rotation test for stray-load loss24 in polyphase induction motors. This method is the most convenient yet proposed for direct measurement of stray-load losses in squirrel-cage motors, and it is recommended that it be included in the AIEE Test Code for Polyphase Induction Machines.27 Proposals for this revision are made.

Synchronous Starting of Generator and Motor

Abstract: A SYNCHRONOUS motor, generator, or condenser can be started from rest, by means of shaft torque, induction-motor (amortisseur winding) torque, or synchronizing torque. This paper presents data on the last method of starting. The system studied consists of a prime mover driving a synchronous generator, and a synchronous machine driven electrically by the generator. The whole system is started from rest by means of torque applied to the generator shaft, the motor being accelerated to normal speed by the synchronous torque developed. The performance of such a system was determined both by tests on several machines and by calculations with the aid of the differential analyzer at the University of Pennsylvania, and limiting conditions and criteria for successful starting were found in terms of the various pertinent system parameters. In a few cases a system consisting of a generator and two motors was studied.

Optimum Air Gap for Various Magnetic Materials in Cores of Coils Subject to Superposed Direct Current

Abstract: A method is developed for calculating optimum air gap and core size for choke coils whose windings must carry direct current in addition to alternating current. It is employed with data on typical magnetic materials to give curves from which design dimensions can be obtained readily to fulfill specified requirements for inductance, resistance, and d-c burden.

The Combination of Supervisory Control With Other Functions on Power-Line Carrier Channels

Abstract: THE PRACTICE of using a single power-line carrier channel to perform several different functions is becoming increasingly common. This practice is encouraged by the savings in equipment and in carrier-channel space that can be effected when a single carrier transmitter and receiver are used jointly by some combination of relaying, telemetering, communication, load control, and supervisory-control equipment. The recent introduction of a wide line of individual rack-mounted carrier components1 makes it possible to select exactly the apparatus necessary for the combination of functions to be performed and further encourages the use of a single carrier assembly for several co-ordinated functions.

Field Tests and Performance of Heavy-Duty High-Speed 138-Kv Circuit Breakers-Oil and Air-Blast

Abstract: The heavy expansion brought about on the Central System of the American Gas and Electric Company in response to demands for power during the defense and war periods has produced a requirement for circuit-breaker rupturing duties close to 3,500 megavolt-amperes. In order to test the interrupting performance and reliability of two types of 138-kv 3,500-megavolt-ampere circuit breakers, the first an oil, the second an air-blast design, and also to explore faster reclosing cycles than now offered by the most improved oil circuit breakers, high-capacity, field tests were carried out at the Philo Plant of The Ohio Power Company. In these tests, involving 20 interruptions on each breaker, there has been accomplished for the first time successful interruption of a full three-phase short circuit of 3,500 megavolt-amperes with three-cycle interruption and with 13-cycle reclosure. The results of these tests, it is believed, indicate that a goal of 5,000 megavolt-amperes with 12-cycle reclosure definitely is attainable.

Damping and Synchronizing Torques of Power Selsyns

Abstract: SELSYN systems are used very widely as power drives and as indicators when it is necessary to have the position of an element correspond synchronously with that of a controlling element which is remotely located. The receiver Selsyn is used either directly as the output driving motor or as an input to a following power-amplifying stage of a control system.∗ In the study of such Selsyn systems and of the control systems of which Selsyn systems form one of the links, it becomes necessary to determine the hunting-torque characteristics of these machines (that is, the damping and synchronizing torques for small oscillations) as affected by speed, load, oscillation frequency, and, of course, the various design factors. The direct calculation of these hunting-torque characteristics is difficult, but within the past few years methods have been developed whereby the machine performance may be represented by equivalent static electric circuits. The purposes of this paper are: 1. To show how these hunting-torque characteristics can be simply determined by measurements on equivalent electric circuits set up on an a-c network analyzer. 2. To present some of the results of studies made of specific Selsyn systems.

Impulse-Failure-Detection Methods as Applied to Distribution Transformers

Abstract: Investigation of several methods for the detection of impulse failures in distribution transformers has strengthened our belief in the inadequacy of the methods described in American Standard C57.2. All of the methods are discussed in detail, and the most hopeful one is comnpared with the present method of analyzing the voltage wave and making the physical observations as outlined in the Standards. Data are presented on transformers utilizing present and proposed methods.

Rectifier Relay for Transformer Protection

Abstract: THE BASIC PRINCIPLE of differential protection of electric equipment consists of measuring the sum of the currents at the various terminals of the generator, transformer, or bus. If the vector sum of these currents is substantially zero, there is no fault; if the vector sum is not zero, a fault condition is indicated.

Electric Drives for Steam-Electric Generating-Station Auxiliaries

Abstract: For several years there has been an increasing trend toward all-electric drives for steam-station auxiliaries on account of the recognized advantages in flexibility, convenience, low operating cost, and comparable investment cost Substantial economies in first cost also have been obtained along with further improvements in flexibility through the use of transformers as the sole means of station power supply Gratifying reliability of performance has been achieved by co-ordinating design, backed by extensive tests, including momentary interruptions of station power supply, and has been incorporated in approximately 500,000 kw of modern plants of the 850-pound 900-degrees-Fahrenheit powdered-fuel-fired unit type Operating experience has demonstrated the over-all reliability and economy of all-electric drives for station auxiliaries and of the use of transformers as the sole source of station power supply

Static Voltage Regulator for Rototrol Exciter

Abstract: THE CONCEPT of a generator voltage regulator as an amplifier which produces a large correction in field current for a small departure from normal voltage is quite well known.1 In the conventional regulator, such as a directacting type, this amplification is secured partly in the regulator and partly in the exciter. A rotating amplifier-type regulator provides the amplification almost entirely in the rotating machines. Exciters may be used to obtain twoor more stages of amplification, or a single machine having high amplification such as a Rototrol exciter may be used. An example of two-stage excitation is a system with the regulator working in a pilot exciter field.

Formulas for Calculating Temperature Distribution in Transformer Cores and Other Electric Apparatus of Rectangular Cross Section

Abstract: THIS paper comprises solution of a very general problem in the mathematical theory of heat; application of it to effect formulas for the temperature distribution T, the maximum temperature T m , and the average temperature T a in transformer cores; and indication of its use with reference to other electric apparatus of rectangular cross section and of such general shape that the temperature distribution is essentially two dimensional. As theory indicates and experiment confirms that this condition is often fulfilled in practice, these formulas ought to be of considerable interest to designers of such equipment. For, commonly, the maximum electric loading of an electric device is determined by the permissible maximum or hot-spot temperature in it. Hence knowledge of this maximum temperature and of the temperature distribution in general is desired by the designer faced with making up new designs, improving operating performance of existing designs, or deciding upon maximum, yet safe, overload limits for apparatus already in service.

The electrical resistivity of resin-treated wood and laminated hydrolyzed-wood and paper-base plastics

Abstract: WOOD in the dry state is an excellent dielectric, having a volume resistivity in the range of 3 × 1017 to 3 × 1018 ohmcentimeters.2 The resistivity decreases rapidly, however, with an increase in moisture content, reaching values of 105 to 106 ohm-centimeters at the fiber-saturation point (30-per-cent moisture content on the basis of the dry weight of the wood).5 This tremendous change in the electrical resistance of wood with changes in moisture content, which so overshadows the variations due to varying species and specific gravity and ash content of the wood, 4,6 furnishes an excellent means of measuring the moisture content of wood.6,12

Insulation Resistance and Dielectric-Absorption Characteristics of Large A-C Stator Windings

Abstract: Insulation-resistance and dielectric-absorption data have been presented which give a comprehensive picture of average and normal spread in insulation characteristics of new large a-c synchronous and induction machines having mica insulation. Dielectric-absorption characteristics have been analyzed. Average curves and normal variations are given. Ratio of insulation resistance at 25 degrees centigrade as measured after ten minutes and after one minute of voltage application has been found to increase from one, for relatively moist windings, to approximately four, for moderately dry windings, and then to remain substantially constant over a wide range in insulation resistivity. Ratio for well-dried insulation is of the same order. Average temperature-insulation resistance characteristics for machines based on data available are given. Temperature-insulation resistance characteristics of well-dried asphalt-bonded mica insulation are given as a function of various times of voltage applications. Indications are that variation of absorptive current with temperature for asphaltic-bonded mica insulation does not even approximate a simple logarithmic function. Considerations involved in the proper selectin of a safe minimum value of insulation resistance are discussed. A linear formula which takes into account effects of speed, kilovolt-ampere rating, and voltage rating, with adequate precision when consideration is given to other variations involved, is suggested for large class B a-c induction and synchronous machines. Work is being continued on the study of variations involved and significance which may be attached to insulation-resistance measurements.

Orthomagnetic Bushing Current Transformer for Metering

Abstract: BUSHING current transformers are ideal for many reasons They are compact, convenient, economical, and, from the operator's standpoint, they eliminate a separate piece of equipment But they have one inherent limitation, namely, an accuracy generally not satisfactory for metering Many efforts therefore have been made in the past to overcome this inherent limitation of the conventional design, with considerable success jn the laboratory but limited success in practice